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Vol. 26, Ho. 9 
Page 5 
since 1976 with a total count of 2,106 birds In the Mississippi Valley and 2,526 
birds in the Illinois Valley during 19-0. Although cormorants are more frequently 
observed in the fall (between mid-September and mid-i'ovember) than in the spring, 
the peak numbers for a single flight in recent years occurred duringjate March 
with 533 birds counted in the Illinois Valley in 1979 and ^2. birds in the 
Mississippi Valley in 19^0. These observations indicate that the populations 
of the once-abundant cormorant may be recovering slightly. 
White pelicans are observed during aerial censuses in September and October. 
The total numbers of birds counted have varied greatly each fall since 197^, but 
the Mississippi Valley consistently hosts the majority of the migrants. Peak 
numbers of pelicans sighted on a single flight since 1976 were 10b in the 
Mississippi Valley and 16 in the Illinois Valley on 27 September 1977- 
Aerial census observations help provide information on the migration and 
distribution of occasional migrants in Illinois, such as whistling swans and 
pelicans. Observations of the endangered double-crested cormorant may provide 
a useful index to their population dynamics. Thus, aerial censuses supply a 
valuable data base for common and uncommon avian visitors to the Illinois and 
Mississippi river valleys. 
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