COLD AND WARM WEATHER BIRDS. II 
ganser are true cold-weather birds, hunting the icy 
streams for frozen fish, breeding north of 45°, whereas 
the hooded merganser is more of a warm than a cold 
weather bird, breeding from 25° north, yet it will en- 
dure very severe cold weather as long as it can find 
open water and live fish to supply its wants. Again, 
take the mallards—the yellow-leg or ice mallard—a 
true cold-weather bird, that breeds sparingly even at 
50° north latitude, compared with the red-leg mal- 
lard or its cousin the black duck, both warm-weather 
birds and breeding from 30° to 35° northward. 
I attribute the fact of a warm-weather bird adapting 
itself to cold weather, to acclimation; for the first issue 
ot any bird, diver or non-diver, breeds the farthest 
north; the second and third in like proportions; for 
ali our ducks which breed far south—between 35° and 
45°—are birds which formed the third or last issue in 
their spring migration, the gradual advance north of 
all species being a case of necessity, having been 
forced northward by the march of civilization which 
has with rapid strides altered the nesting places and 
food supply by deep drainage, tiling and cultivation. 
It may be claimed by some that the age of the bird 
determines the northern limit and that the young birds 
are the most southerly nesters; but I think the birds 
that were hatched in the far north would instinctively 
return to the same places, or, at least, the same lati- 
tude, provided the surroundings were unchanged. 
Hybrids as well as albinos seem to occur more 
frequently amongst the non-divers, judging from the 
fact they are more frequently observed and specimens 
obtained. 
