WES TEEN BLUEBIED 619 



the flight is so far above the earth that the birds are quite beyond the 

 range of vision of an observer stationed on the ground, only the mellow 

 call notes giving indication of the passage of the birds overhead. When 

 bluebirds are in flocks the formation is never compact or coherent; indi- 

 viduals move here and there among their companions and single birds or 

 groups join and depart at intervals. 



The Western Bluebird has two common calls which are used more or 

 less throughout the year, and generally speaking these are the only notes 

 which the bird utters. One of these is a soft kew, the other a harsh but 

 not loud che-oheck. These two notes are used by solitary birds or by 

 members of a flock and although given when the birds are at rest they are 

 heard more often when flocks are moving from place to place. On occasion, 

 during the nesting season, the male can be heard giving voice to extended 

 series of notes similar to the above 'flock' or 'location' calls. At Pleasant 

 Valley on May 24, 1915, and near Coulterville on May 11, 1919, this 'song' 

 was heard. In the latter case there was repetition of the soft kew about 

 as fast as a person could pronounce the syllable distinctly, though the bird 

 did not maintain perfectly uniform intervals. Interpolated after every 

 ten or so of the soft notes the harsher che-check would be given. In other 

 words, the Western Bluebird 's song is a very simple affair, just the common 

 call notes uttered over and over again with monotonous persistence. 



With the arrival of the warm days of early spring the bluebirds com- 

 mence their nesting activities. Much time is spent in prospecting for a 

 site, so that it is not until late April or early May that the nest is com- 

 pleted and eggs are laid. Our earliest data are for May 8 (1919) near 

 Lagrange when one pair was seen carrying food to a nest in an old wood- 

 pecker hole while another pair had a nest with 4 fresh eggs. On May 9, 

 near Hayward, adults were carrying food for young. In 1915, near 

 Pleasant Valley, adults were seen carrying food on May 16, and young 

 out of the nest were observed there on May 24 and 30. At Smith Creek a 

 brood of 5 young was seen to leave the nest on June 5, 1915. 



In spring after the pairs separate off they turn their attention to the 

 oak trees and search for nest holes; for these birds, unlike the thrushes 

 and robin, rear their broods in cavities. Old woodpecker holes are occu- 

 pied when available, but failing to find one of these the birds will use 

 some naturally formed opening in a tree. The decay of stubs of medium- 

 sized branches often results in the formation of cavities in the heart wood 

 of an oak which are appropriate in form and size for use by the bluebirds. 

 It is not improbable that the mistletoe, which is of such direct service to 

 the birds in winter by way of furnishing them with food, may render 

 additional help in promoting, by its parasitic growth, the death of branches 

 which with ensuing decay eventually afford nesting places for the birds. 



