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Barbara E. Kus

Publications and source records attributed to Barbara E. Kus.

At least 55 records · Page 3Linked to original sources
USGS2023

Distribution and abundance of Southwestern Willow Flycatchers (Empidonax traillii extimus) on the upper San Luis Rey River, San Diego County, California—2022 data summary

Executive Summary We surveyed for Southwestern Willow Flycatchers ( Empidonax traillii extimus ; flycatcher) along the upper San Luis Rey River near Lake Henshaw in Santa Ysabel, California, in 2022. Surveys were completed at four locations: three downstream from Lake Henshaw, where surveys occurred from 2015 to 2021 (Rey River Ranch [RRR], Cleveland National Forest [CNF], Vista Irrigation District [VID]), and one at VID Lake Henshaw (VLH) that has been surveyed annually since 2018. There were 71 territorial flycatchers detected at 3 locations (RRR, CNF, VLH), and 6 transient flycatchers of unknown subspecies detected at VID and VLH. Downstream from Lake Henshaw, four territorial flycatchers, including two males and two females, were detected at RRR and CNF. In total, two territories were established consisting of two pairs at these locations. At VLH, we detected 67 territorial flycatchers, including 30 males, 34 females, and 3 flycatchers of unknown sex. In total, 40 territories were established, containing 35 pairs (24 monogamous pairings and 5 polygynous groups consisting of 4 males each pairing with 2 different females, and 1 male pairing with 3 different females), and 5 flycatchers of undetermined breeding status (3 males and 2 flycatchers of unknown sex). Brown-headed cowbirds ( Molothrus ater ; cowbird) were detected at all four survey locations. Flycatchers used five habitat types in the survey area: (1) mixed willow riparian, (2) willow-cottonwood, (3) willow-oak, (4) willow-ash, and (5) oak-sycamore. Of the flycatcher locations, 83 percent were located in habitat characterized as mixed willow riparian, and 92 percent were in habitat with greater than 95-percent native plant cover. Exotic vegetation was not prevalent in the survey area. There were 22 nests incidentally located during surveys: 5 were successful, 1 was seen with eggs on the last visit, 10 failed, and the outcome of the remaining 6 nests was unknown. Three of these nests were parasitized by cowbirds. There were 13 juveniles detected at VLH; no juveniles were detected at RRR or CNF. Five banded flycatchers were detected during surveys, three of which were confirmed to be adults that held territories in previous years. In addition, two flycatchers with a single dark blue federal band, indicating that they were banded as nestlings in a previous demographic study downstream from Lake Henshaw (Howell and others, 2022), were resighted during surveys.

California↗
USGS2023

Distribution and abundance of Least Bell’s Vireos (Vireo bellii pusillus), Southwestern Willow Flycatchers (Empidonax traillii extimus), and Coastal California Gnatcatchers (Polioptila californica californica) at the Santa Fe Dam, Los Angeles County, California—2022 data summary

In 2022, we surveyed for Least Bell’s Vireos ( Vireo bellii pusillus ; vireo), Southwestern Willow Flycatchers ( Empidonax traillii extimus ; flycatcher), and Coastal California Gnatcatchers ( Polioptila californica californica ; gnatcatcher) in the Santa Fe Dam detention basin and along the San Gabriel River upstream from the Santa Fe Dam near Irwindale, California. Four vireo surveys were completed between April 21 and July 13, 2022; three flycatcher surveys were completed between May 18 and July 13, 2022; and four gnatcatcher surveys were completed between April 21 and July 13, 2022. We detected seven territorial male vireos, including four that were paired and three with undetermined breeding status. We also detected one transient vireo. Two juvenile vireos were observed during surveys. Vireo territories were found in riparian scrub, willow ( Salix spp.)-cottonwood ( Populus spp.), and mixed willow habitat, with mixed willow the most commonly-recorded habitat type. Black willow ( S. gooddingii ) was the dominant plant species in most vireo territories. We detected 10 transient flycatchers in riparian scrub (5 individuals), mixed willow (4 individuals), and non-native vegetation (1 individual). Black willow and mule fat ( Baccharis salicifolia ) were the predominant plant species in flycatcher locations. We detected four territorial male gnatcatchers, two of which were paired and two of undetermined breeding status. We also detected one territorial female gnatcatcher. One juvenile gnatcatcher was observed during surveys. All gnatcatchers were detected in coastal sage scrub. The dominant shrub species at gnatcatcher locations were California sagebrush ( Artemisia californica ) and scale broom ( Lepidospartum squamatum ).

California↗
USGS2023

Prioritizing the risk and management of introduced species in a landscape with high indigenous biodiversity

Risk analysis protocols for prioritizing the management of non-native species are numerous, yet few incorporate risk and management in the same analysis or accommodate a broad diversity of taxa outside of a specific geographic area. We adapted a protocol that accounts for these factors to address non-native animal species in the Southern California/Northern Baja California Coast Ecoregion near the international border in San Diego County, an area with high indigenous biodiversity and high numbers of species of conservation concern. This stepwise, semi-quantitative protocol is applicable to any animal group in any predefined geographic area, relies on consensus-building among taxonomic experts, and has been vetted through previous use and in peer-reviewed literature. Our results show that the final prioritization was driven mainly by management feasibility, with top-ranked species having multitrophic effects that favor other non-native invaders over native residents. Conditions within the assessment area required some modification to the protocol as it was originally designed, namely a shift in emphasis from eradication to control, given that eradication is implausible for most non-native species in the assessment area. We call attention to taxon-specific issues that surfaced during the analysis, identify areas for improvement in this first-ever risk assessment for invasive animal species in the Natural Communities Conservation Plan/Habitat Conservation Plan (NCCP/HCP) reserve system of San Diego County, and provide suggestions for further refinement of the protocol. This study builds on the effort to standardize risk analysis for invasive species globally, given that many of the same invaders present threats to indigenous biodiversity worldwide.

