1917 BIRDS OF THE SOUTHERN CALIFORNIA ISLANDS 15 



Judging by the data in hand, the whole life cycle of the smaller insular sub- 

 species and species, on the more southern islands at least, is shifted a month or 

 six weeks earlier than that of the corresponding mainland forms. On San Cle- 

 mente Island in 1915, we collected during the last week in March juvenile 

 Shrikes, Song Sparrows, Horned Larks, House Finches and San Clemente Wrens 

 that were strong on the wing and with well grown tails. These were not isolated 

 cases, for after the first day seen, the youngsters at once became common. On 

 April 9 I shot a young Song Sparrow that had almost completed the post-juvenal 

 molt. On the same date, on San Clemente, however, the larger birds, such as the 

 Bald Eagle and the Raven, were not farther advanced in breeding operations 

 than one would expect. On Todos Santos Island, April 16, 1910, a pair of Baru 

 Owls had a nest containing a chick two-thirds grown, while during the first part 

 of the month, on the mainland, I examined two occupied nests which as yet held 

 no eggs, though of course Barn Owls sometimes do lay before this date. As pre- 

 viously mentioned, there were yoimg House Finches there at the same time that 

 were ready to leave the nest, but on the mainland there is not mucli use looking 

 for Linnets ' eggs before the last of March. 



This early nesting may be due to obscure and unrecognized causes, but it is 

 partly influenced by the mild winters, and to a greater extent, by the abundant 

 food supply. In regard to the latter, it is hard to make comparisons, for on parts 

 of the mainland where trees occur, there are large numbers of insects in the tops 

 of these, while on an island such as San Clemente they are under one's feet and 

 more readily noticed. Be that as it may, on some of the islands insects are every- 

 where, and as there is no frost to reduce their numbers, the birds do not have to 

 wait in the spring until the presence of a new generation of bugs enables them to 

 begin nesting operations. 



The molt, also, takes place earlier than is usual upon the mainland, antl 

 birds in fresh plumage may be taken in early August, if not before. iMarch speci- 

 mens are sometimes as ragged and faded as mainland ones taken in late June, 

 and by the time the new feathers begin to grow some of the birds are almost 

 naked. 



Small birds on the islands are particularly numerous, due partly to the 

 abundant food supply, in large measure to the absence of many predaceous 

 forms, and to the excellent cover afforded by the patches of cactus and thorny 

 scrub Avith which the islands abound. Here they usually nest and roost, secure 

 from everything except, in the case of the smaller ones, an occasional marauding 

 mouse. 



The birds of the Santa Barbara Islands have not lost any of their fear of 

 man, as have, for instance, those of the Galapagos Archipelago. The aborigines 

 inhabited some of the islands for a long time, and white men have been visiting 

 them for many years. On the Coronados I have had Song Sparrows hopping 

 about within two feet of my head, but, on the other hand, the Island Shrike is 

 the most wary land bird for its size that I have ever encountered. 



The formation of insular races is so shrouded in mystery that it is unsafe to 

 speculate as to causes and effects save in a most general way. We can see that 

 climate has played an important part in this. As mentioned previously, the gen- 



