Notes from the field: The Illusion of abundance

The surviving chick in Box 18 is only a couple of weeks old so it is still soft with down, but its legs are strong, and when I remove the nest box’s cover it wedges itself into a corner, peering up at me. I reach in and pick it up. It peeps in protest before hunkering down in the crook of my arm. I reach for the calipers so I can measure its various parts—its bill, its wing, its foot.

The chick is a pigeon guillemot; the nest box it considers home is on Protection Island National Wildlife Refuge, in the Strait of Juan de Fuca off the northern coast of the Olympic Peninsula. Bird and box are part of a study led by Sarah Converse, a biologist at the University of Washington, and Liam Pendleton, her graduate student. (For my part I’m something of a collaborator, in an academic sense.)

Last spring, Converse and Pendleton, along with colleagues from the U.S. Fish and Wildlife Service and the Washington Department of Fish and Wildlife, put out nearly four dozen nest boxes along the island’s northern shores. Their aim is to follow the guillemots that occupied the boxes. For the past several months they have noted how often those guillemots are seen, where they are foraging for fish, the growth rates of their chicks, and whether those chicks survive to fledge. All of this will help Converse and Pendleton build models that not only describe a bevy of guillemot vital rates, but also look at how these rates relate to environmental factors, and so on.

Converse was drawn to guillemots in part because they are relatively easy to work with, rather than they require managers’ urgent attentions. Among the several seabirds that breed at Protection Island and in the Salish Sea more generally, the pigeon guillemot is thought to be doing pretty well. A small auk with a black body and bright red bill and feet, it is widespread in the Salish Sea region. As such it is not listed as a species at risk in Washington, although there is the caveat that the state’s population has “probably declined” even as it is “not well known”; at the federal level, the U.S. Fish and Wildlife Service considers the guillemot to be of Moderate Risk; globally, the International Union for Conservation of Nature, or IUCN, has its status as one of Least Concern—the most relaxed designation.

This seeming security, however, is all the more reason to look closely at species that people might feel they do not have to fret over. The question of the best way to assess a population is durably thorny, especially as traditional methods are found more and more to be wanting in potentially troublesome ways. A recent study of endangered Tristan albatrosses, on which Converse was a co-author, showed that, while the numbers at the species’ main breeding site were outwardly steady, the overall population was likely declining sharply. This was because the dynamics of the portion of the population most closely observed—the adult albatrosses at the colony—were not representative of the population as a whole. Count only the breeders, as most researchers do because it is easier, and you can be fooled into thinking everything is fine. But build a model that incorporates not only the breeders but also survival and breeding success rates, while also accounting for all the albatrosses that might not be present at a breeding colony—juveniles, adults taking the year off, whatever—and suddenly the picture becomes a lot less rosy.

So: Appearances can be deceiving. Stability can be just as much of an illusion as putative abundance. Rare animals might be even rarer than we think. True enough. Thankfully, though, the albatross study did not rest on a glum message of cryptic loss. Eradicate invasive mice from the colony, and according to the model, the albatrosses’ prospects would improve markedly. There were steps people could take to help, in other words. With other seabirds it might not be so easy, what with climate change and all of its effects on things more difficult to manage. But I tried not to dwell on that as I finished taking the guillemot chick’s vitals, put it back in its box, and replaced the cover. Sometimes the most you can give something is your attention.