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Results for “The Southwestern Naturalist”

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At least 181 records · Page 10Linked to original sources
USGS1991

Habitat use and movements of canvasback broods in southwestern Manitoba

Canvasback (Aythya valisineria) broods (n = 69) accompanying marked females were observed during five summers in southwestern Manitoba. We evaluated movements of broods of different age classes ( 14 days old, 15-28 days old, and >28 days old) among ponds of different size and wetland class. Of 202 brood sightings, 7% occurred on seasonal ponds, 81% on semipermanent ponds, and 12% on permanent ponds. Pond size ( 0.2 ha vs. >0.2 ha) was a significant factor in brood use whereas wetland class was not. Canvasback broods used larger ponds as brood age class increased. Broods moved an average of 195 m between sightings. Eighty-three percent of broods observed within seven days of hatching (n = 46) had moved from the nesting pond. No significant differences in frequency or distance of movements were detected among years or among brood age classes. Extensive movements among ponds of various sizes and classes emphasize the importance of wetland complexes for providing diverse habitats needed for nesting and brood-rearing canvasbacks.

Prairie Naturalist↗
USGS2017

Landscape movements by two species of migratory nectar-feeding bats (Leptonycteris) in a northern area of seasonal sympatry

Animals often migrate to exploit seasonally ephemeral food. Three species of nectar-feeding phyllostomid bats migrate north from Mexico into deserts of the United States each spring and summer to feed on blooms of columnar cactus and century plants ( Agave spp.). However, the habitat needs of these important desert pollinators are poorly understood. We followed the nighttime movements of 2 species of long-nosed bats ( Leptonycteris yerbabuenae and L. nivalis ) in an area of late-summer sympatry at the northern edges of their migratory ranges. We radio-tracked bats in extreme southwestern New Mexico during 22 nights over 2 summers and acquired location estimates for 31 individuals. Both species cohabitated 2 major day roosts that were 30 km apart and in different mountain ranges, and individual bats sometimes moved between the roosts. Sampling was opportunistic and limited, but there were no obvious qualitative differences in observed patterns of movement between species or years, or among sex, age, and reproductive groups. Both species were observed foraging most often in the mountain range that had a relatively higher observed density of presumed food plants ( Agave palmeri ); when roosting in an adjacent mountain range, bats sometimes commuted >20 km one way to forage. Contrary to evidence indicating these species partition resources farther south in Mexico, our findings suggest that L. yerbabuenae and L. nivalis seasonally share common roost and food resources during late summer in this northern area of sympatry.

Western North American Naturalist↗
USGS2021

Southwestern bats and their external bacteria

Bat species diversity within the United States is greatest in the Southwest, with approximately 30 species present. At least 16 of these bat species hibernate and are susceptible to white-nose syndrome (WNS), which is caused by the fungus Pseudogymnoascus destructans . Since 2006, millions of bats from 35 U.S. states and 7 Canadian provinces have died from WNS. In previous studies of external surfaces of bats sampled from southwestern states, Actinobacteria were detected that were shown to have antifungal properties against P. destructans in laboratory testing. These studies motivated us to expand our research to sites that represent possible gateways for P. destructans to enter the Southwest so that we could establish a baseline of bat microbiota before the arrival of WNS. We surveyed for the presence of bats and their external microbiota at 3 national parks and monuments located in southeastern Colorado and northeastern New Mexico. Our results document new occurrence records of bat species and their external bacteria at each sampling location. Additionally, we provide insight on the composition of bat external microbiota in the absence of P. destructans , while revealing information about the Streptomyces and other possible native defenses of bats against P. destructans at a gateway into the Southwest.

Western North American Naturalist↗
USGS2006

Response of Rocky Mountain elk (Cervus elaphus) to wind-power development

Wind-power development is occurring throughout North America, but its effects on mammals are largely unexplored. Our objective was to determine response (i.e., home-range, diet quality) of Rocky Mountain elk (Cervus elaphus) to wind-power development in southwestern Oklahoma. Ten elk were radiocollared in an area of wind-power development on 31 March 2003 and were relocated bi-weekly through March 2005. Wind-power construction was initiated on 1 June 2003 and was completed by December 2003 with 45 active turbines. The largest composite home range sizes (>80 km2) occurred April-June and September, regardless of the status of wind-power facility development. The smallest home range sizes (<50 km2) typically occurred in October-February when elk aggregated to forage on winter wheat. No elk left the study site during the study and elk freely crossed the gravel roads used to access the wind-power facility. Carbon and nitrogen isotopes and percent nitrogen in feces suggested that wind-power development did not affect nutrition of elk during construction. Although disturbance and loss of some grassland habitat was apparent, elk were not adversely affected by wind-power development as determined by home range and dietary quality.