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USGS2023

Interstate 15 wildlife crossing design considerations for focal wildlife species - Santa Ana-Palomar Mountains Linkage southern California

The Nature Conservancy (TNC) and the California Department of Transportation (Caltrans), along with landowners including San Diego State University, California Department of Fish and Wildlife, Western Riverside Regional Conservation Authority and Riverside County Flood Control District are developing wildlife crossing infrastructure projects along a 3-mile stretch of Interstate 15 (I-15) in the Santa Ana-Palomar Mountains Linkage (hereafter ‘Linkage’) in southern California. These crossings will provide a critical missing link that will help reconnect wildlife in the coastal Santa Ana Mountains west of I-15 with those in the interior Palomar and Eastern Peninsular ranges to the east of I-15. The Linkage supports intact and diverse habitats including coastal sage scrub, grasslands, chaparral, and oak and riparian woodlands, and has been a focus of regional conservation efforts for the last 30 years. The three wildlife crossing infrastructure projects include enhancement of the existing Temecula Creek I-15 Bridge, construction of a new vegetated wildlife overcrossing, and construction of a new stand-alone wildlife culvert. Given the challenges and level of financial investment required to secure wildlife crossings for I-15 in the Linkage, TNC and Caltrans proposed that planning efforts would benefit from input by taxonomic experts on design concepts that meet the needs of the broadest range of wildlife. While wildlife crossings are becoming more common, optimal designs that meet the needs of a variety of wildlife species are largely unknown and can be site specific. To address this challenge, we held a workshop in February 2022 that brought together over 50 wildlife experts to brainstorm and identify specific design considerations for various focal wildlife species groups (medium/large mammals, small animals, birds, bats, plants, and invertebrates) that might use the identified I-15 wildlife crossings (The Nature Conservancy 2022). Lead experts for each focal species group worked together to identify specific wildlife crossing features or attributes for each of the three proposed wildlife crossings. Specific attributes evaluated by experts for each crossing type and species group included, at a minimum: • Crossing Structure Attributes; o Habitat features? (cover, habitat structure, substrate, moisture, light and noise mitigation) • Crossing Approach Area Features; o Habitat features (cover type/density, substrate, water, light and noise mitigation) • Barrier design to reduce roadkill and/or to funnel wildlife to the crossing; • Additional research to resolve uncertainties related to crossing design Based on the design considerations for each potential crossing type, the experts then weighed in on the suitability of the existing location and probability of use by their focal species or groups of species. With proposed design features, Temecula Creek Bridge has moderate or high probability of use by 27 of the 36 focal wildlife species assessed, while the vegetated overcrossing could meet the needs of 26 of the 36 species. When combined, Temecula Creek Bridge and the vegetated overcrossing have a moderate or high probability of use for 34 of the 36 species. The wildlife culvert has a moderate or high level of expected use by 10 of the 36 focal species and could serve connectivity needs for representative species from all but the bird and plant species groups.

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USGS2022

Distribution and demography of Southwestern Willow Flycatchers in San Diego County, 2015–19

We surveyed for Southwestern Willow Flycatchers ( Empidonax traillii extimus ; flycatcher) at 33 locations along multiple drainages in San Diego County, including portions of Agua Hedionda Creek, Cottonwood Creek, Escondido Creek, Los Penasquitos Creek, Otay River, San Diego River, San Dieguito River, San Luis Rey River, Sweetwater River, and Tijuana River. Resident flycatchers were only found on two drainages in San Diego County, at San Dieguito and San Luis Rey Rivers, with 99 percent occurring on the San Luis Rey River. Resident flycatchers were detected at 18 percent of survey locations (Bonsall, Cleveland National Forest, Rey River Ranch, San Dieguito, and Vista Irrigation District [VID], and VID Lake Henshaw). Resident flycatchers were documented for the first time at Lake Henshaw, the only new location surveyed that supported flycatchers. We detected a minimum of 80 resident flycatchers from 2015 to 2019, most of these were upstream and downstream from Lake Henshaw. Transient flycatchers were found at 42 percent of survey locations; 38 transient individuals were detected at Agua Hedionda Creek, Otay River, San Diego River, San Dieguito River, and the San Luis Rey River. Over the course of this study, 11 locations historically occupied by resident flycatchers were resurveyed; only 5 were found to have resident flycatchers: (1) Bonsall, (2) Cleveland National Forest, (3) Rey River Ranch, (4) San Dieguito, and (5) Vista Irrigation District. The number of resident flycatchers declined from previous high counts at all five locations. Collectively, the number of resident flycatcher territories within the historically occupied area of the upper San Luis Rey River downstream from Lake Henshaw (Cleveland National Forest, Rey River Ranch, and Vista Irrigation District) declined 71 percent between 1999 (48) and 2019 (14); 42 percent of the decline occurred between 1999 and 2016, with an additional decline (50 percent) occurring between 2016 and 2019. In 2016, the distribution of flycatcher territories at the historically occupied area of the upper San Luis Rey River changed relative to the distribution in 1999: the proportion of territories at Cleveland National Forest and Rey River Ranch decreased to 36 percent each, while Vista Irrigation District increased to 29 percent, creating a more equal distribution of territories across the historically occupied area. By 2019, the distribution changed relative to 2016, with most of the territories spread equally between Cleveland National Forest and Rey River Ranch (43 percent each), while the proportion of territories at Vista Irrigation District declined to 14 percent. During countywide surveys, we documented the dispersal of two natal banded flycatchers; both were females that were originally banded as nestlings at Marine Corps Base Camp Pendleton and were seen for the first time as breeding adults. One of the females dispersed to San Dieguito, a distance of 41 kilometers, and a second female dispersed to Cleveland National Forest, a distance of 55 kilometers. We also documented the within-season movement of a uniquely banded male that was seen at the beginning of the 2017 breeding season at Bonsall and was later documented at San Dieguito, a movement distance of 31 kilometers. We completed nest monitoring activities along the upper San Luis Rey River near Lake Henshaw in Santa Ysabel, California from 2016 to 2019. Monitoring occurred at three locations: (1) Cleveland National Forest, (2) Rey River Ranch, and (3) Vista Irrigation District, collectively the upper San Luis Rey River monitoring area. The number of flycatcher territories monitored each year ranged from 14 to 27. We observed polygynous pairings (one male paired with multiple females) in all years, with the lowest rate of polygyny (number of polygynous pairs/total number of pairs) observed in 2016 (10 percent) and the highest in 2017 (70 percent). The proportion of paired males that were polygynous ranged from 5 to 54 percent between 2016 and 2019. We monitored the nesting activity of 14–27 pairs annually during the course of the study. Most of the first nesting attempts were initiated during late May and early June. We monitored 18–41 Southwestern Willow Flycatcher nests per year from 2016 to 2019. Apparent nest success ranged from 11 to 37 percent and differed significantly by year, with higher success in 2016 and 2017 compared to 2018 and 2019. Predation was the presumed to be the primary source of nest failure, with 63–84 percent of failures annually attributed to predation. Although none of the failures were attributed to Brown-headed cowbird ( Molothrus ater ) parasitism, 4–27 percent of nests were parasitized annually from 2016 to 2019, with increased parasitism rates observed in 2018 and 2019 compared to 2016 and 2017. We “rescued” 11 parasitized nests between 2016 and 2019 by removing cowbird eggs; if those nests had been allowed to fail, apparent nest success would have been up to 45 percent lower annually. Flycatcher egg clutch size ranged from 2.8±0.8 to 3.1±0.8 annually and did not vary significantly between years. The number of fledglings per pair ranged from 0.5±1.0 to 1.6±1.5 annually from 2016 to 2019. There was a significant difference in the number of young fledged per pair between years, with pairs in 2016 producing more than three times the number of fledglings compared to 2019. The percent of pairs fledging at least one young ranged from 18 to 62 percent annually but did not vary significantly by year. Analysis of flycatcher daily nest survival rates suggested that both early and late winter precipitation influenced nest survival, with increases in early winter precipitation positively influencing nest survival and later winter precipitation negatively influencing nest survival. The second-best supported model included year, with the lowest daily nest survival occurring in 2018 and 2019. A total of 119 flycatchers were newly banded over the course of this study; 36 adult flycatchers were banded with a unique color combination, and 83 nestlings (57 of which survived to fledging) were banded with a single band on the left or right leg. In addition, two adults that were banded before 2015 were observed in the monitoring area. Between 2015 and 2019, we accumulated 94 resights of 49 individual color-banded adult flycatchers that ranged in age from 1 to 8 years old. Banding allowed us to examine differences in annual survivorship among flycatchers of different ages and sexes. We estimated annual survivorship of adult males to be 69±7 percent, which is higher than estimates of female survivorship (45±10 percent). Annual survivorship of first-year flycatchers ranged from 24 to 41 percent, which is roughly half the estimates calculated for adult flycatchers (52–75 percent). We found no evidence that precipitation in the previous breeding year had an effect on flycatcher survival. We were also able to observe dispersal and movement among adults and first-year flycatchers. Average first-year dispersal distance was 3.1±2.6 kilometers, with the longest dispersal (8.5 kilometers) by a natal female dispersing from the monitoring area to Lake Henshaw. Of the first-year flycatchers, 65 percent returned to the monitoring area to establish an adult breeding territory, while the remaining 35 percent dispersed to Lake Henshaw. Territory fidelity among adult flycatchers was high with 69±13 percent of returning adults occupying the same territory (or within 100 meters) from the previous year. There was no significant difference in territory fidelity between males and females, or across years. Nesting success in the previous year appeared to be a strong driver of territory fidelity, with adults more likely to return to the same territory following years when they successfully fledged young. The average between-year movement for returning adult flycatchers was 0.5±0.8 km. We documented the movement of two adult males from the monitoring area to Lake Henshaw. Between-year movement distances did not differ by sex or year. Resident flycatchers in the upper San Luis Rey River monitoring area used five habitat types from 2016 to 2019: (1) willow-oak, (2) willow-ash, (3) oak-sycamore, (4) mixed willow riparian, and (5) willow-sycamore, with willow-oak the most commonly used habitat type. The most commonly recorded dominant species at flycatcher territories included coast live oak ( Quercus agrifolia ), red or arroyo willow ( Salix laevigata or Salix lasiolepis ), California sycamore ( Platanus racemosa ), and velvet ash ( Fraxinus velutina ). In 2018, we anecdotally began to observe dead and dying oaks in the monitoring area, which we believe to be the result of goldspotted oak borer ( Agrilus auroguttatus ) infestation. At the conclusion of this study, we investigated the overall change in normalized difference vegetation index (NDVI) in flycatcher territories within the monitoring area. The greatest negative change in NDVI occurred in territories closest to Lake Henshaw, and many of the affected territories were no longer occupied in the later years of the study. Flycatchers used 13 plant species for nesting at the monitoring area from 2016 to 2019; 70 percent of all nests were placed in coast live oak. None of the nest characteristics including host height, nest height, distance to the edge of the host, or distance to the edge of the vegetation clump where the nest was placed differed between years. In 2016, successful nests were placed higher than unsuccessful nests; no other within-year differences were observed.

