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Eben H. Paxton

Publications and source records attributed to Eben H. Paxton.

89 records · Page 5Linked to original sources
USGS2014

Productivity of forest birds at Hakalau Forest NWR

Hawai‘i has some of the most endangered avian species in the world, which face numerous threats from habitat loss, disease, climate change, and introduced species. This report details the results of a two-year productivity study of all forest bird species at Hakalau National Wildlife Refuge, Hawai‘i Island. We found and monitored nests from seven native species and three common non-native species of forest birds at three sites across the refuge. In addition to gathering important baseline information on productivity of forest birds, we examined differences in productivity between years, sites, and as a function of nest height. The weather differed greatly between the two years, with much more rain occurring in 2014. The daily survival rate (DSR) of nests was found to have an inverse relationship with the amount of rainfall, and accordingly was much lower in 2014 compared to 2013. Nest success was lower at a regenerating forest site compared with mature rainforest, indicating negative environmental factors affecting nest success may be exacerbated in reforested areas which have lower canopies. Nest success was also impacted by nest height, with a positive relationship in the drier 2013, and a negative relationship in 2014 for the canopy nesting honeycreepers. The large difference in weather and DSR between years illustrates the need for long term demographic studies that can capture the vital rates of this community of birds.

Hawaii↗
USGS2013

Tamarisk in riparian woodlands: A bird’s eye view

This chapter presents a “bird's eye” view of tamarisk and examines some issues surrounding the management of tamarisk in riparian woodlands. The focus on birds is based on the fact that they are a relatively well-studied group that can provide important insights into the role of tamarisk in riparian ecosystems. Because the decline of native riparian habitat occurred concurrently with the spread of tamarisk, this invasive species has been portrayed as a key factor in the reduction of riparian breeding bird numbers. The chapter begins with an overview of the early perceptions and realities of why and how birds use tamarisk before turning to a discussion of the history of tamarisk control and its effects on birds. It then considers some of the changing perspectives about the management of tamarisk and riparian habitats in western North America.

Book chapter↗
USGS2013

Home range and use of habitat of western yellow-billed cuckoos on the middle Rio Grande, New Mexico

The western yellow-billed cuckoo (Coccyzus americanus occidentalis) is a Distinct Population Segment that has been proposed for listing under the Endangered Species Act, yet very little is known about its spatial use on the breeding grounds. We implemented a study, using radio telemetry, of home range and use of habitat for breeding cuckoos along the Middle Rio Grande in central New Mexico in 2007 and 2008. Nine of 13 cuckoos were tracked for sufficient time to generate estimates of home range. Overall size of home ranges for the 2 years was 91 ha for a minimum-convex-polygon estimate and 62 ha for a 95%-kernel-home-range estimate. Home ranges varied considerably among individuals, highlighting variability in spatial use by cuckoos. Additionally, use of habitat differed between core areas and overall home ranges, but the differences were nonsignificant. Home ranges calculated for western yellow-billed cuckoos on the Middle Rio Grande are larger than those in other southwestern riparian areas. Based on calculated home ranges and availability of riparian habitat in the study area, we estimate that the study area is capable of supporting 82-99 nonoverlapping home ranges of cuckoos. Spatial data from this study should contribute to the understanding of the requirements of area and habitat of this species for management of resources and help facilitate recovery if a listing occurs.

New Mexico↗
USGS2013

Abundance, distribution, and population trends of the iconic Hawaiian Honeycreeper, the ʻIʻiwi (Vestiaria coccinea) throughout the Hawaiian Islands

