Selås Vidar, Kålås John Atle
Department of Ecology and Natural Resource Management, Norwegian University of Life Sciences, As, Norway.
Oecologia. 2007 Sep;153(3):555-61. doi: 10.1007/s00442-007-0767-2. Epub 2007 Jun 5.
Two recent studies on territory occupancy rates of goshawk Accipiter gentilis and gyrfalcon Falco rusticolus report a 2-3-year-delayed numerical response to grouse numbers, which is a requirement for a hypothesis of predator-generated grouse cycles. The time lags were assumed to reflect the average age of sexual maturity in the raptor species. In southern Norway, however, subadult (two-year-old) goshawk hens occupied only 18-25% of territories where occupancy was not recorded in the preceding year, and there was no significant relationship between the proportion of subadults among recruits and grouse indices two years earlier. We argue that territory occupancy rates are not appropriate indices of total raptor population levels, but rather reflect the proportion of territorial pairs that attempt to nest. Because this depends on the body condition of the hens, fluctuations in other important winter resident prey species (most important for the goshawk) and winter weather (most important for the gyrfalcon) should also be addressed. During 1988-2006, the annual proportion of goshawk territories with recorded nesting attempts in southern Norway was most closely related to the preceding autumn's population indices of black grouse Tetrao tetrix and mountain hare Lepus timidus, whereas the annual proportion of gyrfalcon territories with observations of falcons or with confirmed breeding attempts in central Norway were best explained by population indices of willow grouse Lagopus lagopus and ptarmigan L. mutus from the previous autumn, and by December temperatures. Hence, our studies do not support the predation hypothesis for grouse cycles.
最近两项关于苍鹰（Accipiter gentilis）和矛隼（Falco rusticolus）领地占有率的研究报告称，它们对松鸡数量的数值响应延迟了2至3年，这是捕食者引发松鸡数量周期假说的一个必要条件。时间滞后被认为反映了猛禽物种的平均性成熟年龄。然而，在挪威南部，亚成年（两岁）苍鹰雌鸟仅占据了前一年未记录到领地占有情况的领地的18%至25%，新加入的亚成年个体比例与两年前的松鸡数量指数之间没有显著关系。我们认为，领地占有率并非猛禽总种群数量水平的合适指标，而是反映了试图筑巢的领地配对比例。因为这取决于雌鸟的身体状况，还应考虑其他重要的冬季常驻猎物物种（对苍鹰来说最为重要）的数量波动以及冬季天气（对矛隼来说最为重要）。在1988年至2006年期间，挪威南部有记录筑巢尝试的苍鹰领地的年度比例与前一年秋季黑琴鸡（Tetrao tetrix）和山地兔（Lepus timidus）的种群数量指数最为密切相关，而在挪威中部，观察到矛隼或有确认繁殖尝试的矛隼领地的年度比例，最好由前一年秋季柳雷鸟（Lagopus lagopus）和岩雷鸟（L. mutus）的种群数量指数以及12月的气温来解释。因此，我们的研究不支持松鸡数量周期的捕食假说。
