Deeper Dive - More FAQs

1:  What is the size of the Double-crested Cormorant?

Roughly the size of a goose or a loon.  They weight from about 1.67 to more than 2.1 kilograms (about 3 ½ to 4 ½ pounds).  Stretched out from tip of beak to tip of tail they measure about 78 to 91 cm (about 30 ½ inches to about 3 feet) and have a wingspan of approximately 137 cm (about 54 inches).  By comparison a Common Loon weights from 2.78 to 4.48 kilograms, and so is larger, but with its short tail the loon is about the same length as a cormorant, although the flying loon’s feet extend well past the tail, while a flying cormorant’s feet do not reach the tip of the tail.

2:  Where do Double-crested Cormorants in the Great Lakes Basin go in the winter?

Winter destinations of cormorants who nest in the Great Lakes Basin are not entirely known, but most probably winter in the Gulf of Mexico or the lower Mississippi Valley, east to the Atlantic coast of Florida.  Birds can stray, especially after breeding, and Double-crested Cormorants have shown up, however unexpectedly, as far away as the UK, Europe and the Azore Islands.

3:  What is the distribution (range) of the Double-crested Cormorant?

They have a “disjunct” breeding range, meaning there are gaps where they are absent as a breeding species because of lack of suitable habitat in which to produce and protect their nests and young find food. They are found as a breeding species in Alaska, on Pacific Coast islands and coastlines south to Baja California and the Sea of Cortez, and inland through the prairies north into the boreal forests and south as far as Utah in the central part of the continent, east through the Great Lakes as far as the coasts of Newfoundland and Labrador.  They winter along the Pacific coastline from the Alaskan Aleutian Islands all the way south to Baja California and southern Mexico, and along the east coast of the U.S.A., the Gulf of Mexico, Florida and the West Indies, and inland up large river systems such as the Mississippi and Rio Grande.  A small number winter as far north as the Great Lakes Basin, when there is open water.  On migration they may appear on open water almost anywhere in temperate North America.  Their range is expanding as their numbers recover from persecution, and as climate changes alter the environment.  Cormorants are strong flyers, so stray birds, especially if caught up in strong winds, can occur far from where they might normally be expected, with there even being a few rare records of them appearing in the U.K. and Europe.

4:  How many eggs do Double-crested Cormorants lay?

Usually 3 or 4 eggs but they may lay as few as one or two to as many as seven.  Incubation lasts from about 25 to 29 days.  In all, the parents look after their young for about 70 days.

5:  What was the largest Double-crested Cormorant colony on record?

Apparently, it was one on San Martin Island, off Baja California, that at one time was estimated to have as many as 1,800,000, although we can’t know for sure. That is probably as many or more than now occur in all of North America, indications being that in the days before excessive persecution (still very much occurring); the decline in so many fish populations because of badly managed commercial fisheries; the introduction of DDT and various toxic substances into the environment, including toxic algae blooms as a result of nutriment run-off from agriculture; the encroachment of human disturbance into potential nesting sites and general environmental degradation all took a huge, and continuing, toll on the species.  While the San Marin Island colony appears to have collapsed as a direct result of human disturbance bird colonies of all species continually undergo changes in numbers in response to multitudes of environmental and other factors.

6:  Why do some Double-crested Cormorants nest in trees, others on the ground and others on cliffs or even human-made structures such as bridges?

They are opportunistically flexible in nest site choice, with their nests consisting of bulky accumulations of interlocking sticks, seaweed where available and other found materials, including plastic waste, that can be held within the crotch of a tree, amid tree branches, on cliff ledges or on the ground.  There must be enough fish nearby of an accessible size for the cormorants to feed themselves and their young.  They need to have access to nesting materials, which they may carry to the colony from some distance away.  And they need to be reasonably isolated from predators that can eat eggs, young, or even adults, which is why islands, cliffs and isolated headlands are often favored. There are probably more subtle factors involved in nest site selection, such as wind strength and direction, but most certainly they need food and safety.

7:  Why are Double-crested Cormorants black or brown or pale?

When hatched, cormorants are naked and black.  They quickly develop a coat of short, black downy feathers.  Fledged chicks are mostly brown with light bellies, although some can be paler than the majority. Adults in breeding plumage are iridescent black with brown backs, the feathers edged in black. Those in between are subadult birds, which sometimes attempt to breed.  Males and females are identical, apparently even to the cormorants, who have to sort that out among themselves. Once they do, however, they form strong and lasting pair bonds. Although it is extremely rare, perhaps one in millions, an all white bird, or a very pale, creamy colored bird (see http://www.jeaniron.ca/2018/AberrantDCCO_OB_De2018.pdf) that seems to be accepted by the others has been reported. The crests that give the species its name only last for a few weeks in the spring and early summer, and the colors of the eye, face and throat pouch may intensify in breeding condition as a result of changes in hormonal balances.

