Geology topics

Mary J. Whitfield

Publications and source records attributed to Mary J. Whitfield.

5 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↗

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↗