Foraging behaviour and habitat use of chick-rearing Australasian Gannets in New Zealand

Abstract

Patchily distributed marine pelagic prey present considerable challenges to predatory seabirds, including Gannets (Morus spp.) departing from large breeding colonies. Here, for the first time, we used GPS data loggers to provide detailed spatial, temporal, and habitat metrics of chick-rearing Australasian Gannets (Morus serrator) foraging behaviours from two distant colonies in New Zealand. Our goal was to examine the extent to which Gannet foraging tactics vary across disparate habitats, and determine whether the observed differences are consistent with predictions derived from foraging studies of other gannet species. Foraging trip performance was highly consistent between colonies, and sexes, and no significant differences in any of the variables analyzed were observed. However, Gannets from Farewell Spit (FS) dove in shallower waters (0 50 m) than birds from Cape Kidnappers (CK, [50 m), which is consistent with previous dietary studies suggesting that FS Gannets feed mainly on coastal prey, whereas CK birds feed on species with a more oceanic distribution. Diving frequencies were similar in the two colonies suggesting that Gannets were foraging in habitats with similar levels of food availability. Further studies are needed to understand the relationship between prey availability, oceanography and geographic features, to better interpret foraging tactics of Australasian Gannets.Keywords Foraging range Á Diving behaviour Á Morus serrator Á Food sources Á GPS data loggers Á Seabirds Communicated by C. Barbraud. G. E. Machovsky Capuska (&)Á

Sex-specific macronutrient foraging strategies in a highly successful marine predator: the Australasian gannet

“…Drastic shifts in climate-related regimes are believed to be responsible for the decrease in availability of high-quality prey species (in terms of energy and lipid contents) and an increase in lowquality foods, which has negatively influenced marine predator populations around the world (Österblom et al 2008). Operating in such a complex environment, marine predators require particularly sophisticated foraging strategies that enable them to balance self-and offspring-feeding, and also in many circumstances simultaneously consider the nutritional constraints of their partners (Weimerskirch et al 1994;Machovsky-Capuska et al 2014a;Malinowski and Herzing 2015). Seabird chicks are under constant age-related fluctuations in lipid, protein, water and energy density until they reach functional maturity and are able to feed for themselves (Navarro 1992).…”

“…Gannets are carnivorous central place foragers , 2014a, and a developing model species for testing field-based nutritional ecology questions (Tait et al 2014). Here we combined the use of dietary analysis, proximate composition and nutritional geometry (right-angled mixture triangle nutritional models-RMT) to examine the macronutrient preferences of Australasian gannets at Farewell Spit gannetry (FS) in New Zealand.…”

Seed dispersal but not seed germination facilitated by seabirds: seed ecology of Cook’s scurvy grass

“…Seed seawater exposure would also depend on the part of the seabird to which it attached. Australasian gannet (Morus serrator) foraging trips involve bouts of short dives interspersed with periods of resting on the surface of the water which represent 70-80% of the foraging trip time (Machovsky-Capuska et al 2014). Therefore, seeds attached to areas immersed during resting, such as the legs and abdomen, would experience seawater exposure for up to 30 hours in seawater, whereas the upper parts of the body would have shorter seawater immersion.…”

Using non-systematic surveys to investigate effects of regional climate variability on Australasian gannets in the Hauraki Gulf, New Zealand

“…Gannets feed mainly on pelagic fish and squid (Machovsky-Capuska et al, 2011a;Robertson, 1992;Schuckard et al, 2012;Tait et al, 2014). These highly specialized marine predators have been reported to travel for food as far as 388.5 km (Machovsky-Capuska et al, 2013a, 2014 with the ability to assess prey density to increase foraging success (Machovsky-Capuska et al, 2013b). Their populations have been increasing since the 1980s around New Zealand and the 1990s in Australia (Bunce et al, 2002).…”