Stable isotope composition of feathers and foraging behavior parallel bill shape divergence of Island Scrub-Jays (Aphelocoma insularis) in pine and oak habitats

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 co..., , , # Stable isotope composition of feathers and foraging behavior parallel bill shape divergence of Island Scrub-Jays (Aphelocoma insularis) in pine and oak habitats

Dataset DOI: [10.5061/dryad.q83bk3jpb](10.5061/dryad.q83bk3jpb)

## Description of the data and file structure

**Foraging data:** Opportunistically collected foraging data between September to November 2009-2012 from Island Scrub-Jays on Santa Cruz Island. For focal observations, observers waited for 5 min for an individual to acclimate to their presence before observing foraging through binoculars and recording details into digital voice recorders. We recorded the following details: food item taken (insect, acorn, fruit, seed), whether the individual was successful at taking the food item (consuming, carrying away), and foraging maneuver.

**Stable isotope data**:  Measured δD, δ15N, and δ13C in breast feathers collected from 50 adult (>1-year-old) Island Scrub-Jays between 2009 and 2011. Analyses were conducted at the Smit...,