Elevational gradients cause profound eco-climatic variation over short distances. We study how interacting axes of environmental variation impact movement, physiology, and and genetic structure of mountain birds, including elevational migrants and high-elevation residents. To do this, we employ a creative suite of approaches: For example, we designed a lightweight backpack tracking harness that we used to follow the migration of giant hummingbirds (genus Patagona) breeding at sea level in central Chile. We uncovered that coastal populations travel >8,300 km roundtrip, shifting >4,100 m in elevation during migration––the world's longest hummingbird migratory journey with the most extreme ascent. Migratory and high-elevation resident populations differ strikingly in their physiology. Genomes revealed that the two forms diverged ~2-3 million years ago and have since evolved under phenotypic stasis, although they are vocally diagnostic. We are continuing to integrate movement tracking, whole genomes, transcriptomes, physiological and morphological data, DNA from historic museum specimens, and modeling to answer questions about migratory connectivity, evolution, physiological plasticity, and resilience to environmental change. 

Most migratory birds occupy similar elevations between seasons, but a subset make large-scale shifts in elevation between breeding and non-breeding areas. We've uncovered 105 populations from 30 families that undertake 'extreme' biannual shifts of 2,000 meters or more, transitioning between drastically different atmospheric pressures. This behavior, called elevational niche-shift migration (ENSM), is very physiologically demanding. It therefore has important consequences for adaptation, gene flow, range dynamics, species interactions, and diversification. We study the specific ecological and physiological challenges that accompany 'extreme' elevational migration, its functional genomic consequences, and its effects on gene expression and physiological plasticity. This work involves involves field physiological assays, movement tracking, phylogenetic approaches, and comparative biology with museum specimens. 

Low oxygen pressure at high elevations is a strong environmental stressor. We study how blood traits that underpin blood-oxygen carrying capacity vary across short timescales of acclimatization and long timescales of adaptation, examining how these relationships facilitate survival and persistence at high elevations and promote or inhibit elevational range expansion. We work on diverse clades––from songbirds to hummingbirds, combining field sampling, molecular techniques, and phylogenetic comparative approaches. Our work has shown that evolutionary solutions to reduced oxygen availability can occur in fundamentally similar ways across individual and phylogenetic timescales, suggesting that 'rules' of elevational variation in blood-oxygen carrying capacity are set by the physics of gas exchange. Additionally, species differences in elevational range are important when examining the underlying mechanisms of blood-oxygen carrying capacity adjustment, highlighting unique aspects of species adaptation at extreme elevations.

Parasites and pathogens are important drivers of species distributions and diversity. We study malaria-causing haemosporidian blood parasites and their avian hosts to understand community structure, patterns of turnover, and the effects of shifting climatic conditions on host-parasite ranges. Our work encompasses community-level surveys of parasite composition in both mountain and island systems, host specificity in breeding birds distributed along environmental gradients in the southwestern USA and Peru, as well as detailed examination of host-parasite relationships in single species and clades, such as Audubon's Warblers (Setophaga auduboni) and vireos (family: Vireonidae), using phylogenetic models and genomic tools. Our research suggests that interactions among hosts and parasites can reciprocally limit individual species ranges and have 'trickle up' effects to shape the composition of entire communities. We have recently expanded this work to study lung fungal mycobiome pathogens of Sandhill Cranes and songbirds.

We are always excited to observe and ask questions about bird behaviors and interactions––particularly in the field. These observations are often essential for understanding species' ecologies, population connectivity, disease transmission, and resilience in the face of environmental change. We have documented odd hybrids (such as a ghost warbler (right) and a scarlet "grosserbeak"), unusual brood parasite interactions, unexpected 'skyscraper' nesting behavior of coastal marsh birds, and the role of freshwater parasites in dispersal. In the neotropics, our research has contributed to greater understanding of reproductive biology and life history information for deficient species, such as the Golden-plumed Parakeet (Leptosittaca branickii) and the Andean Ibis (Theristicus branickii). Closer to home, we regularly document natural history observations and submit records of rare or unusual bird sightings to relevant records committees. These data complement eBird checklist observation details and make occurrence records more accessible to broad audiences.