Geology topics

Mary J. Whitfield

Publications and source records attributed to Mary J. Whitfield.

8 recordsLinked to original sources

USGS2023

Historical DNA reveals climate adaptation in an endangered songbird

To cope with climate change, species may shift their distributions or adapt in situ to changing environmental conditions. However, clear examples of genetic changes via adaptation are limited. We explore evolutionary responses to climate change in the endangered southwestern willow flycatcher ( Empidonax traillii extimus ) through whole-genome comparisons between historical specimens, collected from 1888 to 1909 near San Diego, California, United States, and contemporary individuals from across the breeding range. Genomic analyses revealed that introgression into San Diego increased adaptive potential over time and shifted genome-wide population structure towards that of neighbouring populations. In contrast, loci linked to climate (dew point temperature and precipitation) shifted away from neighbouring populations and in a direction consistent with adaptation to climate change in southern California. This research highlights the role of admixture in facilitating adaptive shifts through its impact on genome-wide genetic variation and represents one of the few studies to document climate adaptation in a wild population.

Nature Climate Change↗

USGS2021

Linking climate niches across seasons to assess population vulnerability in a migratory bird

Global loss of biodiversity has placed new urgency on the need to understand factors regulating species response to rapid environmental change. While specialists are often less resilient to rapid environmental change than generalists, species-level analyses may obscure the extent of specialization when locally adapted populations vary in climate tolerances. Until recently, quantification of the degree of climate specialization in migratory birds below the species level was hindered by a lack of genomic and tracking information, but recent technological advances have helped to overcome these barriers. Here we take a genome-wide genetic approach to mapping population-specific migratory routes and quantifying niche breadth within genetically distinct populations of a migratory bird, the willow flycatcher ( Empidonax traillii ), which exhibits variation in the severity of population declines across its breeding range. While our sample size is restricted to the number of genetically distinct populations within the species, our results support the idea that locally adapted populations of the willow flycatcher with narrow climatic niches across seasons are already federally listed as endangered or in steep decline, while populations with broader climatic niches have remained stable in recent decades. Overall, this work highlights the value of quantifying niche breadth within genetically distinct groups across time and space when attempting to understand the factors that facilitate or constrain the response of locally adapted populations to rapid environmental change.

Global Change Biology↗

USGS2020

Management of the brown-headed cowbird: Implications for endangered species and agricultural damage mitigation

The brown-headed cowbird ( Molothrus ater ; cowbird) is unique among North American blackbirds (Icteridae) because it is managed to mitigate the negative effects on endangered songbirds and economic losses in agricultural crops. Cowbird brood parasitism can further affect species that are considered threatened or endangered due to anthropogenic land uses. Historically, cowbirds have often been culled without addressing ultimate causes of songbird population declines. Similar to other North American blackbirds, cowbirds depredate agricultural crops, albeit at a lower rate reported for other blackbird species. Conflicting information exists on the extent of agricultural damage caused by cowbirds and the effectiveness of mitigation measures for application to management. In this paper, we reviewed the progress that has been made in cowbird management from approximately 2005 to 2020 in relation to endangered species. We also reviewed losses to the rice ( Oryza sativa ) crop attributed to cowbirds and the programs designed to reduce depredation. Of the 4 songbird species in which cowbirds have been managed, both the Kirtland’s warbler ( Dendroica kirtlandii ) and black-capped vireo ( Vireo atricapilla ) have been removed from the endangered species list following population increases in response to habitat expansion. Cowbird trapping has ceased for Kirtland’s warbler but continues for the vireo. In contrast, least Bell’s vireo ( V. bellii pusillus ) and southwestern willow flycatcher ( Empidonax traillii extimus ) still require cowbird control after modest increases in suitable habitat. Our review of rice depredation by cowbirds revealed models that have been created to determine the number of cowbirds that can be taken to decrease rice loss have been useful but require refinement with new data that incorporate cowbird population changes in the rice growing region, dietary preference studies, and current information on population sex ratios and female cowbird egg laying. Once this information has been gathered, bioenergetic and economic models would increase our understanding of the damage caused by cowbirds.

