252 BULLETIN 196, UNITED STATES NATIONAL MUSEUM 



Dr. Herbert Friedmann (1929) says that the bluebird is "a very 

 uncommon victim" of the cowbird, and cites about 15 records. 

 Later (1934) he reports seven additional records and states: "Although 

 the bluebird is still to be considered a rather infrequent victim of the 

 cowbird, it is by far the most often parasitized of hole-nesting birds." 

 Mr. DuBois writes to me that he found five bluebirds' eggs and two 

 cowbirds' eggs in a box in his yard ; all the eggs hatched, except one 

 bluebird's egg, which was found on the ground, punctured; the other 

 six eggs hatched, but the sun was very hot and most of the young 

 perished from the heat; one cowbird and possibly one bluebird sur- 

 vived, though he could not find the latter. 



Dr. Musselman (1942) once found in one of his boxes a filthy nest 

 with four half-grown bluebirds cuddled in the bottom ; and above them 

 was a two-thirds-grown starling sitting complacently on the smaller 

 birds; "the droppings of the larger bird had soiled and in one case 

 almost covered the head of one of the tiny birds below; one eye was 

 entirely covered and there was a stench which is unusual about such 

 a nest." He destroyed the young starling, washed the young blue- 

 birds, rebuilt a clean nest and returned the young bluebirds to it; 

 the mother bluebird accepted the change and raised her young 

 successfully. "In the many years that I have carried on my Blue- 

 bird experiment, I have never before found a Starling roosting in or 

 employing one of my boxes for a nest site. In fact, only upon three 

 or four occasions have I found Cowbird eggs in the normal nest. 

 Only when somebody has removed the top of a box thus allowing an 

 approach of the female Cowbird through the aperture above has 

 there been molestation on the part of the Cowbirds." 



Competition for nesting sites is one of the bluebird's greatest 

 troubles. House wrens have always been aggressive competitors, 

 but the bluebirds have generally been able to resist them and some- 

 times to evict them. Edward R. Ford has sent me the following note: 

 "When young bluebirds left the 6 by 7 by 7 inch nesting box, June 20, 

 I cleaned it out at once. By noon of the same day, house wrens took 

 possession and began filling it with twigs. A few days later I noticed 

 that bluebirds were still about the box, and when I looked into it on 

 June 29 it held three bluebird's eggs. When the second brood had 

 flown, August 2, an investigation showed that the bluebirds had 

 assumed ownership before the wrens had completed the usual true 

 nest in the twig mass and had made a scanty one of their own with a 

 few dry grass stems." 



When the English sparrows came the bluebirds had to face a de- 

 termined competition ; often the bluebirds were more than a match for 

 the sparrows; but when the sparrows came injgroups or droves they 



