Birds [Aves]

Feathers set birds apart from other vertebrates, allowing them to take flight. Feathers grow from follicles under the skin, providing downy insulation, outer contouring and flight airfoils. One or more times a year a bird goes through a molt process that sheds old feathers and grows new ones, either whole or in part. This allows it to replace lost or worn feathers, and don plumage in keeping with the stage or season of its life. Juveniles of some species vary from adults in the design and color of their plumages, for one or more years. Many females have subdued colors for camouflage. Breeding birds have seasonally-bright colors to attract mates.

When you hold up a flight or contour feather, you are gripping the bottom of the shaft. Growing out in diagonal lines from either side of it are many barbs. The barbs, in turn, have many barbules growing from either side of them. Each is lined with tiny hooks, which hitch to neighboring barbules. When a bird’s feathers become ruffled, it preens them for optimal flight, waterproofing, sun block and parasite protection. Preening involves fluffing the feathers and then combing them with the beak to zip the barbules back together. Bird bills are suited for this since they have certain degrees of serration instead of teeth. The extra vertebrae in the necks of birds give them flexibility to reach all around their body.

Most birds are also equipped with an oil gland near their rumps, which they can stimulate when preening. The oil keeps their feathers flexible, waterproofed and protected from parasites.

Other ways birds are built for flight include lightweight bills; hollow bones, in many cases; and the ability to breed by laying hard-shelled eggs outside their body.

All birds have nasal glands behind the bill above the eyes. In seabirds, these glands remove salt from the blood stream and release it as a concentrated salt solution from nostrils in the beak. This allows shore birds to survive on salt water without dehydrating.

The estuary is a great place to observe many kinds of birds, including seabirds, shore birds, wading birds, waterfowl, birds of prey and marsh birds. Some of these are year-round residents of the estuary. Many more migrate south in the fall and return in the spring. Others are seen only for brief periods during their migrations to and from northern nesting grounds in the spring and fall.

Seabirds

Gulls must be the most adaptable birds of the estuary, their habitat and food preferences have such a wide range. Rather than declining from increasing human activity in the ecosystem, many gull species have become common. We take gulls for granted, seeing them practically everywhere—from intertidal rocks by the sea and inland waterways, to store parking lots and landfills. Some gull species were hunted extensively for their plumage and eggs until their populations dropped drastically in the early 1900's. Under the protection of the Migratory Bird Treaty Act of 1918, they have definitely rebounded. Here are a few of the gulls in the estuary.

The herring gull (Larus argentatus) is probably the most familiar, with its white body, gray wings, black and white wing tips, yellow bill, and pink legs and feet. It nests from this area to the north, and winters in this area to the south. Herring gulls grow to 25", and can live to 15 or 20 years.

The ring-billed gull (Larus delewarensis) looks much like the herring gull, except for the black ring around the end of its bill, and its greenish-yellow legs. These grow to only 19” long, but can live to 20 years or more. They nest from the Great Lakes on north to parts of Canada, and Atlantic coast populations winter from Nova Scotia south to Florida.

The great black-backed gull (Larus marinus) grows to 30". Its white body is in contrast with its black back and black wings, which span five and a half feet. It has a yellow bill and pink legs. The great black-backed gull nests in this area to northern Canada, and winters from the northern coasts of Canada south to Florida.

Scientists call gulls “opportunistic omnivores,” which means they’ll eat just about anything available, dead or alive: crabs and other invertebrate delicacies of the intertidal zone, forage fish scared to surface waters by large predators, waste tossed from fishing boats, berries, insects, reptiles, amphibians, rodents, carrion, eggs from other nesting shorebirds birds, and assorted garbage. Larger species steal fish from other birds, eat eggs and chicks of their own kind, and have been known to go after young lambs. Herring gulls are clever enough to crack open mollusks by carrying them aloft and dropping them onto rocks or pavement. Despite the abundance of menu possibilities, gulls still have a tendency toward nasty squabbles over food.

A solitary gull can be seen on a scavenging expedition, or riding high with its long wings on thermal updrafts. But often gulls are found together loafing on a sun-warmed parking lot in cold weather, clamoring around a food source, and always while nesting. They breed in colonies with females laying eggs onto nests that amount to ground scrapes covered with matted vegetation and debris. Ring-billed gulls sometimes conceal nests under vegetation, herring gulls often do. These also feather their nests. Incubation and fledging times vary (from three to four weeks for incubation; and four to six weeks for fledging), each taking longer the larger the gull species.

