FEEDING ECOLOGY OF A TOP MARINE PREDATOR IN RELATION TO OCEANOGRAPHY AND CLIMATE AND ASSESSMENT OF POTENTIAL FOR MONITORING OF PELAGIC ECOSYSTEMS IN THE FACE OF GLOBAL WARMING

Funder

Organizational Unit

Publications

When males are more inclined to stay at home :Insights into the partial migration of a pelagic seabird provided by geolocators and isotopes

Publication . Perez, Cristóbal; Granadeiro, José Pedro; Dias, Maria P.; Alonso, Hany Rafael de Drummond Ludovice Garcia; Catry, Paulo

Partial migration has never been studied in pelagic seabirds, but investigating old unresolved questions in new contexts can provide useful fresh insights. We used geolocators and stable isotopes to investigate this phenomenon in a migratory pelagic seabird, the Cory’s shearwater (Calonectris diomedea). Although most birds migrated to the southern hemisphere, 8.1% of studied birds (N = 172) remained close to the breeding colony (Selvagem Grande, Madeira, Portugal), foraging within the Canary current. Almost all resident birds were males, while age or body size did not predict migratory status. Despite displaying a high repeatability (R = 0.72) in the choice of wintering area, residency was not a fixed strategy and individuals could switch between migrating and staying in the Canary current in different years. The predictions resulting from the “body size” and the “social dominance” hypotheses, in which larger individuals or dominant individuals, respectively, remain closer to the breeding areas, were not supported by our data. Resident males were able to occupy the nesting burrows much earlier than migratory males and arrival time in this species is known to affect the probability of engaging in a reproductive attempt. The selective pressure to arrive early at the colony is therefore the most likely explanation for the maintenance of this partial migration system.

2014Journal article

Restricted access

The diet of a nocturnal pelagic predator, the Bulwer’s petrel, across the lunar cycle

Publication . Waap, Silke; Symondson, William O. C.; Granadeiro, José Pedro; Alonso, Hany Rafael de Drummond Ludovice Garcia; Gonçalves, Catarina Serra; Dias, Maria P.; Catry, Paulo

The lunar cycle is believed to strongly influence the vertical distribution of many oceanic taxa, with implications for the foraging behaviour of nocturnal marine predators. Most studies to date testing lunar effects on foraging have focused on predator activity at-sea, with some birds and marine mammals demonstrating contrasting behavioural patterns, depending on the lunar-phase. However, to date no study has focused on how the lunar cycle might actually affect predator-prey interactions in the upper layers of the ocean. Here, we tested whether the diet of the predominantly nocturnal pelagic predator, the Bulwer's petrel (Bulweria bulwerii) would change throughout the lunar cycle, using molecular analysis to augment detection and taxonomic resolution of prey collected from stomach-contents. We found no evidence of dietary shifts in species composition or diversity, with Bulwer's petrel always consuming a wide range of mesopelagic species. Other co-variables potentially affecting light availability at-sea, such as percentage of cloud cover, did not confound our results. Moreover, many of the species found are thought not to reach the sea-surface. Our findings reveal that nocturnal predators are probably more specialized than previously assumed, irrespective of ambient-light, but also reveal deficiencies in our current understanding of species vertical distribution and predation-dynamics at-sea.

2017Journal article

Open access

Temporal and age-related dietary variations in a large population of yellow-legged gulls Larus michahellis : Implications for management and conservation

Publication . Alonso, Hany Rafael de Drummond Ludovice Garcia; Almeida, Ana Pereira; Granadeiro, José Pedro; Catry, Paulo

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.

2015Journal article

Restricted access