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USGS2022

Distribution and abundance of Southwestern Willow Flycatchers (Empidonax traillii extimus) on the Upper San Luis Rey River, San Diego County, California—2021 data summary

We surveyed for Southwestern Willow Flycatchers ( Empidonax traillii extimus ; flycatcher) along the upper San Luis Rey River near Lake Henshaw in Santa Ysabel, California, in 2021. Surveys were completed at four locations: three downstream from Lake Henshaw, where surveys occurred from 2015 to 2020 (Rey River Ranch [RRR], Cleveland National Forest [CNF], Vista Irrigation District [VID]), and one at VID Lake Henshaw (VLH) that has been surveyed annually since 2018. There were 78 territorial flycatchers detected at 3 locations (RRR, CNF, VLH), and 1 transient flycatcher of unknown subspecies was detected at VID. Downstream from Lake Henshaw, five flycatchers, including three males and two females, were detected at RRR and CNF. In total, three territories were established, consisting of two pairs and one male of undetermined breeding status. At VLH, we detected 73 flycatchers, including 32 males, 38 females, and 3 flycatchers of unknown sex. In total, 43 territories were established, containing 38 pairs (22 monogamous pairings, 7 confirmed polygynous groups consisting of 7 males each pairing with 2 different females, and 1 suspected polygynous group consisting of 1 male and 2 females), and 5 flycatchers of undetermined breeding status (2 males and 3 flycatchers of unknown sex). Brown-headed cowbirds ( Molothrus ater ; cowbird) were detected at all four survey locations. Flycatchers used five habitat types in the survey area: (1) mixed willow riparian, (2) willow-cottonwood, (3) willow-oak, (4) willow-ash, and (5) sycamore-oak. Eighty-seven percent of the flycatchers were detected in habitat characterized as mixed willow riparian, and 94 percent of the flycatchers were detected in habitat with greater than 95-percent native plant cover. Exotic vegetation was not prevalent in the survey area. There were 15 nests incidentally located during surveys: 1 was successful, 2 were seen with eggs or nestlings on the last visit, 9 failed, and the outcome of the remaining 3 nests was unknown. Three of these nests were parasitized by cowbirds. There were 13 juveniles detected at VLH during surveys; no juveniles were detected at RRR or CNF. Of the 10 banded flycatchers detected during surveys, 7 were resighted and confirmed to be adults that held territories in previous years. Three flycatchers with a single dark blue federal band, indicating that they were banded as nestlings in the former demographic study area downstream from Lake Henshaw, were resighted during surveys. In 2021, we documented both adult and natal flycatchers moving from the former demographic study area downstream from Lake Henshaw upstream to the habitat surrounding Lake Henshaw. Three natal flycatchers that were originally banded as nestlings and three adults that previously held territories downstream dispersed to Lake Henshaw in 2021.

