Excluding the eight species mentioned above, each species of terrestrial 

 mammal should be present in suitable habitat throughout the characterization 

 area, with the exception of the offshore islands. Expanses of salt water 

 present a formidable barrier to most species of mammals, so they are absent 

 from all but the nearest or largest offshore islands. Mammals reach islands 

 by swimming, rafting on debris, crossing ice bridges, or by coming with 

 people. Two deer reportedly swam over 2 miles (3.2 km) and another swam 

 nearly 7 miles (11.3 km) to the mainland from islands on which they had been 

 released (Schemnitz 1975). Morse (1966) also reported deer swimming freely 

 between Hog Island and the mainland but this was only a distance of a few 

 hundred yards. Rafting is used most likely by small mammals that get trapped 

 on pieces of earth or debris that break loose from the mainland during storms. 

 Ice bridges are used by wide-ranging species such as deer, fox (Morse 1966), 

 and raccoon. Mammals brought by people probably include mice, rats, and 

 voles that are small enough to stow away on boats, and domestic animals (dogs, 

 cats, sheep). Species lists of mammals present on some of the larger islands 

 have been compiled and are summarized in appendix table 10. 



Islands also present problems other than accessibility that prevent species 

 from becoming established. Populations of colonizing species are small 

 initially and natural fluctuations may cause their extinction (Crowell 1973) . 

 Colonizing individuals may have to compete with closely-related species that 

 are already present. Native species seem to have an advantage in these 

 situations, perhaps because of their larger numbers (Crowell and Pimm 1976). 

 Some of these factors were seen among the small mammals that were studied by 

 Crowell (1973) and Crowell and Pimm (1976) on the islands off Deer Isle 

 (region 4). Meadow voles are the most abundant species on small islands; they 

 seem more capable of reaching islands and they reproduce rapidly once 

 established. Deer mice are present only on larger islands, where their 

 populations can build up sufficiently to preclude chance extinctions. Red- 

 backed voles seem to have a poor dispersal capability, low reproductive 

 potential initially, and little or no ability to compete successfully with 

 meadow voles . 



Habitat Preferences 



Within its geographical range each species has preferred or optimal habitats 

 in which it will most likely be found. Each species also has less-preferred 

 or marginal habitats in which it will be found less frequently and usually in 

 fewer numbers (figure 17-2). Some species, such as beaver, otter, or flying 

 squirrels, occupy only a few habitat types, while others (i.e., coyote, red 

 fox, short-tailed shrew) inhabit a wide range of habitat types. Species with 

 restricted habitat preferences are generally less adaptable and do not 

 tolerate disturbance as well (Gill and Bonnet 1973). Planners need to be 

 aware of species with restricted habitat preferences so that if these species 

 are found within areas scheduled for development the impact of the habitat 

 loss on their populations can be assessed. Critical habitats in a region 

 need to be identified, and protected. The number of preferred and acceptable 

 habitats is summarized in figure 17-2. Species that may be of concern 

 ecologically, because of their narrow habitat preferences, are the water 

 shrew, some of the bats, and the aquatic furbearers. 



17-7 



10-80 



