Chapter 4. Conclusions

Continual decrease of the grouse since the 1960’s in Finland has been considered to be a consequence of changes in the forest structure. Although grouse are the main prey of the goshawk, goshawk has probably not decreased so markedly. This witnesses for its adaptiveness that is documented in dietary and in evolutionary respect. Goshawk has thus found new sources of food. Evidently increase of the amount of clear-cuts and young forests has elevated the average density of voles but also that of hares that seem to form a remarkable source of winter food for females. Because hares are out of male’s reach the controversy between the sexes in respect to food supply has increased, which probably explains the opposing changes in the size of the sexes. Males could, however, compensate for the losses of grouse by moving to settlements and dump sites where rats, corvids and domestic pidgeons are available in winter. Changes in the structure of forests, the diet and the morphology of the goshawks may have several consequences to the relationship between the goshawk and the grouse. In spite that decrease of old forests has adversely affected the biotopes of the grouse, the fragmentation of the forests may also have altered the searching efficiency of the goshawks. Depending on the grade of fragmentation and the goshawks’ possibilities to compensate for the loss of grouse by some alternative prey the final outcome in this predator-prey interaction may lead to dampening out of the cyclicity and a lower average density of the main prey as predicted by the general predation theory. Thus, goshawks, may have contributed to the decline of the grouse populations in Finland while they also have suffered and will suffer if the decline of the grouse will continue. Goshawks are not the main reason for the decline of the grouse but may play in concert with other predators the whole process ultimately hanging on the large scale changes in the forest structure caused by man.