Research
Extreme weather over short time scales
Climate change isn’t just gradually raising temperatures worldwide, it’s greatly increasing the frequency and intensity of extreme weather events that take place over months, weeks or even days, such as heat waves, cold snaps, and drought. In my recent position in the Zuckerberg lab at UW-Madison and in collaboration with the Cornell lab of Ornithology, I used eBird, a citizen science database, and NASA satellite weather data to examine how diverse North American bird species are responding to extreme heat and drought in the summer and polar vortexes in the winter. By examining how responses vary across species, we can anticipate which species are most likely to be at risk with climate change.
Animal movement for mitigating and responding to climate change
In my current position in the Center for Biodiversity and Global Change at Yale University, I developed a novel approach to estimate niche loss and range redistributions from citizen science data while accounting for human observer bias and found that across 384 species of North American birds, most species experienced several degrees of warming over the past 20 years despite moving north and upslope (Cohen et al. Nature Ecology and Evolution). Only species that relocated their geographic ranges the farthest north have experienced little climate change exposure, while species that did not relocate experienced up to seven degrees of warming in winter. In an additional project, species tracked both the mean and variability of seasonal weather conditions via migration based on their functional traits, hinting at their susceptibility to increasing weather variability with climate change (Cohen et al. 2023, Global Ecology and Biogeography). In an ongoing collaboration with a colleague at Berkeley and the USGS and USFWS, we are exploring how individual animals move in response to extreme weather events.
Understanding Biodiversity Patterns at Continental Scales
Additionally, in my current position in the Center for Biodiversity and Global Change, I modeled the seasonal distributions of over 650 North American bird species to understand biodiversity patterns and further conservation efforts in conjunction with the 30x30 initiative to conserve 30% of land and water by 2030. Based off that work, I explored how coarse-resolution models bias biodiversity predictions in heterogenous regions and for habitat specialist species especially during the breeding season (Cohen et al 2025 Global Ecology and Biogeography). Currently, I am exploring how the use of extreme weather risk in species distribution models influences predictions especially at range edges as well as continental biodiversity predictions.
Climate change influences outbreaks of deadly wildlife diseases
Amphibians are the most threatened vertebrate taxa on Earth, partially because they are highly susceptible to the emerging infectious disease chytridiomycosis, caused by a deadly fungal pathogen that has spread worldwide over the last 60 years. It has widely been suspected that temperature plays an important role in driving outbreaks of this disease, but the precise conditions that best promoted outbreaks remained uncertain. My PhD work in the Rohr lab at the University of South Florida involved examining how the ecology of the host influences the impact of temperature in driving chytridiomycosis outbreaks. Using lab and field data, we found that cold-adapted hosts experienced greatest disease risk under unusually warm conditions, while warm-adapted hosts were at greatest risk when it was unusually cool. We have since extended this framework to predict disease outbreaks across a wider variety of wildlife species and project global shifts in wildlife disease risk under climate change. This research resulted in an outstanding dissertation award for the 2016-7 academic year at the University of South Florida.
The timing of annual events is shifting
One of the most well-known responses of wildlife species to climate change involves shifting of phenology, or the timing of annual events including migration, breeding, and emerging from hibernation. In the last 50 years, numerous wildlife species have been documented advancing the timing of these activites earlier in the spring. During my PhD work in the Rohr lab, I conducted a meta-analysis across over 100 published studies and found that invertebrates and amphibians are shifting much faster than birds and mammals, suggesting that predators may be arriving or emerging too late, missing peaks in prey availability. Further, we showed that phenological shifts in temperate areas are primarily driven by temperature, while precipitation plays a greater role in driving shifts in subtropical areas.