92 PACIFIC COAST AVIFAUNA No. 9 



Tree Swallow. Iridoprocne bicolor (Vieillot). 



The Tree Swallow is the only representative of the family Hirunclinidae that 

 is to be found in Fresno County during the winter months. The species is mi- 

 gratory to a great extent, but a small number winter in this part of the San Joa- 

 quin Valley each year, being met with in the vicinity of ponds and sloughs more 

 often than elsewhere. 



November 29, 1904, two Tree Swallows were seen flying over a small body 

 of water near New Hope, and the following day a flock of a dozen birds was 

 noted flying over another pond near the same place. January 25, 1905, a lone 

 bird was observed near Clovis as it flew overhead, traveling toward the south and 

 twittering cheerfully. February 13, 1906, another was seen travelling in the same 

 direction. February 27, 1906, and the following day, several were noted, all 

 southward bound. This tendency of theTree Swallows to travel toward the south 

 during January and February has been mentioned before (Condor, xiii, 191 1, p. 

 168) ; but I have not yet been convinced that these same individuals are a part of 

 the migrant host that appears from the south during early March (6, 7, and 13, 

 1906), just in advance of the other species of swallows that summer with us or 

 pass on through the valley. 



April 26, 1909, a scattered colony of Tree Swallows was nesting in vari- 

 ous natural cavities and behind loose bark, in a number of large old sycamore 

 trees growing in a wide grassy flat near the San Joaquin River above Riverview. 

 None of the nests were examined but the reluctance with which the birds left 

 their nests seemed to indicate that they were incubating full sets of eggs. Else- 

 where T have come upon but one colony of this species, and that was at Shaver 

 Lake in the Sierras, at an elevation of about 5300 feet, where the nests were in 

 dead pine stubs standing in the lake. The date was May 28, 1908, and the nests 

 contained small young or eggs highly incubated. 



It is a difficult matter to determine just when those individuals that spend 

 their summer north of Fresno pass through this place in the fall, but probably 

 their departure is made at the same time as. and in company with, the flocks of 

 other swallows. This, however, is merely conjecture, as I find that after the 

 breeding season an entire colony will scatter over the valley and gradually 

 diminish in numbers, until the observer finally comes to realize that the species 

 has all but disappeared, leaving no clue to the time or cause of departure. 



Northern Violet-green Swallow. Tachycineta thalassina lepida Mearns. 



This species occurs commonly and sometimes abundantly as a migrant 

 through this part of the San Joaquin Valley, arriving in the spring about the 

 same time as, but not always in company with, the several other species of 

 swallows that pass through in large numbers. Two of my earliest dates for 

 spring arrivals near Fresno, are March 16, 1903, and March 17, 1906. The great 

 majority of these swallows pass on northward, but a few small colonies find con- 

 ditions suitable for their requirements along the San Joaquin River just where 

 it comes out of the hills. No time is lost after their arrival, in beginning the 

 serious business of nest building. A small colony encountered March 25, 1906, 

 just eight days subsequent to the date of the first arrival that year, was flying 

 around and into the cavities of a dead sycamore stub that contained a dozen or 