California↗

USGS2018

Ecological genomics predicts climate vulnerability in an endangered southwestern songbird

Few regions have been more severely impacted by climate change in the USA than the Desert Southwest. Here, we use ecological genomics to assess the potential for adaptation to rising global temperatures in a widespread songbird, the willow flycatcher ( Empidonax traillii ), and find the endangered desert southwestern subspecies ( E. t. extimus ) most vulnerable to future climate change. Highly significant correlations between present abundance and estimates of genomic vulnerability – the mismatch between current and predicted future genotype–environment relationships – indicate small, fragmented populations of the southwestern willow flycatcher will have to adapt most to keep pace with climate change. Links between climate‐associated genotypes and genes important to thermal tolerance in birds provide a potential mechanism for adaptation to temperature extremes. Our results demonstrate that the incorporation of genotype–environment relationships into landscape‐scale models of climate vulnerability can facilitate more precise predictions of climate impacts and help guide conservation in threatened and endangered groups.

Ecology Letters↗

USGS2005

Parasitism, productivity, and population growth: response of Least Bell's Vireos (Vireo bellii pusillus) and Southwestern Willow Flycatchers (Empidonax traillii extimus) to cowbird (Molothrus spp.) control

Cowbird (Molothrus spp.) control is a major focus of recovery-oriented management of two endangered riparian bird species,the Least Bell's Vireo (Vireo bellii pusillus) and Southwestern Willow Flycatcher (Empidonax traillii extimus). During the past 20 years, annual trapping of cowbirds at Least Bell's Vireo and Southwestern Willow Flycatcher breeding sites has eliminated or reduced parasitism in comparison with pretrapping rates and, thereby, significantly increased seasonal productivity of nesting pairs. Enhanced productivity, in turn, has resulted in an 8-fold increase in numbers of Least Bell's Vireos; Southwestern Willow Flycatcher abundance, however, has changed little, and at some sites has declined despite cowbird control. Although generally successful by these short-term measures of host population response, cowbird control poses potential negative consequences for long-term recovery of endangered species. As currently employed, cowbird control lacks predetermined biological criteria to trigger an end to the control, making these species' dependence on human intervention open-ended. Prolonged reliance on cowbird control to manage endangered species can shift attention from identifying and managing other factors that limit populations--in particular, habitat availability. On the basis of our analysis of these long-term programs, we suggest that cowbird control be reserved for short-term crisis management and be replaced, when appropriate, by practices emphasizing restoration and maintenance of natural processes on which species depend. /// El manejo orientado hacia la recuperación de dos especies de aves ribereñas Vireo belli pusillus y Empidonax trailli extimus se ha focalizado principalmente en el control de los Molothrus spp parásitos. Durante los pasados 20 años, la captura anual de los Molothrus en las áreas de nidificación de Vireo belli pusillus y Empidonax trailli extimus ha eliminado o reducido el parasitismo en comparación con las tasas previas a la captura y, en consecuencia, ha incrementado significativamente la productividad estacional de las parejas reproductivas. Ese mejora en productividad, a su vez, ha resultado en que el número de Vireo belli pusillus se incrementara 8 veces. La abundancia de Empidonax trailli extimus en cambio, ha variado poco, e incluso en algunos sitios, se ha reducido a pesar del control de los Molothrus. Aunque aparentemente el control de Molothrus fue exitoso por los resultados obtenidos a corto plazo, el control de los Molothrus posee consecuencias potencialmente negativas para la recuperación a largo plazo de las especies en peligro. De la forma en que es actualmente aplicado, el control de los Molothrus carece de criterios biológicos predeterminados que permitan dejar de aplicarlo. Esto implica que las especies que se quiera proteger dependan eternamente de la intervención humana. El hecho de que que el manejo de las especies en peligro se base en la dependencia prolongada en el control de los Molothrus podría distraer la atención sobre la identificación y el manejo de otros factores que limitan dichas poblaciones-en particular, la disponibilidad de hábitat. Basándonos en nuestro análisis de estos programas a largo plazo, sugerimos que el control de Molothrus quede reservado para las crisis de manejo de corto plazo. Cuando fuera apropiado, es de esperar que dicho manejo sea reemplazado por prácticas enfatizadas hacia la restauración y el mantenimiento de los procesos naturales de los cuales esas especies en realidad dependen.