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USGS2022

Distribution and demography of coastal Cactus Wrens (Campylorhynchus brunneicapillus) in southern San Diego County, California — 2021 Data summary

We surveyed for coastal Cactus Wren ( Campylorhynchus brunneicapillus ) in 378 established plots in southern San Diego County in 2021, encompassing 3 genetic clusters (Otay, Lake Jennings, and Sweetwater/Encanto). Two surveys were completed at each plot between March 1 and July 31. Cactus Wrens were detected in 130 plots (34 percent of plots), remaining virtually the same as the percentage of plots occupied in 2020 (35 percent). There were 113 Cactus Wren territories detected across all survey plots in 2021, an increase from 109 in 2020. At least 86 percent of Cactus Wren territories were occupied by pairs, and 50 fledglings were observed in 2021. We observed 48 color-banded Cactus Wrens in 2021, 44 of which we could identify to individual. Adults of known age ranged from 2 to at least 7 years old. Adult Cactus Wrens moved, on average, 0.1 kilometers (maximum 0.5 kilometers) from their 2020 territories to their 2021 territories. No known-identity Cactus Wrens moved between genetic clusters from 2020 to 2021. Vegetation at Cactus Wren plots typically was dominated by coastal sage scrub shrubs, such as California sagebrush ( Artemisia californica ), California buckwheat ( Eriogonum fasciculatum ), lemonadeberry ( Rhus integrifolia ), and San Diego sunflower ( Bahiopsis laciniata ). Twenty-nine percent of plots contained blue elderberry ( Sambucus nigra ssp. caerulea ), and Cactus Wrens occupied proportionally more plots with elderberry than plots without elderberry. Very little dead or unhealthy cactus was observed within all survey plots, and the plots that were occupied by Cactus Wrens were likely to contain more healthy cactus than plots that were not occupied by Cactus Wrens. Thirteen percent of plots had 5 percent or less of the cactus crowded or overtopped by vines and shrubs. Although in 2020, Cactus Wrens occupied proportionally more plots with 5 percent or less of cactus crowded or overtopped by vines and shrubs, this pattern was not found in 2021. Non-native annual cover was 5 percent or less at 29 percent of plots and, unlike in 2020, Cactus Wrens appeared to occupy proportionally more plots with less non-native annual cover than plots with more than 5-percent annual cover.

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USGS2022

Distribution and demography of Coastal Cactus Wrens in Southern California, 2015–19

Surveys and monitoring for the coastal Cactus Wren ( Campylorhynchus brunneicapillus ) were completed in San Diego County between March 2015 and July 2019. A total of 383 plots were surveyed across 3 genetic clusters (Otay, Lake Jennings, and Sweetwater/Encanto). From 2015 to 2019, 317 plots were surveyed 8 times (twice per year in 2015, 2017–19). Additional plots were added in later years as wrens were discovered in new locations. We found differences in the proportion of plots occupied in the genetic clusters, with a lower proportion of plots occupied in the Otay cluster than in the Lake Jennings and Sweetwater/Encanto clusters in all years. Plot occupancy increased each year in the Otay and Sweetwater/Encanto clusters but not in the Lake Jennings cluster. The number of Cactus Wren territories increased from 2015 through 2018, and then decreased in 2019 in all three genetic clusters. We monitored nesting activities for two populations of Cactus Wrens in southern San Diego County. The Otay population consisted of two sites within the Otay genetic cluster, and the San Diego population consisted of two sites within the Sweetwater/Encanto and Lake Jennings genetic clusters. Nest monitoring occurred at 10–13 territories per year in the Otay population and 14–18 territories in the San Diego population from 2015 through 2019. All territories were occupied by pairs except two territories in 2015, five in 2016, and two in 2019. Between 46 and 74 Cactus Wren nests were monitored each year, which totaled 295 monitored nests from 2015 to 2019. To evaluate the direct influence of precipitation on breeding success, bio-year precipitation (“precipitation”) was calculated from July 1 of the prior year through June 30 of the breeding season year. Overall apparent nest success was positively influenced by precipitation with the lowest apparent nest success of 50 percent in 2015 and the highest apparent nest success of 72 percent in 2017, corresponding to the second lowest and the highest precipitation years, respectively. Apparent nest success also was higher in the Otay population than in the San Diego population. The number of brood nests initiated per pair and the number of renesting attempts per pair also were higher in years with more precipitation. Other metrics of Cactus Wren nesting success and productivity were positively influenced by the amount of precipitation, including clutch size and egg hatching success. The percent of hatchlings that fledged was greater in the Otay population than in the San Diego population but was not influenced by precipitation. The number of fledglings per pair was higher in years with more precipitation and was greater in the Otay population than in the San Diego population. Predation was the predominant cause of nest failure in both populations. Analysis of Cactus Wren daily nest survival rate indicated that there was a population, and possibly a precipitation effect on nest survival, with the daily survival rate for the Otay population significantly higher than for the San Diego population and weak increase in the daily survival rate with more precipitation. A total of 629 Cactus Wrens were banded during the course of the study, 360 in the San Diego population and 269 in the Otay population. Between 2015 and 2019, we resighted 301 color-banded adult birds that ranged between 1 and 8 years old. One additional color-banded bird was resighted in San Pasqual Valley (as part of a separate study); this bird originated in the San Diego population and was excluded from our analyses. Annual survival was higher for adult Cactus Wrens (ranging from 60 to 70 percent) than for first-year wrens (ranging from 20 to 28 percent) and varied by year. Annual survival was also weakly but positively correlated with precipitation. Annual survival was higher for first year and adult Cactus Wrens following years with increased precipitation. We found no evidence that survival differed by population. Banding also allowed us to examine whether there were differences in movement of adult and first-year Cactus Wrens by year or by population. We found that average dispersal distance for first-year Cactus Wrens was 1.9 kilometers in the Otay population and 1.6 kilometers in the San Diego population and did not differ by population or year. Dispersal between populations was not common. We detected five instances of movement of first-year wrens between the San Diego and Otay populations. All movements into and out of the San Diego population were from or into territories in the Sweetwater area. We detected no movement between the Lake Jennings site and either of the Sweetwater or Otay sites; however, we did detect one wren that dispersed from Lake Jennings to the San Pasqual Valley population in 2019, which was a distance of 26.4 kilometers. Adult Cactus Wrens were site-faithful, with 87 percent of adults remaining on the same territory between breeding seasons. Precipitation may be a weak driver of movement for adult Cactus Wrens, with adults more likely to remain on the same territory following years of increased precipitation. There was no difference in adult movement between populations. Arthropods were collected in pitfall traps and by vacuum in 23 Cactus Wren territories during 3 sampling periods in 2016 (early nesting, peak nesting, and late nesting). Arthropods of 19 orders and at least 128 families were collected. Analysis of 43 Cactus Wren fecal samples identified 10 arthropod orders that were present in more than 10 percent of fecal samples. The most abundant arthropod order collected was Hymenoptera; however, Cactus Wrens consumed arthropods in the order Hymenoptera significantly less than their availability, suggesting that this order was avoided. No other orders were significantly selected or avoided; however, selection indices of arthropod families identified that two families of arthropods (Isopoda Porcellionidae [woodlice] and Hymenoptera Formicidae [ants]) were avoided. After excluding the taxa that were avoided or not represented in fecal samples, 95 percent of Cactus Wren prey items were collected in pitfall traps and 5 percent were collected by vacuum. The most abundant prey orders captured were Diptera, Coleoptera, Hemiptera, Hymenoptera, and Aranea. Analysis of the abundance of Cactus Wren prey items by vegetation type and sampling period indicated that vegetation type by itself was not a significant predictor of arthropod abundance but interacted with sampling period. Seasonal availability of arthropods was highest in the peak nesting period, followed by early and late nesting periods for California sagebrush ( Artemisia californica ), lemonadeberry ( Rhus integrifolia ), non-native grass, and bare ground, whereas availability increased from early to late nesting periods for blue elderberry ( Sambucus mexicana spp. caerulea ), cactus ( Opuntia spp. and Cylindropuntia spp.), California buckwheat ( Eriogonum fasciculatum ), native bunch grasses, and black mustard ( Brassica nigra ). During the early nesting period, arthropods were most abundant in native bunch grasses and least abundant in lemonadeberry. During the peak nesting period, arthropods were most abundant in native bunch grasses and in areas of bare ground and were least abundant in cactus and blue elderberry. During late nesting, arthropods were most abundant in blue elderberry and non-native grass and least abundant in lemonadeberry and mustard. Each year from 2015 to 2019, vegetation data were collected at the same 23 territories where arthropods were sampled: 9 territories in the Otay population and 14 territories in the San Diego population. Cactus, California buckwheat, and non-native grasses were detected within at least 60 percent of sampling points in the Otay population. Cactus, California sagebrush, California buckwheat, non-native grass, and black mustard each were detected within an average of 40 percent of sampling points in the San Diego population. No native bunch grass or lemonadeberry were recorded at the Lake Jennings site within the San Diego population. The cover of shrub species was relatively stable throughout the 5 years. Cover of herbaceous species and bare ground had greater annual variation than shrub species. We found that vegetation cover varied widely among territories, with territory accounting for 69 percent of the variation in vegetation cover. Redundancy analysis allowed us to identify the vegetation types that accounted for the most variation. We used the top scores from the redundancy analysis to identify six vegetation types to be used in generalized linear mixed models analyzing the relationships between vegetation type, precipitation, and Cactus Wren breeding productivity. Three vegetation variables influenced the number of fledglings produced per pair. California sagebrush had a positive effect on the number of fledglings per pair whereas non-native grass and black mustard had a negative effect. Breeding productivity, survival, and movements of adult and first-year Cactus Wrens indicated that the Otay population behaved similarly to, if not out-performed, the San Diego population during the span of our project, suggesting that the driving forces behind low numbers of Cactus Wrens in the Otay population before 2015 were no longer in effect. The Cactus Wren populations in Otay and San Diego reached a peak in 2018, which followed a year of high productivity and survivorship, both of which were correlated with high precipitation. This peak in population size was consistent with reproductive timing and productivity in other bird populations in semi-arid ecosystems that were linked to precipitation and arthropod abundance. We did not find a strong link among arthropod abundance, vegetation composition, and Cactus Wren breeding productivity, likely in part because arthropod abundance varied by vegetation type and sampling period, suggesting that different vegetation types provided important sources of prey at different periods of the breeding season. Arthropod abundance also may not represent arthropod availability when vegetation structure discourages the ground foraging behavior of species such as Cactus Wrens. Cover of non-native grass negatively influenced breeding productivity, although arthropods were abundant in non-native grass. Other factors that could have influenced differential breeding productivity between the Otay and San Diego populations were habitat restoration, control of annual herbaceous vegetation, human disturbance, lingering effects of wildfire, and nest predation. Overall, precipitation appeared to be a driver of Cactus Wren breeding productivity and possibly survival, potentially obscuring proximate effects of arthropod or vegetation composition.

