Chapter IV.--Order Pelecaniformes (Family Phalacrocoracidae: 
Cormorants) 
Double-crested Cormorant 
Literature on producitvity and survival 
The usual clutch of Phalacrocorax auritus is variously given 
by the older writers as 2-5 (Forbush 1925, p. I6I), 3 or 4 (Bent 1922, 
p. 246), and 4-5 (Roberts 1932, p. 166), with sets up to 7 being reported 
(Dunlop 1915). On the Gulf of St. Lawrence, the great majority of 
double-crested cormorants are reported by Lewis (1929, p. 37) to possess 
a complete clutch of h eggs; Mendall (1936, p. 50) and Gross (19h, 
pp. 521-533) have reported on the number of eggs seen on visits to 
cormorant colonies in Maine (table 15). Mendall's summary (which 
does not give the number of nests actually seen) can be construed to 
represent a mean of 3.5 eggs per nest. Gross's census data yield 
a mean of 3.1. His Mains observations of course represent minimal 
estimates of full clutches. In this region, it therefore seems 
likely that the average clutch size is between 3 and lh; and in later 
computations this value will be kept in mind. 
Table 15.--Double-crested Cormorant Clutches in the Literature 
Size of Lewis (1929), Mendall (1936) Gross (19Lh), Maine 
Clutch Gulf of St. Lawrence Maine No. Seen Per Cent 
1 - - 201 8 
2 = 8% 391 15 
3 ‘perhaps 5-10% LOZ 1030 39 
4 great majority 50% 95) 37 
5 very rare 2% 3 1 
6 ~ one record - - 

The average number of eggs to hatch and young to fledge is 
yet to be calculated. Gross (19) mentions 80 nests censused in 
Maine in which the average number of young was 2.2. This may be 
close to the probable number of young leaving the nest in that region. 
In the Netherlands, where European cormorants (Phalacrocorax carbo 
sinensis) are increasing at the rate of about 10 per cent per year, 
Kortiandt (192) has calculated that 1.1 to 1. young fledge for 
each breeding female. 
No survival studies of this species have been published. 
Kortlandt has intensively studied the age structure of the Netherlands 
- population of the European cormorant. He concluded that mortality 
rates drop from about 36 per cent per year for birds in their first 
year of life after leaving the nest, to about 22 per cent for the 
second year, and about 16 per cent for the third year. For mature 
males it averaged 7-12 per cent per year, and for mature females 9-1) © 
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