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Advisor(s)
Abstract(s)
There was an extraordinary increase in the numbers
of European gulls during the twentieth century which has been
linked to higher availability of food derived from human activities.
At Berlenga island (Portugal), the population of
yellow-legged gulls Larus michahellis increased from 2600
individuals to a peak of 44,698 gulls (1974–1994), after which
control measures have been put in place. Despite the management
effort, little is known about the feeding ecology of this
population. To investigate temporal and age-related variations
in the diet of yellow-legged gulls at Berlenga, 1668 adult
pellets and 145 chick regurgitates were collected and analysed
between 2009 and 2012. Contradicting the generally accepted
idea that these birds depend mainly on human-related food,
adult gulls relied substantially on a locally abundant natural
prey, the Henslow’s swimming crab Polybius henslowii.
Nevertheless, large amounts of refuse and fish were consumed
in periods of apparent lower availability of swimming crabs.
Despite the large temporal shifts in diet and feeding areas
(change from marine to terrestrial prey), adult gulls consistently
provisioned their chicks with a fish-based diet and chick
condition remained constant. These results not only highlight
the great resilience of this population to changes in food availability
but also indicate that food from different human activities
remain highly accessible. With the implementation of
recent EU legislation regarding the reduction of fishery discards,
and the increase of urban populations in the mainland,
the monitoring and appropriate management of gull populations
will be decisive for the healthy conservation of coastal
systems used by these gulls.
Description
Keywords
Swimming crabs Feeding ecology Biological control Fishery discards Landfills Urban gulls
Citation
European Journal of Wildlife Research, 61, 819-829. doi: 10.1007/s10344-015-0958-9
Publisher
Springer