Annual variation in diets, feeding locations and foraging behaviour of gannets in the North Sea: flexibility, consistency and constraint

Abstract

Many seabirds nesting in areas bordering the North Sea have recently experienced large annual variation in breeding success, including reproductive failures in some cases. In contrast, the breeding success of northern gannets Morus bassanus has remained remarkably stable. The present study examines data from the large gannet colony at the Bass Rock (southeast Scotland) across 3 years, to assess the extent to which such stability may reflect both flexibility and consistency in diets and foraging behaviour. Adults exhibited great flexibility both in the species and sizes of prey consumed and in foraging trip durations, ranges and total distances travelled. They also showed a high degree of consistency in bearings of foraging trips and in behaviour at sea; the sinuosity of foraging tracks and average speed of travel was very similar each year and birds in all years spent about half their time at sea in flight. Adults returned to the nest at higher speeds from more distant foraging locations up to ca. 300 km from the colony, but speeds decreased for the farthest destinations (>ca. 400 km). Moreover, the relationship between trip duration and distances travelled at sea was asymptotic beyond ca. 60 h. These non-linear relationships probably reflected constraints on energy expenditure during flight. As a result, nest attendance was low in years with long average trip durations and chicks were left unattended and vulnerable to attack by conspecifics. These data suggest that while adults have so far been able to maintain high reproductive success in years of low prey availability, they may not be able to do so in future years if providing sufficient food for chicks entails any further increases in trip duration or foraging effort. KEY WORDS: Morus bassanus · Wildlife telemetry · Geolocation · Home range · Optimal foragingResale or republication not permitted without written consent of the publisher

Mesoscale fronts as foraging habitats: composite front mapping reveals oceanographic drivers of habitat use for a pelagic seabird

“…Many marine predators, including seabirds, are known to repeatedly return to the same foraging areas [5,7,40,63], which is generally attributed to the presence of oceanographic features that are predictable in time and space. In the Celtic Sea, these predictable foraging areas are associated with persistent mesoscale thermal and rsif.royalsocietypublishing.org J. R. Soc.…”

“…Gannets are large, mediumranging marine predators, which feed on a wide variety of piscivorous prey [7,[39][40][41]. Foraging plasticity in gannets has been linked to oceanographic variability over a range of scales [40,[42][43][44].…”

Consistency pays: sex differences and fitness consequences of behavioural specialization in a wide-ranging seabird

“…Our results also suggest that males still exhibit variation in trip duration. Many studies suggest that while seabirds are spatially consistent, they demonstrate an element of plasticity in temporal measures as this is likely to be an adaptive response to aspects of oceanic unpredictability and variation in foraging success [12,22,23].…”

Hitting the buffers: conspecific aggression undermines benefits of colonial breeding under adverse conditions

“…In extreme circumstances, parents may need to forage simultaneously, leaving their chick unattended: such chicks may gain protection within colonies from the proximity of neighbouring birds, providing a further buffer against adverse foraging conditions. However, they may also be at risk from conspecifics such as nonbreeders attempting to usurp nest sites (Anderson et al 2004;Hamer et al 2007).…”