individuals are not able to establish a territory in some other part of the 

 habitat they may become part of a floating, nonbreeding segment of the 

 population, which wanders from one territory to the next until a vacant area 

 is found. 



This dispersal is an important mechanism of population regulation for many 

 species of mammals (e.g., bears, voles, hares, beavers). The fate of 

 dispersing individuals is (1) they settle in unoccupied territories when 

 available, (2) they try to survive in suboptimal habitats, or (3) they die 

 from lack of suitable habitat. Dispersing individuals suffer higher mortality 

 from predation and accidents than resident animals because they are less 

 familiar with their surroundings and their increased movement brings them into 

 contact with a greater number of hazards (Ambrose 1977). 



Species of mammals that are not territorial, such as deer and moose, do not 

 possess a dispersal mechanism for controlling abundance. Although passive 

 dispersal may occur populations that are increasing continue to do so until 

 some resource, usually food, becomes limiting. Mortality from starvation 

 usually occurs during the winter, when energy requirements are highest. This 

 may be due to inadequate food supplies in late summer or fall when fat stores 

 necessary for winter survival must be built up. Winter mortality can be an 

 important mechanism of control for deer populations in Maine. Mild winters 

 allow the population to increase above the ability of the habitat to support 

 it through normal winters. Widespread deaths then occur when normal or severe 

 winters follow. This is illustrated by the deer harvest in the coastal 

 regions, which, when adjusted for season length and hunting effort, reflects 

 the status of the deer population. Figure 17-4 shows the adjusted harvest of 

 deer in each of the six coastal regions for the years 1959 to 1977. In almost 

 all instances the harvest is low after severe winters and high after mild 

 winters. This is complicated in some cases (i.e., 1973 and 1976) when mild 

 winters were followed by hunting seasons in which poor hunting conditions 

 existed due to lack of tracking snow. 



Mammals experience other forms of mortality such as predation, diseases, 

 parasites, and weather-related mortality. The importance of these factors 

 among mammal populations along the coast of Maine generally is unknown. The 

 importance of natural predation in controlling small mammal populations has 

 been studied extensively outside Maine. Some authors (Craighead and Craighead 

 1969) have suggested that predation can control populations but it is 

 generally accepted that predation alone is not sufficient (Pearson 1964; and 

 Errington 1963). Keith (1974), studying the 10-year cycle of snowshoe hares 

 in Alberta, has shown that predation can keep numbers low after they have 

 declined (crashed), but it is not responsible for the significant rapid 

 population declines (which may be due to food shortage caused by 

 overpopulation) . 



Predation has been shown to be important in controlling populations of some 

 large mammals, such as moose in Michigan (Mech 1966) and Dall sheep in Alaska 

 (Murie 1944). In Maine, however, there are no serious predators of moose or 

 deer and losses due to bobcats, coyotes, and dogs seem to be relatively low. 

 During the years 1969 to 1977 an average of 256 deer and less than one moose 

 were reported killed by predators. These figures do not represent total 

 losses for the entire State but only reported losses. 



17-17 



10-80 



