Robin C. writes:
Thank you for your column. Something I wonder about is the predator-prey chain here in Cambridge. Did we get coyotes because of the new rabbits? Do the coyotes and hawks compete for the rabbits? Who is eating the turkeys? Are any predators keeping down the rat population?
These are all very good questions, Robin. As you may know, coyotes (Canis latrans) are not native to the Northeast. They evolved on the prairies of the Midwest. In the 1800s, people in the Northeast hunted mountain lions and wolves to extinction, leaving a niche that coyotes filled over time. In the early 1900s, coyotes traveled east through Canada north of the Great Lakes, and by the 1930s had trickled into upstate New York, reaching western Massachusetts by the 1950s. Today they live throughout the state, even in urban areas, and have become a top predator in our region.
We know a good amount about what coyotes eat — there are more than 510 published studies of their diet! Urban coyotes and rural coyotes have different diets. They both eat small mammals, geese or turkey eggs, and even white-tailed deer, but human foods (beef, chicken, pork, fruit) make up as much as 70 percent of what urban coyotes consume.
As for local wild turkeys (Meleagris gallopavo), coyotes are one of their chief predators, along with bobcats and great horned owls. In the wild, where coyotes prefer hunting in grassland or open areas, turkeys choose more wooded locations to forage. At night, turkeys roost in trees, protecting them from coyotes, which, while mostly nocturnal, cannot climb trees.
Turkeys become more vulnerable during mating season (March through June), when male turkeys attract hens by strutting, gobbling, and displaying feathers in open areas. (Male turkeys have to balance their fear of being eaten with their desire to find a mate.) But, turkeys construct nests on the ground. That allows coyotes to eat turkey eggs and take young turkey chicks in the spring and summer. These nests are also vulnerable to raccoons, opossums, skunks, foxes, crows and ravens. Even so, our turkey population seems to be doing just fine.
Urban coyotes also prey on Canada geese nests and chicks. Canada geese (Branta canadensis) populations have increased in urban areas due to an abundance of grass and suitable nesting sites along rivers and ponds, and coyotes in the spring often can be found along the edges of waterways, where geese build their nests. Researchers in Chicago discovered that coyotes conducted almost 80 percent of the raids on Canada goose nests, lowering goose population growth to 1 to 2 percent per year. (Without coyotes, Canada goose populations increased by 10 percent per year.) Coyotes will bury extra goose eggs, saving them to eat later. (This study found that raccoons were the second most common predator of Canada goose eggs.)
The Chicago researchers found a much larger coyote population than anticipated. Instead of a few packs totaling several dozen coyotes, they tagged more than 200 and estimated there were several thousand coyotes in Chicago. While urban environments might seem less hospitable to coyotes, their populations are denser in cities because there is more food available. Coyotes in rural areas have to range farther to find food.
Eastern coyotes are larger than western coyotes, so are more likely to hunt white-tailed deer, especially in deep snow, which slows deer. Last winter, a family of coyotes worked together to take down a deer on the frozen Charles River near West Roxbury. Coyotes also hunt fawns in the spring. Since coyotes also scavenge, they might also feast on deer carrion.
Urban coyotes do eat rats and rabbits, but rats tend to be quite bad for their health, because these are easiest to catch when suffering from the effects of rat poison, which can take several days to kill them. The level of poison in an individual rat isn’t likely to kill a coyote. But as poison accumulates it severely weakens the immune system, which makes a coyote susceptible to mange — a contagious skin disease caused by microscopic burrowing mites. Mange mostly causes hair loss, scabbing, and itchy skin, but in winter hair loss mean it will freeze to death. If enough rat poison is ingested, the blood will not clot, which can lead to a slow death by internal bleeding. In one recent study of 585 coyote carcasses, almost all urban coyotes (98 percent) had rat poison in their system.
As for rabbits, coyotes and red-tailed hawks (and foxes and racoons) hunt them, especially bunnies. For this reason, half of all baby rabbits do not survive long enough to leave their nests, and only about 20 percent live to their first birthday. Adult female rabbits, therefore, produce many offspring — as many as 30 babies per year.
Again, though, discarded human food seems to be the most significant part of urban coyotes’ diets, followed by small mammals, including rabbits and rats.
The predator-prey relationship is complicated. Coyotes are opportunistic and will move anywhere there is food, which usually includes rabbits and rats. Whenever coyotes move into an area, it decreases the numbers of their competitors. That means fewer foxes, raccoons, skunks, opossums and domestic or feral cats. As those numbers decline, bird numbers increase, because coyotes are less likely to prey on birds and their eggs. Thus, the presence of coyotes tends to help birds, such as hawks.
Have you taken photos of our urban wild things? Send your images to Cambridge Day, and we may use them as part of a future feature. Include the photographer’s name and the general location where the photo was taken.
A stronger
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