Seabird predation by great skuas Stercorarius skua -: intra-specific competition for food?
Seabird predation by great skuas Stercorarius skua -: intra-specific competition for food?
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DOI：
10.1111/j.0908-8857.2007.03893.x
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发表时间：
2007-03-01
影响因子：
1.7
通讯作者：
Furness, Robert W.
中科院分区：
文献类型：
--
作者：
Votier, Stephen C.;Bearhop, Stuart;Furness, Robert W.
对食物的竞争被广泛认为是鸟类殖民的重要代价，支持这一假设的许多证据来自对殖民食鱼海鸟的研究。然而，对于能够在不同猎物类型之间切换的通才海鸟来说，食物供应对群体大小的作用尚不清楚。在这里，我们调查模式的消费海鸟猎物在一个通才海鸟，大贼鸥Stercorarius skua，在设得兰群岛，英国的殖民地规模。在种群水平上，贼鸥主要以沙鱼和渔业丢弃物为食，但对鱼类供应的下降作出反应，以捕食其他海鸟。通过比较7个不同大小的殖民地，包括人工减少贼鸥（公平岛）的数量的一个殖民地之间的海鸟的消费，我们调查是否消费的海鸟猎物是贼鸥种群规模的影响，同时测量海鸟猎物的可用性。五年的数据也使我们能够调查环境条件的年度变化对海鸟消费的影响。使用的身体状况和生殖性能的措施，我们调查生活在不同大小的殖民地的后果，这可能会提供洞察筑巢在高人口密度的最终成本。贼鸥的饮食各不相同的殖民地和海鸟的猎物在饮食中的比例呈负相关的贼鸥殖民地的大小，尽管类似的人均海鸟数量的殖民地。在殖民地，贼鸥的数量被人为地控制住了，但贼鸥的人均消费比例却更高。在海鸟捕食高度显着的年效应进行了观察，但殖民地之间的模式保持一致，随着时间的推移。两项措施的成年身体状况（胸肌指数和平均红细胞体积）显示，成年大贼鸥在最大的殖民地（Foula）条件较差，但繁殖性能并没有显着改变殖民地之间。这项研究提供的证据表明，贼鸥之间的种内竞争可能会限制机会，获得海鸟的猎物，这可能是特别重要的，在此期间，可利用性差的沙笛和渔业丢弃物，并评估贼鸥对海鸟种群的影响。
Competition for food is widely cited as an important cost of coloniality among birds and much of the evidence in support of this hypothesis comes from studies of colonial piscivorous seabirds. However, for generalist seabirds able to switch between different prey types, the role of food availability in relation to colony size is unclear. Here we investigate patterns of the consumption of seabird prey in relation to colony size in a generalist seabird, the great skua Stercorarius skua, in Shetland, UK. At the population level skuas feed mainly on sandeels Ammodytes marinus and fishery discards, but respond to declines in fish availability to facultatively prey on other seabirds. By comparing the consumption of seabirds among seven different sized colonies, including one colony with artificially reduced numbers of skuas (Fair Isle), we investigate whether consumption of seabird prey is influenced by skua population size, while simultaneously measuring seabird prey availability. Data from five years also enables us to investigate the influence of annual variation in environmental conditions on seabird consumption. Using measures of body condition and reproductive performance we investigate the consequences of living in different sized colonies, which may provide insight into ultimate costs of nesting at high population density. Skua diets varied among colonies and the proportion of seabird prey in the diet was inversely related to skua colony size, despite similar per capita numbers of seabirds across colonies. At the colony where their numbers were artificially suppressed, skuas consumed a greater proportion of seabirds per capita. Highly significant year effects in seabird predation were observed but the pattern among colonies remained consistent over time. Two measures of adult body condition (pectoral muscle index and mean corpuscular volume) revealed that adult great skuas were in poorer condition at the largest colony (Foula), but reproductive performance did not alter significantly among colonies. This study provides evidence that intra-specific competition among skuas may limit opportunities for obtaining seabird prey, which may be particularly important during periods of poor availability of sandeels and fishery discards, and has implications for assessing the impact of skuas on seabird populations.