the species making up these totals influences the results. It should be pointed 
out that there were no data gathered on mortality of young before they reached 
their first water area, as this would have required an intensive nesting study. 
Table 17. Average brood sizes by age class. 
Average of 

Class I Class II Classe IIT all ages 
Species Number Bro er Bro er Bro er sro 
of size of size of size of size 
broods broods broods broods 
Baldpate e 20 1 ° el 
Blue-winged teal 3% @=67 B 15 7.9 8 8.6 59 8.0 
Canvasback 31 5.5 36 5.6 ann Sok 81 5.6 
Gadwall 5 8.6 ~= =< = Je 5 8.6 
Green-winged teal 2 6.5 2 7.5 1 5.0 5 6.6 
Mallard 7 5.7 7 5.9 10 6.6 2h 6.3 
Pintail 4 3.8 6 8.2 6 5.0 16 5.9 
Redhead 27 6.1 7 6.) -- -- 34 6,2 
Ruddy 9 7.2 5 7.8 -- -- 14 Tel 
Shoveller h 8.0 8 7.8 3 6.0 15 705 

(Percent difference between Class I and Class III = },.7%) 
Possible Decimating Factors - Only two young ducks were found dead during the 
course of the study. The young mallard found in pothole No. 1 with lacerations on 
the head and neck may well have been killed by black terns. The marked mallard 
found near the nest was probably killed by thirteen-lined ground squirrels. 
Other predators present were at least one horned owl (Bubo virginiams), one 
feral house cat (Felis domesticus), several red foxes (Vulpes fulva), numerous 
marsh hawks (Circus cyaneus), a pair of Swainson's hawks (Buteo swainsoni), a pair 
of red-tailed hawks (Buteo jamaicensis), and a few mink. None of these species 
was observed attacking ducklings. 

Dispersion of Broods 
Age at Dispersal -- The age at which broods became scattered varied considerably 
with the species and depended to some extent on the constancy of the mothers, River- 
duck hens were judged more "faithful" mothers than the diving ducks as only 19 per- 
cent of the river-duck broods were seen without hens, while 23 percent of canvasback 
and redhead broods and 39 percent of ruddy broods seen were motherless. 
The following table, showing the percentage of motherless broods in the three 
age classes, indicates that diving-duck and ruddy-duck hens desert their broods at 
an earlier age than do river-duck hens. 
Table 18. Percent of broods without hens. 
Age class - River ducks Diving ducks Ruddy ducks 
T 6% 9 13% 
II 1% 23% S7% 
III 2% 64% 100% 