8: How do Double-crested Cormorants care for their babies?

Cormorants are devoted parents who share in the incubation of the eggs and the care and feeding of the chicks.  Incubation usually commences when the third egg is laid.  One parent will guard the young, or brood, while the other goes off to find food for them.  The baby cormorants are vulnerable to heat or chill, and the parents will help maintain appropriate temperature by sharing body warmth, or by shading them, and even by carrying water to them to help cool them off on very hot days.  The parents stay with the young through the summer.  By the time they are about seven weeks old the young can fly and swim well enough to accompany their parents in search of food.  The young will eventually disperse, but the adults maintain their pair bond.

9:  Other than humans, what are the main threats to the Double-crested Cormorant population, or to individual chicks or adults?

Water quality and healthy fish populations are essential to maintaining cormorant populations.  Cormorants have declined in the past due to human-derived pollutants such as PCBs and DDT that bioaccumulate up the food chain.  Regionally, they are vulnerable to pollutants and declines in prey.  Fish populations are predicted to change due to warming water temperatures as a result of ongoing climate change.  Also, like other waterbirds, cormorants are susceptible to Newcastle’s disease (avian paramysovirus – APMY-1), an often lethal viral infection that damages the central nervous system of the birds. It can wipe out poultry flocks but is usually harmlessly asymptomatic to humans. 

Various avian predators (gulls, ravens, crows, jays, herons) and mammalian predators (foxes and coyotes, raccoons, skunks, and opossums, mink) prey on eggs or chicks, while Bald Eagles and Great Horned Owls are capable of preying on adults.

Storms and storm surges can also be harmful to nesting colonies.

10: How many cormorant species have been found in the Great Lakes basin?

Three, although so far only one, the Double-crested, has been found nesting in the region. The Great Cormorant, native to both sides of the North Atlantic, and widely distributed in Eurasia, Africa and Australia, has reached the Great Lakes from the east. The Neotropic Cormorant historically occurred no further north than the lower Rio Grande Valley region but is now expanding its range in North America, with the odd one having been identified in the Great Lakes basin. Both the Great and the Neotropic Cormorant are very similar in appearance to the Double-crested Cormorant, and it takes an expert to distinguish one species from the other.

11: How many cormorant species are there in North America?

Six. The Red-faced Cormorant is mostly confined to Alaska west and south, via the Kamchatka Peninsula, to Japan. Both the Brandt’s and the Pelagic Cormorant are found on the Pacific coast of North America.  The Great Cormorant is mostly confined in North America to the North Atlantic coast, while the Neotropic is a southern species in North America, and the Double-crested is the most widely distributed. The largest known cormorant, the Spectacled, was found on Bering Island and may have occurred in Alaska but was exterminated before the region’s wildlife was fully documented.

12: How many kinds of cormorant are there in the world?

For technical reasons explained here experts vary in their answer to this question, but the number would be around 38 to 40.

13: Are any species of cormorant rare or endangered, or extinct historically or in recent times?

Yes. The Spectacled Cormorant, first identified by science in 1741, and said to have tasted delicious when properly baked, was extinct by 1850. It lived for sure on Bering Island and probably others of the Komandorski Islands and nearby Kamchatka Peninsula coast of northeastern Russia, and possibly as far east as Alaska, with ancient fossils of it, from 120,000 years ago, unearthed in Japan.

There are three more cormorants close to extinction, the Cape Cormorant (southern Africa), the Bank Cormorant (southern Africa) and the Pitt Shag (Pitt Island, Chatham group, southern oceans east of New Zealand). 

In total there are more than a dozen threatened species, including the Flightless Cormorant (Galapagos Islands); Chatham Shag; Macquarie Shag; Heard Shag; Rough-faced Shag; Auckland Shag; Stewart Shag; Crozet Shag; Bounty Shag; Pygmy Cormorant. “Shag”, a name derived from the shaggy crest of some cormorants, is an alternative name for “cormorant”, often applied to the smaller species, especially the many black and white ones found in the southern hemisphere.

14: What is the lineage or ancestry of cormorants?

Ancient. There are fossils of birds ancestral to both cormorants and a related family of birds, anhingas (also known as darters) that date back sixty million years. They were primitive birds that shared the environment with dinosaurs. But by about thirty million years ago cormorants were a group distinct even from any other families of birds.

