TREE SWALLOW 387 



paired males, who often desert their former mates for the new- 

 comers." 



Observers have sometimes seen more than a single pair of adult 

 birds feeding young in a nest, and Forbush (1929) says "occasion- 

 ally three birds, usually two males and one female, engage in pre- 

 paring a nest, incubating the eggs and feeding the young." 



Harrison F. Lewis writes to Mr. Bent: "A pair of tree swallows 

 nested on the grounds about my residence near Quebec, Canada, in 

 1920. The young birds left the nest on July 13, a few days later 

 than did many other broods in the general vicinity. On July 11 I 

 noticed that the young in my box were being fed by two adult males 

 and one adult female. Later in the day I saw one adult tree swallow 

 on the box, one on the wire nearby, and at the same time four more 

 circling close overhead. It would appear that the young swallows 

 in the box were being cared for by four to six adults, of which at 

 least three were males and at least one a female. The males seemed 

 to work together very harmoniously, but the female sometimes acted 

 as if she objected to having so many males about her home. Whether 

 the assistants to the actual parents of the brood were birds that had 

 not bred successfully or were the parents of other broods already able 

 to feed themselves is a matter of speculation." 



Seth H. Low (1934) accounts for some instances of such behavior. 

 He studied a colony of tree swallows whose broods had been deci- 

 mated by a summer hail-storm, after which he says: "Three and 

 even four adults were caught actually bringing food to the same 

 brood. In each of three different boxes a female whose young had 

 previously died was caught along with the rightful parents feeding 

 the brood. Apparently this is a carrying-over of the maternal in- 

 stinct." 



Nesting. — Before North America was settled the tree swallow built 

 its nest in hollow trees, but with the advent of civilized man the bird 

 quickly appropriated as nesting sites the houses that our ancestors 

 put up to accommodate the purple martins — always a popular bird 

 with the early settlers. Both Wilson and Audubon mention this 

 habit. 



At the present time tree swallows still build in old apple orchards 

 and in holes in trees, especially when they stand in open ground near 

 meadows or bodies of water, but they seem to prefer wooden boxes, 

 even ramshackle affairs affording incomplete shelter. 



The Austin Ornithological Research Station recently made an in- 

 teresting experiment with tree swallows on Cape Cod, Mass. They 

 put up a large number of breeding boxes and obtained astonishing 

 results that indicate that the birds sometimes have difficulty in finding 

 places to nest. Seth H. Low (1933), summarizing the results, says: 

 "With 98 wooden boxes, mostly in the open, the population jumped 



