86 THE CONDOR Vol. XXIII 
weight after November, but the number of late birds weighed is too small to be 
reliable. 
In my previous notes I ealled attention to the varying weights and plumages 
of Mallards brought down by successive storms, and ascribed the flights of light. 
immature birds, which often follow heavy mature birds, to late northerly hateh- 
ings and long travel. Subsequent observations show no evidence to controvert 
this as to Mallards. But I now suspect that various breeding grounds, regardless 
of latitude, produce ducks of widely varying weights and plumages.  Albu- 
querque Canvas-backs and Red-heads, for instance, weigh right around two 
pounds throughout the open season; and both species, though fat, nearly always 
show a very dull color and peculiarly frazzled plumage. Reliable hunters inform 
me, however, that the Canvas-backs of Lake Burford, in northern New Mexico, 
even on the opening day (October 16), are always big, heavy, bright-colored birds 
weighing up to four pounds. I doubt the four pounds, but everybody seems to 
agree that they are bigger and heavier in October than the ones shot at Albt- 
querque at any season. I have also heard sportsmen from the northern Rocky 
Mountain states talk about ‘“‘big and little cans’’. I conelude that Lake Burford 
and Albuquerque are on different migration routes and draw their Canvas-bacis 
from different breeding grounds producing differently developed birds. 
The theory that weights vary with breeding grounds is corroborated by the 
small range of weight exhibited by Black Mallards (species not yet agreed upon 
by taxonomists), most of which are probably raised here in the Southwest, as 
compared with the great range of weight exhibited by ordinary Mallards, which 
are probably drawn from many breeding grounds extending from here to the far 
north. The graph shows the average weights of the two species to be about the 
same, but the spread of the dots for the latter species is twice that of the first. 
The graph shows the maximum abundance of Pintails to be in. October and 
January, with very few in November and December. These January Pintails 
are return flights during the January thaws, and during 1920 at least these 
return birds were nearly all full plumaged males. Every year males preponder- 
ate in these return Pintails. The graph shows that Blue-wing Teal are all gone 
by November 1, but a few Green-wings winter. Spoonbills mostly leave by De- 
cember 15. Gadwalls show some tendency to be more abundant in October and 
January than in November. Mallards, of course, stay, but are least abundant in 
December. 
A preliminary table showing relative abundance of species, based on two 
years’ kill (1917 and 1918) has already been published’. The same method, ap- 
pled to four years kill, 1917-1920, gives the following corrected table: Mallard 
30 percent; Green-wing Teal, 15; Pintail, 12; Baldpate, 11; Spoonbill, 10; Mer- 
gansers, 5; Black Mallard (sp.?), 4; Blue-wing Teal, 4; Gadwall,3 ; Canvas-back. 
2; Redhead, Bluebill, Bufflehead, Ruddy and Golden-eye, 4. 
Albuquerque, New Mexico, March 4, 1921. 
eee Abundance of Ducks in the Rio Grande Valley, Condor, XXI, May, 1919. 
p. : 