15: Are Double-crested Cormorants the same everywhere? 

Almost.  There are very minor variations in size and appearance that mostly go unnoticed. For example, birds on our west coast tend to have white or partly white crests of feathers that are longer and straighter than those of eastern birds.  Of course, those crests last a fairly short time and when shed, the birds all look alike. Birds that breed in the Bahamas are smaller than the ones that breed in the Great Lakes, but the difference is too little to be noticed in the field.  Cormorants nesting in the southeastern U.S. also tend to average smaller than Great Lakes birds, but when the northern birds migrate south and join them in the winter, they all look about the same.

16: What other birds are related to cormorants?

It used to be thought that all seabirds that had all four toes joined together with webbing were more closely related to each other, than to other kinds of birds. Thus pelicans, frigatebirds, tropicbirds, gannets and boobies, anhingas, and cormorants and shags, were all different families of birds, put in one “order”, meaning they were thought to be more closely related to each other than to any other birds. But various sophisticated molecular and morphological studies – the accumulation of more knowledge – determined that in fact the toe webbing and other shared physical features were not necessarily all that indicative of relationships. There is still debate and varying opinions among scientists, but it is fairly safe to suggest that the forty some-odd species of cormorants are most closely related to the five species of frigatebird, ten species of gannets and boobies and four species of anhinga. But they are no longer thought to be in the same order as the pelicans, which are now thought to belong to their own order, closely related to two odd looking African wading birds, the Shoebill and the Hamerkop, and, going further back in time, the progenitors of herons, ibises and spoonbills.  If you go still further back in time, all had a common ancestor, but while both pelicans and cormorants have lots of physical similarities (including throat pouches, although those of cormorants are much smaller than those of pelicans; hooks on the tips of their beaks and, of course, that webbing that joins all four toes) and habits (their colonial nesting habits and fondness for a mostly fish diet) they are not as closely related as they were once thought to be.

17:  What is the association between American White Pelicans and Double-crested Cormorants?

American White Pelicans share many features with cormorants, including a long, straight beak with a hook on the end, a “gular pouch” – the extended “throat pouch” – that is huge and obvious in pelicans, much smaller in cormorants; a diet consisting mostly of fish; large feet with all four toes joined by webbing; colonial nesting behavior; co-operative fishing whereby birds will “herd” fish into shallow waters or confined spaces the easier to catch and eat them. Both have chicks that are born naked that are soon covered in down. Perhaps, then, it is not surprising that where both species occur, they often nest together in colonies (at times in proximity with gulls, terns, herons, ibises, and/or other colonially nesting bird species). The American White Pelican (most of whose breeding range is in Canada – “American” refers to North America in distinction from Eurasia, Africa and Australia where other species of pelicans that are also mostly white in color occur) only nests on the ground. One possible advantage of mixed colonies for both or all species involved is the variety, which can confuse potential predators, and assist each other in the detection of danger – or food. For a more complete discussion go here:

18: What other species of birds and other wildlife compete with Double-crested Cormorants?

When biologists and ecologists talk about “competition” they mean something a little different, perhaps, than the term implies in common usage. However, broadly speaking interspecific competition means two or more species vie – compete – for a common resource, such as nesting material, nesting territory, food, and perhaps more subtle needs such as perches where they can keep watch, preen, or, in the case of cormorants, dry their feathers. When it comes to food, all species that eat the same thing, in the same space, compete with each other. But each species does things a bit differently from others, thus occupying a species-specific “niche”, a place in the greater scheme of ecological dynamics that will overlap that of some other species, but be unique to any given species, on average. For example, while American White Pelicans and cormorants both eat fish and nest together, pelicans can’t dive as deeply as can cormorants but can eat bigger fish, stay in the water longer and, with their big throat pouches, perhaps obtain more nutriment per degree of effort, while requiring more return on that effort because of their larger size.

19.  Why are some people so fond of cormorants and wanting to protect them?

Fondness comes, if it does, from familiarity. Hatred is the foe of knowledge. Once one understands the role cormorants play as part of the ecological whole, their presence in the environment can be seen as being not only natural, but indicative of a healthy, properly functioning ecosystem. Some of us may dislike their actions, but see them as unfolding in accordance with natural forces dating back to the origins of life on the planet.  Some people seem to need hatred in their lives, fear knowledge and see introspection as weakness, but for most of us, once we get to know them, cormorants are an assertion of life, of nature, of a world more vast, complex and wondrous than we are able to comprehend, but sadly at risk to ignorance, fear and hatred.