Naturalists in the 1800s described the ʻIʻiwi (Vestiaria coccinea) as one of the most abundant forest birds, detected in forested areas from sea level to tree line across all the major Hawaiian Islands. However, in the late 1800s, ʻIʻiwi began to disappear from low elevation forests, and by the mid-1900s, the species was largely absent from low- and mid-elevation areas. Today, ʻIʻiwi are restricted to high-elevation forests on the islands of Hawaiʻi, east Maui, and Kauaʻi, with a few birds apparently persisting on Oʻahu, Molokaʻi, and west Maui. ʻIʻiwi are highly vulnerable to introduced disease, and the prevalence of avian malaria in low and mid-elevations is believed to be the cause of ʻIʻiwi being restricted to high elevations where temperatures are too cold for the development of the disease and its mosquito vector. With global warming, it is feared that the disease will move quickly into the high-elevation forests where the last ʻIʻiwi reside, threatening their viability. The U.S. Fish and Wildlife Service was petitioned to list the ʻIʻiwi as an Endangered Species in 2010, and this report provides a comprehensive review of the abundance, distribution, and trends using historical survey data as well as the most recently available survey information (up to 2012). We estimate the total population size of ‘I‘iwi at 550,972–659,864 (mean = 605,418) individuals. Of these, 90 percent are on the island of Hawaiʻi, followed by east Maui (about 10 percent), with less than 1 percent on Kauaʻi. ʻIʻiwi population trends vary across the islands. ʻIʻiwi population in Kauaʻi has experienced sharp declines, with a projected trend of 92 percent decline over a 25 year period based on the 2000–2012 surveys. On East Maui, the northeastern region has experienced declines (34 percent over a 25 year period), while the southeastern region has been stable to moderately increasing. On the island of Hawaiʻi, population trends are mixed. On the windward side, populations are largely declining, although the northern section (Hakalau Forest) has stable populations. On the leeward side, results suggest a strongly increasing population, with estimates of as much as a 147 percent increase over a 25 year period from the Puʻu Waʻawaʻa region. However, it is unclear how much these results from the leeward side of Hawaiʻi show a population trend contrary to population trends in all other areas or are an artifact of a sparsely sampled area. Trends by elevation suggest a large decrease in numbers of ʻIʻiwi at elevations below 1,200 meters on Kauaʻi and northeast Maui. Low elevation ʻIʻiwi populations also appear to have decreased in other regions, although low-elevation areas are not surveyed as often as other areas because of their lack of native forest birds. An exception to this pattern was the lower portions of the Hakalau Forest National Wildlife Refuge Kona Unit in the central leeward part of the island of Hawaiʻi, where populations appeared stable at the lower elevations. Based on the most recent surveys (up to 2012), approximately 50 percent of ʻIʻiwi live in a narrow, 500-meter band at elevations of 1,200–1,700 meters, suggesting that ʻIʻiwi are vulnerable to future shifts in climate.

Hawai'i↗
USGS2013

Immunological markers for tolerance to avian malaria in Hawai`i `Amakihi: new tools for restoring native Hawaiian forest birds?

We evaluated three assays for non-specific or innate immune capacity to see if measurements were independent of malarial infection and capable of distinguishing malaria-tolerant, low-elevation Hawaiʽi ʽAmakihi from malaria-susceptible, high-elevation ʽAmakihi. ʽAmakihi were captured at Malama Ki Forest Reserve (20 m), Hakalau Forest National Wildlife Refuge (1800 m), and Upper Waiakea Forest Reserve (1700 m), bled for collection of plasma and packed erythrocytes for malarial diagnostics, and either transported to Kīlauea Field Station Aviary and held in captivity for 48 hours for inoculation of wing webs with phytohemagglutinin A (PHA) or released immediately in the field after collection of a blood sample. All birds were tested by polymerase chain reaction (PCR) and microscopy to determine infection status. We found no significant association between malarial infection status and degree of wing web swelling after inoculation with PHA (T = -0.174, df = 13, P = 0.864) and no association between origin of birds from low- and high-elevation populations and degree of wing web swelling (T = 0.113, df = 52, P = 0.911). Infected ʽAmakihi from low elevation had significantly higher small molecule plasma antioxidant capacity than uninfected individuals from the same population (T = -2.675, df = 21, P = 0.014), so we limited comparisons to uninfected birds. Uninfected ʽAmakihi from low elevations did not differ in small molecule plasma antioxidant capacity from uninfected ʽAmakihi from high elevation (T = -0.260, df = 46, P = 0.796). Compared to high-elevation birds, low-elevation ʽAmakihi had significantly higher titers of natural antibodies (NAb) as measured by complement-mediated lysis of rabbit erythrocytes (Mann-Whitney U = 27, X 2 = 32.332, df = 1, P < 0.0001). This innate immunological difference may be related to ability to survive malarial infection and may prove to be important for understanding possible mechanisms for the evolution of disease tolerance in Hawaiʽi’s native bird species.

