Social associations, patterns of urban habitat use and their implications for fitness in an avian long-distance migrant

Abstract

The rapid expansion of the human population and a global trend towards urban living has resulted in wildlife and humans co-existing in a shared landscape. These areas of high human density are complex and dynamic habitats for animals trying to optimise their foraging opportunities while minimising perceived risks associated with human interactions. Over the last two decades the field of urban ecology has advanced rapidly and studies have illustrated both the costs and benefits for urban dwelling animals. However, these studies have focused on resident species and neglected those migratory species reliant on urban areas at different stages along their route. This thesis will address this gap, aiming to assess the effect of urbanisation on the movement patterns and foraging behaviour of a long-distance avian migrant at their winter staging area.

This study is focused on the East Canadian High Arctic population of light-bellied Brent geese (LBBG), Branta bernicla hrota, overwintering in Dublin, Ireland. As a capital breeder LBBG are reliant on resources acquired from the winter and spring staging areas to fuel their migratory flight and initiate breeding upon arriving in the Arctic. Given this, the availability and accessibility of adequate resources in the heterogenous landscape of Dublin are crucial to the survival and reproductive success of LBBG. In chapters 2 and 3 I used fine-scale GPS tracking data from 59 individuals during either the 2018/19 or 2019/20 winter combined with environmental data to explore the drivers of individual variation in movement patterns, habitat use and foraging behaviour. The social structure and non-random associations of this group forager were assessed in chapter 4 to determine implications for foraging success. From the 2019/20 cohort there were six tracked individuals that recorded a full migration cycle. Therefore, in chapter 5 I was also able to track pre- and post-breeding migratory characteristics, highlighting variation in phenology and individual strategies.

The research carried out in this thesis reveals i) urban centric LBBG have flexible movement patterns, travelling further each day, demonstrating less repeatability between foraging trips and using larger home range, when compared to rural counterparts; ii) the preferred habitat is always wetlands/intertidal areas, however urban LBBG also rely on sports pitches despite high levels of vigilance being displayed on these sites; iii) foraging with familiar individuals enabled LBBG to prioritise feeding and reduce vigilance rates and iv) variation in pre- and post-breeding migratory strategy reflects temporal and physiological constraints commonly associated with a capital breeding life history strategy. Collectively the chapters in this thesis provide novel advances into the ecology of a long-distance migrant relying on an urban environment during their winter staging. They advance our knowledge of migrants’ ability to overcome the constraints associated with resource acquisition in an anthropogenic habitat and provide empirical evidence to inform the implementation of adaptive management strategies.