Kate O'Brien

U.S. Fish and Wildlife Service · National Wildlife Refuge System

Targeted, single‐species management and ecosystem‐based management are generally considered disparate conservation approaches. In imperiled ecosystems, these approaches may be complementary, when habitat management for targeted at‐risk species provides broad ecosystem benefits through an umbrella or surrogate species effect. In the northeastern Uni...

Here we report on the results of a long-term study of mercury exposure in a songbird species, the saltmarsh sparrow (Ammodramus caudacutus). We measured total mercury concentrations in blood (n = 840) and feathers (n = 560) of adult saltmarsh sparrows at six locations between 2000 and 2017: Rachel Carson National Wildlife Refuge (RCNWR) in Wells, M...

The Gulf of Maine has long been recognized as a major stopover area for shorebirds in fall. Knowing how birds move within and beyond the region will be paramount to protecting threatened shorebird habitat. To determine stopover behavior during fall migration (2013–2017) in Maine, 180 (104 AHY, 76 HY) Semipalmated Sandpipers, Calidris pusilla, were...

If individuals can perceive and manage risks, they may alter their behaviors based on prior experience. This expectation may apply to nest site selection of breeding birds, for which adaptive behavioral responses may enhance fitness. Birds that nest in tidal marshes have adapted to the challenges posed primarily by periodic, monthly tidal flooding...

Evolutionary theory suggests that natural selection should favor the ability of animals to modify their offspring sex ratios when the fitness benefits of producing one sex over the other vary in relation to environmental conditions. The Saltmarsh Sparrow (Ammodramus caudacutus) is an extreme habitat specialist, with breeding behavior influenced by...

The balance of abiotic and biotic stressors experienced by a species likely varies across its range, resulting in spatially heterogeneous limitations on the species' demographic rates. Support for spatial variation in stressors (often latitudinal gradients) has been found in many species, usually with physiological or correlative occupancy data, bu...

Demographic rates are rarely estimated over an entire species range, limiting empirical tests of ecological patterns and theories, and raising questions about the representativeness of studies that use data from a small part of a range. The uncertainty that results from using demographic rates from just a few sites is especially pervasive in popula...

Conservation of threatened or endangered species in a hybrid zone requires a comprehensive understanding of interspecific dynamics over time and space. We evaluated changes in location and composition of a hybrid zone over a 15-year period (with replicated sampling in 1997–2000 and 2011–2013) for saltmarsh (Ammodramus caudacutus) and Nelson’s (A. n...

The range of a species is determined by the balance of its demographic rates across space. Population growth rates are widely hypothesized to be greatest at the geographic center of the species range, but indirect empirical support for this pattern using abundance as a proxy has been mixed, and demographic rates are rarely quantified on a large spa...

Coastal marshes are one of the world's most productive ecosystem's. Consequently, they have been heavily used by humans for centuries, resulting in ecosystem loss. Direct human modifications such as road crossings and ditches and climatic stressors such as sea-level rise and extreme storm events have the potential to further degrade the quantity an...

The effects of hybridization on evolutionary processes are primarily determined by the differential between hybrid and parental species fitness. Assessing the impacts of hybridization can be challenging, however, as determining the relationship between individual fitness and the extent of introgression in wild populations is difficult. We evaluated...

Landscape modification and habitat fragmentation disrupt the connectivity of natural landscapes, with major consequences for biodiversity. Species that require patchily distributed habitats, such as those that specialize on early successional ecosystems, must disperse through a landscape matrix with unsuitable habitat types. We evaluated landscape...

Results of Parameteration of Full Population Model Resistance Surfaces. Mantel and partial Mantel correlations between genetic distance and least cost path distances from models with alternate resistance values for the full study area extent. (DOCX)

Optimal Resistance Values. Resistance values determined for each study area from best fit of New England cottontail genetic data with least cost path cost distances. (DOCX)

Mantel Results for Univariate Models. Mantel and partial Mantel r correlations of least cost path effective distances with New England cottontail gene flow for each landscape feature in Kittery and Cape Elizabeth study areas. (DOCX)

Mantel Test Resuls for Buffered Roads and LiDAR Models. Mantel and partial Mantel r correlations for models with the addition of buffered roads1 and LiDAR2 compared to models not including these features. (DOCX)

Genetic distance matrices. Pairwise Rousset's a and Dps individual genetic distance matrices for New England cottontails in the Kittery and Cape Elizabeth study areas. (XLSX)

Hybridization is influential in shaping species' dynamics and has many evolutionary and conservation implications. Identification of hybrid individuals typically relies on morphological data, but the assumption that hybrids express intermediate traits is not always valid, because of complex patterns of introgression and selection. We characterized...

Evidence of biological responses to climate change continues to grow. Long-term monitoring programs are critical in documenting these changes as well as identifying the primary stressors that may influence a species’ ability to adapt to changing climate. Eastern North American salt marshes support the greatest number of endemic salt marsh vertebrat...

Successful recovery of populations of rare and cryptic species requires accurate monitoring of changes in their distribution and densities, which in turn necessitates considering detection rates. Development of population monitoring protocols is needed to aid recovery of the New England cottontail (Sylvilagus transitionalis; currently the top-prior...

Landscape features of anthropogenic or natural origin can influence organisms' dispersal patterns and the connectivity of populations. Understanding these relationships is of broad interest in ecology and evolutionary biology and provides key insights for habitat conservation planning at the landscape scale. This knowledge is germane to restoration...

Limiting the spread of invasive plants has become a high priority among natural resource managers. Yet in some regions, invasive plants are providing important habitat components to native animals that are at risk of local or regional extirpation. In these situations, removing invasive plants may decrease short-term survival of the at-risk taxa. At...

Understanding the spatial scale of gene flow can yield valuable insight into the ecology of an organism and guide conservation strategies. Fine-scale genetic structure is uncommon in migratory passerines because of their high vagility and presumed high dispersal abilities. Aspects of the behavior and ecology of some migratory species, however, may...

Shortly after the landing of Pilgrims at Plymouth Rock, Massachusetts, settlers arrived at the southern portion of the Province of Mayne, now the State of Maine (Butler 2005). While the area remained largely undeveloped for nearly two hundred years, by the mid- and late 1800 s the then well-settled Town of Wells, Maine, embarked on a series of coas...

Environmental mercury exposure of birds through atmospheric deposition and watershed point-source contamination is an issue of increasing concern globally. The saltmarsh sparrow (Ammodramus caudacutus) is of high conservation concern throughout its range and the potential threat of mercury exposure adds to other anthropogenic stressors, including s...

Hybridization between Saltmarsh Sparrow (Ammodramus caudacutus) and Nelson's Sparrow (A. nelsoni) has been documented in areas where the two species occur sympatrically, increasing the difficulty of accurate species identification. We developed a DNA barcoding restriction fragment length polymorphism (RFLP) test to discriminate between Nelson's Spa...

Many invasive plants and animals disperse preferentially through linear networks in the landscape, including road networks, riparian corridors, and power transmission lines. Unless the network of interest is small, or the budget for surveillance is large, it may be necessary to draw inferences from a sample rather than a complete census on the netw...

Trophic cascades are regarded as important signals for top-down control of food web dynamics. Although there is clear evidence supporting the existence of trophic cascades, the mechanisms driving this important dynamic are less clear. Trophic cascades could arise through direct population-level effects, in which predators prey on herbivores, thereb...