Date of Thesis

Spring 2025

Description

In Black-legged kittiwakes (Rissa tridactyla), a seabird species, competition between siblings can arise when more than one chick is present in a nest. The first-hatched chick, known as the “A” chick, frequently establishes dominance over the second-hatched chick, known as the “B” chick. Many different factors can drive the presence and intensity of this competition, including the size discrepancies between chicks, and their physiological state. A likely factor is resource limitation, seen in many instances of sibling competition to be a prominent component because limited food must be allocated between both chicks by parents. In some cases, competition can escalate into siblicide, with the A-chick showing aggression towards and out-competing (killing) the B-chick. Siblicide attempts can manifest in attacks on the B-chick, with the A-chick sometimes forcing the other out of the nest entirely or pecking them to death. Although siblicide is facultative in Black-legged kittiwakes – occurring frequently but not always – the reasons it occurs in some nests but not others remain unclear. To understand why siblicide only occurs in some nests, it is important to investigate how key factors might predict its likelihood. Some of these factors include environmental context, physiology, and the behavior of chicks. Previous research has shown that chick behavior and condition can be linked to the environment in which they live. In this study, chick behavior was observed during one-hour recordings from 50 nests when the A-chick was 5 days old. These behaviors were quantified to determine the frequency of specific behaviors that could potentially indicate siblicide. While the discrepancy between the A-chick and B-chick in the proportion of begging events that successfully elicited feeding by parents (“successful begging”) was the most reliable predictor of siblicide out of all behaviors observed, none of the behaviors showed a significant ability to predict siblicide overall. Ketones, which can indicate the body condition, of both A-chicks and B-chicks were measured from blood samples after the videos were recorded. Additionally, measurements of the chicks were taken at this time. Both these assessments allowed for the determination of chick quality and condition at this time, to test if this could indicate the chance of siblicide occurring. Among all the physiological factors, the mass of the B-chick showed the most significant ability to predict the occurrence of siblicide, with lighter chicks more likely to die. Another influence on chick survival could be resource availability. Of the 50 nests examined, 24 were provided 3 times daily with supplementary food, and 26 were not provided with any additional food. Feeding treatment played a marginally non-significant role in its interaction with key predictors of siblicide, particularly the mass of the B-chick. More pronounced effects were observed in the unfed group, where the differences in B chick mass between nests with and without siblicide were amplified. This study provides valuable insights into what factors are at play when siblicide occurs in black-legged kittiwake nests. This highlights the importance of B-chick mass as a predictor and how this can be exacerbated by resource limitation. These results contribute to a deeper understanding of the environmental and biological factors that drive siblicide and underscore the significance of early chick conditions in determining survival outcomes.

Keywords

Facultative siblicide, Black-legged kittiwakes, Chick mass, Behavior, Sibling competition, Resource limitation

Access Type

Honors Thesis

Degree Type

Bachelor of Science

Major

Animal Behavior

First Advisor

Z Morgan Benowitz-Fredericks

Second Advisor

Reggie Gazes

Third Advisor

Douglas Collins

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