- Research & Education
- Cape Cod
Dolphin Fleet Birdwatching Notes: 30 May – 15 June 2008
John C. Conlon
Any birdwatcher knows that walking a half mile between habitats makes a difference in what we find for bird species. The same is true when making a half mile transition from land to sea. I am thus surprised when I ask who on whalewatch trips is a birdwatcher and then discover that some birdwatchers have left their birding field guides and binoculars in the car. For people even mildly interested in birds a whalewatch trip is time well spent with regular opportunities to see birds not seen locally on land.
If you are thinking of coming on a Dolphin Fleet whalewatch a guide book will get you ahead on your pelagic birding skills. For those online: www.neseabirds.com lists seabirds seen in the greater Gulf of Maine, and www.whalewatch.com, of the Dolphin Fleet has for the past two years posted records of seabird sightings from our summer trips. When you are ready to get onto the boat you might bring National Geographic’s Birds of North America, Peter Harrison’s Seabirds: An Identification Guide, or David Sibley’s Guide to Birds. You might also refer to Sibley’s Guide to Bird Behavior. These guides will help with field identifiation.
Once you are on the boat here are some hints for sea-based birdwatching. Given birds’ distance from the boat do not look for color as such but rather look for contrast; dark vs. light contrast on different areas of the body. Contrast is important because in the sea’s ambient light coloring is washed out. Also, look at proportion rather than actual size. Look for narrow vs. broad wings, proprortion and body shape forward of the wings (long vs. short neck) and aft of the wings (long tail vs. short tail or long dangling legs).
Pay attention to behavior. Northern gannets (Morus bassanus ) and Wilson’s storm petrels (Oceanites oceanicus ) are two nonconfusable but useful examples. Gannets often hover 75 or more feet above the water’s surface while Wilson’s storm petrels are rarely more than 3 to 6 feet above the surface. If you see any seabird 40 feet in the air it is likely not a Wilson’s storm petrel. Use the process of elimination to your advantage!
These behaviors help us understand the ecological niche that any species occupies. An ecological niche is that particular portion of the ecosystem that a species uses to sustain its life. Where does the bird get its food or nest? Gannets plunge dive from the air to catch schooling fish that are well beneath the surface. Diving from 50 to 75 feet or more in the air gives gannets greater speed and momentum to reach 30 foot depths. This altitude is not helpful to storm petrels that sit on or prance just above the water’s surface and pull copepods and krill from just beneath the surface. These two species thus occupy different ecological niches while staying out of the other’s way.
Over the past two weeks we are seeing our last gannets as most have headed north toward Gaspe and Newfoundland for their summer nesting season. If you are patient you may see scattered small groups of juvenile to third year gannets: first year mottled grey-brown plumage progressing to third year and on to subadult plumage of black outer wing ends, sparsely spotted white back, and white belly. If you are also patient you will see scattered individuals or small groups of Wilson’s storm petrels. They are arriving into our area for their winter (yes, their winter) nonbreeding season. Some of these 7.25 inch-long storm petrels may have arrived from as far away as coastal Antarctica to pass our summer. These two species thus not only work different ecological niches spatially in both water and air but for the most part do so during different seasons.
The most obvious thing that pelagic birds have in common is their tendancy to spend much of their life above or in sea water. Seabirds have adapted to this lifestyle. One important adaptation is that seabirds can drink seawater. They have a high body temperature and high metabolism. They need a lot of water. This is especially true of oceanic species including northern gannets. It is also true for the copepod and krill feeding birds such as Wilson’s storm petrels. Salt glands near the eye sockets excrete a heavy salt solution through the nasal area that soon drips from the bird’s beak.
The legs of seabirds are also adapted for life in sea water. Generally seabird legs are far back along the body allowing seabirds to use those legs for underwater propulsion. Thus many seabirds need long running starts to fly from the water. Sooty shearwaters are a good example. Over the past two weeks we are seeing small though growing numbers of sooty shearwaters. They are arriving for their nonbreeding season from islands off southern South America. After returning to the water’s surface from below (using their feet and wings to persue schooling fish) the shearwaters take running starts. They flap their wings hard and often slap the water while taking flight. The loons that have now left for the summer do the same. Listen to hear their wings slapping the water.
Temperature regulation is also an important aspect of seabird biology. Countercurrent circulation helps seabirds with this issue. Heat is lost through uninsulated legs. Arterial blood vessels flow close to the veins that return blood toward the heart. Arterial blood warms the blood that has lost heat through featherless legs before that cold blood reaches the heart. We must also remember that generally well oiled and tightly spaced down and contour feathers insulate most,but not all, seabird species. Indeed, feathers probably originally evolved for insulation rather than flight.
Another aid to temperature regulation is the fat layer just beneath a bird’s skin. Both pelagic birds and whales live in a watery medium that conducts heat from the body some 22 times faster than air. You get colder faster in 80 degree water than you do in 70 degree air. The need for energy stored as fat (blubber in whales) is a major reason for the evolution of fat reserves. That energy need in seabirds (and whales) changes seasonally in response to temperature, migration and reproduction requirements. While fat is not as effective an insulator as feathers it does add more protection against heat loss.