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Chesapeake Cormorants

Could these long-necked fish-eaters be a ­looming threat?

The double-crested cormorant has a prodigious appetite.

I noticed the first few cormorants on the Bay in the early 1990s, though I didn’t think much about their appearance at the time. Cormorants had been absent from the Chesapeake, their numbers driven down by pesticides, particularly DDT. The otherwise large populations stretching across the northeast coast down through Florida cushioned them from total exhaustion.
    Over the intervening years, since the banning of those pesticides, their numbers have been rapidly expanding to include a Chesapeake Bay population. The double-crested cormorant, the species now common throughout the Bay, is a large, heavy-bodied black seabird with a sharp beak (curved at the end for catching fish) and a small patch of yellow-orange facial coloring. During their nesting season, both sexes sport prominent white-feathered crests above their eyes for which they’ve earned their double-crested name.
    Airborne, they resemble a small goose with an even wing beat and often fly in large groups called flights. They are a handsome bird, with a slim head, long neck and graceful profile, Though cormorants have a slender profile, their necks are expandable and they can swallow fish 10 to 12 inches in length.
    As diving birds, cormorants can chase their prey, virtually any species of fish, deep underwater, swimming with the aid of their wings. They are able to stay submerged for minutes at a time and cover large distances underwater.
    Most birds are hollow-boned to aid in flight, but the cormorant’s bones are solid to provide strength as well as weight to help them dive. Their feathers are not completely waterproof, again an aid to diving, and that is also why you see the birds perched, holding their wings open to dry and enable them to once again get airborne. Perched and drying their wings, they have an ominous, dark appearance. Worse, say some commercial fishermen, is their appetite.
    Pound netters suffer particularly as the birds have learned to target their fish traps where menhaden, herring, alewife, perch and rockfish make easy pickings. Flocks can gather quickly and eat ravenously. One area waterman told me cormorants had gathered in the hundreds to devour thousands of small white perch that had become trapped in his pound net.
    Seeing large flights of cormorants this season, I wondered if they could become a problem for free-swimming fish. Maryland Department of Natural Resources confirms a resident Chesapeake population of some 4,000 nesting pairs. Those resident birds annually consume an estimated three million pounds of fish of all species. Northerly cormorants also make the Bay their southern wintering grounds — and bring their appetites.
    Adding to the problem is guano from nesting cormorants, which has killed areas of critical wetlands vegetation. Their presence has also driven other species of native Bay seabirds off their traditional and limited nesting grounds.
    Hunting cormorants was banned during earlier periods of population decline. So we may be seeing another surge in a bird population that can be unhealthy, particularly in sensitive areas such as the Chesapeake.