Roseate Migration

August is a strange time of year. I consider it a summer month, but migrating birds draw my mind towards Autumn. My Fish and Wildlife internship has ended, drawing my mind towards winter.

Least tern chicks.

I was very fortunate to spend the summer monitoring piping plovers, least terns, and American oystercatchers. I spent nearly every day walking on the beach and looking at birds; paradise! I especially enjoyed watching the subtle ways the beach changed – plants reestablishing on dunes, the Card’s Pond breach opening and closing, and the shift in which bird species were present or absent. The piping plover season ended early this year, which means that while there are still piping plovers running around and growing fat on insects, worms, and crustaceans, all of their chicks have fledged and are nearly indistinguishable from their parents. All of the oystercatcher chicks have also fledged, but there are still some least tern chicks hanging around, sitting on the beach and waiting for their parents to bring them fresh fish. I hope they grow quickly and well, for much like piping plovers, least terns are migratory birds. Autumn is coming and they have a long journey ahead of them: piping plovers to the south Atlantic and Gulf coasts, least terns to Central and South America.

Roseate tern.

Nor are they the only migrating birds; in the past month I have seen numerous sanderling, ruddy turnstones, common terns, and roseate terns, to name but a few of the species passing through. I am especially heartened to see the roseate terns because they are an endangered species and this is the first time I’ve seen them. They’re gorgeous birds, with long, elegant wings and a deeply forked tail. They have a pale gray upper body, a white underside, and during the breeding season they have a black bill and matching black cap. They also have a faint rosy wash on their breast feathers, but it’s very subtle and all of the birds I’ve seen have already begun transitioning to their nonbreeding plumage.

Although it is part of their historic range, roseate terns don’t breed in Rhode Island. They breed on select coastal islands extending from New York to Canada and currently their biggest colonies are at Great Gull Island in New York and Bird and Ram Island in Massachusetts. Most of the time roseate terns nest near common tern colonies. Although both species nest directly on the ground, common terns prefer to nest in open areas while roseate terns generally prefer to nest under rocks and vegetation. Their ground nesting strategy leaves both species vulnerable to predators, especially great horned owls, mink, and raccoons. To protect their nests, eggs, and chicks, adult birds will dive bomb any predator that approaches, pooping on them for good measure. 

Banded roseate tern.

Due to their endangered status, roseate tern colonies are intensively monitored and protected. Many of the young birds are captured and banded before being released. Currently, each bird is given two bands: a service band on one leg and a field readable band on the other leg. The service band is metal and contains a number unique to that individual bird, but in very small numbers. It can only be read if the bird is recaptured. Field readable bands have larger numbers and are easier to read; they can be either metal or plastic. Plastic field readable bands come in different colors and are numbered. They are designed to be read from a distance with the aid of a scope, or bird telescope, so that the birds can be identified without recapturing them. Banding birds allows scientists to study survival rates, migration, and reproductive success among other things.

Migration is a long and risky process. Roseate terns fly all the way to Brazil, where they spend the winter. Since Brazil is so far away, roseate terns don’t fly the entire way at once. Instead they stop along the way at various locations known as staging areas. Staging areas give migrating birds a place to rest and forage, gathering their energy while they wait for favorable winds to continue their migration. Although all of the juvenile roseate terns at staging areas have learned how to fly, they are still learning how to hunt and are dependent on their parents for food. Parents that return with fish are duly greeted by their loud, hungry young, bills wide open.

I spent the last couple weeks of my internship monitoring mixed species flocks of staging terns at three different beaches in Rhode Island: Trustom Pond, Napatree Point, and Sandy Point. Access is limited to prime staging habitat in all three areas to limit disturbance to the birds. This is necessary because every time they are disturbed, roseate terns (and other migratory birds as well) waste valuable energy flying away instead of resting or eating. If they are disturbed too often, they may abandon their young.

Me (left) and Brandi-Lyn Colacone (right) using spotting
scopes at Trustom Pond. Photo courtesy of Tori Lima.

The flock size at each beach varied day to day, from zero to over six hundred terns. To avoid flushing the birds, I would set up my scope at a nonthreatening distance and creep closer, sometimes no more than a few steps at a time. Either with a partner or on my own, I first estimated the flock size, then conducted an exact count of the flock size, before settling down to go through the birds one by one to determine their species (common tern, roseate tern, black tern, etc) and age (juvenile, adult). Given enough time, I would also search for banded birds. 

Certain species are distinct and easy to identify (black tern, Forster’s tern, sandwich tern), but the majority of the flock was always composed of common terns and roseate terns, who look very similar once they’re in nonbreeding plumage. The juveniles aren’t too hard to tell apart – roseate terns have darker foreheads, black bills with no hint of orange, black legs instead of pink, heavier scalloping on their back feathers, and no carpal bar on their wings – but the adults are a different story. The key differences between adult common terns and roseate terns are how much black they have on their bill, how dark their plumage is (kind of light grey

Juvenile Forster's terns.

versus very light grey), and how dark the tips of their wing feathers are. To increase the difficulty, many of the birds I saw were sitting down (can’t see their legs), preening (can’t see their bills), facing the wrong way (can’t see their bills), or hiding behind another bird (can’t see anything). Sometimes the entire flock would flush and fly away due to a pedestrian walking by, a helicopter, or no discernable reason - perhaps they all spontaneously decided they wanted to sit three inches to the left of where they were sitting before. I learned to balance speed, accuracy, and patience. I also learned to appreciate subtle differences between the birds and focus on markings I would never notice under different circumstances. I got to watch small, intimate moments like a roseate tern preening its breast feathers or a common tern feeding its overgrown chick. I got to watch a common tern return from sea with a fish, only to be chased by several other terns and a seagull, all screaming at the top of their lungs. I saw species I’ve never seen before and may never see again, including two sandwich terns that were at Trustom Pond for a single day several weeks back.

Roseate terns are still passing through Rhode Island, so I humbly ask that you help make their migration a success. Respect any fencing and closed off areas. If you flush the birds or they appear agitated, then you’re too close. Back off a little way and watch them from a distance. Roseate terns perceive dogs as predators, so leave your pets at home for just a little while longer.

Thank you.