Along the Delaware River in Philadelphia we can find two species of cormorants – Great and Double-crested. While Double-crested is common and widely distributed throughout the US, Great is found along the northeastern and mid-Atlantic coast and the lower reaches of major rivers, such as the Delaware, leading to the Atlantic.
With winter nearing an end, most Great Cormorants will be heading further north to the Canadian Maritimes to breed. The photo illustrates the difference between these two species, with the largest of North America’s cormorant, the Great, on either side of a Double-crested.
There is clearly a size difference between the two species, with the Great being at least 10% larger (and almost twice as heavy) with a blocky head, thick neck and more robust bill. By mid-winter adult Greats begin to get their diagnostic white flank patch which is very obvious when it stands and in flight. Another difference can be seen on the face. Double-crested have an orange gular (bare skin on the throat) that has a rounded border, whereas Greats have a smaller duller orange gular with a pointed at the back, outlined with a broad white border. Even at a distance this is most noticeable.
As the birds near peak breeding plumage, thin white feathers can be seen on the side at the top of the neck on Great Cormorants, and a shaggy nape also appears. Though from the distance that this photo was taken, it is hard to see, but the Double-crested is just beginning to get its crests! These are feathers, or tufts, growing out on either side of the top of the head, and from where it gets its name.
photo © adrian binns