AMERICAN ROBIN OR MIGRATORY THRESH. 
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, 
ZenaidaDove, Booby Gannet, several Terns, Gallinules, Herons, and others 
which are by no means deficient in the power of flight, were nothin a- n!-e 
required. 
Another thought has frequently recurred to me while making ob.servati 
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 