Hawai'i↗
USGS2013

A landscape-based assessment of climate change vulnerability for all native Hawaiian plants

In Hawaiʽi and elsewhere, research efforts have focused on two main approaches to determine the potential impacts of climate change on individual species: estimating species vulnerabilities and projecting responses of species to expected changes. We integrated these approaches by defining vulnerability as the inability of species to exhibit any of the responses necessary for persistence under climate change (i.e., tolerate projected changes, endure in microrefugia, or migrate to new climate-compatible areas, but excluding evolutionary adaptation). To operationalize this response-based definition of species vulnerability within a landscape-based analysis, we used current and future climate envelopes for each species to define zones across the landscape: the toleration zone; the microrefugia zone; and the migration zone. Using these response zones we calculated a diverse set of factors related to habitat area, quality, and distribution for each species, including the amount of habitat protection and fragmentation and areas projected to be lost to sea-level rise. We then calculated the probabilities of each species exhibiting these responses using a Bayesian network model and determined the overall climate change vulnerability of each species by using a vulnerability index. As a first iteration of a response-based species vulnerability assessment (VA), our landscape-based analysis effectively integrates species-distribution models into a Bayesian network-based VA that can be updated with improved models and data for more refined analyses in the future. Our results show that the species most vulnerable to climate change also tend to be species of conservation concern due to non-climatic threats (e.g., competition and predation from invasive species, land-use change). Also, many of Hawaiʽi’s taxa that are most vulnerable to climate change share characteristics with species that in the past were found to be at risk of extinction due to non-climatic threats (e.g., archipelago endemism, single-island endemism). Of particular concern are the numerous species that have no compatible-climate areas remaining by the year 2100. Species primarily associated with dry forests have higher vulnerability scores than species from any other habitat type. When examined at taxonomic levels above species, low vulnerabilities are concentrated in families and genera of generalists (e.g., ferns or sedges) and typically associated with mid-elevation wet habitats. Our results replicate findings from other regions that link higher species vulnerability with decreasing range size. This species VA is possibly the largest in scope ever conducted in the United States with over 1000 species considered, 319 of which are listed as endangered or threatened under the U.S. Endangered Species Act, filling a critical knowledge gap for resource managers in the region. The information in this assessment can help prioritize species for special conservation actions, guide the management of conservation areas, inform the selection of research and monitoring priorities, and support adaptive management planning and implementation.

Hawai'i↗
USGS2012

Elucidating spatially explicit behavioral landscapes in the Willow Flycatcher

Animal resource selection is a complex, hierarchical decision-making process, yet resource selection studies often focus on the presence and absence of an animal rather than the animal's behavior at resource use locations. In this study, we investigate foraging and vocalization resource selection in a population of Willow Flycatchers, Empidonax traillii adastus , using Bayesian spatial generalized linear models. These models produce “behavioral landscapes” in which space use and resource selection is linked through behavior. Radio telemetry locations were collected from 35 adult Willow Flycatchers ( n = 14 males, n = 13 females, and n = 8 unknown sex) over the 2003 and 2004 breeding seasons at Fish Creek, Utah. Results from the 2-stage modeling approach showed that habitat type, perch position, and distance from the arithmetic mean of the home range (in males) or nest site (in females) were important factors influencing foraging and vocalization resource selection. Parameter estimates from the individual-level models indicated high intraspecific variation in the use of the various habitat types and perch heights for foraging and vocalization. On the population level, Willow Flycatchers selected riparian habitat over other habitat types for vocalizing but used multiple habitat types for foraging including mountain shrub, young riparian, and upland forest. Mapping of observed and predicted foraging and vocalization resource selection indicated that the behavior often occurred in disparate areas of the home range. This suggests that multiple core areas may exist in the home ranges of individual flycatchers, and demonstrates that the behavioral landscape modeling approach can be applied to identify spatially and behaviorally distinct core areas. The behavioral landscape approach is applicable to a wide range of animal taxa and can be used to improve our understanding of the spatial context of behavior and resource selection.

