At certain times of year, both Deering Oaks and Back Cove are brimming with waterfowl. Big brown Canada Geese are waddling and crapping everywhere, and Mallards quack beneath your feet as they chase bread crumbs. Then, other times of the year, they’re all gone. What’s going on with them?
Well, nothing unnatural, thankfully, but definitely something interesting. Turns out, paying attention to the waterfowl at Back Cove and Deering Oaks Park can tell you a lot about how waterfowl move around during different seasons.
Let’s compare the numbers. Using data from eBird, the vast bird-sighting database from Cornell, I can see how numbers of Mallards and Canada Geese fluctuate throughout the year. These two parks are not the same.
Let’s start with Mallards. At Deering Oaks, Mallards are present in good numbers, about 60 individuals, throughout the summer, and peak at around 200 individuals in October before crashing to near zero for the winter. There are barely any Mallards on Back Cove in the summer, but their numbers climb through the fall and peak over the winter, at around 80 individuals in February.
The story is slightly different for Canada Geese. They’re not really found at Deering Oaks at all apart from the late September and early October, where their numbers peak around 65 birds. They’re not on Back Cove at all in the summer, but pour into the bay in the fall, with numbers peaking at near 100 in early November and lingering around 30 into the spring.
So what’s happening here? Not many birds in the spring and summer, a lot of birds in the fall, and some birds on Back Cove in the winter but none at Deering Oaks.
These trends are all part of the natural cycle of waterfowl. Both of these species are, to some extent, migratory, but their motivations are different from the songbirds that arrive in Maine each spring to dine on insects. The seasonal movement of Maine’s waterfowl are governed by habitat availability: they need to leave before their freshwater homes freeze solid in the winter.
So that’s what they do. Hundreds of millions of ducks, geese, and other waterbirds head south from their breeding lakes in northern North America each fall, fleeing the dropping temperatures. They’re looking for open water to ride out the winter. Some flocks pass through Maine on their way further south, which explains the peaking waterfowl numbers at both Deering Oaks and Back Cove in late fall. It also explains why there are no birds at all on Deering Oaks in the winter: it’s solid ice!
But Back Cove doesn’t often freeze solid in the winter. Most of the Cove is open water, and so remains tolerable habitat for waterfowl for much longer. Some ducks and geese can ride the whole winter out on the bay, especially when a lack of snow makes the grass at Payson Park available. It’s always easier for a bird not to migrate if it doesn’t need to, and they will stick it out in Back Cove for as long as the weather tolerates.
But, eventually even the Cove gets too cold or icy, and the birds must move further south to find better accommodations. This explains the decrease in waterfowl populations on Back Cove as the winter drags on.
As for summers, that’s breeding season. Both of these species could breed in Deering Oaks or Back Cove, and likely do in small numbers. But the habitat isn’t great for them — too many people. There are plenty of better, quieter, wilder options that have opened up in the north, and most of Portland’s waterfowl will migrate up there to take advantage.
Nick Lund of Cumberland is outreach and network manager at Maine Audubon. He has written about nature for the National Audubon Society, Down East, National Parks Magazine, The Washington Post, and others. He can be found online at TheBirdist.com and on Twitter @TheBirdist.