California↗
USGS2022

Recent declines in genetic diversity with limited dispersal among coastal cactus wren populations in San Diego County, California

Habitat loss and fragmentation can lead to smaller and more isolated populations and reduce genetic diversity and evolutionary potential. Conservation programs can benefit from including monitoring of genetic factors in fragmented populations to help inform restoration and management. We assessed genetic diversity and structure among four major populations of the Cactus Wren ( Campylorhynchus brunneicapillus ) in San Diego County in 2011–2012 and again in 2017–2019, using 22 microsatellite loci. We found a significant decline in heterozygosity in one population (San Pasqual) and a decline in allelic richness and effective population size in another (Sweetwater). Genetic diversity in the remaining two populations was not significantly different over time. Local diversity declined despite evidence of dispersal among some populations. Approximately 12% of genetically determined family groups (parents, offspring, siblings) included one or more members sampled in different territories with distances ranging from 0.2 to 10 km. All but one inferred dispersal events occurred within the same genetic population. Population structure remained relatively stable, although genetic differentiation tended to increase in the later sampling period. Simulations suggest that at currently estimated effective sizes, populations of Cactus Wrens will continue to lose genetic diversity for many generations, even if gene flow among them is enhanced. However, the rate of loss of heterozygosity could be reduced with increased gene flow. Habitat restoration may help bolster local population sizes and allelic richness over the long term, whereas translocation efforts from source populations outside of San Diego may be needed to restore genetic diversity in the short term.

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USGS2022

Subspecies differentiation and range-wide genetic structure are driven by climate in the California gnatcatcher, a flagship species for coastal sage scrub conservation

Understanding genetic structure and diversity within species can uncover associations with environmental and geographic attributes that highlight adaptive potential and inform conservation and management. The California gnatcatcher, Polioptila californica , is a small songbird found in desert and coastal scrub habitats from the southern end of Baja California Sur to Ventura County, California. Lack of congruence among morphological subspecies hypotheses and lack of measurable genetic structure found in a few genetic markers led to questions about the validity of subspecies within P. californica and the listing status of the coastal California gnatcatcher, P. c. californica . As a U.S. federally threatened subspecies, P. c. californica is recognized as a flagship for coastal sage scrub conservation throughout southern California. We used restriction site-associated DNA sequencing to develop a genomic dataset for the California gnatcatcher. We sampled throughout the species' range, examined genetic structure, gene–environment associations, and demographic history, and tested for concordance between genetic structure and morphological subspecies groups. Our data support two distinct genetic groups with evidence of restricted movement and gene flow near the U.S.- Mexico international border. We found that climate-associated outlier loci were more strongly differentiated than climate neutral loci, suggesting that local climate adaptation may have helped to drive differentiation after Holocene range expansions. Patterns of habitat loss and fragmentation are also concordant with genetic substructure throughout the southern California portion of the range. Finally, our genetic data supported the morphologically defined P. c. californica as a distinct group, but there was little evidence of genetic differentiation among other previously hypothesized subspecies in Baja California. Our data suggest that retaining and restoring connectivity, and protecting populations, particularly at the northern range edge, could help preserve existing adaptive potential to allow for future range expansion and long-term persistence of the California gnatcatcher.

