INSTINCT AND INTELLIGENCE IN BIRDS 



545 



and repeatedly fed at the same visit. Indeed the movements are so 

 rapid that it is not certain that they are effective in every ease. These 

 conditions lead to irregular muting, and to practical difficulties in re- 

 gard to the sanitation of the nest, or more particularly of the nest-site. 

 To the acts recorded above we have to add (g) incidental behavior 

 at the nest, more or less related to care of the young, as brooding, 

 shielding or spreading over the nestlings in heat (Figs. 1 and 2), or 

 rain, whether sitting or erect, bristling, puffing or swelling out the 

 throat, — possibly with air-sacs distended, — preening, gaping in hot 

 weather, stretching and yawning, with the guarding and fighting in- 



Fig. 7. Black-billed Cuckoo approaching Nest with Food. First stage in reaction 

 of nestlings ; wings vibrating in young which gives most vigorous response. 



stincts, called into evidence as occasion may arise. Sporadic- additions 

 are sometimes made to the nest, and I have seen the white-bellied 

 martin return to her nest-box a feather which the wind had blown out 

 (Fig. 13). Eagles and hawks will occasionally bring fresh sprays of 

 hemlock or seaweed to their eyries and the great herring gull while 

 incubating or brooding will sometimes bend over and pull fresh grass 

 and weeds within the reach of her bill, and tuck them under her body. 

 Most of these acts are probably instinctive in origin, but they are far 

 from predictable. 



