Stable isotope composition of feathers and foraging behavior parallel bill shape divergence of island scrub-jays (Aphelocoma insularis) in pine and oak habitats
Individual variation can shape ecological and evolutionary outcomes, and Island Scrub‑Jays offer a clear example. Using stable isotopes (δD, δ13C, δ15N) from feathers and direct foraging observations, this study examined habitat‑linked diet differences between jays in pine and oak habitats on Santa Cruz Island, California. Jays in pine habitat showed greater 13C enrichment and consumed more arthropods, using more probing, sallying and pecking maneuvers. Jays in oak habitat were more enriched in 15N. Although overall diets overlapped, these patterns parallel known bill‑shape divergence between habitats. Findings highlight how habitat‑linked phenotypic variation may influence behavior and diet in this endemic species.
Subject Tags
- Forest
- Biodiversity
- Wildlife
Abstract
Individual differences within populations have important ecological and evolutionary implications for understanding population-level responses to environmental variation. We found evidence of habitat-linked differences in stable isotopic composition of feathers and foraging behavior of Island Scrub-Jays (Aphelocoma insularis), endemic to Santa Cruz Island, California, USA, which parallel phenotypic divergence in jay bill shape between pine and oak habitats. We used stable isotopes of hydrogen (δD), carbon (δ13C), and nitrogen (δ15N) from feathers and direct observations of foraging behavior to infer habitat-specific diet variation among Island Scrub-Jays. Although hydrogen isotope composition of feathers did not differ between habitats as we expected, jays sampled in pine habitat were more enriched in 13C, whereas jays sampled in oak habitat were more enriched in 15N. Foraging observations indicated that diets largely overlapped in the 2 habitats, but jays in pine were more likely to consume arthropods. Jays in pine habitat also used relatively more probing, sallying, and pecking foraging maneuvers to capture prey. These findings suggest new avenues of research for understanding how habitat-linked, phenotypic divergence shapes behavior and diet of the omnivorous Island Scrub-Jay.
Citation
Yeatts, B., Cheek, R. G., Mouton, J. C., Pesendorfer, M. B., Morrison, S. A., Sillett, T. S., & Ghalambor, C. K. (2025). Stable isotope composition of feathers and foraging behavior parallel bill shape divergence of island scrub-jays (Aphelocoma insularis) in pine and oak habitats. Western North American Naturalist, 85(2), 280-292. https://doi.org/10.3398/064.085.0214
TNC Authors
-
Scott A. Morrison
Director of Conservation Science & Programs, California
The Nature Conservancy
Email: smorrison@tnc.org