Diagnosing the Endangered Murrelet

The ESA blog posted a thoughtful contribution about the philosophy of and a possible solution to "diagnosing" the ecology of endangered species, the author presenting his own work with the endangered Marbled Murrelet as an example:

It's a simple question that I often get asked about an endangered species: "What caused it to decline?" but I find it to be one of the hardest to answer without giving a hand-waiving response. Determining causes of decline for a species based on data-driven conclusions rather than informed opinion is challenging because it first requires figuring out which demographic rate is depressed and then requires evidence linking it to one or more causes. Yet, to provide clear recommendations for recovering a threatened species, is there any more meaningful question to answer than what is causing it to decline?

I like to use an analogy with medicine to understand how ecologists can produce credible evidence to begin to diagnose the cause of population decline. Demographic rates are basic measures of population health for a declining population. Estimating demographic rates is equivalent to taking the temperature and blood pressure of a patient. Deviations from "healthy" birth and survival rates are symptoms that inform us how forces causing population declines are acting.

Unlike medicine, ecologists have no set of established reference points for healthy demographic rates for threatened species that have no thriving populations. Until about 30 years ago, systematic studies of the birth and death rates of wildlife species were rare. That changed after 1972 with the passage of the Endangered Species Act, which required biologists to assess a species' risk of extinction. It would be incredibly useful if we could turn back the hands of time and estimate demographic rates for species when their populations were presumably healthy.

We tried to do exactly that in our paper ( Ecology 88:296-305) by using age ratios of museum specimens collected 100 years ago to reconstruct rates of reproduction and survival for the Marbled Murrelet (Brachyramphus marmoratus), an endangered seabird that flies inland to lay its single egg in depressions on mossy, platform-like limbs 50-120 m above the ground in old growth forests of the Pacific Northwest, Canada and Alaska.

The entire post is definitely worth a read. You can watch a short clip about the dangerous lives of Murrelet chicks here.