About 20 years ago an improbable avian protagonist emerged in the “War in the Woods” — the battle over whether to log or preserve the remaining old-growth forests along the Pacific Coast. A beguiling little seabird called the marbled murrelet became the new spotted owl — a flagship species and an ESA-enabled champion for forest protection.
The marbled murrelet had long been a bird of mystery: No one knew where it went to breed, and the Audubon Society famously offered a $100 reward to anyone who could find a nest. It wasn’t until 1974 that someone finally did, and science figured out the weird domestic life of these shy little birds.
Unlike other seabirds — even other murrelets — marbled murrelets don’t nest on cliffs or beaches; they fly into the forest (sometimes as much as 50 miles) and lay their solitary eggs on the wide, moss-cushioned horizontal branches on big old trees. Then each day they fly back and forth to the sea to fetch fish for baby. Like salmon, they have the bad luck of depending on not one but two very different habitats, doubling their exposure to human impacts.
Public and policy attention has however focused almost exclusively on just one of those habitats — the trees. In 1992, the State of California listed the marbled murrelet as endangered because of threats to its woodland nesting habitat. In 1993, the federal government listed it as threatened, for the same reason. Conservation groups petitioned to block timber sales for the murrelets’ sake, and logging companies had to conduct surveys and prepare plans showing they wouldn’t wreck or upset murrelet nests to get at their booty.
All noble and exemplary; anything that protects heritage forests seems like a good thing. Still, I sometimes wonder if Chinese demand for timber means logging is just displaced to much more vulnerable and biodiversity-rich tropical forests in places like Borneo. Either way, even with the curbed timber sales, the murrelets’ numbers kept declining.
The list of potential culprits in the marbled murrelet’s plight gradually grew. Oil spills hurt them as they do other seabirds and, like other birds, they get caught in fishing nets. Washington state restricted gillnetting in the 1990s to protect them.
It soon became evident that, like the spotted owl, the marbled murrelet is particularly vulnerable to opportunistic predators that thrive in altered landscapes, gaining entree when human activity opens up the forest canopy: Barred owls for the spotted owls, nest-raiding crows and Steller jays for the murrelets. In 2004, researchers reported that murrelets in Central California had plenty of good nesting branches — but they spent too much time trying to find food. For the most part, this meant they failed to breed successfully. Nest predation and lack of fish were the presumed culprits, but were hard to pin down in so elusive a species.
Nevertheless, policy-making and popular media continued to fixate on the trees as the determining survival factor. The Wikipedia article on the murrelet gives merely a passing nod to “climate-driven changes in ocean conditions” as an “additional factor” in its decline. As recently as 2005, an entire book on the marbled murrelet, Maria Mudd Ruth’s "Rare Bird," neglected that factor and the whole question of the murrelets’ food supply almost entirely.
That same year, however, scientists at UC-Berkeley published an undernoted study that answered that question in ingenious fashion. They collected breast feathers from newly captured birds and from decades-old murrelets kept skinned, stuffed and filed away like old tomes in natural history museums around the country. One of them was the University of Washington’s Burke Museum of Natural History, though it’s not mentioned in the paper that came out of the study. One of the murrelets whose feathers the Burke supplied was 130 years old.
The Berkeley team then compared the ratios of stable isotopes of two common elements, carbon and nitrogen, in the feathers. These isotopes revealed what the birds ate.
What the researchers found was impressive, and alarming. In the 19th and early 20th centuries, marbled murrelets relied heavily on sardines and anchovies — fat, fatty jumbo packages of nutrition. But the North Pacific sardine fishery, immortalized in John Steinbeck’s "Cannery Row," collapsed in the 1940s, thanks to overfishing and (at that time) cooling waters. It has yet to recover. Northern anchovy stocks also shrank — by 75 percent since 1974 alone. Market squid, another traditional murrelet staple, have also been overfished in recent years. Too many bars serving fried calamari.
The murrelets have responded as any self-respecting threatened species would — by eating what they can get. Sand lance — skinny little inshore fish that are much smaller and lower-calorie than sardines — have become a bigger and bigger part of their diet. More recently, they’ve shifted to ephausids, or krill. These fingernail-size swimming crustaceans are even less substantial. According to the Berkeley paper, it takes 80 krill to replace the calories in one average sardine and 45 to replace one anchovy. In the lingo, the murrelets are experiencing a “declining trophic level” — i.e., they’re moving down the food chain.
Even if adult murrelets can feed themselves on krill, feeding their progeny is another story. Unlike other seabirds that swallow a bunch of food, then regurgitate it back at the nest as “stomach milk,” murrelets carry their prey back whole. In "Rare Bird," Ruth marvels at the sight of a chick downing a fish nearly as long as it is.
Even the upswing in nest predation at least partly reflects the downswing in food resources. The more (or the longer) trips a nesting bird has to make to bring home the bacon, the longer she’s away, and the more chance the jays and crows have to clean out her nest.
Further research confirmed and amplified these findings. A 2007 analysis of murrelets from the Georgia Basin collected by Canadian museums over a 107-year span found that the birds’ numbers varied according to the percentage of fish, rather than krill, in their diet. Both had declined since the 1950s.
Rob Faucett, who manages the Burke Museum’s ornithology collection, sees this retrospective research as professional vindication; “a classic example of why natural history collections are important…. The only way to learn new things about past populations is by utilizing specimens that were collected and archived before the questions were asked.”
I can’t help also finding this gratifying — and, perhaps, justification for part of my own misspent youth. Instead of parking us in front of the TV, my parents would drop us off at the local university’s natural history museum, the counterpart to the Burke. Each dusty stuffed hawk and toucan seemed like an old friend. From the age of eight, I assembled my own cabinet of curiosities, saving wings and feathers from every bird that hit a window, gathering nests and unhatched eggs (after the season) from the surrounding woods and swamps, and labeling each by species. Maybe I should have stuck at it.
But where it counts, in the wide, wild world, this tale of archival discovery is unsettling. It shows that, while saving the forests may be necessary to saving the murrelet (as well as desirable for many other reasons), it won’t be sufficient. It suggests that, though they don’t live so close to the nutritional edge as the murrelets and so aren’t showing so much stress yet, other seabirds may also be moving down the food chain, switching to less-sustaining forage as fish stocks decline.
And it reminds us once again that, as in climate change, it’s not just what happens on land that affects the fate of life there.
Update, May 14, 2013: Maria Mudd Ruth's book Rare Bird will be reissued in paperback this autumn by The Mountaineers, with an epilogue discussing the effects of crashing fisheries on the marbled murrelet.