If you have walked the Lake Ontario shoreline lately, you have probably seen them: long lines of jet-black birds standing shoulder to shoulder on a breakwater, some holding their wings out like laundry on a line. Those are double-crested cormorants, and the sight in the photo above is pure Lake Ontario in late summer.
Cormorants are large diving waterbirds, roughly the size of a goose, with dark plumage, a snake-like neck, and a hooked bill built for gripping fish. That famous wings-spread pose is not showing off. Unlike ducks, cormorants’ feathers are not fully waterproof, which helps them dive deeper, so they perch and hold their wings out to dry.
What do they eat?
About 99 percent of a cormorant’s diet is fish. On Lake Ontario, studies have found that alewife make up roughly two-thirds of what local birds eat, with the rest a mix of round goby, yellow perch, smelt, and other small fish. They hunt by diving from the surface, chasing prey underwater with powerful feet, typically reaching depths of 5 to 25 feet and staying under for 30 to 70 seconds. A cormorant may fly five to ten miles from its colony to find a good feeding spot, then swallow its catch whole, sometimes tossing it in the air to get it down headfirst.
How do they nest?
Cormorants are colonial nesters, returning to the Great Lakes by April. The male claims a nesting territory, and then both mates build the nest together, a sturdy platform of sticks and stems lined with grasses and debris, finished in about four days. They nest on the ground on rocky islands and also in trees, and the same site may be reused year after year. A pair lays three to four eggs, both parents take turns incubating for about four weeks, and the chicks are fed regurgitated fish by both parents. One brood a year is the norm.
Their colonies are famous. Little Galloo Island in the lake’s eastern basin once held more than 5,400 nests, one of the largest colonies in North America, and cormorants still breed on islands across Lake Ontario. Their guano is so acidic it kills the trees they nest in, leaving eerie white “ghost” groves behind them.
The comeback story
Cormorants nearly vanished from the Great Lakes by the mid-20th century. DDT thinned their eggshells so badly that eggs broke before hatching, and persecution kept numbers low even after the pesticide was banned. Once the water cleaned up and the shooting stopped, and with alewife abundant, the Little Galloo colony grew roughly 36 percent a year after 1974. It is one of the great wildlife recoveries in the region, and not without controversy: anglers blame the birds for eating sport fish, New York wildlife biologists have oiled eggs at Little Galloo to limit growth, and Ontario now holds a fall cormorant hunting season.
Love them or not, those black silhouettes drying their wings on the breakwater are a sign of a lake that came back. Watch them a while and you will see the dive, the chase, and the whole wild economy of Lake Ontario playing out in front of you.