Monomoy is a unique haven for common terns, piping plovers and American oystercatchers – birds that fail to reproduce in many areas on the mainland, but thrive on the island. Absent of people, the island Wildlife Refuge provides some species of birds better reproductive success than anywhere else in Massachusetts. Monomoy is one of the few remaining wilderness areas in the Northeast, along a coastline that is almost exclusively developed and trafficked by people.
Thousands of common terns have settled on Monomoy to breed in a dense, cacophonous colony. These ground-nesting birds are attracted to remote barrier islands because they are absent of mammal predators, and given how scarce good breeding habitat is in the Northeast, it is advantageous for the terns to invest their nesting effort into a single, uniquely perfect area of land.
The downside of nesting in groups is that a large colony of terns, along with their eggs and chicks, creates a large aggregation of easy prey. By literally placing all their eggs in one basket, the terns attract potential predators to a virgin island.
Common terns have evolved effective defenses against native predators who might visit their colony. Should a fox, skunk or raccoon walk through the colony in search of tern eggs, the birds will swarm the mammal, pecking and pooping on it, and drive it out of the colony. They will do the same to peregrine falcons, red-tailed hawks and bald eagles, and their group-defense strategy works a treat.
Coyotes are still an unfamiliar predator to these birds and significantly more imposing than raccoons and skunks, against whom the terns have evolved a successful defense system. When a coyote passes through a tern colony, swarming behavior by the terns can escalate to a point where the entire colony – more than 20,000 birds – will leave its nesting grounds for twenty minutes or longer, exposing chicks and eggs to the cold. This can be deadly to an entire population of terns.
Coyotes are not a native part of this ecosystem, and their intrusion on Monomoy poses a serious threat to the reproductive success of native breeding species. In 2006, the stomach of a coyote killed on the refuge contained 69 common tern chicks, which it likely ate in one night. In 2009, the stomachs of two coyotes contained 75 tern chicks between them (USFWS 2016, Appendix J).
In an effort to mitigate the damage coyotes cause to native birds, the Fish and Wildlife Service has established a practice of killing coyotes found on Monomoy. This is done only during Spring and Summer, when the predators pose a threat to nesting shorebirds. In April, contracted hunters use dogs to search the island for denning coyotes. The goal is to destroy any coyotes that have made dens on Monomoy and kill their pups, who are usually born in March.
David Warren, who works for the USDA’s Wildlife Services division, hunts coyotes that visit the island during the summer months.