Chicks battle to survive

Posted July 02, 2010, at 8:19 p.m.
Last modified Jan. 29, 2011, at 12:27 p.m.

It’s that time of the year — the breeding season is in full swing and young birds are appearing everywhere.

Eider ducks with chicks in tow have been taking advantage of our protected little cove. I first saw three hens with seven young and an additional two hens trailing this group a little more than a week ago.

It was entertaining to watch the chicks emulating the adults by diving for food. They were little more than brown fluff-balls, probably less than a week old, and still very buoyant. They had to expend extra energy to propel themselves down through the water, actually jumping clear of the surface before arcing down, as would a dolphin or porpoise. Then, up they would pop, like little corks.

Amusing, as well, was when the chicks would raise their forefronts from the water and flap their little “wings,” which at this point were still tiny, down-covered stubs. I observed the hens doing this as well, and wondered if it was simply functional or part of a ritualized behavioral pattern. Drake ducks are known to employ this move during courtship season and throughout the year, and from what I was able to glean, females may also.

Common eiders are colonial nesters, choosing offshore islands on which to lay their eggs to lessen the chances of mammalian predation. According to “The Birds of North America,” species account, females that nest together are often related, and will time their clutches so that each hatches around the same time as the others.

I was interested to learn that females are entirely on their own once they’ve selected a nest site. They build or rebuild their nests (they often use the same sites every year), and incubate their eggs without any assistance from their mates, which go off to molt at around this time. During the entire incubation period of approximately 26 days, the brooding mothers may only leave the nest to get a drink of fresh water. Sometimes they may just resort to drinking rainwater that has collected on their feathers, and they forego eating altogether, loosing almost half of their body mass by the time their chicks hatch.

The chicks are “precocial” upon hatching, fully covered with down and able to leave the nest within a day. The BNA states that chicks are able to dive and feed themselves within one hour of leaving the nest, capturing small, soft food items such as herring eggs, sandworms, and insects.

Often, hens will group together with their chicks, forming “creches.” Hens that have failed to breed or have lost their own broods for whatever reason will also join these creches as “aunts.” Unfortunately, the presence of extra adults does not lessen the chances of predation upon the chicks, according to the BNA. The group of seven chicks I saw the first day was gradually reduced to five, then three, then one—assuming this was the same group of ducks I was seeing every day. I thought they might be, as the group always had the same number of adults and always occupied the same area of the cove.

Eider duck chicks have many predators. Large gulls (such as the great black-backed gull), ravens, American crows, jaegers, and infrequently, gyrfalcons and bald eagles, will prey upon them. My first thought was that the increasing gull populations could have a devastating impact on eider chicks. However, the BNA states eider populations can withstand large gull colonies; it is only during years of low food availability and chick starvation that gull predation becomes severe.

Risk of predation also increases with human disturbance of eider duck creches, so it is a good idea to remain at a distance if observing a group.

I haven’t seen this group of eiders for a few days. It could be they’ve moved on to another protected cove; I hope at least one of the chicks has survived.

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