Lemmings, if they survive into the summer, and leverets can support falcon reproduction through the nestling period into August. At the time female gyrs are incubating eggs in late May and June, the leverets of Arctic Hare become available, and Gyrfalcons utilize them heavily where they are common. Whether or not Gyrfalcons can exploit adult hares effectively at this time remains a question that needs study. Early spring flocks of male Snow Buntings may also help. Where the Collared Lemming occurs and reaches “peak” numbers in some years, it apparently serves as a substitute, abetted by whatever ptarmigan are available. Ptarmigan are now rather sparse in the High Arctic and apparently seldom build up to numbers that can support Gyrfalcon reproduction without supplementation by other prey. Most Gyrfalcon populations depend on an abundance of ptarmigan (Lagopus spp.) for their food during the critical period of establishing a pairbond and laying eggs in late winter (mid-April and May in the High Arctic). The distribution and abundance of these principal prey are highly variable in time and space, and consequently the serviceability of eyries is unpredictable and largely determined by the abundance of food in a particular year. Some level of synchrony in population fluctuations between neighbouring subareas was detected, although this was statistically significant in only one pair of neighbouring subareas.Ī BSTRACT.-Gyrfalcons (Falco rusticolus) breeding in the High Arctic Canadian Islands and in northern Greenland have available to them widely scattered nesting sites on cliffs throughout much of this region, but their food resources are limited to four principal species, Rock Ptarmigan (Lagopus muta), Snow Bunting (Plectrophenax nivalis), Collared Lemming (Dicrostonyx torquatus), and Arctic Hare (Lepus arctica), with seabirds, waterfowl, and shorebirds playing a role in some localities. We checked for cyclicity in the population fluctuations by testing the significance of the parameters in an autoregressive log-linear model fitted to the time series, but failed to detect cyclicity in any of the time series. Additionally, we present data from the Zackenberg Research Station and the Karupelv Valley Project within the same general study area. ![]() The material from three of the subareas was of sufficient quality for statistical analyses. The material has been collected by the Danish military dog sledge patrol Sirius in North and Northeast Greenland during the period 1977-2006. The present study analyses data of the northernmost subspecies of Rock Ptarmigan Lagopus mutus captus in Greenland. Also, synchrony in these fluctuations – both between and within species – has been found in several bird species and other animals. Cyclicity in population fluctuations has been described in a number of tetraonid species.
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