Distribution of Bats of the California Channel Islands

The power of flight has preadapted bats for island colonization. This accounts for their disproportionately high representation in the terrestrial mammalian fauna of the California Islands. Of the eighteen species of native mammals found on the islands (excluding man and marine mammals), eleven, or 61 per cent, are bats. Some bat species are better dispersers than others, but not only must a bat be capable of crossing the water barrier, it must find suitable food and habitat upon its arrival. Bats have voracious appetites and may consume up to 25 percent of their body weight in insects daily. Some are specific in their food requirements, while others are generalists and opportunists, snatching up any insect within a certain size class. Needless to say, generalists are better island colonizers since the specialist may not find its favorite food item present on the island. Bats with specific roost preferences, such as trees or rock crevices, may find a barren sandy island a difficult place on which to live and reproduce. In this paper, I will attempt to summarize what is known about the distribution of bats on the islands and provide new data resulting from my own field work.