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USGS2022

Least Bell's Vireos and Southwestern Willow Flycatchers at the San Luis Rey flood risk management project area in San Diego County, California: Breeding activities and habitat use—2021 Annual report

Executive Summary Surveys and monitoring for the endangered Least Bell’s Vireo ( Vireo bellii pusillus ; vireo) were done at the San Luis Rey Flood Risk Management Project Area (Project Area) in the city of Oceanside, San Diego County, California, between April 4 and August 4, 2021. We completed four protocol surveys during the breeding season, supplemented by weekly territory monitoring visits. We identified a total of 122 territorial male vireos; 111 were confirmed as paired and 8 were confirmed as single males. For the remaining three territories, we were unable to confirm pair status. Five transient vireos were detected in 2021. The vireo population in the Project Area decreased by 24 percent from 2020 to 2021. Vireo populations decreased across San Diego County, with a 14-percent decrease documented at Marine Corps Base Camp Pendleton (MCBCP); a 5-percent decrease on the Otay River; a 6-percent decrease on the middle San Luis Rey River; and a 44-percent decrease at Marine Corps Air Station (although this decrease was likely exaggerated by large-scale vegetation clearing that occurred prior to the 2021 breeding season). We used an index of treatment (Treatment Index) to evaluate the impact of on-going vegetation clearing on the Project Area vireo population. The Treatment Index measures the cumulative effect of vegetation treatment within a territory (since 2005) by using the percent area treated weighted by the number of years since treatment. We found that the Treatment Index for unoccupied habitat was more than two times that of occupied habitat, indicating that vireos selected less treated habitat in which to settle. We monitored vireo nests at three general site types: (1) within the flood channel where exotic and native vegetation removal has occurred regularly (Channel), (2) three sites next to the flood channel where limited exotic and native vegetation removal has occurred (Off-channel), and (3) three sites that have been actively restored by planting native vegetation (Restoration). Nesting activity was monitored in 85 territories, 8 of which were occupied by single males. Of the completed nests, 39 percent were successful, and nest success did not differ among the three sites. Clutch size was greater in the Channel than the Off-channel sites, and the proportion of hatchlings that fledged was greater in Off-channel sites than Channel and Restoration sites. There were no other nest-level differences detected among site types, nor were there any differences in territory-level measures of productivity (young fledged per pair, double-brooding) among the sites. Overall, breeding success and productivity were slightly lower in 2021 than in 2020, with 66 percent of pairs fledgling at least one young and pairs fledging an average of 1.9±1.7 young. To investigate if the cumulative years of treatment had an impact on vireo reproductive effort, we looked at the effects of the Treatment Index on reproductive parameters. Results from generalized linear models indicated that treatment did not have an effect on vireo nesting effort or the number of vireo fledglings per pair produced in 2021. Similarly, our analysis of nest survival for 2021 revealed no effect of Treatment Index on daily survival rate. Analysis of vegetation data collected at vireo nests from 2006 to 2021 did not indicate an effect of vegetation at the nest on daily survival rate. We also found no differences in nest-placement characteristics among site types or successful/unsuccessful nests. Red/arroyo willow ( Salix laevigata or Salix lasiolepis ) was the species most commonly selected for nesting by vireos in all three site types. Black willow ( Salix gooddingii ) and mule fat ( Baccharis salicifolia ) also were commonly used. Vireos used a wider variety of species for nesting in Channel and Off-channel sites (seven and eight species, respectively) compared with Restoration sites (three species).

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USGS2022

Distribution and abundance of Least Bell’s Vireos ( Vireo bellii pusillus ) and Southwestern Willow Flycatchers (Empidonax traillii extimus) at the Mojave River Dam, San Bernardino County, California—2021 Data summary

Executive Summary We surveyed for Least Bell’s Vireos ( Vireo bellii pusillus ; vireo) and Southwestern Willow Flycatchers ( Empidonax traillii extimus ; flycatcher) at the Mojave River Dam study area near Hesperia, California, in 2021. Four vireo surveys were conducted between April 16 and July 16, 2021, and three flycatcher surveys were conducted between May 27 and July 16, 2021. We detected four territorial male vireos, including two that were paired and two with undetermined breeding status. No juveniles were observed during surveys. Vireo territories were found in three habitat types: (1) riparian scrub, (2) willow-cottonwood, and (3) willow-sycamore, with willow-cottonwood being the most commonly recorded habitat type. Red or arroyo willow ( Salix laevigata or lasiolepis ) was the dominant plant species in most vireo territories. No territorial or transient flycatchers were observed.

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USGS2022

Distribution and abundance of Least Bell’s Vireos ( Vireo bellii pusillus ) and Southwestern Willow Flycatchers ( Empidonax traillii extimus ) at the San Antonio Dam, Los Angeles and San Bernardino Counties, California—2021 Data summary

Executive Summary We surveyed for Least Bell’s Vireos ( Vireo bellii pusillus ; vireo) and Southwestern Willow Flycatchers ( Empidonax traillii extimus ; flycatcher) at the San Antonio Dam near Upland, California, in 2021. Four vireo surveys were conducted between April 16 and July 15, 2021, and three flycatcher surveys were conducted between May 27 and July 15, 2021. We detected one transient vireo and one transient flycatcher. No territorial vireos or flycatchers were observed. The vireo was found in riparian scrub habitat dominated by native mule fat ( Baccharis salicifolia ), whereas the flycatcher was using habitat dominated by non-native tamarisk ( Tamarix ramosissima ).

