Sept., 1919 DIFFERENTIAL SEX MIGRATIONS OF MALLARDS 183 
These conclusions could easily be offered on the basis of ocular observa- 
tions alone. During October one may see whole flocks of Mallards without a 
drake. During November I have seen many flocks without a hen, and have 
brought in bags of 7 drakes and 1 hen, 9 drakes and 4 hens, ete. Duck hunters 
will readily appreciate that, inasmuch as the bag is almost always derived 
largely from single birds and pairs, regardless of any effort to pick the green- 
heads the above figures indicate a preponderance of drakes, Jn fact the arti- 
ficial selection of drakes may simply be regarded as a constant factor which 
does not affect the conclusions here drawn. | 
It may, of course, be suggested that the observed preponderance of hens 
in October is not reliable because of the obscure coloration of the birds early 
in the season. In this locality, however, the drakes on October 16 have the 
chestnut breast patch, white ring around the neck, and green head well devel- 
oped. There are still spots on the under parts and rusty feather-tips on the 
head, but the general effect is unmistakable. 
Two other questions might be raised as bearing on the significance of these 
conclusions. First, were the birds observed migrants or local? They must be 
migrants. Since the stoppage of spring shooting a few Mallards have nested 
here; but the movement of ducks begins in August, and by October 16 there 
are many more ducks of more species, more widely distributed, than could be 
accounted for as local birds. Second, may this not have been an accidental 
phenomenon peculiar to 1917 and 1918? As to this point I have nothing to 
offer except an intended continuance of my observations. The testimony of 
hunters who do not keep written notes is valueless on questions of this kind, 
no matter how extended their experience. 
To sum up the foregoing discussion, the writer has concluded that there 
is a differential sex migration of Mallards in the Rio Grande Valley, the fe- 
males arriving first and the males afterward. A normal proportion of sexes 
1s not reached until the main flight is over and only the wintering ducks remain. 
How may this differential migration be accounted for? 
I have no answer to this question. A few tagged ducks so far reported in- 
dicate that in general this part of the Southwest is on the same migration route 
as Great Salt Lake. Is there possibly a difference between the sexes in the 
time of completion of the plumage after the flightless period? Is there possi- 
bly a differential routing of sexes? Does the migratory impulse seize the fe- 
males first? Has the phenomenon of differential sex migration been observed 
elsewhere, in this or other species? Any evidence on these questions might 
throw light on this very interesting problem. 
Albuquerque, New Mexico, February 1, 1919. 
