Improving species reintroductions
Aplomado Falcon. Credit David Bontrager.
Climate and habitat changes can also impact species interactions. Grasslands of coastal Texas, are the only habitat of the highly threatened Aplomado Falcon in the United States. However, grasslands are being degraded by encroachment of woody shrubs and trees. We hypothesized that niche overlap between generalist and resident species increased due to habitat encroachment, increasing predation and competition pressure on resident species. David Bontrager (Masters 2024) found that the distribution of two generalist owl species was positively associated with trees and shrubs that have encroached into grasslands of southern Texas. David also found that nests in areas with higher occupancy of Great Horned Owls had lower nest productivity. Thus, intraguild predation by Great Horned Owls is the likely mechanism by which habitat encroachment is hindering recovery of these threatened falcons. Knowledge of the mechanisms by which habitat change hinders recovery of endangered species is key to developing effective conservation strategies. Using a Graph Theory approach, Rebecca Thomas-Kuzilik (EEB PhD) will integrate maps of Great Horned Owl and Barn Owl distributions with maps of nest productivity and nest occupancy of Aplomado Falcons to identify priority areas for habitat restoration and for Aplomado Falcon reintroductions, thanks to an ongoing collaboration with The Peregrine Fund, Texas Fish and Wildlife and Laguna Atascosa National Wildlife Refuge.
Black-tailed jackrabbit. Credit Jen Cruz.
Credit to Trevor Jensen, Piute Ground Squirrel
Effects of habitat degradation on predators and prey in dryland ecosystems
Drylands are one of the most threatened ecosystems on Earth. Black-tailed jackrabbit and ground squirrels were historically widespread but appear to have undergone widespread declines although research is lacking to confirm current trends. We hypothesized that ongoing habitat degradation is hindering population recovery of these primary prey. Since 2021, we have conducted landscape-level monitoring of black-tailed jackrabbits and ground squirrels in the Morley Nelson Snake River Birds of Prey National Conservation Area (NCA). We developed and tested cost-effective field sampling techniques that allowed landscape-level assessments.
The NCA hosts the largest concentration of nesting raptors in the United States. Clearly, sustained prey declines, facilitated by habitat degradation, scale up via the tropic web to potential dramatic impacts on their raptor predators. Zoe Bonerbo (Masters) is assessing impacts of low ground squirrel numbers on Prairie Falcons, which are commonly described as ground squirrel specialists. However, this description is too simplistic. Instead, we posit that ground squirrel population cycles have promoted diverse dietary adaptations within the Prairie Falcon population. We hypothesized that parents that hunt diverse prey will
have higher nest productivity in low squirrel years, while parents that are ground squirrel specialists will do better in high squirrel years. Averaging dietary preferences to the population-level masks individual differences. We will compare historical data with current data evaluated at the nest level to test this hypothesis. Research on primary prey dynamics will be relevant to predators in dryland ecosystems of the United States and will also contribute more broadly to our understanding of how habitat and climate changes impact predator-prey population cycles.
Aplomado Falcon. Credit David Bontrager
Consequences of a changing planet on species demography
Gyrfalcon nestling. Credit Jen Cruz.
The Artic is changing faster than anywhere else in the world and is therefore an excellent ecosystem to help us understand the consequences of rapid anthropogenic change. Along with The Peregrine Fund and Alaska Fish and Game, we are researching the impacts of Arctic changes on raptors and their prey. Michael Henderson (EEB PhD) is studying the demographic impacts of climate change on raptors in Nome, Alaska. For Michael’s first chapter, he found that sustained bouts of bad weather appears to have the biggest impact on Gyrfalcon nestling survival via thermoregulatory stress, as parents are able to successfully feed their young in bad weather conditions. For his second chapter, Michael will be assessing the impacts of changing weather on overwinter survival of Gyrfalcons, while his third chapter will take a community-level approach, evaluating how changing a climate modifies interactions among raptor species breeding in the Artic.
​
The changing climate is also facilitating the rapid encroachment of willow shrublands.
Encroaching willows may be intensifying niche overlap between resident herbivore species. Michaela Gustafson (Masters 2024) found that Artic ground squirrels and Rock Ptarmigan are more abundant in habitats without willow shrubs, while Willow Ptarmigan are more abundant in areas with willows. Kara Beer (Masters from 2026) will build on this research to determine how willow encroachment has altered the abundance and distribution of Willow Ptarmigan and Rock Ptarmigan in Nome, Alaska. We predict that Willow Ptarmigan’s niche overlap with the other two species has increased with habitat encroachment.