Seabirds of Stellwagen Bank: Gulls
Sunday, Jan 20 2013 07:10 PM | bird research, birdwatching, Cape Cod, Hyannis, seabirds, Stellwagen Bank National Marine Sanctuary, whale watch, whale watchers, whale watching, whales
Even as a whale watch naturalist, and an avid birdwatcher, it is still hard not to type the word seagull as this post is drafted. When we think of the big white birds that are as ubiquitous as clam shells on our Cape Cod beaches, we think seagulls.
Nicknames like rats with wings, dump ducks, picnic plunderers, whatever you call them, the family of birds we describe as gulls (Laridae) are a prominent part of our coastal land/seascape, and as the colorful names imply, they are not overly loved! We are beginning our blog series on seabirds of Stellwagen Bank National Marine Sanctuary with this important, but oft- misunderstood group of birds.
Worldwide, there are roughly 50 species of birds that we refer to as gulls. On Cape Cod whale watches we regularly encounter four species: greater black-backed gull, herring gull, ring-billed gull and laughing gull with several other species being rare or seasonal visitors.
Gulls range in size and distribution from the largest, the greater black-backed gull (body- 30 inches, wingspan- almost 5 feet), a resident top predator in the North Atlantic, down to the smallest species: the little gull (body- 10 inches, wingspan- 2 feet), which frequents shallow freshwater wetlands in Eurasia. In South America, the andean gull is a common sight along watercourses up to 14,000 ft while the near-endemic and completely nocturnal Swallow-tailed gull makes its home on the Galapagos and other remote islands. Gulls are able to populate such diverse habitats because they are opportunistic omnivores, successfully adapted to thriving at the interface of land and water.
The general form of a gull is fairly unremarkable. They have thick, stout bodies, medium necks, strong bills, short legs, webbed feet, and long tapering wings. This well proportioned body is designed for just about every type of activity. Gulls can fly, swim, and walk equally well; getting them to wherever the next meal may present itself. Their resourcefulness allows them to successfully exploit diverse food resources under a broad range of situations.
Gulls have excellent eyesight and are highly maneuverable fliers. They are excellent swimmers, though unable to dive. Gulls are able to drink both fresh and salt water. They can feed standing, swimming or flying and they will eat almost anything that is edible.
|Gulls are opportunistic feeders!|
Gulls diets include a wide range of prey. Known food items include: marine and freshwater invertebrates, terrestrial invertebrates, rodents, eggs, carrion, offal, reptiles, amphibians, other birds, seeds and fruits, human refuse and garbage. The type of food depends on circumstances and season. Food may be scouted by land, sea, or air. As scavengers, gulls play a vital role in keeping our coastline clean.
Gulls aren't above scavenging!
Gulls get their food through a variety of feeding behaviors. Gulls on the wing can swoop to pick up food, and some species will plunge-dive on prey as well. Some gull species have learned to fly above hard surfaces and drop mollusks to crack the shells. Many gull species forage on the ground walking or wading at the waters edge or at the local landfill. Since gulls can’t dive, they rely on other animals to drive the food to the surface.
On our Cape Cod whale watching trips, finding the whales is always the first order at hand. To help us do this, we are constantly scanning the water for groups of birds circling over predator/prey interactions. With their sharp eyesight, if whales are feeding, gulls are among the first birds to arrive. The gulls will scan the water for fleeing baitfish, and carefully observe the whales’ behaviors.
|Feeding humpback whales attract gull species looking for a free meal!|
Humpback whales are well known for their use of bubble traps to corral bait, and this well known to the gulls. The whale dives beneath the school of fish, and then blows clouds or columns of bubbles to corral the fish before lunging through the cover of the bubbles and taking hundreds of gallons of water and fish into its expanded lower jaw. The whale finishes by closing its mouth and filtering the fish using its baleen plates as it collapses its lower jaw tissue. While the whale is filtering at the surface, the gulls swarm in, hoping to catch wounded or fleeing baitfish. We have even seen brave (or foolish) gulls pick fish right out of the whale’s mouth!
|Brave or Foolish?|
Gulls are a whale watchers constant companion, and it pays to identify and observe the different species that live on Cape Cod. There are only 4 to learn, but knowing them and their relative sizes will make IDing more challenging groups and species of seabirds easier in the future. Building personal knowledge and appreciation for the species we encounter Stellwagen Bank can only make the future brighter for whales, dolphins and even seagulls!
Join us for our next post where we’ll meet some more seabirds!