CASUAL RECORDS loi 



tropical species encountered in temperate regions. 

 Though conceivably such birds may occasionally 

 have established themselves in new ranges, this 

 would happen far less frequently than with birds 

 working out short distances beyond the edge of the 

 normal range. To this agency, however, we must 

 look to explain the presence of small land birds on 

 oceanic islands, where there has never been conti- 

 nental connection, as in the Leeward Islands of the 

 Hawaiian group, where a finchlike bird of the family 

 Drepanididae, another smaller species of the same 

 group, and an Old World warbler, are found on the 

 island of Laysan, an isolated bit of sand built up 

 through filling in an atoll, with less than two square 

 miles of land surface. (The warbler, Conopoderas 

 familiarisy and one of the Drepanidids, Himatione 

 fraithii^ are now extinct.) 



Dr. Grinnell ^ has stated that of the 576 forms of 

 birds recorded for the State of California to 1922, 

 there are 2S that have been found on only one occa- 

 sion. These represent mainly casual visitants far 

 from their usual range. A few more — ten, to be 

 exact — have been detected twice, while for six 

 there are three records of occurrence. On the basis 

 of observations extending over thirty-five years, he 

 finds that new additions to the list for the state have 

 come at the average rate of if per year. Since these 



^ Auk, 1922, pp. 373-375. 



