18 June, 2000
18 June 2000
Seabird Reproduction - Different Strokes For Different Folks
Today we are on our way back to the ice. We left Nuuk, Greenland this morning and should arrive at our next test site location sometime tomorrow afternoon. Next up is a test of the dredging capabilities of the shipís systems before we start to work on coring. While we are on our way, and waiting to get back to work, I spend a lot of time on the bridge or the foredeck looking for sea life - especially birds and mammals. Birding is something Iíve enjoyed for a long time and the arctic has many species not found elsewhere in the world. The seabirds are especially interesting to me because I spent some time studying them when I was in college. One of the things I find fascinating about them is how they solve the problem of reproducing, so today while we wait for more science to get underway here, I ím going to give you a brief natural history lesson in seabird breeding ecology.
Seabirds are so well adapted for living out on the oceanís waters that they could spend their entire lives out at sea if it werenít for the problem of where to lay eggs. So, the only time many of them return to land is to reproduce. However, different birds solve the challenges of reproducing on land in different ways. Letís focus on three somewhat representative birds - Black-legged Kittiwakes, Common Puffins, and Thick-billed Murres. These species are found in the arctic, but the first two can also be found farther south.
Black-legged Kittiwakes (Rissa tridactyla) are small gulls that feed primarily on fish. When they reproduce, they build a nest of plant matter, mud, and their own droppings, on the edges of steep cliffs. A breeding pair will takes turns incubating the one to three eggs the female laid until they hatch. If a predator, like a large gull or raven, comes near, all the adults will fly out and chase it off. The chicks are born with a fuzzy coat of down to keep them warm, and the parents take turns watching them and bringing them food. Food brought back to the nest is regurgitated by the adult, then the chicks battle over their fish dinner. In years where limited food is available, the older and bigger chicks survive, while the smaller ones end up starving. It doesnít take long for the chicks to grow big enough to fly on their own, then off to sea they go.
Common puffins (Fratercula arctica) do things a little bit differently. Puffins have short stubby wings that prevent the acrobatic flight seen in kittiwakes. They protect their eggs from predators by laying them in holes in the cliff or ground. They are unable to fill up their gut and regurgitate like kittiwakes, but they are able to catch several fish at a time in their colorful bills. They take turns doing this while incubating and then feeding their downy covered young, but once the chick gets to a certain size, they both begin collecting food for it. While both parents are out, the chick is safe back inside its little hole. Once the chick is grown enough to fly, it heads out to sea for the food.
Thick-billed Murres (Uria lomvia), are known in Europe as Brunnichís Guillemot, and are similar to puffins, but have a straight, black bill. These birds have yet another variation on the strategy of reproducing on ocean-side cliffs. Murres also breed in pairs and the female lays a single egg which they take turns incubating. The egg is laid directly on ledges on the cliffs and pairs literally breed side by side. There may hundreds on a ledge, or even thousands on top of a large rock projecting out of the sea. They are not proficient fliers and like puffins, are unable to mob predators the way that kittiwakes do. Unlike puffins, they only bring back one fish at a time to their young, and one adult usually stays with the chick to protect it from predators and the harsh arctic winds. The murres solve the problem of being able to bring a limited amount of food to the young by bringing their young to the food. Murre chicks leave the cliffs long before they are capable of flying. They simply jump off the cliff, encouraged by a parent, to the sea below where they head offshore with the adults to dine a little closer to the food source.
As you can see, each species of seabird has its own solution to coming back to land for reproduction. Each is well suited for the strategy it uses and they obviously work because each of the species is present in abundance throughout the waters of the arctic realm. If you are looking for more information about birds, try visiting your local library and looking at field guides or books on the natural history of birds.
(Illustrations from ďGreenlands dyr og planterĒ by Benny Gensbol and Carl Christian Tofte)
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