Class Year

2025

Document Type

Student Research Paper

Date of Creation

Spring 2025

Department 1

Environmental Studies

Abstract

Rapid warming in the Gulf of Maine has coincided with changes in phenology across trophic levels. Phenological change has yet to be studied in black guillemots (Cepphus grylle), a widely distributed benthic forager that is showing population decline in the region. Because black guillemots nest in burrows, their phenology can be challenging to study. I developed methods to track black guillemot phenology on Petit Manan Island, a seabird breeding colony in the Gulf of Maine. Specifically, I asked Q1) Can daily tower count data be used to predict black guillemot breeding phenology? Q2) How is black guillemot breeding phenology shifting over time? Q3) If phenology impacts chick growth rate, can size-based equations still accurately predict black guillemot hatch date? To answer these questions, I used long-term datasets on daily population tower counts (2000 to present) and chick growth and hatch dates (2007 to present) collected on Petit Manan Island. I tested for relationships among these parameters and for changes in these parameters over time using a series of linear and generalized additive models, with model selection based on AIC.

I found an abrupt change in black guillemot population size and phenology in 2010, which coincides with a widely recognized regime shift in the Gulf of Maine. Black guillemots had an average daily tower count of 275.94 prior to the regime shift, and an average count of 158.10 following this shift. Though the tower count data did suggest a phenological pattern, they did not show a consistent relationship with nest-check data, so tower counts are unlikely to be useful in tracking guillemot phenology (Q1). Nest check data suggested that the date when 25% of eggs hatched has advanced non-linearly by over 15 days since 2007 (Q2). In 2024, the linear growth rate for a subset of chicks showed a positive relationship with hatch date, indicating that later-hatched chicks grew faster. The equation used by USFWS to back-estimate hatch dates underpredicted age for all chicks, and the accuracy of this equation did not depend on hatch date (Q3). Future studies on PMI should examine how increased sea surface temperature influences black guillemot phenology, continue to collect tower count data, and designate a subset of nests that are checked daily to obtain exact hatch dates.

Comments

Written for ES 460: Individualized Study - Research

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