American Midland Naturalist↗
USGS1984

Seed predation due to the yucca moth symbiosis

All species of Yucca (Agavaceae) require the pollinator services of a species of moth in the genus Tegeticula ( Lepidoptera : Incurvariidae). These moths oviposit in the ovary of the plants and the larvae are entirely dependent upon Yucca seeds for food. The extent and distribution of larval seed predation was examined in nine Yucca species in the southwestern United States. The proportion of seeds destroyed by the yucca moth ranged from 3 % in Y. schidigera from coastal southern California to 45 % in one population of Y. angustissima from southern Utah. This sampling was done in 1979 at which time the Y. schidigera population averaged 0.6 larvae per fruit and the population of Y. angustissima averaged 9.3 larvae per fruit. A second sampling of these populations in 1982 averaged 0.5 for Y. schidigera and 5.6 for Y. angustissima . Several species showed significant differences between populations in the number of larvae per fruit. Contrary to expectation, based on the dogma that fruit production is dependent upon Tegeticula pollination (which is always followed by oviposition), a large number of fruits were found without larvae. The proportion varied greatly between populations but was as high as two thirds of all fruits in some populations. Observations suggested that these flowers had been pollinated by Tegeticula and the moths had oviposited in them but that the eggs failed to hatch.

American Midland Naturalist↗
USGS2003

Recurrence of Mexican long-tongued bats (Choeronycteris mexicana) at historical sites in Arizona and New Mexico

The Mexican long-tongued bat ( Choeronycteris mexicana ) is a nectar-eating species that seasonally inhabits the southwestern United States. Since 1906, fewer than 1500 individuals of C. mexicana have been documented throughout the range of the species. We conducted a field survey in Arizona and New Mexico during summer 1999 to check historically occupied areas for recurrence of C. mexicana . We observed C. mexicana occupying a majority (75%, n = 18) of visited sites. Multiple individuals were observed at many sites, including young-of-year. Choeronycteris mexicana roosted in lighted areas close to entrances within mine adits, abandoned buildings, wide rock crevices, and caves. All occupied sites were in Madrean evergreen woodlands or semidesert grasslands where species of Agave were present. Most sites were located near a water source and, with the exception of a single site, near areas of riparian vegetation. Sites at which we did not encounter C. mexicana were frequently disturbed, difficult to search, or historically occupied by single individuals. Based on the relatively high rate of bat recurrence, we do not believe that populations of C. mexicana in the region have declined dramatically over the past several decades.

Western North American Naturalist↗
USGS2025

Pleistocene porcupine (Erethizontidae) records in arid southwestern North America and comparisons with the modern distribution of Erethizon dorsatum in southern California and Arizona

he North American porcupine ( Erethizon dorsatum ) is widely distributed throughout many ecosystems on the continent from northern Mexico to the Arctic Ocean, except for the southeastern portion of the United States. Habi­tats include the arid Desert Southwest region where modern records are generally sparse. The paleogeographic range in the Desert Southwest is not unlike the modern distribution of Erethizon , with some exceptions. Although there are early Pleistocene records of Erethizon for southern California, no late Pleistocene records (Rancholabrean North American Land Mammal Age [NALMA]) are known for Imperial, Inyo, Riverside, or San Bernardino Counties in southern California or in Mexico. This is surprising given late-Pleistocene records in Arizona, Nevada, and New Mexico and modern records from southern California and Mexico. Pleistocene habitats for porcupines were similar to those occupied today, just at different elevations due to differing climates. Modern preferred habitats in the Desert Southwest include conifer-clad high-elevation areas and associated pinyon pine / juniper belts, and occasionally riparian corridors in desert environments. The overall rarity of porcupines today in arid parts of the Desert Southwest is likely due to the combination of increasing aridity in the region during the Holocene, past persecution by humans, and increasing predator populations.

