Population dynamics 
The mortality rates for double-crested cormorants explored 
in this chapter are so considerably higher than those calculated for 
European cormorants by Kortlandt (192) that one is tempted to regard 
the results as conflicting and contradictory. A simple analysis of 
the presently known population dynamics of the two species suggests 
consistency rather than contradiction within each species. 
European cormorants, which have been reported to lay l-6 
eggs (Forbush 1925, p. 161), actually have an extremely low production 
of young in the Netherlands, Kortlandt finding only 1.25 * 0.125 young 
per nest in his censuses and estimating 1.12-1.25 young per female as 
the number successfully fledged. The breeding potential is likewise 
lowered by delay in the onset of sexual maturity, the adult plumage 
not being attained until the birds are 3 years old (Forbush 1925, p. 
158). It is at this age that most of the Netherlands birds of this 
species begin to breeds; individuals, however, often do not nest until 
2 years later (Kortlandt 1942, pp. 277-278). These adverse conditions 
are more than canceled out by the extremely low mortality apparently 
encountered. This is not only true of the subadult and adult years 
usually considered in abridged life tables but also of the short period 
immediately after the fledglings leave the nest. 
On the other hand, Gross's (19h),) census data from the Maine 
coast suggest that double-crested cormorants have a relatively high 
production of young. Lewis (1929, p. 58) has concluded that adult 
plumage (except for the crests) is acquired in 3 years. I would expect 
a slightly higher percentage of auritus to begin breeding at this age 
than of carbo, on the principle that larger birds tend to mature at 
later ages than do smaller birds; the actual difference between the two 
may, however, be relatively slight. The assumption of high production 
in the double-crested cormorants seems to be effectively counter-balanced 
by the relatively high mortality rates obtained in this study. 
Summary 
The picture here assembled is one of low production and low 
mortality rates in the European cormorant, high production and high . 
mortality rates in the double-crested. 
The mean clutch for double-crested cormorants, according to 
the literature, appears to be close to k in the Gulf of St. Lawrence 
and between 3.0 and 3.5 on the coast of Maine. Eighty nests censused 
by Gross (19) had an average of 2.2 young. Mortality rates for young 
birds, once they leave the nest, are either unknown or require further 
study. 
More than twice as many fresh-water-banded birds of this 
species were recovered as marine-banded, the difference being apparently 
due to the greater accessibility of carcasses inland and the greater 
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