Don’t Count Your Chickens Before They’re Fledged

Cooper Island, Alaska, Aug. 12, 2009 — Of all the questions people ask me about guillemots, one of the least common is “What the heck does ‘guillemot’ mean?”. This surprises me, since I would think that would be one of the first things people would wonder about the bird. It turns out that “guillemot” is the diminutive of Guillaume – the French version of “William”. But it also turns out that no one seems to know why the genus Cepphus — or in England the closely related members of the genus Uria — are called guillemots. When talking to school groups I sometimes mention that the name means “tiny bill” in French, and when compared to puffins and other alcids, guillemots do have a tiny bill. But that is certainly not how they got their name.

Diminutive guillemots have occupied my time over the past three weeks as I monitor the daily growth of the chicks. Guillemots emerge from their egg at about 35 grams and are continuously brooded by the parents for about six days. While in the nests the chicks provide a unique opportunity for study. One of the problems in studying seabirds is that they, by definition, spend much of their time at sea. Terrestrial researchers, like humans, can watch seabirds from shore or from a boat, but it is at seabird colonies, where there are lots of land-bound nestlings being fed by sea-going parents, that much seabird research is done. Studying the growth and survival of chicks can reflect local variation in the abundance and type of prey available to parent seabirds raising young. In recent decades, as short and long-term changes in marine ecosystems have become issues of concern, there has been an increasing awareness that seabirds, as “apex predators”, can be used to monitor seasonal and annual changes in marine ecosystems. This is especially true in the Arctic, where a lack of commercial fisheries and limited sampling, due to both logistical and funding issues, means that major changes can occur but go unnoticed by scientists and resource managers.

Black Guillemot parents and their nestlings have some characteristics that make them excellent monitors of prey (fish) availability. Reasons for this include:

• The limited foraging range of the species of about 25 km means there is a rather clearly delineated area being sampled. Compare this to albatross chicks being fed in Hawaii, whose parents may fly thousands of miles north to the Aleutian Islands for food.

• Parent guillemots return to the nest holding a single prey item sideways in their bill, so the type of prey being returned can be monitored by photographs or observations. Many seabirds return to the nest and regurgitate to feed their chicks, so that the prey being provided cannot be easily ascertained.

All of these characteristics have assisted in monitoring changes in prey availability in the waters off Cooper Island in recent years. Arctic cod, a high fat fish associated with cold waters, were the primary prey fed to chicks for first 25 years. There was some minor annual variation in cod availability with slower chick growth in some years but with large adult cod remaining the primary prey returned to nestlings. It was not until this century that we began to frequently see sculpin, a near shore bottom fish, being brought back to chicks in numbers later in the nestling period.

Sculpin are abundant in the near shore throughout the summer and guillemots apparently turn to them when Arctic Cod are no longer available. Sculpin are less fatty than cod and have a bony and horny head that can lodge in a chick’s throat. Some chicks appear to have a natural aversion to sculpin, letting them pile up in the nest site while waiting for an alternate prey.

Up until the last week, Arctic cod were readily available off Cooper, as evidenced both by growth rates and observations of fish, but as the last of the ice melted from just north of the island changes began to occur that I will discuss in a future post. The other factor that has become an issue this year in monitoring chick growth is the number of nests lost to polar bears and chicks killed by the horned puffins. This has reduced the sample size of chicks that can be weighed daily and parents that can be observed carrying fish.. With the late summer retreat of the pack ice, mid to late August has been the time when seasonal changes in prey have been most pronounced and this year there are fewer than normal chicks to monitor the changes in prey that will be taking place.

The reasons for the small number of active nests at this point in the breeding season are something I will discuss later this week. Suffice it to say the past ten days have demonstrated one of the shortcomings of using seabird nestlings as monitors of prey availability, in that a range of factors not directly related to guillemot prey can reduce nestling survival. Which is to say one shouldn’t buy guillemot futures in a bear market — a variation on don’t count your chickens before they’re fledged.

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