Ornithological Monographs↗

USGS2003

Food habits of the southwestern willow flycatcher during the nesting season

The food habits and prey base of the endangered Southwestern Willow Flycatcher ( Empidonax traillii extimus ) are not well known. We analyzed prey remains in 59 fecal samples from an intensively-studied population of this flycatcher at the Kern River Preserve in southern California. These samples were collected during the nesting season in 1996 and 1997 from adults caught in mist nets, and from nestlings temporarily removed from the nest for banding. A total of 379 prey individuals were identified in the samples. Dominant prey taxa, both in total numbers and in percent occurrence, were true bugs (Hemiptera), flies (Diptera), and beetles (Coleoptera). Leafhoppers (Homoptera: Cicadellidae), spiders (Araneae), bees and wasps (Hymenoptera), and dragonflies and damselflies (Odonata) were also common items. Diet composition was significantly different between years, due to a large difference in the numbers of spiders between 1996 and 1997. There was also a significant difference between the diet of young and adults, with the diet of young birds having significantly higher numbers of odonates and beetles. There was a trend toward diet differences between males and females, but this was not significant at the P = 0.05 level.

Studies in Avian Biology↗

USGS2000

Breeding season ecology: Chapter 6 in Status, ecology and conservation of the Southwestern Willow Flycatcher (RMRS-GTR-60)

The willow flycatcher ( Empidonax traillii ) breeds across much of the conterminous United States and in portions of extreme southern Canada. As might be expected in such a wide-ranging species, willow fly- catchers in different portions of the range exhibit differences in appearance, song, and ecological characteristics. The intent of this chapter is to provide information on the breeding-season ecology of the southwestern subspecies, E.t. extimus . However, most ecological studies to date have dealt with other willow flycatcher subspecies. Relatively few studies have been published on E.t. extimus , and much of what is currently known is presented in unpublished literature (e.g., agency and consulting firm reports); these sources are relied upon heavily in this chapter. This chapter does not address habitat characteristics in depth, other than for nest sites (refer to A Survey of Current Breeding Habitats for additional details). Although southwestern willow flycatchers are frequent victims of nest parasitism by brown-headed cowbirds ( Molothrus ater ), this chapter will not address the topic of parasitism and its effect on breeding ecology (refer to The Ecology of Brown-headed Cowbirds and their Effects on Southwestern Willow Flycatchers for details). Readers interested in more details of willow flycatcher biology and ecology are encouraged to read McCabe’s (1991) treatise, which is based on over a decade of willow flycatchers research in Wisconsin and includes comparisons with other populations and subspecies.

General Technical Report↗

USGS1999

Range-wide impact of brown-headed cowbird parasitism on the southwestern willow flycatcher (Empidonax traillii extimus)

We present datasets from long-term studies of brood parasitism of Southwestern Willow Flycatcher ( Empidonax traillii extimus ) populations at the South Fork Kern River (SFKR), California, the Grand Canyon, Arizona, and from other intensive flycatcher studies in Arizona. In the two main study areas, we recorded high parasitism rates for the flycatcher. We found that 75 % of Willow Flycatcher nests failed completely when parasitized and that an extremely low percentage of Willow Flycatcher eggs survived to fledging in parasitized nests (11% vs. 47% in unparasitized nests). Our data show that cowbird parasitism also delayed the fledging of young flycatchers. However, contrary to our expectations, we did not find a significant difference between the return rates of “early” versus “late” fledged birds. To evaluate how important cowbird parasitism is to the population decline of the endangered Southwestern Willow Flycatcher, we reviewed the current level of parasitism on this species throughout its range in six states using a large number of datasets from different sites. We also reviewed the historic pattern of increase in Brown-headed Cowbird ( Molothrus ater ) populations in the southwest between 1872-1997 using both nest record and egg collections and documentary evidence. Given the level of impacts to flycatcher productivity inflicted by cowbird parasitism that we observed at SFKR and Grand Canyon, it is likely that cowbirds played a role historically in reducing many local Southwestern Willow Flycatcher populations. Also, cowbirds continue to play a role in slowing or preventing the recovery of this subspecies.

Studies in Avian Biology↗