The secret life of urban gulls
: Habitat use, foraging behaviour and flight energetics of urban-nesting lesser black-backed gulls, Larus fuscus

  • Anouk Spelt

Student thesis: Doctoral ThesisDoctor of Philosophy (PhD)

Abstract

Urbanisation generally negatively affects biodiversity, but some opportunistic animals, like gulls, are able to adapt to urban environments and are increasing in numbers in cities. At the same time, traditional non-urban gull colonies (especially in the UK) are declining. Different aspects of the - supposedly better - living conditions in the city have been proposed for this increase in urban areas, such as fewer predators, ample nesting sites, predictable
anthropogenic food sources and favourable weather conditions. However, the impacts of urban living on gull behaviour and movement ecology is relatively unstudied and little is known about how they use urban environments. Therefore, the overall aim of this thesis was to study the movement ecology of urban-nesting gulls by quantifying their habitat use, foraging behaviour
and flight energetics. Between 2016 and 2019, 12 lesser black-backed gulls, Larus fuscus, were tracked with UvA-BiTS GPS tracking devices during the breeding season. These tracking devices collected high-resolution positional and acceleration data, the latter used to identify gull-specific behaviours and energy budgets. Additionally, observations were conducted at the nesting areas
to quantify their breeding status and at feeding grounds to observe their foraging behaviours in distinct habitats. These datasets were then combined with habitat maps of Bristol and weather data from weather stations to quantify habitat use, foraging behaviour and flight energetics of urban-nesting gulls. Firstly, it was found that urban-nesting gulls in Bristol spent the majority of
their time during the breeding season in suburban and urban areas, but also utilised rural areas surrounding the city. Additionally, they used distinct foraging behaviours in different habitats, appearing to adapt their behaviour to suit resource availability. Secondly, it was found that gulls matched their foraging schedule to the timing of school breaks and the opening and closing times of a waste centre, but that gull activity in a park appeared to correspond with the availability of natural food sources. This suggests that gulls are able to adjust their foraging behaviour to artificial time schedules when beneficial. Thirdly, it was found that favourable weather conditions in the city, such as the potential for thermals and orographic updrafts, affected the gulls’ flight
behaviour, but surprisingly, did not result in substantial differences in time investment or energy costs. This suggests that gulls are able to modify their flight behaviour to keep a relatively consistent energy budget across a wide range of weather conditions. Overall, this work shows that urban-nesting gulls are highly flexible behaviourally and are able to take advantage of a wide variety of terrestrial habitats by using a range of foraging strategies. They also time their foraging behaviour with the peak availability of food sources and are able to maintain their energy costs over a range of weather conditions by shifting their flight style to optimise their use of the aerial environment. The multiple levels of behavioural flexibility demonstrated by gulls appear to enable them to be successful in the diverse dynamic urban environment.
Date of Award29 Sep 2020
Original languageEnglish
Awarding Institution
  • The University of Bristol
SupervisorShane P Windsor (Supervisor)

Cite this

'