102 THE MIGRATIONS OF BIRDS 



casual visitants may come from anywhere on the 

 continent, he estimates on the basis of these figures 

 that there is a possibility of record of occurrence for 

 the entire group of birds known from North America 

 north of Mexico in the course of a little more than 

 400 years. 



Casual records of straying birds in continental 

 areas are subject to considerable chance, since the 

 area suited for them is broad. Species of striking 

 appearance are more liable to be noticed than those 

 of ordinary character, since the latter merge with the 

 ordinary avian population. The frigate bird of sub- 

 tropical and tropical seas has been found in the in- 

 terior in Kansas, Iowa, Wisconsin, Ohio, and Nova 

 Scotia, the fork-tailed flycatcher in Mississippi, 

 Kentucky, Maine, and Bermuda, and a form of 

 kingbird {T^yr annus melancholicus satrapd) of the 

 tropics has been taken recently at Scarboro, 

 Maine. These are all single instances. Occasionally 

 flocks of sea birds appear inland as, for example, the 

 dovekie, Wilson's petrel, and others. 



Detection of straying migrants in insular areas is 

 more usual perhaps than on continents, since in 

 limited land space strangers become more conspicu- 

 ous. The list of birds known for the British Isles in 

 191 5 numbered 475, of which 149 had been recorded 

 as accidental visitors. In this list, in addition to 

 forms from near-by continental areas, there are 