Arizona, California↗
USGS2005

Sonoran Desert winter annuals affected by density of red brome and soil nitrogen

Red brome [ Bromus madritensis subsp. rubens (L.) Husn.] is a Mediterranean winter annual grass that has invaded Southwestern USA deserts. This study evaluated interactions among 13 Sonoran Desert annual species at four densities of red brome from 0 to the equivalent of 1200 plants m −2 . We examined these interactions at low (3 μg) and high (537 μg NO 3 − g soil −1 ) nitrogen (N) to evaluate the relative effects of soil N level on survival and growth of native annuals and red brome. Red brome did not affect emergence or survival of native annuals, but significantly reduced growth of natives, raising concerns about effects of this exotic grass on the fecundity of these species. Differences in growth of red brome and of the three dominant non nitrogen-fixing native annuals at the two levels of soil N were similar. Total species biomass of red brome was reduced by 83% at low, compared to high, N levels, whereas that of the three native species was reduced by from 42 to 95%. Mean individual biomass of red brome was reduced by 87% at low, compared to high, N levels, whereas that of the three native species was reduced by from 72 to 89%.

American Midland Naturalist↗
USGS2024

Diet of Myotis ciliolabrum from six sites in the southwestern United States

With bat populations declining in many parts of the world, detailed life history information will be critical for assessing vulnerabilities of bat populations and associated trophic effects. Myotis ciliolabrum (western small-footed bat) is a species of insectivorous bat distributed from the Great Plains to the Pacific Coast and from British Columbia to Central Mexico. The species is spottily distributed within this wider range but is locally abundant in areas containing appropriate rocky habitat. Despite M. ciliolabrum being relatively common, little information is available about its feeding ecology. Earlier studies have suggested that skull morphology can be used to determine whether insectivorous bats select for soft- or hard-bodied prey, but we hypothesized that M. ciliolabrum may feed opportunistically on a variety of insect types. To test this hypothesis, we examined the feeding habits of western small-footed bats captured during 2000–2022 at 6 national parks and 1 national conservation area across the Southwest. Visual analysis of prey remains in guano revealed that western small-footed bats within our study area consumed insects belonging to 7 orders (Lepidoptera, Coleoptera, Hymenoptera, Hemiptera, Neuroptera, Diptera, and Odonata) and 20 families. Diet varied over time and across geographic space, though we observed a general trend in which the orders Lepidoptera, Coleoptera, and Hymenoptera were consumed at the highest volumes. This varied diet indicates opportunistic feeding in which M. ciliolabrum makes use of locally abundant resources.

Colorado, New Mexico, Texas↗
USGS2004

Estimating the use of morphometric measurements from museum specimens for sex determination in Mountain Plovers (Charadrius montanus)

The Mountain Plover ( Charadrius montanus ) is a shorebird species endemic to the dry, terrestrial ecosystems of the Great Plains and southwestern United States. Breeding Bird Survey data suggest that Mountain Plover populations have declined by >60% in the last 30 years. A better understanding of the population dynamics of the Mountain Plover is important in determining future management goals for this species. However, this effort is hampered by the inability to determine the sex of Mountain Plovers accurately under field conditions. In an effort to develop a simple method for sexing plovers in the hand, we measured external morphometric characteristics from 190 museum specimens of adult Mountain Plovers in alternate (breeding) plumage. Logistic regression and discriminant function analyses were performed on 10 external morphometric measurements (lengths of unflattened wing chord, 10th primary, central rectrix, outer rectrix, total head length, exposed culmen, culmen, bill depth, bill width, and tarsus). The results of these analyses indicated that Mountain Plover sexes were similar for all measures except culmen length. However, further analysis determined that culmen length accurately predicted sex in less than two-thirds of the specimens, suggesting that this measure is a poor predictor of sex in Mountain Plovers. Structurally, Mountain Plovers appear to be nearly identical between the sexes, and other methods of sexing birds (e.g., plumage characteristics, behavioral observations, or molecular markers) should be further assessed for devising a simple method for sexing Mountain Plovers under field conditions.

