Seabirds of Stellwagen: Terns
Sunday, Feb 3 2013 07:31 PM | bird research, birdwatching, Cape Cod, Hyannis, Stellwagen Bank National Marine Sanctuary, whale watchers, whale watching, whales
Hyannis Whale Watcher Cruises welcomes you back to our seabird blog series. Our goal is to introduce whale watchers to the types of seabirds that visit the waters off Cape Cod. Their behaviors are amazing, their natural history is fascinating, and the open ocean environment they call home is unforgiving. Viewing seabirds is an incredible bonus ball in the world of whale watching! Today we will talk about more gull relatives, the terns.
Worldwide, there are over 40 species of terns. The largest species, the caspian tern, is a very rare visitor to our whale watching grounds, while the world's smallest tern species, the least tern, is a breeding summer resident on Cape Cod. Other species regularly encountered on whale watches include: common tern, forsters tern, and the endangered roseate tern. Several other species make occasional appearances and are considered rarities by bird watchers. Terns are seasonal visitor and are largely absent from late fall through April and May.
Terns are more specialized at taking prey than gulls, using a combination of hovering and plunge diving. Terns are experts at taking small schooling fish from the surface of fresh and salt-water habits. Fish form the majority of most species diets, though a few species rely on insects as well. They are skilled hunters but are not beyond stealing catches from other terns in mid-air.
|Common tern in a plunge-dive.|
Photo- Jim Rosso-USGS
Though flocks of wheeling terns, sometimes tens of thousands, are encountered on whale watches, they are never in direct association with feeding baleen whales the way gulls and some other seabirds often are. They do not actively exploit the efforts of feeding whales. What we often see while watching whales, are adult terns carrying fish back to their chicks at their nesting sites, and later in the Cape Cod summer, recently fledged juvenile terns following and begging food from their parents.
Terns are colonial nesters in coastal and inland habitats. Nesting in large colonies provides safety in numbers for the birds. Courtship, as with gulls is complex and sometimes endearing. Courtship feeding involved males bringing perspective females gifts of food.
Most terns nest on the ground, not that they usually build much of a nest. For most species, a shallow scrape in the sand, perhaps lined with grass or seaweed is the extent of their nest-building effort. Regardless, the few square feet that make up a territory are vigorously defended and the adults will aggressively dive-bomb intruders, human or otherwise. The author once witnessed a wayward beach ball mercilessly attacked by least terns as it rolled along the waters edge! If you don't believe us, watch this video!
Despite their hardy nature and successful feeding strategies, several New World species including the least, and roseate terns, are threatened or endangered with drastic declines recorded in the past century. Encroachment by human activities and subsequent habitat loss are the overwhelming cause. Tern identification is tough even for seasoned birders, so study up before your trip and ask your naturalist if he/she can help with IDs!