Utah↗
USGS2012

One year of migration data for a western yellow-billed cuckoo

In 2009, we studied the migration of the Western Yellow-billed Cuckoo by capturing 13 breeding birds on the middle Rio Grande, New Mexico, and attaching a 1.5-g Mk 14-S British Antarctic Survey geolocator to each bird. In 2010, we recaptured one of the cuckoos, enabling us to download its geolocation data. The cuckoo had flown approximately 9500 km during its southward migration, traveling through Central America to winter in portions of Bolivia, Brazil, Paraguay, and Argentina. The spring migration route differed somewhat from the fall route, with the cuckoo bypassing Central America to migrate through the Caribbean. Additionally, it moved between New Mexico and Mexico at the end of summer in 2009 and again in 2010 before being recaptured at its breeding site. Our results, albeit from one individual, hint at a dynamic migration strategy and have broad implications for the ecology and conservation of the Western Yellow-billed Cuckoo, a species of conservation concern.

Western Birds↗
USGS2012

2011 Kiwikiu (Maui Parrotbill) and Maui 'Alauahio abundance estimates and the effect of sampling effort on power to detect a trend

The Kiwikiu ( Pseudonestor xanthophrys ), also called the Maui Parrotbill, is an endangered, forest bird found only in high elevation, wet forest of the eastern portion of Maui Island. Recent surveys, conducted at five year intervals, have revealed wide variation in abundance estimates (Camp et al. 2009). Effective management and conservation requires accurate estimates of abundance, which is difficult for rare species such as the Kiwikiu because low density leads to few observations, resulting in low sample size and high uncertainty in abundance estimates. In addition to being rare, they occur in remote, difficult to access terrain, which makes them difficult to detect and further reduces the accuracy of counts. The Maui `Alauahio ( Paroreomyza montana ), sometimes called the Maui Creeper, historically occupied the entire island of Maui (Gorresen et al. 2009). It has since been extirpated from much of its original habitat and now occurs in forested areas of East Maui where its habitat overlaps with that of the Kiwikiu. Though they share the same habitat, the `Alauahio is much more abundant—by more than two orders of magnitude—and occurs over a wider range than the Kiwikiu. Both species appear to have no statistically significant population trend from 1980–2001, but abundance estimates vary widely from survey to survey and have wide uncertainties (Camp et al. 2009). Ideally survey design should result in estimates precise enough to be able to detect significant declines in abundance that may trigger management intervention. We wished to improve the accuracy of Kiwikiu abundance estimates and the ability to detect significant trends in abundance. To that end, in 2011, repeated point count surveys were conducted across the Kiwikiu range, excluding Haleakalā National Park (Figure 1). The increased sampling effort increases sample size and improves the precision of estimates, and repeat samples also allowed us to partition within-year and between-year variation in surveys, increasing the statistical power to detect trends.

Hawaii↗
USGS2011

Winter distribution of willow flycatcher subspecies

Documenting how different regions across a species' breeding and nonbreeding range are linked via migratory movements is the first step in understanding how events in one region can influence events in others and is critical to identifying conservation threats throughout a migratory animal's annual cycle. We combined two studies that evaluated migratory connectivity in the Willow Flycatcher ( Empidonax traillii ), one using mitochondrial DNA sequences from 172 flycatchers sampled throughout their winter range, and another which examined morphological characteristics of 68 museum specimens collected in the winter range. Our results indicate that the four subspecies occupy distinct but overlapping regions of the winter range. Connectivity between specific breeding and winter grounds appears to be moderate to strong, with distributions that suggest migration patterns of both the chain and leap-frog types connecting the breeding and nonbreeding grounds. The Pacific lowlands of Costa Rica appear to be a key winter location for the endangered Southwestern Willow Flycatcher ( E. t. extimus ), although other countries in Central America may also be important for the subspecies.

The Condor↗
USGS2011

Tamarisk biocontrol using tamarisk beetles: Potential consequences for riparian birds in the southwestern United States

