38 
Table 19. Productivity of the study area. 

Pairs/Square oods/ Square’ Ratio: 
Species mile mile Rroods/Pair 
Mallar a * 0. 
Canvasback 10.8 73 0.7 
Blue-winged teal 17.7 6.6 O.4 
Baldpate 5h 53 1.0 
Ruddy Sek 5.3 1,0 
Redhead Seal 4.7 0.9 
Pintail 5.4 4.0 0.7 
Shoveller 3.8 1.3 0.3 
Green-winged teal 1.5 1.3 0.9 
Gadwall 2.3 0.7 0.3 
Unidentified teal --- 3.3 aes 
Unidentifed “== 0.7 ee 
Totals 88.1 49.8 0.56 

There were sufficient data for the mallard and blue-winged teal to indicate 
that vroductivity of these species was low. Nesting data on 52 nests also showed 
poor success of individual nesting attempts. The canvasback not only produced 70 
broods per 100 pairs but also had a high nest success (80 percent). As previously 
discussed, there appeared to be no renesting in this species. The data indicate 
that under such conditions as were found at Minnedosa, 88 breeding pairs per square 
mile raised 50 broods. A weighted-average Class III brood size of 6.3 (Table 17) 
indicates that 315 young per square mile were produced in this region. This is 
similar to data obtained by Lynch (in Williams 1949) who found that in 3 Saskat- 
chewan potholes 36) pairs produced 193 broods (53 percent), 
A glance at the population curves of the broods of the various species 
(Plates XIII and XIV) serves to point out the possible inaccuracy of the data 
gained on the study area, which was apparently too small. The effect of movement 
on and off the area was quite marked, This effect would have been decreased on a 
larger area where the ratio of circumference to areas and therefore the effect of 
influxs would have been less. 
A better measure of production might have been obtained by dividing the total 
numer of brovd-days each species spent in the area by the average period of pre- 
flight devegopment for the species, However, the study was not carried out in 1949 
for a sufficient length of time to cover the entire span of the brood season. 
Moreover, there are not sufficient data on the growth rate of wild birds to accurately 
determine how long a period should be used to indicate the period of brood develop- 
ment. 
VIII, POTHOLE PREFERENCES OF BREEDING ADULTS AND FLYING YOUNG 
Use of Potholes by Breeding Pairs 
Cover Type Preference -- During the first count of breeding pairs and search 
for nests from June 13 to June 18, notes were made on the locations where breeding 
adults were found. Plate XVIII shows the use made of the various types by 91 breed- 
ing pairs during this period. (Broods and incubating hens were not included. ) 