Western North American Naturalist↗
USGS2006

Transverse and longitudinal variation in woody riparian vegetation along a montane river

This study explores how the relationship between flow and riparian vegetation varies along a montane river. We mapped occurrence of woody riparian plant communities along 58 km of the San Miguel River in southwestern Colorado. We determined the recurrence interval of inundation for each plant community by combining step-backwater hydraulic modeling at 4 representative reaches with Log-Pearson analysis of 4 stream gaging stations. Finally, we mapped bottomland surficial geology and used a Geographic Information System to overlay the coverages of geology and vegetation. Plant communities were distinctly arrayed along the hydrologic gradient. The Salix exigua Nuttall (sand-bar willow) community occurred mostly on surfaces with a recurrence interval of inundation shorter than 2.2 years; the Betula occidentalis Hooker (river birch) community peaked on sites with recurrence intervals of inundation between 2.2 and 4.6 years. The hydrologic position occupied by communities dominated by Populus angustifolia James (narrowleaf cottonwood) was strongly related to age of trees and species composition of understory shrubs. The fraction of riparian vegetation on surfaces historically inundated by the river decreased in the upstream direction from almost 100% near Uravan to <50% along the South Fork of the San Miguel River. In upstream reaches much of the physical disturbance necessary to maintain riparian vegetation is provided by valley-side processes including debris flows, floods from minor tributaries, landslides, and beaver activity. Where valley-side processes are important, prediction of riparian vegetation change based on alterations of river flow will be incomplete.

Western North American Naturalist↗
USGS2019

The bee fauna of coastal Napatree Point and two inland sites in southern Rhode Island

We surveyed the bee fauna at Napatree Point, a coastal barrier beach in southwestern Rhode Island, using bee-bowl and netting samples, and compared results to bee-bowl samples at 2 inland sites. We collected a total of 53 species and morphospecies at Napatree Point, including 5 likely Rhode Island state records and several coastal dune and sand-nesting species that were not found inland. The comparative bee-bowl samples (colored bowls with soapy water placed at the sites to collect visiting bees) captured 35 species at Napatree Point and 66 at the inland sites (which included 6 likely state records, 2 shared with Napatree). The Napatree fauna shared numerous species with the inland sites, but overall species composition differed substantially. Both Napatree and inland sites showed greatest bee activity and species richness in spring. During spring, the most common bees at Napatree were twig- and cavity-nesting species such as Ceratina dupla and Osmia simillima , and the wood-nesting Lasioglossum oblongum , while the most abundant bees inland were the soil-nesting Andrena nasonii and Augochlorella aurata . Netting samples differed from bee-bowl samples in that they captured larger species and species foraging at flowers distant from the bee-bowl transects, but they missed several diminutive species that were captured by bee bowls. Use of 2 sampling methods, therefore, provided a broader view of the bee fauna than would have been possible with a single collection method.

Rhode Island↗
USGS2020

Identifying life history traits that promote occurrence for four minnow (Leuciscidae) species in intermittent Gulf Coastal Plain streams

- Life history traits of stream fishes partly reflect adaptations to disturbance regimes, which in turn shape assemblage composition via environmental filters. In this study, we focused on life history traits of four morphologically similar leuciscid species in coastal plain streams of southwestern GA that are shifting from historically perennial to intermittent flow. We evaluated differences in reproductive timing, sex ratio, body size at maturity, reproductive investment, and diet, traits hypothesized to influence species persistence in intermittent streams. We first ordinated published species occurrence data for samples of fish communities in perennial and intermittent streams in the study region, and identified four focal taxa as differing in their associations with intermittency. We then periodically sampled individuals of the focal taxa in 14 streams over a year (May 2016-April 2017). We found that for Pteronotropis harperi (Redeye Chub), a species strongly associated with intermittent streams, reproductive timing did not overlap with typical seasonal stream drying. Redeye chub also had the significantly smallest minimum length at maturation and the greatest reproductive investment. Fishes associated with perennial streams (Pteronotropis grandipinnis (Apalachee Shiner) and Notropis petersoni (Coastal Shiner)), or not associated with either stream type (Notropis texanus (Weed Shiner)), had at least a portion of their reproductive timing overlapping with times when streams were likely to dry, and had similar and significantly lower reproductive investment than Redeye Chub. Redeye Chub displayed no shift in diet when streams ceased flowing, while Apalachee Shiner showed decreases in terrestrial prey. Our results suggest that the size at maturity, reproductive timing, and reproductive investment may promote persistence by the Redeye Chub given projections of more frequent and intense periods of stream intermittency.

