Habitat-specific foraging strategies in Australasian gannets

Abstract

Knowledge of top predator foraging adaptability is imperative for predicting their biological response to environmental variability. While seabirds have developed highly specialised techniques to locate prey, little is known about intraspecific variation in foraging strategies with many studies deriving information from uniform oceanic environments. Australasian gannets (Morus serrator) typically forage in continental shelf regions on small schooling prey. The present study used GPS and video data loggers to compare habitatspecific foraging strategies at two sites of contrasting oceanographic regimes (deep water near the continental shelf edge, n=23; shallow inshore embayment, n=26), in south-eastern Australia. Individuals from the continental shelf site exhibited pelagic foraging behaviours typical of gannet species, using local enhancement to locate and feed on small schooling fish; in contrast only 50% of the individuals from the inshore site foraged offshore, displaying the typical pelagic foraging strategy. The remainder adopted a strategy of searching sand banks in shallow inshore waters in the absence of conspecifics and other predators for large, single prey items. Furthermore, of the individuals foraging inshore, 93% were male, indicating that the inshore strategy may be sex-specific. Large inter-colony differences in Australasian gannets suggest strong plasticity in foraging behaviours, essential for adapting to environmental change.

Short‐term prey field lability constrains individual specialisation in resource selection and foraging site fidelity in a marine predator

“…; Spiegel & Crofoot ; Wells et al . ). Our results confirm that both mechanisms can occur in parallel, as shearwaters shared a limited number of foraging areas across their consecutive trips, and different individuals shared some foraging areas at similar time.…”

“…; Wells et al . ). In contrast, if prey distributions are unpredictable, information cannot allow maintaining ISRS.…”

“…Individual specialisation in resource selection offers a selective advantage if individuals increase foraging efficiency by reducing search times, and this is related to their abilities to locate prey (Spiegel & Crofoot 2016) and to prey predictability . When prey distributions are predictable, predators can reduce search time using memory (Weimerskirch 2007;Wakefield et al 2013) and/or public information (Weimerskirch et al 2010;Wells et al 2016). In contrast, if prey distributions are unpredictable, information cannot allow maintaining ISRS.…”

Positive Interactions among Foraging Seabirds, Marine Mammals and Fishes and Implications for Their Conservation

“…Natural selection favoring interspecific interactions is likely to vary greatly through years, seasons and age, and depend on the presence or absence of particular taxa in foraging associations. Individual specialization has been documented in many seabird species, in which some individuals for example, forage in interspecific associations whereas others forage independently with implications for relative fitness as resources fluctuate (e.g., Wells et al, 2016). With more diffuse coevolution, there may be selection for facultative foraging associations in many circumstances, but the behavioral patterns observed, and the ubiquity of feeding associations among pelagic predators, indicate that strong selection is likely to be operating, and that there are fitness benefits.…”

“…Niche variation is frequently observed in seabirds, in which some individuals of a population feed in interspecific associations and others forage independently (Ceia and Ramos, 2015;Wells et al, 2016), and can have a frequency dependent effect with profound implications for population stability (Bolnick et al, 2003). Further research is merited measuring the degree of specialization (Bolnick et al, 2002) and the dependence on interspecific associations-and the vulnerability of populations if specialized feeding associations are lost.…”