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THE NATURALIST
by Dave Evans

Murrelets and Economic Theory
July 23, 2003

One of our Park dog-walkers flagged my truck down the other evening. She'd seen what looked like an injured bird in the road leading into Fort Abercrombie. We both assumed it might have been hit by a car. I went to take a look, and there, so still that it looked like a rock from a distance, was an eight-inch long mottled brown bird with a long pointed beak, luminous brown eyes, and webbed feet.

The bird followed my movements with those big brown eyes (and that sharp pointed beak). I put on heavy leather gloves, picked the bird up and put it in my truck. I remembered I'd seen a similar situation at the Park a couple of years ago. This was not an injured bird. It was a young marbled murrelet, fatigued and disoriented. Murrelets are diving birds, with legs set far back on the body. This is a fine arrangement for diving and moving rapidly underwater, but practically useless for maneuvering on flat ground. The birds fly best with a leaping start, and have great difficulty making a standing takeoff.

I released the bird at the shoreline, and was amazed to see a transformation. Tired as it was, the murrelet responded to its normal environment by diving and rocketing away underwater. It flew submerged and gracefully, rapidly beating its narrow wings and steering with its webbed feet. It sped away underwater until I lost sight of it, and I never did see it come to the surface.

The marbled murrelet feeds on small fish and other marine organisms that it actively and effectively pursues underwater. In another phase of its activity, it is tied to a rather unlikely habitat for a seabird. It nests in the moss cushioning the branches of our Sitka spruce trees. In the summer breeding season, the birds can actually be seen flying in fast circles high up in the forest, especially when light levels are low. This anomalous breeding behavior and twilight flight activity around their inaccessible nesting habitat has made the marbled murrelet the Mystery Seabird to biologists. It was only about 25 years ago that the location of their nests was discovered.

Kodiak, with its old growth moss-covered Sitka spruce forests covering rocky coastline cliffs, provides prime habitat for this somewhat rare species. Marbled murrelets are seabirds of the rain forest. My disoriented murrelet had lost both the ocean and treetop parts of its habitat, and was rendered helpless. I began wondering whether this was just a less astute individual, or whether this stranding was a fairly normal occurrence among these birds. It could represent a particularly weak link in the life cycle of all birds of this species. It would ultimately have resulted in my bird's being selected out of the murrelet gene pool. I wasn't a predator, but easily could have been.

The marbled murrelet's specialized use of dual forest and coastline habitats may be demonstrating a way in which Biology is being informed by economic theory recently. This thinking presumes that while every biological innovation may have benefits to an organism, it also has costs. Successful organisms are those that can optimize this cost/benefit ratio and go on to reproduce successfully. Their own offspring also bear the genes for cost/benefit optimization. Adaptations that emerge from this process don't necessarily need to be superb; in fact they tend to be compromises that maximize benefits and minimize costs. My young murrelet may have been an unsuccessful optimizer.

The marbled murrelet species shows this cost/benefit situation that faces a biological innovator. A predatory seabird that reproduces in the rain forest faces little competition for that way of life. It gets nesting protection from the tall trees and abundant food by its underwater oceanic flights. But this specialization comes at a cost, which is the loss of the ability to be mobile in all parts of forest environment. On the forest floor, it's one dead seabird.

David A. Evans, Naturalist, Fort Abercrombie State Historical Park


http://www.kadiak.org/naturalist/murrelets.html Updated 2003 August 20

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