Graduation Year

2025

Document Type

Campus Only Senior Thesis

Degree Name

Bachelor of Arts

Department

Biology

Abstract

Bird populations have declined significantly in the past fifty years, with the loss of over 2.9 billion individuals. Most of these losses are migratory birds, species who can face special challenges during their migration, as they rely on multiple different habitats. As urban and suburban centers expand further into native habitats, it is crucial to understand if migratory species facing population loss can use suburban habitat as overwintering grounds. This study focuses on one species of migratory bird, Gambel’s White-crowned sparrows (Zonotrichia leucophrys gambelii) some of which spend their overwintering months in Claremont, California. The goal of this study was to determine if suburban habitats can provide comparable environments to a bird’s natural habitat. We wanted to examine how specific factors within contrasting environments may affect the migratory and overwintering behaviors of White- crowned sparrows. The study took place in two locations, an area of native shrub habitat in the Bernard Field Station (BFS) and a local neighborhood in a suburban area. We hypothesized that the BFS would provide more suitable habitat for overwintering sparrows than the surrounding suburban area due to higher habitat suitability and complex native vegetation. In line with this hypothesis, we predicted to see higher between-winter return rate of birds to the BFS, a higher body condition score for birds in the BFS, higher overwintering site fidelity in the BFS, and shorter distances traveled between traps by birds in the BFS due to more suitable habitat around each site. The methods utilized included trapping White-crowned sparrows for two 4-week intervals, once at the beginning of the overwintering period in the fall of each year and again in the spring. Individual birds were banded with unique number and color combinations to identify them in following trapping seasons, and camera traps were also used to identify birds. Vegetation was sampled in each site across both locations. The study used data from 3 overwintering periods, from 2022-2025. Contrasting to our predictions, we saw similar return rates of birds to both locations, and no significant difference in the body condition of birds in either location. The BFS had higher overwintering site fidelity in one winter, and the suburbs showed higher overwintering the next. Individual birds traveled on average the same maximum distance between traps in both locations despite our predictions. These results imply that suburban areas can prove to be suitable habitat for overwintering migratory species. We also saw that factors such as native vegetation and supplemental feeders can greatly increase individual returns to suburban sites. Results from this study can be utilized to understand the patterns of return rate and migration for these birds in non-native habitat, as natural habitats face increasing declines.

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