25 
A sharp drop occurred in late Jwly in the population of some of the species 
and in the total population as shown in Plate XIIa, suggesting mass movement 
away from the area. In order to check this, graphs have been draw up to 
show the variations in total population and age composition of broods on the 
study area, Plate XIIb shows the relative abundance of the species during 
the entire season. 
Normobile Broods -= The age composition and population of baldpate and 
ruddy duck broods (Plate XIII) give an indication of what can be expected 
when there is neither renesting nor sufficient movement of broods to bring 
about a marked change in the population. Most individuals of both species 
hatched their broods during a very short period and there was no indication 
of renesting on the study area, In both cases, there was little drop in 
the population once the peak had been reached, Class I broods changed to 
Class IT without showing any losses or gains in abundance. 
The blue=winged teal shows a similar situation, There was a sharp 
drop in early August, but this can be accounted for by the large number of 
Class III and Class II broods in late July, many of which were flying by 
August 1. A few late nests are indicated by the presence of Class I broods 
late in August. This probably can be accounted for by the ability of these 
ducks to renest as reported by Sowls (199) who found positive evidence that 
2 out of 17 marked hens of this species renested after he had destroyed their 
nests. Apparently there was no population fluctuation of this species due 
to movement. 
Although there were few broods of the shoveller on the area, data for 
this species, like the blue=-winged teal, indicate low mobility. 
Mobile Broods <= Redhead broods were not present in great mmbers, but 
did show same indications of renesting as shown by Class I broods as late as 
the middle of August. The erratic fluctuations in age ratios indicate that 
there was considerable movement of broods of this species onto and off the 
study area. 
The canvasback (Plate XII) took a sharp drop of nearly 50 percent from 
its early July population. Since there were only enough Class III broods 
present in early July to account for 20 percent of this loss and no flying 
young were seen until August, it must be assumed that during this period 
the mmber of broods which moved off the study area exceeded the mmber 
which moved onto it. The lack of Class I broods late in the season, 
indicating a lack of renesting, may be accounted for by the high success of 
initial attempts by this species. 
In contrast to the loss in canvasback broods, mallard broods showed a 
100=percent increase in mid-July. Only 75 percent of this can be 
attributed to newly hatched broods even when one assumes that all the un-aged 
birds on the area during the period from July to 12 might have been Class I, 
The assumption was made that during this period more mallard broods. moved onto 
the study area than away from it, 
The pintail had an increase in Class TII broods in early July and a loss 
of Class I's in early August, indicating considerable overland travel. 
Too little data were gathered concerning the gadwall or green-winged 
teal to give mich indication of the condition of their population. Both 
gadwall broods left the study area soon after hatching, The green-winged 
teal broods stayed within its boundaries, although one had apparently not 
hatched on the area but had moved onto it in eary July. 
