Birds of Stellwagen: Gannets
Wednesday, Apr 3 2013 04:27 AM | Cape Cod, gannets, whale watching, bird research, Stellwagen Bank National Marine Sanctuary, birdwatching, seabirds
This week we return to our blog series on seabirds at Stellwagen Bank after a brief topical hiatus. We endeavor to introduce interested readers to soe of the birdlife we may encounter during our whale watches and to highlight their adaptations to life at sea. This week we'll look at the northern gannets.
The northern gannet is the largest seabird regularly seen on our whale watches. They belong to a bigger taxonomic family that includes their close relatives, the boobies (no, this is not sixth grade potty humor, there are birds called boobies), and pelicans. Pelicans and boobies are generally found in tropical waters, while gannets occupy the same ecological role in temperate waters.
There are three to four species recognized world-wide, but the northern gannet is the only species that breeds in the northern hemisphere . Generally found in coastal waters out to the continental shelf, northern gannets, with a wing-span of nearly seven feet, are hard to miss, but are often overlooked as oversized seagulls.
|An adult northern gannet checking out the Whale Watcher! Note the|
enormous wing-span, larger than any gull species.
A comparison in the positioning of the eyes on a a northern gannet and a herring gull highlights one of these adaptations. The eyes of the gannet are positioned far forward and together on the head giving the bird binocular vision. This helps the bird acquire moving prey, and lets it judge distances very accurately. The gannets bill also is much longer and pointier than the gull's. This hefty bill can spear or grasp larger fish species and other prey items. The gull's bill features a hooked tip for tearing off bits of flesh. Gannets don't need this as they usually swallow their prey whole!
Gannets locate their prey on patrols as high as 300 feet, by watching for the surface activity of schooling fish, and by watching other birds. Once prey is located, the bird will momentarily hover, lock onto their target, and then plunge. On the drop, the wings are tucked in toward the body and the bird plummets toward waters' surface looking much like an earthbound lawn dart!
|Northern gannet in plunge dive! |
Wings are tucked back, and neck is straight.
Photo: Michael Pennington-Wiki Commons
|The infamous lawn-dart for those|
too young to remember.
The bird may strike the water's surface at nearly a hundred miles per hour which could injure the animal if not for air-filled sacs in the tissues around the breast and neck, an adaptation which cushions the impact.
The inertia of these dives may take the bird to 30 feet below the surface allowing them to exploit fish that would be out of reach of gulls and other non-divers. Additionally, gannets can swim underwater, if not gracefully, to pursue fleeing prey to depths reported to over 50 feet.
Gannets don't interact with whales at Stellwagen Bank National Marine Sanctuary, but they are present throughout our whale watching season. At times, hundreds of gannets form enormous feeding flocks, sometimes in proximity to where whales are feeding, providing whale watchers incredible opportunities to catch the action. The following is footage shot in Canada near the largest western Atlantic breeding grounds at Gaspe' Peninsula in Quebec. It captures the thrill of witnessing such a spectacle of nature close-up!
Gannets are most commonly seen on our whale watches from the start of the season in April and May with most adults departing for their breeding grounds by mid-May. At the end of August, and through the Fall, we se returning adult gannets with dark plumaged immature birds. On your next whale watch, save a few pictures on your camera in the hope that we encounter these largest of north Atlantic seabirds! Next week we'll look into Shearwaters and Storm Petrels!