BLUE-GRAY GNATCATCHER 349 



tions of the nests, the thickness of the pads of resilient, closely felted 

 material between the weight of the contents and the surface of the 

 supporting branch. It is not unlikely that the remarkable tenacity 

 of these tiny nests under stresses of weather buffeting and family 

 struggles resides in the elasticity of their thick, resilient foundations. 

 A moment's consideration of the proportions of the deep cup of the 

 nest — 1% by \){ inches — and of the slim length of the little bird that 

 must crowd itself into these narrow confines explains why the incu- 

 bating gnatcatcher can assume no other posture than with bill and 

 tail pointing straight upward. 



Most observers agree that both sexes work at the construction of 

 the nest, and my experience in northern Florida is that they share 

 this labor fairly equally. W. E. C. Todd (1940) stated that, in 

 Pennsylvania, the male never assists in nest building but that he 

 "always remains near at hand and takes a great interest in the work." 

 W. P. Proctor, reporting from southern Michigan, writes (MS.) that 

 in one instance of the three observed by him, the female alone did 

 the building, and that on one shared task the female did more than 

 the male. Aretas A. Saunders, however, writing (MS.) from central 

 Alabama, finds that where there is an unequal division of labor the 

 male bears the heavier burden, and also that the male is a more 

 persistent worker than his mate and that he is less sensitive to inter- 

 ference by human intrusion. He cites an instance of one male bird 

 that was seen to bring nesting material five times in six minutes. 

 Slower than this high-speed worker was a building pair reported by 

 Mrs. Nice (1931), who counted 27 trips to the nest with material in 

 an hour. It always gives an observer a start, when he is watching 

 nest construction and has seen material brought in and placed in 

 position to, have a bird come in with a seemingly empty bill, yet 

 work as diligently at the structure as before. It is more in keeping 

 with the known industry of this species to account for this apparently 

 wasteful gesture as the placing of invisible lengths of spider web rather 

 than as mere "boondoggling." 



The length of time required for nest construction is subject to 

 extreme and inexplicable variation. W. E. C. Todd (1940) stated 

 that it requires between one and two weeks of constant labor to 

 complete a nest. But Edward R. Ford (MS.) writes of a nest that 

 he saw under construction from the very beginning that, after only 

 three days, "appeared, from the ground, to be completed." Perhaps 

 the important factor in this variation is the size of the "building 

 crew" — one bird alone, or both birds. 



A practice, apparently peculiar to the gnatcatcher, and one that 

 has been commented upon by almost every observer familiar with its 

 ways, is its habit of tearing up a completed or partly built nest and 



