Glacier Bay National Park & PreservePage 50 of 97
How seabirds live in Glacier Bay: colonies, diving and a salt-shedding body
Seabirds can live 20 to 60 years, yet they breed late and raise few young. Glacier Bay is an important nesting place in particular for murres, alcids, guillemots and puffins, and the National Park Service explains how these birds make a living on cold, salty water.
A group of murres in the park. NPS photo.
People and seabirds
The relationship is long and varied. Early seafarers watched seabirds to find land. Alaska's Native peoples relied on them too, telling time by the birds' movements and using parts of them for food, clothing and decoration. Seabirds appear in Native stories and on totem poles, have long been a source of food for travelers and hunters, and have told fishermen where a good catch might be.
Colonies and breeding
Seabirds are colonial, but only to breed: non-breeders group together only when a predator threatens. Colonies are typically dense and sit on cliff ledges, on isolated islands such as South Marble Island, in trees and in underground burrows. Compared with other birds, seabirds breed later in life and have fewer young, on whom they spend a great deal of time. Most have one clutch a year, hatched in late June, and both parents care for the hatchlings, sometimes for as long as six months. After the season, many species migrate, some across immense distances.
Feeding
Seabirds eat krill, squid and small fish, but not all feed alike. Some feed in flight, some while swimming. Some take food from the surface, using the turbulence and bounty of tidal currents. Others dive, in styles that differ by species. Still others steal food from other birds or eat what they leave.
Pigeon guillemots on a buoy. NPS photo.
Built for the sea
| Problem | Adaptation |
|---|---|
| Swallowing seawater while eating and drinking | A desalination system and special glands that remove salt |
| Catching different food | Bills suited to the feeding style: filters, hooks, or a longer lower mandible in skimmers, which eat without landing |
| Predators | Drab color and sometimes countershading (dark on top, light below) |
| Staying dry | Oil from the base of the tail, spread when preening |
| Cold | Many more feathers than most birds, with heavy down underneath |
| Swimming | Legs set farther back on the body; heavy bones in diving species, which lessens buoyancy |
| Diving | More blood for their body weight, which stores oxygen in the muscles |
| Flying and feeding | Shorter wings in diving birds, much longer wings in birds that live solely on the ocean |
Threats
Many seabirds die in fishermen's drift gill nets, and oil pollution can keep them from flying. Toxins and other pollutants have taken a toll. Overfishing has led some species to change what they eat, while others breed less and decline. The source calls the largest threat the human introduction of exotic species into their habitat, especially foxes, and also cats and rats.
Sources
- National Park Service, Glacier Bay National Park & Preserve, "Seabirds in Glacier Bay" (https://www.nps.gov/articles/glba-seabirds.htm); rewritten in hubnx's own words.