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USGS2022

Distribution and abundance of Least Bell’s Vireos ( Vireo bellii pusillus ) and Southwestern Willow Flycatchers ( Empidonax traillii extimus ) on the Middle San Luis Rey River, San Diego County, southern California—2021 Data summary

Executive Summary We surveyed for Least Bell’s Vireos ( Vireo bellii pusillus ; vireo) and Southwestern Willow Flycatchers ( Empidonax traillii extimus ; flycatcher) along the San Luis Rey River, between College Boulevard in Oceanside and Interstate 15 in Fallbrook, California (middle San Luis Rey River), in 2021. Surveys were conducted from April 13 to July 14 (vireo) and from May 18 to July 13 (flycatcher). We found 180 vireo territories, at least 125 of which were occupied by pairs. The vireo population size decreased by 6 percent from 2020 to 2021. In 2021, vireo territories decreased by 14 percent in the portion of the middle San Luis Rey River that burned in 2017 and decreased by 2 percent outside of the burned area. Vireos used six different habitat types in the survey area: (1) willow-cottonwood, (2) mixed willow riparian, (3) riparian scrub, (4) upland scrub, (5) willow-sycamore, and (6) non-native. Forty percent of the vireos were detected in habitat characterized as willow-cottonwood, and 97 percent of the vireos were detected in habitat with greater than 50-percent native plant cover. Of the 14 banded vireos detected in the survey area, 3 were resighted with a full color-band combination. There were 10 other vireos with single (natal) federal bands that were recaptured, identified, and color-banded in 2021. One vireo with a single dark blue federal band, indicating that it was banded as a nestling at the lower San Luis Rey River, could not be recaptured for identification. The 10 natal vireos that were recaptured on the middle San Luis Rey River dispersed from 2.0 to 11.7 kilometers from their natal territories. Banded vireos with a known age ranged from 1 to 7 years old. One resident flycatcher, of undetermined breeding status, was observed in the survey area in 2021. The resident flycatcher (male) was detected in a territory of mixed willow habitat with greater than 50-percent native plant cover. He was detected from May 20 to June 4, 2021, and no evidence of pairing or nesting was observed. The male flycatcher was resighted with a unique color-band combination and had occupied the same territory since 2018.

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USGS2021

Impacts of a non-indigenous ecosystem engineer, the American beaver (Castor canadensis), in a biodiversity hotspot

Non-native species having high per capita impacts in invaded communities are those that modulate resource availability and alter disturbance regimes in ways that are biologically incompatible with the native biota. In areas where it has been introduced by humans, American beaver ( Castor canadensis ) is an iconic example of such species due to its capacity to alter trophic dynamics of entire ecosystems and create new invasional pathways for other non-native species. The species is problematic in several watersheds within the Southern California-Northern Baja California Coast Ecoregion, a recognized hotspot of biodiversity, due to its ability to modify habitat in ways that favor invasive predators and competitors over the region's native species and habitat. Beaver was deliberately introduced across California in the mid-1900s and generally accepted as non-native to the region up to the early 2000s; however, articles promoting the idea that beaver may be a natural resident have gained traction in recent years, due in large part to the species' charismatic nature rather than by presentation of sound evidence. Here, we discuss the problems associated with beaver disturbance and its effects on conserving the region's native fauna and flora. We refute arguments underlying the claim that beaver is native to the region, and review paleontological, zooarchaeological, and historical survey data from renowned field biologists and naturalists over the past ~160 years to show that no evidence exists that beaver arrived by any means other than deliberate human introduction. Managing this ecosystem engineer has potential to reduce the richness and abundance of other non-native species because the novel, engineered habitat now supporting these species would diminish in beaver-occupied watersheds. At the same time, hydrologic functionality would shift toward more natural, ephemeral conditions that favor the regions' native species while suppressing the dominance of the most insidious invaders.

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USGS2021

Distribution and abundance of Southwestern Willow Flycatchers (Empidonax traillii extimus) on the upper San Luis Rey River, San Diego County, California—2020 data summary

We surveyed for Southwestern Willow Flycatchers ( Empidonax traillii extimus ; flycatcher) along the upper San Luis Rey River, near Lake Henshaw, in Santa Ysabel, California, in 2020. Surveys were completed at four locations: three downstream from Lake Henshaw, where nest monitoring occurred from 2015 to 2019 (Rey River Ranch [RRR], Cleveland National Forest [CNF], Vista Irrigation District [VID]), and one at VID Lake Henshaw (VLH) that was previously surveyed in 2018 and 2019. There were 62 territorial flycatchers detected at 3 locations (RRR, CNF, VLH); no flycatchers were detected at VID. Within the former nest monitoring study area, 11 flycatchers, including 5 males and 6 females, were detected at RRR and CNF. In total, seven territories were established, consisting of six pairs (two polygynous groups consisting of two males each pairing with two different females) and one male of undetermined breeding status. Upstream from the former nest monitoring study area at VLH, we detected 51 flycatchers, including 24 males and 27 females. There were 28 territories established, containing 27 pairs (23 monogamous pairings and 4 confirmed polygynous pairings consisting of 1 male and 2 females) and 1 male of undetermined breeding status. Brown-headed cowbirds ( Molothrus ater ; cowbird) were detected at all four survey locations. Flycatchers used four different habitat types in the survey area: (1) mixed willow riparian, (2) willow-oak, (3) willow-ash, and (4) willow-sycamore. Eighty percent of the flycatchers were detected in habitat characterized as mixed willow riparian, and 83 percent of the flycatchers were detected in habitat with greater than 50-percent native plant cover. Exotic vegetation was not prevalent in the survey area. There were 17 flycatcher nests incidentally located during surveys: 2 were successful, 3 were seen with nestlings on the last visit, 10 failed, and the outcome of the remaining 2 nests was unknown. Five of these nests were parasitized by cowbirds. There were 10 juveniles detected during surveys: 2 at RRR and 8 at VLH. Of the 17 banded flycatchers detected during surveys, 8 were resighted and confirmed to be adults that held territories in previous years. Seven flycatchers with a single dark blue federal band, indicating that they were banded as nestlings in the former nest monitoring study area downstream from Lake Henshaw, were resighted during surveys; 86 percent of these “natal” flycatchers held territories at VLH. In 2020, we documented both adult and natal flycatchers moving from the former nest monitoring study area downstream from Lake Henshaw upstream to the habitat surrounding Lake Henshaw. Six natal flycatchers that were originally banded as nestlings and two adults that previously held territories downstream dispersed to Lake Henshaw in 2020.

