Class Year

2026

Document Type

Student Research Paper

Date of Creation

Spring 2026

Department 1

Environmental Studies

Abstract

Seabirds are central-place foragers that breed in multi-species colonies, providing an opportunity to study species coexistence. I quantified interspecific competition among four seabird species (common terns Sterna hirundo, Arctic terns Sterna paradisaea, Atlantic puffins Fratercula arctica, black guillemots Cepphus grylle) breeding in the Gulf of Maine in 2022, 2024, and 2025. I hypothesized that, throughout the breeding season, 1) seabird diet would change and 2) interspecific overlap in diet would increase. I compared diets across species and time using direct observation of prey feeds and stable isotope values of seabird egg membranes and blood, which provide information on foraging habitat and trophic level. Where relevant, I tested for significance using generalized linear models and Wilcoxon signed-rank tests.

I found mixed support for my first hypothesis, with shifts varying by species and years. Terns and puffins generally showed more inshore and lower trophic level diets during pre-breeding than chick rearing, while guillemots remained inshore throughout the breeding season. Similarly, I found variable support for my second hypothesis. The two species of tern generally showed high dietary overlap across time. Overlap with puffins was low-to-moderate and did not consistently increase throughout the season, while overlap with guillemots was consistently low. Overall, my results highlight the complexity of interspecific competition and the importance of using multiple approaches to study diet.

Comments

Written for ES 460: Individualized Study - Research

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