PS 1-6 - Comparing Foraging Efforts of Sierra Nevada Gray-crowned Rosy-Finches (Leucosticte tephrocotis dawsonii) in Contrasting Environments

Abstract: Foraging behavior is a critical determinant of survivorship and an important indicator of species adaptability to environmental changes, particularly in resource-limited alpine habitats that are vulnerable to climate-driven transformations. Alpine environments are both resource limited and vulnerable to climate change. As temperatures warm, lower elevation ecosystems are projected to shift upwards, reducing available habitat for the highest elevation alpine organisms. Gray-Crowned Rosy-Finch (Leucosticte tephrocotis dawsoni, “Rosy-Finch”) is a high elevation alpine species that breeds in the Sierra Nevada and White Mountains in California, USA. Their breeding season occurs during late spring and early summer when alpine food sources are most abundant. They are generalists and forage on a variety of plant foods, but primarily feed on insects off snow or from alpine lakes and rely on these resources to feed their fledglings.

To quantify these changes, we conducted 10-minute time budgets for individual Rosy-Finches in two contrasting environments. In the Sierra Nevada site, tundra, snow and lakes were available, while at White Mountain Peak, is fellfield habitat with several patches of late-lying snow. We observed Rosy-Finch allocation of time to foraging and in each available substrate within each environment. We hypothesized that Rosy-Finches would forage on the most abundant food resource available in each site. At both sites, Rosy- Finches allocated most of their time to foraging. In the Sierra Nevada, Rosy Finches spent ~85% of their time foraging, and 89% foraging at lakes. At White Mountain Peak they spent 61% of their time foraging on only snow. Reduced total foraging time at White Mountain Peak relative to the Sierra Nevada site could reflect higher concentration of food resources on available snowfields than in the more varied available foraging substrates in the Sierra Nevada. Our findings show the value of foraging time for Rosy-Finches and the continued monitoring of their connection to habitats in the Sierra Nevada. This can shed light on climate-drive changes to availability of suitable foraging substrate. As a generalist species, Rosy-Finches may be able to adapt to changing environments, but some breeding sites might lack alternative food sources to buffer against variability and directional change. By informing targeted conservation efforts, our findings can contribute to the long-term persistence of this important alpine species and other breeding birds facing similar challenges in the context of a rapidly changing climate.