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Cormorants

Michelle Bellizzi, Isabel Luevano, and Jennifer Linander

Natural History

Cormorants – aquatic birds known commonly as cormorants and shags – are found on every
continent except Antarctica. In North America, there are six species of cormorants, and their habi-
tats span the continent: Double‐crested Cormorant (Phalacrocorax auritus), Brandt’s Cormorant
(Phalacrocorax penicillatus), Red‐faced Cormorant (Phalacrocorax urile), Pelagic Cormorant
(Phalacrocorax pelagicus), Great Cormorant (Phalacrocorax carbo), and Neotropic Cormorant
(Phalacrocorax brasilianus). While most of these species occupy near‐shore areas exclusively on
U.S. coasts, Double‐crested Cormorants, the most numerous of the species, are found in both
coastal environments and throughout the country’s midland (Dorr et al. 2014).
Cormorants are formidable, opportunistic predators within their niches. Prey items mainly con-
sist of slower‐moving or schooling fish ranging in size from 3 to 40 cm, but the most commonly
caught prey are in the <15 cm range. Cormorants feed on different species of fish, depending on
location and season; they also feed, though less frequently, on insects, crustaceans, eels, and
amphibians. Known for being somewhat clumsy appearing when ambulating on land and requir-
ing long water runways to achieve flight, cormorants are extraordinarily agile under water, where
they pursue their prey by propelling themselves with their feet. Cormorants have been observed
foraging at depths of 75 m, although most commonly they forage in shallower waters of less than
10 m. Cormorants have also been observed forming foraging flocks in crescents to corral fish in
clear waters. An adult Double‐crested Cormorant’s average daily consumption of fish ranges from
436 g/day during nonbreeding season, to 542 g/day during breeding season (Dorr et al. 2014).
Cormorants cast indigestible food pellets encased in a pale, white mucous “shell.” Captive birds
generally produce one pellet/day, but may cast fewer than one per day or none if being fed soft‐bod-
ied fish; and captive cormorants regurgitate readily if agitated or disturbed.
Sexual maturity for most cormorant species occurs at 2–3 years of age. Cormorants nest in a
variety of locations in communal settings or rookeries. Nests may be constructed in trees or on
cliffs, artificial nest structures, transmission lines, or wharves and bridges. Colonies of breeding
cormorants nesting in trees are likely to kill the trees over time. Ground‐nesting cormorant colo-
nies are generally on low‐lying rocky islands or reefs with no vegetation. Nests are composed of
twigs, sticks, grasses, and other readily available materials, and are loosely constructed. Ground‐
nesting cormorant nests are re‐used seasonally and may become built‐up tussocks at a well‐estab-
lished colony.

Hand-Rearing Birds, Second Edition. Edited by Rebecca S. Duerr and Laurie J. Gage.
© 2020 John Wiley & Sons, Inc. Published 2020 by John Wiley & Sons, Inc.