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USGS2021

Least Bell's Vireos and Southwestern Willow Flycatchers at the San Luis Rey flood risk management project area in San Diego County, California—Breeding activities and habitat use—2020 annual report

Executive Summary Surveys and monitoring for the endangered Least Bell’s Vireo ( Vireo bellii pusillus ; vireo) were done at the San Luis Rey Flood Risk Management Project Area (Project Area) in the city of Oceanside, San Diego County, California, between March 31 and July 20, 2020. We completed four protocol surveys during the breeding season, supplemented by weekly territory monitoring visits. We identified a total of 161 territorial male vireos; 145 were confirmed as paired and 4 were confirmed as single males. For the remaining 12 territories, we were unable to confirm pair status. Three transient vireos were detected in 2020. The vireo population in the Project Area increased by 26 percent from 2019 to 2020. Vireo populations increased across San Diego County, with a 39-percent increase documented at Marine Corps Base Camp Pendleton (MCBCP); a 58-percent increase at Marine Corps Air Station; a 78-percent increase on the Otay River; and a 7-percent increase in the population on the middle San Luis Rey River. We used an index of treatment (Treatment Index) to evaluate the impact of on-going vegetation clearing on the Project Area vireo population. The Treatment Index measures the cumulative effect of vegetation treatment within a territory (since 2005) by using the percent area treated weighted by the number of years since treatment. We found that the Treatment Index for unoccupied habitat was more than five times that of occupied habitat, indicating that vireos selected less disturbed habitat in which to settle. We monitored vireo nests at three general site types: (1) within the flood channel where exotic and native vegetation removal has occurred regularly (Channel), (2) three sites next to the flood channel where limited exotic and native vegetation removal has occurred (Off-channel), and (3) three sites that have been actively restored by planting native vegetation (Restoration). Nesting activity was monitored in 100 territories, 4 of which were occupied by single males. Hatching success was higher in the Channel relative to the Off-channel. We found no other differences between Channel, Off-channel, and Restoration nests in terms of clutch size or fledging success. There also was no difference in measures of productivity per pair between Channel, Off-channel, Restoration, and Mixed territories (territories that were classified as one site type but nesting occurred in another site type, or where multiple site types were used for nesting). Overall, breeding success and productivity were lower in 2020 than in 2019, with 69 percent of pairs fledgling at least one young and pairs fledging an average of 2.1±1.7 young. To investigate whether the cumulative years of treatment had an impact on vireo reproductive effort, we looked at the effects of the Treatment Index on reproductive parameters. Results from generalized linear models indicated that treatment did not have an effect on vireo nesting effort or the number of vireo fledglings per pair produced in 2020. Similarly, our analysis of nest survival for 2020 revealed no effect of Treatment Index on daily survival rate. Analysis of vegetation data collected at vireo nests from 2006 to 2020 revealed that vegetation at 1–2 meters (m) from the ground was the most important predictor of daily survival rate. There were differences in nest-placement characteristics among site types and successful/unsuccessful nests. Channel nests were placed higher in the vegetation than Off-channel or Restoration nests. Host plant height, distance to edge of host plant, and distance to edge of vegetation clump were greater at Channel sites compared with Off-channel sites, but were not different from Restoration sites. Within sites, we found only one difference between successful and unsuccessful nests. At Off-channel sites, successful nests were placed higher in the vegetation than unsuccessful nests. Red/arroyo willow ( Salix laevigata or Salix lasiolepis ) and mule fat ( Baccharis salicifolia ) were the species most commonly selected for nesting by vireos in all 3 site types. Vireos used a wider variety of species for nesting in Channel and Off-channel sites (7 and 10 species, respectively) compared to Restoration sites (3 species). Ninety-three vireos banded before the 2020 breeding season were resighted and identified at the Project Area in 2020, all of which were originally banded at the Project Area. Adult birds of known age ranged from 1 to 9 years old. A total of 171 vireos were newly banded in 2020. Twenty-eight adult vireos were banded with a unique color combination, and 143 nestlings were banded with a single dark blue numbered federal band on the left leg. Between 2006 and 2020, survivorship of males (67±10 percent) was consistently higher than females (59±11 percent). First-year birds from 2006 to 2020 had an average over-winter survivorship of 17±5 percent. First-year dispersal in 2020 averaged 2.9±2.9 kilometers (km), with the longest dispersal (13.5 km) by a female that was recaptured at Las Flores Creek, MCBCP. From 2007 to 2012, most returning first-year vireos returned to the Project Area, whereas from 2013 to 2017, the majority of returning birds dispersed to areas outside of the Project Area. In 2018, the trend shifted, and most first-year vireos returned to the Project area. This trend continued in 2020 with most first-year vireos returning to the Project Area; 77 percent of all re-encountered first-year birds returned to the Project Area and 23 percent dispersed to areas outside of the Project Area (upstream to the middle San Luis Rey River and to drainages on MCBCP). Most of the returning adult male vireos showed strong between-year site fidelity to their previous territories. Eighty percent of males (45/56) occupied a territory in 2020 that they had defended in 2019 (within 100 m). Thirty-three percent of females (2/6) detected in 2020 returned to a territory that they occupied in 2019. The average between-year movement for returning adult vireos was 0.1±0.5 km. We completed four protocol surveys for the endangered Southwestern Willow Fycatcher ( Empidonax traillii extimus ; flycatcher) at the Project Area between May 20 and July 20, 2020. No Willow Flycatchers were detected in the Project Area in 2020. A total of 46 vegetation transects (526 points) were sampled at the San Luis Rey Flood Risk Management Project Area in 2020. Seventy-one percent (376/526) of points were in the Channel and 22 percent (115/526) were at Upper Pond. The remaining 7 percent (35/526) were at the Whelan Restoration site. Foliage cover below 1 m was higher at the Channel points compared to Upper Pond and Whelan Restoration. Higher foliage cover in the Channel was attributed to the higher herbaceous component. However, foliage cover from 1 to 3 m was higher at the Whelan Restoration site compared to both Upper Pond and the Channel. Average canopy height was similar at all three site types and was 4.4 m or less. From 2006 to 2020, total foliage cover declined above 1 m in the Channel, from 4 to 5 m at Upper Pond, and above 8 m at Whelan Restoration. Within the Channel, the steepest declines occurred between 2009 and 2013 and between 2014 and 2016. Since 2016, we observed an increase in percent foliage between 0 and 2 m within the Channel, but for other height classes, percent cover remained below levels detected before 2009. Changes in cover at Upper Pond and Whelan Restoration appeared to be driven by the loss of tall tree cover. The vegetation mowing and treatment activities, in combination with lack of precipitation (especially between 2012 and 2016), may have contributed to the decline in foliage cover observed from 2006 to 2020. We sampled vegetation at 49 vireo nests and 49 random plots (“territory” plots) within territories in the Channel and Upper Pond following the 2020 breeding season. Vireos in the Channel selected territories with significantly more foliage cover above 2 m but less cover below 1 m relative to the available habitat. In contrast, Channel vireos selected nest sites within their territories with lower foliage cover above 3 m and were non-selective with regard to cover below 2 m. Vireos at Upper Pond generally were less selective with regard to territory and nest sites but tended to select territories with more foliage cover from 1 to 2 m and above 8 m, and they selected nest sites within their territories with greater foliage cover from 0 to 1 m.

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