1.5. Winter ecology of goshawks

Winter is a time of extreme conditions in the north. Temperatures can drop to -30 C. Another harmful point for diurnal animals is a short day length, which reduces the time for searching for food. This is especially problematic for raptors whose food source, prey animals, is not very predictable. In addition, prey animals adopt different anti-predator behaviours, like flocking (Angelstam 1984) and snow-roosting (Marjakangas 1990). Crypticity of prey also decreases finding probabilities of prey. Yet, in spite of these difficulties goshawks are able to spend winter in the north. Due to their secretive life habits very little is known about their habits outside the breeding season. By adopting radio-telemetry as a research tool new information about the goshawk’s winter ecology has recently been obtained. (Kenward 1977, Kenward et al. 1981, Kenward 1982, Ziesemer 1981, Widen 1985, Widen 1989, Kenward et al. 1991, 1993). Important questions like population structure, demography, movements, survival, causes of death, habitat selection and winter diet can be cleared up more accurately than before. A crucial aspect in the conservation of the goshawk derived from these themes is its response to change in forest structure due to modern forestry. Goshawks are known to be old forest dwellers based on nest site preferences (e.g. Link 1986). Clear-cuts have produced a mosaic landscape where old forest patches are becoming smaller and smaller. In landscape ecology it has been found that beyond a certain limit of habitat loss the population will decrease more than the habitat loss alone would explain (Andren 1994). There are indications that the goshawk might have decreased in recent decades in Fennoscandia, at least locally (Linden & Wikman 1983, Forsman & Ehrnsten 1985, Tommeraas 1993, Halley 1996, Widen 1997). However, in agricultural areas of Sweden and Central Europe goshawks are rather well adapted to landscape containing less than 50% forest (Kenward et al. 1981, Kenward 1982, Ziesemer 1982).