The tamarisk beetle ( Diorhabda spp.), a non-native biocontrol agent, has been introduced to eradicate tamarisk ( Tamarix spp.), a genus of non-native tree that has become a dominant component of riparian woodlands in the southwestern United States. Tamarisk beetles have the potential to spread widely and defoliate large expanses of tamarisk habitat, but the effects of such a widespread loss of riparian vegetation on birds remains unknown. We reviewed literature on the effects of other defoliating insects on birds to investigate the potential for tamarisk beetles to affect birds positively or negatively by changing food abundance and vegetation structure. We then combined data on the temporal patterns of tamarisk defoliation by beetles with nest productivity of a well-studied riparian obligate, the Southwestern Willow Flycatcher ( Empidonax traillii extimus ), to simulate the potential demographic consequences of beetle defoliation on breeding riparian birds in both the short and long term. Our results highlight that the effects of tamarisk biocontrol on birds will likely vary by species and population, depending upon its sensitivity to seasonal defoliation by beetles and net loss of riparian habitat due to tamarisk mortality. Species with restricted distributions that include areas dominated by tamarisk may be negatively affected both in the short and long term. The rate of regeneration and/or restoration of native cottonwoods ( Populus spp.) and willows ( Salix spp.) relative to the rate of tamarisk loss will be critical in determining the long-term effect of this large-scale ecological experiment.

Arizona, Colorado, New Mexico, Utah↗
USGS2011

Keeping Hawai’i’s forest birds one step ahead of avian diseases in a warming world: a focus on Hakalau Forest National Wildlife Refuge. A case study from the National Conservation and Training Center Structured Decision Making Workshop

This report is a product of a one-week workshop on using Structured Decision Making to identify and prioritize conservation actions to address the threat of climate change on Hawaii‟s native forest bird community. Specifically, t his report addresses the issue of global warming ‟s likely role in increasing disease prevalence in upper elevation forests of Hawaii, negatively impacting native bird populations susceptible to the disease but currently disease - free because of the cooler temperatures at high elevations.

Hawaii↗
USGS2010

Geographic variation in the plumage coloration of willow flycatchers Empidonax traillii

The ability to identify distinct taxonomic groups of birds (species, subspecies, geographic races) can advance ecological research efforts by determining connectivity between the non-breeding and breeding grounds for migrant species, identifying the origin of migrants, and helping to refine boundaries between subspecies or geographic races. Multiple methods are available to identify taxonomic groups (e.g., morphology, genetics), and one that has played an important role for avian taxonomists over the years is plumage coloration. With the advent of electronic devices that can quickly and accurately quantify plumage coloration, the potential of using coloration as an identifier for distinct taxonomic groups, even when differences are subtle, becomes possible. In this study, we evaluated the degree to which plumage coloration differs among the four subspecies of the willow flycatcher Empidonax traillii, evaluated sources of variation, and considered the utility of plumage coloration to assign subspecies membership for individuals of unknown origin. We used a colorimeter to measure plumage coloration of 374 adult willow flycatchers from 29 locations across their breeding range in 2004 and 2005. We found strong statistical differences among the mean plumage coloration values of the four subspecies; however, while individuals tended to group around their respective subspecies' mean color value, the dispersion of individuals around such means overlapped. Mean color values for each breeding site of the three western subspecies clustered together, but the eastern subspecies' color values were dispersed among the other subspecies, rather than distinctly clustered. Additionally, sites along boundaries showed evidence of intergradation and intermediate coloration patterns. We evaluated the predictive power of colorimeter measurements on flycatchers by constructing a canonical discriminant model to predict subspecies origin of migrants passing through the southwestern U.S. Considering only western subspecies, we found that individuals can be assigned with reasonable certainty. Applying the model to migrants sampled along the Colorado River in Mexico and the U.S. suggests different migration patterns for the three western subspecies. We believe that the use of plumage coloration, as measured by electronic devices, can provide a powerful tool to look at ecological questions in a wide range of avian species.

