442 BULLETIN 17 6, UNITED STATES NATIONAL MUSEUM 



it is sometimes literally burst asunder by the pressure of the growing 

 bodies it contains. In one case that came under my observation the 

 nest split down the side, then turned almost inside out and dropped its 

 two helpless occupants on the ground, I found them next morning, 

 after a showery night, in the grass beneath the ruined structure, 

 among wandering fire ants, which probably would eventually have 

 devoured them had I not replaced them on the remains of their nest, 

 where they sat a week more before they were able to fly away. 



Phimages. — Dr. Frank M. Chapman (1925) states that "there is 

 but little variation with sex, age, or season in this species. The male 

 usually has the throat more solid green and the abdomen darker than 

 the female, from which young males are not distinguishable." 



Behavior. — About the habitations of men, where these humming- 

 birds seem most at home, they spend their time probing for insects 

 or nectar in the great red blossoms of Hibiscus sinensis, which is 

 everywhere a favorite shrub for hedges, dooryards, and the town 

 plaza, or else in the blue trumpets of the Thunbergia, which scram- 

 bles over fences and up the sides of houses; or they hover before the 

 coral vine, the blue flowers of CUtoria, or the blossoms of some fruit 

 tree. At other times they enter the banana groves and poise beside 

 the long, pendent inflorescences, where they probe the white blossoms 

 clustered beneath their heavy red bracts, swarming with the little, 

 black, stingless bees, which gather their pollen and rich nectar. 

 Early in the morning one may see them bathing on the dewy surface 

 of the broad banana leaves, over which they glide with vibrant 

 Avings, gathering up the heavy dew drops in their plumage. They are 

 no more sociable than other kinds of hummingbirds and dart fiercely 

 at another of the same or a different species if he ventures too near; 

 but the bird attacked almost invariably retreats at the first dashing 

 onslaught, closely followed by the pursuer; and I have never wit- 

 nessed two birds engage in an encounter face to face, or one inflict 

 injury on another. 



A surprising aspect of the behavior of the Rieffer's hummingbirds, 

 as I watched them near Almirante, Panama, during the early part of 

 1929, was the frequency with which they pilfered material from one 

 another's nests. About our house at the research station larceny 

 of this kind was shockingly prevalent ; and I believe that about half 

 of the failures to rear a brood that came to my attention were to be 

 attributed to this unsocial practice. The condition was probably 

 local and possibly even seasonal; I have never noticed it elsewhere; 

 but then never elsewhere have I seen so great a concentration of 

 hummingbirds' nests. It was induced to a large extent, I think, by 

 the inadequate supply of down for lining the nests, added to the 

 close proximity in which they were placed, sometimes 100 feet or 

 less from each other, which made robbery easier than a long expedi- 



