Multifactorial roles of interannual variability, season, and sex for foraging patterns in a sexually size monomorphic seabird, the Australasian gannet (Morus serrator)
Marine top predators forage in environments that show potentially extreme temporal and spatial variation in prey availability, with reproductive success being crucially linked to food supply. Multiple factors of interannual and sexual variation, as well as variation across breeding stages, can shape patterns of spatial use in foraging seabirds, yet studies that address all of these variables simultaneously are rare. We present spatial assessment of foraging patterns by µGPS tracking of a sexually size monomorphic, long-lived species, the Australasian gannet (Morus serrator). The study spanned the incubation and chick-rearing stages in three consecutive breeding seasons. Our findings revealed high interannual variability in foraging distances and trip durations, but no consistent differences between birds across different breeding stages or the sexes. The exception was that core foraging areas were different for female and male Australasian gannets, although trip durations or distances were similar for both sexes. Our results also indicate bimodality in foraging distance and trip duration in this species, while highlighting interannual variability in the extent of bimodality. These findings contribute to a scarcely documented type of foraging behaviour in the seabird family of the Sulidae. Overall, these spatial use patterns provide a baseline for understanding the evolution of sex-specific foraging differences in biparental seabirds, and the extent to which these differences might help in securing breeding success across years of variable food availability.
We thank the Department of Conservation, New Zealand (DOC), and particularly the DOC Napier office for their helpful support of our work and field accommodation. Our research was supported by an International Doctoral Research Scholarship from Education New Zealand (NZIDRS) to SMHI, and funds from the University of Auckland Research Council to MEH. For assistance and discussions, we thank C. Anagnostou, S. H. Anderson, G. Ballard, D. Dearborn, J. Johnson, N. Leuschner, M. Lenz, A. F. Little, G. Machovsky-Capuska, S. Patel, M. Rayner, P. Samaš, R. Shaw, and B. Stephenson, as well as D. M. Allen for copy-editing, and two anonymous referees and Victor Paiva for helpful reviewing and editing of this paper.
Compliance with ethical standards
Conflict of interest
The authors declare no conflict of interest. All animal handling was conducted under University of Auckland Animal Ethics Approval (R342, R654) and under New Zealand Department of Conservation Research Permits (National Permit number ECHB-23237-RES, DOC File NHS-12-12).
- Angel LP, Wells MR, Rodríguez-Malagón MA, Tew E, Speakman JR, Arnould JPY (2015a) Sexual size dimorphism and body condition in the Australasian gannet. PLoS One 10(12):e0142653Google Scholar
- Angel LP, Barker S, Berlincourt M, Tew E, Warwick-Evans V, Arnould JPY (2015b) Eating locally: Australasian gannets increase their foraging effort in a restricted range. Biol Open 4(10):1298–1305Google Scholar
- Cairns DK (1987) Seabirds as indicators of marine food supplies. Biol Oceanogr 5:261–271Google Scholar
- Carter MID, Cox SL, Scales KL, Bicknell AWJ, Nicholson MD, Atkins KM, Morgan G, Morgan L, Grecian WJ, Patrick SC, Votier SC (2016) GPS tracking reveals rafting behaviour of Northern gannets (Morus bassanus): implications for foraging ecology and conservation. Bird Study 63:83–95CrossRefGoogle Scholar
- Ismar SMH (2010) Foraging and breeding ecology of the Australasian gannet Morus serrator, with applications for rare New Zealand seabirds. PhD thesis, University of Auckland, New ZealandGoogle Scholar
- Machovsky-Capuska GE, Senior AM, Benn EC, Tait AH, Schuckard R, Stockin KA, Cook W, Ogle M, Barna K, Melville D, Wright B, Purvin C, Raubenheimer D (2016) Sex-specific macronutrient foraging strategies in a highly successful marine predator: the Australasian gannet. Mar Biol 163:75CrossRefGoogle Scholar
- Nelson B (1978) The Sulidae: gannets and boobies. Oxford University Press, OxfordGoogle Scholar
- Pettex E, Lorentsen S-H, Grémillet D, Gimenez O, Barrett RT, Pons J-B, Le Bohec C, Bonadonna F (2012) Multi-scale foraging variability in Northern gannet (Morus bassanus) fuels potential foraging plasticity. Mar Biol 159:2743–2756Google Scholar
- R Core Team (2016) R: a language and environment for statistical computing. R Foundation for Statistical Computing, Vienna, Austria. https://www.R-project.org/
- Rishworth GM, Tremblay Y, Green DB, Connan M, Pistorius PA (2014) Drivers of time-activity budget variability during breeding in a pelagic seabird. PLoS One 9(12):e116544Google Scholar
- Stephenson BM (2005) Variability in the breeding ecology of Australasian gannets, Morus serrator, at Cape Kidnappers, New Zealand. PhD thesis, Massey University, New ZealandGoogle Scholar
- Wodzicki K, Robertson CJR, Thompson HR, Alderton CJT (1984) The distribution and numbers of gannets (Sula serrator) in New Zealand. Notornis 31(232):261Google Scholar