Date of Award

2018

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Biology

Abstract

Prey animals are known to communicate information about risk in the environment using various signals. Seen across species, these signals are often directed to other prey individuals, but some signals are also directed towards predators and are called pursuit-deterrent signals. These deterrence signals are paradoxical in that the prey performs seemingly high-risk behaviour, such as approaching the predator or increasing its own conspicuousness and potentially reducing its chance of escape, in an attempt to discourage the predator from attacking. This has motivated considerable theoretical and empirical work, however, there are still gaps in our understanding of pursuit-deterrence. Existing theory is restricted to one prey-one predator games that predict either pure signalling or non-signalling evolutionarily stable strategies (ESS), where the prey always signals or never signals. In chapter one, I develop a two prey-one predator signalling game based on a novel mechanism of decline in patch value to the predator after a signal, and I use game theory and adaptive dynamics to identify pure signalling, non-signalling, and mixed ESSs, where the prey signals with a probability and the predator attacks post-signal with a probability. The model predicts that signalling is more likely to evolve when the prey has a low chance of detecting the predator, and also when the predator can move relatively quickly to a different prey patch of higher value. This model is the first theoretical analysis on the evolution of pursuit-deterrent signalling in group-living prey, and provides clear testable predictions for natural systems. Pursuit-deterrent signals have been studied in a few species, but may be fairly widespread among vertebrates. In chapter two, I examine whether tail-flashing behaviour in dark-eyed juncos ( Junco hyemalis ) during winter has a pursuit-deterrent function. While this behaviour is a component of social displays during the breeding season, continued tail-flashing at cold temperatures motivates the study of predator-related hypotheses. I measured tail-flashing and feeding rates of juncos in different group sizes in two experiments; a predator experiment using a taxidermy hawk model predator, and a cover experiment using brush cover placed at different distances to simulate low and high predation risk. Juncos tail-flashed significantly more when the predator was present rather than absent at the site, and juncos tail-flashed at higher rates when they could see the predator while feeding. There was a consistent negative group size effect across experiments with solitary juncos tail-flashing more than in larger groups. Juncos also tail-flashed more when they were close to cover than far, and this suggests that tail-flashing likely bears an attraction” cost. I found no strong negative association between tail-flashing and feeding, indicating that tail-flashing does not interfere with feeding. This is the first study in this general group of birds to test anti-predator hypotheses of tail movement behaviours as an alternative adaptive function, and provides a discussion for tail-flashing in wintering juncos as a pursuit-deterrent signal.

Download

Share

COinS