2h 
Table 7. Mobility ratings of the ten species of duck broods on the 



study area. - 
Number of Mobility rating Observed travel 
Species Observations of all ages (miles per day) 
Pintail 31 0.20 0,011 
Canvasback 60 0.15 0.013 
Mallard 53 OL; 0.013 
Redhead 16 0.09 0,009 
Blue-winged teal 37 0,09 0.03) * 
Baldpate 15 0.05 0.001 
Ruddy 10 0.03 0.002 # 
Gadwall 3 0.15 0.06 ¥* 
Shoveller 7 0.11 0,021 # 
Green-winged teal 3 0.05 esi 

# Based on one example only. 
It was impossible to determine whether these ratings represent relative 
ability and willingness to walk overland or relative ease with which birds 
become dissatisfied with their environment and travel overland to escape it. 
Population Fluctuation as Evidence of Movement 
Charts for each species as shown in Plate XIb provide the means for 
getting a better picture of its population behavior, particularly with 
regard to movement. With the aid of these charts, the number of brood days 
spent by the species on the study area can be determined for any period, 
Plate XiIa indicates the total seasonal brood population of the area, 
Since this is based on brood days per 8-day period, dividing by 8 gives the 
number of brood days per day, or roughly, the number of broods. For example, 
about 5; broods (3925/8) were using the area at the peak of the season during 
the period July 20 to July 28. 
There was a rapid increase in population as hatching progressed until 
the third week in July and a rapid drop at the end of the season when the 
majority of broods reached flying age. 
The changes in abundance of each species through the course of the study 
varied greatly owing both to the differences in the hatching dates of the 
various species and to movements of broods onto and away from the area, 
