The incredible, indelible cormorant

Along with the ducks, geese, and gulls that frequent the waters of Milwaukee is a bird that may be less familiar to most landlubbers: the cormorant.

A relative of the pelican, these large, black waterbirds can often be spotted perched on harbor breakwalls or in other places near Lake Michigan during the summer months. They are skilled fishers that use their webbed feet and streamlined bodies to dive underwater-often to depths of 25 feet, and sometimes more-in pursuit of a meal. “They’re just as agile underwater as penguins,” said Ken Stromborg, a retired U.S. Fish and Wildlife Service biologist who has studied cormorants for nearly 25 years. 

The Double-crested Cormorant, the species that inhabits the Great Lakes region, is the most common and widespread of six cormorant species in North America. The Double-crested Cormorant gets its name from crests of feathers that appear on either side of its head during the breeding season. The birds have hooked bills and yellow-orange faces, and breeding adults have turquoise eyes and mouths.

Stromborg said the cormorants living here are just like those that people spend thousands of dollars on ecotourism to distant places to see. “There are places where these birds are tourist attractions,” he said. “We’ve got this right here on the Great Lakes, if we’d appreciate them.”

But appreciation for cormorants here has waxed and waned over the past century as human and bird have repeatedly crossed paths.

Prior to European settlement, cormorants lived throughout much of the United States including, some scientists believe, the Great Lakes region. In the late 1800s and early 1900s, however, conflicts with European American settlers led to declines in cormorant populations across much of the country. “Nineteenth century human persecution probably drove them off” the Great Lakes, said Stromborg.

But the birds eventually returned and were documented nesting on western Lake Superior in 1913. Cormorants “probably migrated through the Great Lakes in years prior to 1913, [but] in that year a few of them probably just stayed and set up shop,” said Chip Weseloh of the Canadian Wildlife Service.

Their range and numbers in the Great Lakes expanded greatly between 1920 and 1950. But the cormorant population boom was soon followed by a population bust brought on mainly by reproductive failure due to contamination by the pesticide DDT. Over the next two decades, the cormorant population plummeted, and by the early 1970s, few of the birds remained in the Great Lakes.

But people soon rallied around the bird, changing its fate yet again. In 1972, DDT was banned nationally and the cormorant gained federal protection when it was added to the list of species protected by the 1918 U.S. Migratory Bird Treaty Act. In Wisconsin, the Department of Natural Resources (DNR) installed more than 1,200 artificial nesting platforms around the state between 1974 and 1984. And throughout the Great Lakes themselves, cormorants found an abundant food supply as populations of predatory fish like lake trout declined, leaving populations of invasive prey fish like alewife unchecked.

The Great Lakes cormorant population saw spectacular growth as a result. In Wisconsin, the state’s breeding population grew at an annual rate of almost 25 percent-from 66 nests to 10,546 nests-between 1973 and 1997, according to one study. Today, the state has about 18,000 nests and 42,000 birds, said Stromborg. About 85 percent of those birds live near Lake Michigan, mostly in breeding colonies near Green Bay and Door County; the rest live inland.

But while some people consider the cormorant a conservation success story, others now see the bird as a nuisance. Fisherman say cormorants have caused a decline in the yellow perch population, although studies show the birds actually feed on a wide variety of fish. There is also concern about the impact large numbers of cormorants have on vegetation. On some Wisconsin islands, the birds’ roosting habits and concentrated acidic waste have killed off plants and trees.

In response, Wisconsin and other Great Lakes states have implemented cormorant management programs. In 2005, Wisconsin began oiling eggs to curb reproduction on three islands in the Green Bay area-Hat, Cat, and Jack islands. The goal is to reduce the area’s nesting population to no less than 6,000 nesting pairs, said DNR wildlife biologist Jeff Pritzl. The population on the managed islands has been gradually decreasing so far, he said, and the growth rate of the combined population on managed and unmanaged islands in the area has slowed.

Ultimately, what becomes of cormorant populations in the future will be influenced both by management and by any changes in fish populations-due to new invasive species, for instance-said Stromborg. “Cormorants are a reflection of how much fish biomass is out there,” said Pritzl. “Who’s to say there aren’t food changes around the bend that could affect cormorant populations again?”

Jennifer Yauck is a science writer at the UWM Great Lakes WATER Institute. GLWI (glwi.uwm.edu) is the largest academic freshwater research facility on the Great Lakes.

Sentinel Species

Like other animals at the top of the food chain, cormorants accumulate chemicals found in the fish and other small animals they eat. For that reason, some scientists have looked to cormorants as sentinels of Great Lakes pollution, using the birds’ eggs to detect the presence and relative level of chemicals like fire retardants in the environment. Cormorants are also being looked at as monitors of emerging wildlife diseases such as botulism and avian flu, Stromborg said.

Double-crested Cormorant Profile:

• Weight: About 3 to 6 pounds
• Body Length: About 3 feet or less
• Wingspan: Up to 4 feet
• Feathers: The birds’ feathers absorb moisture, which reduces their buoyancy and helps them stay underwater while diving for fish. Cormorants often hold out their wings to dry after a dive.
• Lifespan: 4 to 5 years, but some have lived more than 20 years.
• Reproduction: Nest in colonies, building bulky nests in trees or on the ground. Lay 3 to 5 pale blue eggs at a time.

Sources: National Audubon Society, Ken Stromborg

Copyright 2010 by Bay View Compass. All rights reserved.
This material may not be published, broadcast, rewritten or redistributed.