Gulf Coast↗
USGS2017

Distribution and abundance of Millicoma Dace in the Coos River Basin, Oregon

The Millicoma Dace Rhinichthys cataractae is a form of Longnose Dace endemic to the Coos River drainage in southwestern Oregon. Sparse species records in the Oregon State University Ichthyology Collection and database and infrequent recent encounters prompted surveys to assess the current status and distribution of the species. In 2014, we surveyed locations that had historically supported Millicoma Dace using backpack electrofishing to describe their current distribution and abundance at these locations. In 2015, we extended these surveys further upstream in the South Coos River basin, outside of the documented historical range. We used an N-mixture model to estimate abundance and capture probability for Millicoma Dace at each sampling location. We evaluated the effects of habitat covariates on both capture probability and abundance at each sample site. We found Millicoma Dace were widespread throughout their historical range and in the South Coos River sites outside of their documented historical range. We only found Millicoma Dace associated with native fishes; we did not collect any nonnative fish during our surveys. We collected Millicoma Dace exclusively from swift-water habitats, which were relatively uncommon in the basin, and found them typically associated with cobble or boulder substrates. Millicoma Dace were most abundant in the South Fork Coos and West Fork Millicoma River subbasins. We estimated capture probabilities for Millicoma Dace ranging from 9% when substrate was dominated by bedrock to 28% when substrate was dominated by cobble or gravel. Abundance estimates ranged from 1 to 560 dace per sampling location with a total estimated abundance (sum of site estimates) of over 3200 dace for the sites we sampled.

Oregon↗
USGS2002

Influence of topography on density of grassland passerines in pastures

Pastures provide substantial habitat for grassland birds of management concern in the Driftless Area of southwestern Wisconsin. The rolling topography in this region is characterized by lowland valleys surrounded by relatively steep and often wooded slopes which are set apart from more expansive treeless uplands. We hypothesized that there would be lower densities of area sensitive grassland passerines in lowland grasslands compared to upland grasslands because of their preference for larger more open grasslands. To test this hypothesis and assess how well pasture area and vegetation structure predicted grassland passerine density compared to upland/lowland status, we conducted point counts of birds in 60 pastures in May-June 1997 and 1998. Upland pastures generally supported greater densities of grassland passerines than lowland pastures. Densities of Savannah sparrow ( Passerculus sandwichensis ) and bobolink ( Dolichonyx oryzivorus ) were significantly higher in upland pastures than in lowland pastures. Grasshopper sparrow ( Ammodramus savannarum ) density was significantly higher on uplands in one of the study years. The density of eastern meadowlark ( Sturnella magna ), western meadowlark ( S. neglecta ) and sedge wren ( Cistothorus platensis ) did not differ significantly between uplands and lowlands. Grassland passerine density was also predicted by pasture size and vegetation structure. Densities of bobolink and grasshopper sparrow were higher in larger pastures. Bobolink and Savannah sparrow occurred on pastures with greater vegetation height-density and less bare ground; bobolink also preferred shallower litter depths. Lowland pastures supported grassland bird species of management concern and should not be neglected. However, we recommend that pasture management for grassland passerines in areas of variable topography favor relatively large upland pastures that will contain higher densities of species of management concern.

Wisconsin↗
USGS2017

Life history attributes of Arizona Grasshopper Sparrow (Ammodramus savannarum ammolegus) and comparisons with other North American subspecies

