538 THE POPULAR SCIENCE MONTHLY 



idea the guarding evoked by the fighting instinct, and supplemented by 

 the instinct to cover or hide the eggs, is responsible for the incubating 

 instinct, which in the modern birds is usually strongest in the female, 

 but is not always confined to that sex. 



The possible stages in the evolution of the instinct of incubation in 

 the reptilian ancestors of birds, upon the basis of selection, may have 

 been as follows : first burying the eggs, like the turtle ; secondly, bury- 

 ing or concealing the eggs and guarding them, the necessary warmth 

 being furnished by decomposing vegetable debris, as in the alligator, 

 and not directly from the sun; thirdly, laying the eggs and sitting 

 over them to conceal as well as to protect them, 3 in a secluded place, 

 the necessary heat now being furnished by the body of the parent. In 

 the first instance the eggs may not have been concealed, but it seems 

 probable that the instincts of both concealment and pugnacity were 

 contemporaneous, as they were certainly very early in origin. 



With incubation is associated a variety of interesting and important 

 instinctive activities, such as rolling the eggs with the bill upon enter- 

 ing the nest, as may be observed in the great herring gull, placing them 

 in position, or stirring them up with the feet, to be seen also in the 

 gull, the domestic fowls and in a great number of wild species ; covering 

 the eggs when leaving them, a common practise of the grebes, or 

 standing over the nest and with spread wings shielding the eggs from 

 intense heat, as I have once observed in the least flycatcher; clean- 

 ing the nest by removal of broken or addled eggs, which must fre- 

 quently occur in many species, which I was once fortunate enough 

 to witness from the tent in the least tern on one of the Weepecket 

 islands in Buzzard's Bay. On a very hot day in July one of the eggs, 

 during the absence of the birds, exploded with the report of a pop-gun 

 and blew a small hole in one side. Upon her return this resourceful 

 bird inspected the nest for a moment, and bending down, inserted her 

 lower mandible in the blow-hole ; then lifting the heavy egg in her bill, 

 she bore it off slowly over the water and dropped it in the sea. At her 

 next visit every particle which might defile the nest was gathered up 

 and carried away. 



The care of the young in the nest (6) embraces a number of fairly 

 well stereotyped, recurrent acts such as (a) the search after prey, its 

 capture and subsequent treatment ; thus some birds regularly mince the 

 prey or beat it into a pulp, while others, like the little house wrens, bring 

 moths and various insects to their nest with wings and legs, or with 

 wings alone, removed. Kingbirds have been seen to bruise unruly in- 

 sects between their bills while at the nest, one assisting the other, and 

 have been photographed in the act, while it is not an unusual sight to 



8 It is evident that pythons, which lie upon their eggs, secure in this way 

 both protection and concealment for their offspring. 



