Spatial assessment of foraging patterns of the Australasian gannet (Morus serrator) during three breeding seasons (2007/08, 2008/09, 2009/10) at Hawke's Bay, New Zealand@en

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.海洋顶级捕食者的觅食环境中，猎物可获得性存在显著的时间与空间变异，而繁殖成功率与食物供给密切相关。年际差异、性别差异以及繁殖阶段差异等多重因素，均可塑造觅食海鸟的空间利用模式，但同时兼顾所有上述变量的研究仍较为罕见。 本研究通过µGPS追踪（µGPS tracking），对一种体型性别单态（sexually size monomorphic）、寿命较长的物种——澳大拉西亚塘鹅（Morus serrator）的觅食模式开展空间评估。研究覆盖了三个连续繁殖季中的孵卵期与育雏期两个繁殖阶段。 研究结果显示，觅食距离与觅食时长存在较高的年际变异性，但不同繁殖阶段或不同性别的个体之间并未呈现一致的差异。唯一的例外是，尽管雌雄个体的觅食时长与距离并无显著差异，但澳大拉西亚塘鹅的核心觅食区域存在性别差异。 本研究结果同时表明，该物种的觅食距离与觅食时长呈现双峰分布特征，且双峰分布的程度存在年际变异性。上述发现填补了鲣鸟科（Sulidae）海鸟觅食行为相关研究中较为匮乏的部分。 总体而言，这些空间利用模式为理解双亲照料海鸟的性别特异性觅食差异演化提供了基准参照，也有助于阐释在食物可获得性逐年波动的背景下，此类差异对保障繁殖成功率的作用程度。