79 
Progress of the Season 
During May, the birds were much in the open, incubation had staried in only 
a few cases, and it is probable that a relatively high percentage of the birds were 
visible from the air. The productivity of these birds could only be guessed at with 
the aid of weather and water data, ' 
During early July, many of these birds had left the breeding grounds or had 
reverted to non-breeding status. Some had produced broods, while considerable 
numbers remained on the breeding grounds and were recorded as "potential later 
broods" (Index 38,118). Those seen greatly exceeded the number of actual broods 
seen from the air (Index 12,287). The "potential later broods" figure is only an 
index to reproductive effort taking place at the time. Most of the broods to appear 
in the few weeks following are in the form of incubated nests, and are not subject 
to census by any method, except as indicated by hens temporarily off their nests. 
However, the birds seen in apparent breeding condition were accepted as a valid 
index to the breeding status of the population as a whole. Considerable work needs 
to be done before we learn to accurately assess their productivity under all conditions. 
In late July, the picture was quite reversed. A considerable number of pairs 
represented by the ''potential later broods" index of 38,118 had been successful in 
producing broods, while a few had dropped out of the picture as non-breeders or 
moulters. The brood index of 31,023 was by then nearly three times as large as the 
"potential later broods'' index and 2 1/2 times as large as the brood index of the two 
weeks earlier. However, even this figure does not, in itself, constitute an index to 
actual production. Some of the young had been flying for some time and were 
scattered widely over the country-side no longer recognizable as broods. Others, 
as indicated by the late July "potential later broods" index, were not yet hatched. 
Conclusions 
It is somewhat difficult to compare this year's data with the data of previous 
years due to the extreme lateness of the season. There is no question but what the 
entire reproductive effort was at least three weeks later than normal.’ A comparison 
of this year's brood index from the second run with indices from previous years, 
although providing only a rough comparison, might be of value. These data are 
shown in table XI1. 
Table XII - Comparison of Aerial Brood Indices, Southern Manitoba, 1950-1954. 

Year otretum A Stratum B 
1950 19, 708 5, 148 
1951 33,178 4,290 
1952 32,141 No Data 
1953 7,976 No Data 
1954 (1st Run) 13,026 14,612 
1954 (2nd Run) 31,023 No Data 