Journal of Avian Biology↗
USGS2010

Saltcedar and Russian olive interactions with wildlife: Chapter 4

Riparian areas of flood plains typically provide a mosaic of productive habitats (Stanford and others, 2005; Latterell and others, 2006) capable of supporting many wildlife species, particularly in the arid and semiarid Western United States. The establishment of nonnative invasive plants can alter riparian habitat by inhibiting native plant recruitment and by increasing the risk of wildfire (Howe and Knopf, 1991; Busch and Smith, 1995). However, the effects of nonnative plants are not necessarily always negative. Many wildlife species will use the exotic plants to some extent, especially when mixed with native vegetation (van Riper and others, 2008), but overall, species of wildlife exhibit a negative or neutral response to exotic habitat. In many areas of the Western United States where riparian systems have been degraded via anthropogenic activities (for example, flood control or groundwater pumping), native vegetation may have difficulty persisting and nonnative vegetation may provide the only available habitat for some species of wildlife (Katz and Shafroth, 2003; Stromberg and others, 2007). Therefore, where possible, the ultimate goal of ecological restoration activities should be the reestablishment of native riparian plant communities and a return to more natural hydrological regimes. Nonnative saltcedar (Tamarix spp.) and Russian olive (Elaeagnus angustifolia) are the second and fifth most abundant plants in riparian areas in the Western United States (see chap. 2, this volume; Friedman and others, 2005). Methods for controlling nonnative vegetation can alter riparian areas, often in unpredictable ways, and have the potential to impact a variety of habitat types used by wildlife (Bateman, Chung-MacCoubrey, Finch, and others, 2008). Therefore, understanding how wildlife utilize saltcedar and Russian olive and the effects of control activities on wildlife are important for resource managers who must balance management decisions such as nonnative plant control with protecting critical wildlife habitat. In this chapter, we present a synthesis of published literature on the use of saltcedar and Russian olive by wildlife and discuss how wildlife respond or are likely to respond to control measures for saltcedar and Russian olive and subsequent restoration efforts. We discuss responses of several groups of wildlife, including arthropods, birds, mammals, herpetofauna, and fish.

Book chapter↗
USGS2008

Using Molecular Genetic Markers to Resolve a Subspecies Boundary: The Northern Boundary of the Southwestern Willow Flycatcher in the Four-Corner States

*Executive Summary* The northern boundary of the endangered Southwestern Willow Flycatcher (Empidonax traillii extimus) is currently approximated as running through southern Colorado and Utah, but the exact placement is uncertain because this subspecies shares a border with the more northern and non-endangered E. t. adastus. To help resolve this issue, we evaluated the geographic distribution of mitochondrial and nuclear DNA by sampling breeding sites across the four-corner states (Arizona, Colorado, New Mexico, and Utah). We found that breeding sites clustered into two major groups generally consistent with the currently designated boundary, with the exception of three sites situated along the current boundary. However, delineating a precise boundary that would separate the two subspecies is made difficult because (1) we found evidence for a region of intergradation along the boundary area, suggesting the boundary is not discreet, and (2) the boundary region is sparsely populated, with too few extant breeding populations to precisely locate a boundary. The boundary region encompasses an area where elevation changes markedly over relatively short distances, with low elevation deserts to the south and more mesic, higher elevation habitats to the north. We hypothesized that latitudinal and elevational differences and their concomitant ecological effects could form an ecological barrier that inhibited gene flow between the subspecies, forming the basis for the subspecies boundary. We modeled changes in geographic patterns of genetic markers as a function of latitude and elevation finding significant support for this relationship. The model was brought into a GIS environment to create multiple subspecies boundaries, with the strength of each predicted boundary evaluated on the basis of how much genetic variation it explained. The candidate boundary that accounted for the most genetic variation was situated generally near the currently recognized subspecies boundary, but should be more biologically meaningful because it incorporates the landscape features that may be driving separation of the subspecies. Even so, we caution that using any narrow boundary line as an indicator of subspecies identity could be misleading because biologically the boundary is a region of intergradation rather than a discrete line. Designating, a boundary ultimately becomes a regulatory and management decision based on how much of the genetic variation unique to a subspecies should be protected. We discuss how the results of this study can help guide this decision process by wildlife policy makers.

Open-File Report↗
USGS2007

The ecology of the Southwestern Willow Flycatcher in central Arizona - A 10-year synthesis report

BACKGROUND From 1996 to 2005, the U.S. Geological Survey (USGS) conducted a demographic study of the Southwestern Willow Flycatcher (Empidonax traillii extimus) in Arizona in collaboration with the Arizona Game and Fish Department (AGFD). The study was begun the year following the listing of the Southwestern Willow Flycatcher as an endangered species. At the time of the listing, very little was known about the biology and threats to the flycatcher, and one of the main objectives of the study was to gather detailed long-term information on the biology of the flycatcher. This report is organized into eight chapters. Following the introductory chapter, we deal with specific aspects of flycatcher ecology and habitat use in each of six separate chapters. We end with a concluding chapter that synthesizes information into broad topical themes that address key management issues. Each of the core chapters (chapters 2 through 7) conclude with a list of management considerations derived from the findings of the respective chapter.

Open-File Report↗