Ammodramus savannarum ammolegus —commonly referred to as the Arizona Grasshopper Sparrow—occurs in the desert and plains grasslands of southeastern Arizona, southwestern New Mexico, and northern Sonora, Mexico. Although a subspecies of conservation concern, this is the first intensive study of its life history and breeding ecology, providing baseline data and facilitating comparisons with other North American Grasshopper Sparrow subspecies. Specifically, I found A. s. ammolegus males generally weighed less than other subspecies (16.0 ± 0.8 g) but with intermediate exposed culmen length (11.6 ± 0.5 mm) and wing chord length similar to the other two migratory subspecies (62.7 ± 1.5 mm). Territory size for A. s. ammolegus was 0.72 ± 0.37 ha, with some variation between sites and among years, possibly indicating variation in habitat quality across spatial and temporal scales. The return rate for A. s. ammolegus males was 39.2%. Nest initiation for A. s. ammolegus was early to mid-July after the monsoons had begun. Domed nests were constructed on the ground, primarily under native bunch grasses, and frequently with a tunnel extending beyond the nest rim, with nest openings oriented north. Clutch size was 3.97 ± 0.68, with no evidence of Brown-headed Cowbird ( Molothrus ater ) nest parasitism. Extreme climate factors in the arid Southwest may have affected the life history and morphology of A. s. ammolegus as compared to other subspecies, influencing body size and mass, culmen length, breeding phenology, and nest orientation. Other geographic variation occurred in return rates, clutch size, and nest parasitism rates. The baseline data for A. s. ammolegus obtained in this study will inform future taxonomic and ecological studies as well as conservation planning. Comparisons of A. s. ammolegus morphometrics with those of other subspecies will assist field biologists in distinguishing among subspecies where they overlap, especially on wintering grounds.

Arizona↗
USGS2006

Populations and habitat relationships of Piute ground squirrels in southwest Idaho

Piute ground squirrels (Spermophilus mollis idahoensis) are normally above ground from late January until late June or early July in the Snake River Birds of Prey National Conservation Area in southwestern Idaho. In 2002 they were rarely seen above ground after early May. Because of the ecological importance of ground squirrels for nesting raptors and other species, we sought to determine the reasons for their early disappearance. We sampled 12 sites from January 2003 through March 2003 to determine if a population crash had occurred in 2002. Tests indicated that Piute ground squirrels had not been exposed to plague within the past year. The presence of yearlings in the population indicated that squirrels reproduced in 2002 and that at least some yearlings survived the winter. Both yearling and adult squirrels appeared to be reproducing at or above normal rates in 2003. The most plausible explanation for the early disappearance of Piute ground squirrels in 2002 is that squirrels entered seasonal torpor early in response to a late spring drought. In addition, the breeding chronology of squirrels may have shifted during the past 2 decades in response to climate change and/or habitat alteration. Shrub habitats provide a more favorable and stable environment for squirrels than grass habitats. Squirrel abundance was higher on live-trapping grids with sagebrush than on grids dominated by grass, and squirrel masses were higher at sites dominated by shrubs and Sandberg bluegrass (Poa secunda). Densities in big sagebrush (Artemisia tridentata) were within the ranges reported for earlier years, but densities in grass were lower than previously reported. Low densities at grassland sites in 2003 support other findings that drought affects squirrels in altered grass communities more than those in native shrub habitats. Long-term shifts in ground squirrel breeding chronology may have implications for raptors that depend on them for food.

Western North American Naturalist↗
USGS2022

Injuries and abnormalities of the southwestern pond turtle (Actinemys pallida) in the Mojave River of California

The southwestern pond turtle ( Actinemys pallida ) is a semiaquatic turtle that occasionally spends time on land to bask, oviposit, make intermittent overland movements, and overwinter in terrestrial locations. Use of both aquatic and terrestrial environments exposes semiaquatic turtles to increased risk of injury or mortality from floods, predation attempts, and other environmental hazards (e.g., human activities such as vehicle strikes, etc.). We collected injury and morphological abnormality data from adult turtles at 3 study sites along the length of the Mojave River in San Bernardino County, California: 1 site on the upper half of the Mojave River (hereafter known as UHMRS) and 2 sites each on the lower half of the Mojave River (hereafter known as LHMRS). The studies were conducted when turtles were most active between May and October 1998–1999 and again from April to September 2016–2019. A total of 84 A. pallida were captured among all sites and all years. Seventeen percent ( n = 8) of the turtles captured at UHMRS exhibited shell abnormalities (natural variations in shell or bone morphology). Injuries (damage inflicted by force to the shell or body) occurred in 68% ( n = 26) of captured turtles at both the LHMRS sites combined and 78% ( n = 36) of turtles captured at the UHMRS alone. A total of 74% ( n = 62) of turtles had injuries at all sites combined. There was no statistical difference in the proportion of injured and noninjured turtles between the sexes for either the 2 LHMRS sites combined or the UHMRS. Mean carapace length was not significantly different between injured and noninjured turtles for these same sites. Injuries occurred in the majority of captured turtles at all sites and may be an indicator of the extent of threats facing these turtles.

Western North American Naturalist↗