
are in like manner representative of sora rail habitats throughout the 
stratum involved, we find rather interesting population indices for 
Alberta. 
One of our parkland study areas (of 3.625 square miles) contained 
5. breeding pairs of sora rails per square mile in 1953 and 5h water 
areas per square mile, Another parkland study area (of 6.375 square 
miles) contained 32 sora rail pairs per square mile and 32 water areas 
per square mile. In the case of a prairie study area of 3,125 square 
miles both sora rail pairs and water areas were observed to be 18 per 
square mile, 
In attempting to expand these limited rail populations over a 
larger area, we find that our aerial surveys show that for the entire 
area of Stratum B, the water area density averaged 20.65 water areas 
per square mile in May. If we use this figure to establish an index 
for sora rails, in the entire area of Stratum B (26,100 square miles) 
then we might interpret it to mean that the average density of rails 
was also 20.65 pairs per square mile or 539,000 pairs in the entire 
stratum of aspen parkland. 
In like manner, we found that in May the prairies (Stratum A, 
22,088 square miles) showed an average water area density of 16.73 
ponds per square mile or 16.73 pairs of rail per square mile, a total 
of 370,000 pairs in the entire stratum. This is a total of 909,000 
sora rail pairs in an area of 48,188 square miles of prairie and park- 
land in Alberta in 1953. Surprisingly enough this index figure is only 
about 50,000 pairs less than the 1953 waterfowl breeding pair index for 
the same area. 
According to the available literature, the clutch size of the sora 
rail ranges from 6 to 16 eggs. If we assime that each pair raised two 
young to maturity, then 1,818,000 adults would produce the same number 
of young or a total of 3,636,000 birds available for the fall flight. 
If only 50 percent of the adult pairs succeeded in raising 2 young per 
pair, then )5,500 pairs would have produced 909,000 young or a total 
of 2,727,000 birds available for migration. These figures are surpris- 
ing, but until further studies are made which can refine our methods, 
our deductions are still in the realm of untested suppositions. 
During the summer of 1954, these studies were continued on the two 
parkland study-areas with rather startling results. It is not known 
at this time whether rail populations are in any way cyclic, subjected 
to excessive reductions in populations periodically or whether they 
shift about appreciably on their breeding grounds. We do know that 
drastic reductions occurred in the populations on the same study areas, 
however. 
Im one area where we had found 5 rail pairs and 5) water areas 
in 1953, we observed only 27.5 pairs of rails and 5) water areas per 
61 
