They are an environmental success story, a species that was once driven to the brink of extinction by chemical pollution but has now rebounded tremendously. But do we have too much of a good thing?
Certainly the Ontario government thinks so. Last year it introduced a proposal to allow cormorants to be hunted, essentially treating them as a nuisance species that needs to be controlled.
The proposal is not yet law, nor is there any timeline as to when it will become law. But it would allow an open season on cormorants that extends from March 15 to December 31, and let anyone with a small game license shoot up to 50 cormorants a day.
It’s quite a change for a bird that was once a rarity.
Double-crested cormorants are native to eastern North America, and are found primarily in the Great Lakes, with smaller populations on inland lakes like those in Muskoka. From the 1950s through to the 1970 their numbers plummeted, mainly due to chemicals like DDT, which caused their egg shells to become too thin. The same effect was seen by peregrine falcons and many other migratory birds, and evidence also mounted that the pesticide was accumulating in humans tissue as well.
DDT began to be phased out in the 1970s. Although it wasn’t fully banned in Canada until 1990, many bird species began to recover early, cormorants among them.
By the early 2000s, cormorant populations had peaked, and some people were getting concerned. Cormorant numbers have stabilized since then, and even declined slightly — which is fairly typical when a species recovers — but the opposition to cormorants remains.
There are two main groups who are in favour of culling cormorants. One is anglers and commercial fishermen, who see cormorants as an effective predator that damages fish stocks. A single cormorant will eat about half a pound of fish a day, and doesn’t much care whether that fish is a bass or trout, or an invasive species like round goby. In fact, the arrival of round gobies and alewives in the great lakes has helped cormorants recover, by providing an abundant food source. (Both are prolific and aggressive fish that are rapidly displacing native fish such as walleye in some areas; studies in Hamilton found that gobies alone make up about 18 percent of a cormorant’s diet, compared to less than 1 per cent for trout, bass and other gamefish.)
Cormorants, the fishing community argues, don’t just eat juvenile sport fish and commercial fish, they also eat the minnows that these desirable fish feed on, creating yet another competitor in an already crowded food chain.
The other main opposition to cormorants comes from landowners, who have seen properties destroyed when a cormorant colony moves in. Cormorants nest in groups, preferring trees on islands and waterfront properties. Because their droppings are highly acidic, they can kill the trees in as little as three years. We’ve all seen “bird islands” on the lakes, many of which are also home to terns, gulls and other species; cormorants are another species that adds their guano to these islands. In some places, like the islands around Point Pelee, the impact can be enormous — 15 per cent of the rare Carolinian forest there was destroyed by a colony of 25,000 cormorants, prompting Parks Canada to begin culling the birds.
In Muskoka, cormorant populations are fairly small and likely to remain that way. It’s unusual to see more than a couple of dozen cormorants nesting in one place. The larger populations are on the Great Lakes, but even those are miniscule compared to the summer populations in Manitoba, where most cormorants breed.
There have been culls in other areas. Some US states have had cormorant hunts, although those were halted when a judge ruled that there wasn’t enough scientific evidence to support continuing them. And some provinces also have limited hunting seasons or government culls in specific places.
Public comment on the Ontario government proposal ended in January, and the government has been silent on the subject ever since.
In the meantime, if you have cormorants nesting or roosting on your dock posts or boathouse, there are a few effective ways to get rid of them. There are devices called Bird Spikes or Bird Spiders, which are designed to sit on posts and make it impossible for birds to roost.
Cormorants are also very aware of threats, and some people have reported great success by hanging strips of reflective mylar tape or “predator eye balloons” which, as the name implies, are balloons printed with eyes that resemble a predator. All these products are widely available online.