TANAGERS 
377 
has a slightly more slender bill, but this feature is not very marked or very constant. 
Western females show a faint striping below that is less apparent in eastern specimens. 
This is the form to be expected from Manitoba westward. 
The Cowbird is our only habitually parasitic bird. It never builds a 
nest nor incubates nor cares for its young. In the absence of the rightful 
owners it takes the opportunity of depositing one of its 
own eggs in the unguarded nest of other birds. Usually 
the birds so imposed upon accept the foreign egg with- 
out protest, at other times there are strong objections 
and final resignation. In a few cases, the nest is deserted 
or a new nest is built over the offending egg, as is 
sometimes done by the Yellow Warbler. On incubation 
an interesting case of adaptation is shown. The Cow- 
bird’s egg usually hatches a few hours before those of 
the original occupant of the nest and consequently Bin of Cowbird nat- 
the interloper is strong and well grown when the proper 
occupants of the nest break their shell. It can monopolize the food, 
thus increasing the difference in strength, and is able finally to hoist its 
competitors from the nest to perish on the ground while it receives the 
attention that should have been given to the rightful brood. Thus practic- 
ally every Cowbird is raised to maturity at the expense of a brood of another 
species and the Cowbird must be considered one of the greatest enemies of 
the species imposed upon. Once the foster parents accept the intruding 
egg they do not make any distinction between it and their own. The 
Cowbird receives its name from its habit of following cattle, evidently 
attracted by the flies and insects which gather about those animals. 
In the early days, it probably followed the buffalo, which suggested 
its old, nearly forgotten name of Buffalo-bird. 
Economic Stains. From a study of their food, Cowbirds would seem 
to be purely useful birds. They consume large amounts of weed seeds and 
harmful insects and only small quantities of grain or fruit, the grain largely 
waste and the fruit wild. Their effect upon other equally useful birds, 
however, puts a different complexion on their activities. Practically 
every Cowbird raised to the fledgling stage means the elimination of a nest 
full of other species. Perhaps the economic effects of the changelings 
equal those of the individuals they displace, but the substitution cannot/ 
be looked upon with equanimity. . / 7 a / £ 
FAMILY — THRAUPIDAE, TANAGERS. 
General Description. Brilliantly coloured birds; in Canada, about the size of, or 
slightly larger than, the English Sparrow. Bills rather sparrow-like in outline, but slightly 
longer, and with an evenly curved culmen. Cutting edge of 
upper mandible toothed and notched as in Figure 465. 
Distinctions. The spring males are very distinctively 
brilliant in colour. Autumn birds and juveniles are gen- 
erally recognized by their soft, uniform yellow-green 
coloration, resembling some of the dull green vireos or 
warblers, but much larger. In the field, most likely to be 
confused with the orioles, but less active, more sluggish, 
and entirely different in action and bearing. 
The tanagers are a typically American 
family that reaches its highest development in 
the tropics and is regularly represented in Canada by only two species. 
As a family the tanagers are so closely related to the sparrows that the 
status of some extralimital species is still undetermined. 
Scarlet Tanager, showing 
notched bill. 
Figure 464 
