AMERICAN ROBIN OR MIGRATORY THRUSH. 19 



pressed by time in prosecuting their journey southward? In consequence 

 of this, the last young broods may be unwilling, perhaps unable, on the 

 approach of spring, to start and follow their stronger companions to the 

 land of their nativity. They may thus remain and breed in their first year's 

 winter quarters, or advance so far as their strength will allow them. In the 

 course of my studies, I have, in a great number of instances, observed that 

 such birds as produced three broods in one season and in the same district, 

 were all much older than those which produced only one brood. Of this 

 any one can easily assure himself by shooting the breeding birds, and either 

 bending or breaking their bones, or tearing asunder their pectoral muscles, 

 which will be found harder or tougher in proportion to their age. Thus I 

 am inclined to believe, that the farther south breeding individuals are found, 

 the younger they are, and vice versa. This general rule is well exhibited 

 in most of the species of birds, whether of the land or of the water, that are 

 known to proceed in spring northward, and to return southward at the 

 appearance of the inclement season; for in them the gradual progress of the 

 young may easily be compared with the much slower advance of the old. 



I have, on many occasions, when certain species returned to the nest or 

 spot where they bred the previous season, observed, that what I considered 

 to be the parents of the first year's young, were again the occupants. In 

 the Swallow tribe, and in some of our travelling Woodpeckers, as well as 

 in the Summer Duck, the Dusky Duck, the Mallard, the Hooded Merganser, 

 Crow Blackbirds, Starlings, Kingfishers, Canada Geese, &c, this has proved 

 correct, in as far as I could ascertain by the comparative softness of their 

 bones and pectoral muscles. I think, further, that such species as merely 

 enter the southern parts of our country in the breeding season, as the Missis- 

 sippi Kites, Fork-tailed Hawks, Roseate Spoonbills, Flamingoes, Scarlet 

 Ibises, &c. would all prove, if their winter retreats were well ascertained, to 

 advance much farther southward than any of those which reach us first, and 

 which continue their movements northward; with the exception of such 

 species, however, as would not be likely to meet with the food they are 

 accustomed to live upon, or the same degree of warmth as that to which 

 they have been habituated, as our Parrakeets, the White-headed Pigeon, 

 Zenaida Dove, Booby Gannet, several Terns, Gallinules, Herons, and.others, 

 w T hich are by no means deficient in the power of flight, were nothing else 

 required. 



Another thought has frequently recurred to me while making observations 

 on the habits of our birds: the nests of all those which advance least to the 

 northward are less bulky than those of the same species found in higher 

 latitudes. This difference I have not considered altogether as depending 

 upon the state of the temperature, but upon the longer time afforded these 