Once hatched, gull chicks are semi-precocial. This means that their eyes are open, they are covered in down and they can walk around, but they stay at the nest to be fed by their parents. The chicks peck a red spot appearing on the lower mandible of breeding adults to stimulate regurgitation of food.

This is a vulnerable period in a gull’s life. Adult gulls in the colony sometimes kill wandering chicks. Outside predators of eggs and chicks abound, including raccoons, foxes, skunks, raptors and other adult gulls. One benefit of colonial nesting is that there are plenty of adults around to literally mob intruders—a good thing to keep mind if you happen upon a gull or tern nesting ground.

By the time they fledge, juvenile gull plumage is mottled or streaked dark gray. With progressive molts, it gradually lightens until adulthood (ring-billed: 3 years; herring: 4 years; great black-backed: 4 years).

Adults can fall prey to harbor seals, bald eagles and falcons.

Common Tern
Sterna hirundo
As part the gull family (Laridae) terns look like small gulls with narrower wings, long pointy bills, and black-capped heads. The common tern has a dark orange bill with blackish tip and dark orange feet.

The common tern consumes mostly small fish, using a different foraging technique than a gull, which merely dips its heads into surface waters to grab its prey. A tern flies high above the water with its head down in search of fish. It hovers over its prey, dives and then plunges into the water to grab a fish crosswise in its bill.

Terns nest in colonies on beaches, lying up to three eggs on scrapes in the ground lined it with grass, shells or seaweed. Incubation takes three weeks to a month, and fledging takes nearly a month. Once fledged, the chicks typically return within two or three years to breed in the same place. Terns are territorial of their nesting areas and if provoked, may mob an intruder with dive-bombing and defecating.

Biologists found a dozen tern nests in 2003 on Hen’s Island, less than a quarter acre of land in the Piscataqua River off Newington, NH. This is encouraging, since many nesting areas for terns have been disturbed or wiped out altogether. Just outside the estuary at Seavey Island, among the Isles of Shoals, terns have made a remarkable comeback. Where there had not been broods since the early 1950s, there were 2,414 pairs of common terns, 63 pairs of roseate terns, and six pairs of Arctic terns in 2003. For more information on the project and groups that made this possible, see:
http://www.nhaudubon.org/research/03terns.htm

New Hampshire Wildlife Journal published this article on tern restoration:
www.wildlife.state.nh.us/Wildlife_Journal/ WJ_sample_stories/WJ_d03_Tern_Restoration.pdf

Double-Crested Cormorant
Phalacrocorax auritas
As you look out over a body of water in the estuary, you are likely to see the thin neck and long hooked bill of a black bird breathing between dives. But not for long. It quickly plunges, leaving you to search the water for up to 30 seconds or more while it hunts herring, sticklebacks and other small school fish. Double-crested cormorants swim with their webbed feet, guided by eyes adapted for underwater vision. Upon seizing a fish it swims to the surface and swallows it headfirst into a large orange throat pouch. When feeding time is over, the cormorant perches with its wings extended on a piling, buoy or other solid surface to dry its outer plumage, which is not waterproof. After a while, it regurgitates a pellet of fish bones and other indigestible materials.

These cormorants grow to nearly three feet and have long tails. Their bones are relatively heavy for a bird. They provide good ballast for dives, but create less than graceful takeoffs from water. After running and flapping for many yards across the surface, cormorants finally gain altitude and fly low to the water with their necks out flat in front.

You can spot these birds along the Atlantic coast, in the estuary, and on its tributaries beyond the reaches of the tides. They breed in colonies on the grounds of remote coastal areas, lining their nests with beach wrack. They also build stick nests in trees along inland waterways.

The Atlantic coast population breeds from northern Massachusetts to the northern Canadian coast. In November and December they migrate, wintering from Long Island south to the Gulf coast.

Shorebirds

Wading Birds

Waterfowl

Birds of Prey

Marsh Birds

Coming soon!

Copyright © 2006 Barbara Driscoll.