Eating locally: Australasian gannets increase their foraging effort in a restricted range

Abstract

During the breeding season, seabirds adopt a central place foraging strategy and are restricted in their foraging range by the fasting ability of their partner/chick and the cost of commuting between the prey resources and the nest. Because of the spatial and temporal variability of marine ecosystems, individuals must adapt their behaviour to increase foraging success within these constraints. The at-sea movements, foraging behaviour and effort of the Australasian gannet (Morus serrator) was determined over three sequential breeding seasons of apparent differing prey abundance to investigate how the species adapts to inter-annual fluctuations in food availability. GPS and tri-axial accelerometer data loggers were used to compare the degree of annual variation within two stages of breeding (incubation and chick rearing) at a small gannet colony situated between two larger, nearby colonies. Interestingly, neither males nor females increased the total distance travelled or duration of foraging trip in any breeding stage (P>0.05 in all cases) despite apparent low prey availability. However, consistently within each breeding stage, mean vectorial dynamic body acceleration (an index of energy expenditure) was greater in years of poorer breeding success (increased by a factor of three to eight), suggesting birds were working harder within their range. Additionally, both males and females increased the proportion of a foraging trip spent foraging in a poorer year across both breeding stages. Individuals from this colony may be limited in their ability to extend their range in years of low prey availability due to competition from conspecifics in nearby colonies and, consequently, increase foraging effort within this restricted foraging area.

Validating accelerometry estimates of energy expenditure across behaviours using heart rate data in a free-living seabird

“…Angel et al, 2015; Green et al, 2009). As we aimed to be able to make quantitative estimates and comparisons of V̇ O 2  using ODBA (question 2), we needed to incorporate the error associated with the conversion from f H to V̇ O 2  into our predictions.…”

Oceanic thermal structure mediates dive sequences in a foraging seabird

“…Changes in the predominance and intensity of one ocean current over another are likely to alter species distributions and thus trophic interactions in the Bass Strait area, as shown previously for the EAC (Oliver et al., 2017; Poloczanska et al., 2007). These changes entrain cascading effects throughout the Bass Strait region's upper‐level predators, such as little penguins (Afán, Chiaradia, Forero, Dann, & Ramírez, 2015; Chiaradia & Nisbet, 2006), Australian fur seals ( Arctocephalus pusillus doriferus ; Hoskins & Arnould, 2014), Australasian gannets ( Morus serrator ; Angel et al., 2015), and short‐tailed shearwaters ( Puffinus tenuirostris ; Berlincourt & Arnould, 2015a).…”

Tracking Cairns: Biologging Improves the Use of Seabirds as Sentinels of the Sea

“…Most studies emphasized that because it is more difficult to collect fish stock data than seabird foraging behavior data, few can link the two-which is, after all, why seabirds are examined as potential indicators of food supply. Five studies collected data over five or fewer colony years, making it difficult to determine whether the relationship between bird behavior and fish stocks is linear or nonlinear (Monaghan et al, 1994;Suryan et al, 2006;Pichegru et al, 2010;Angel et al, 2015). Biologgers also record many foraging parameters, which were not all considered by each study; therefore, some studies might have missed a potentially important correlation.…”