Home & Garden Columns

Forster’s Terns, Food Webs, And Flameproof Pajamas

By Joe Eaton, Special to the Planet
Tuesday August 15, 2006

Hovering over the shallows in search of a fish, the Forster’s tern embodies grace and elegance. Its long, pointed wings and forked tail combine aerodynamic function and esthetic appeal. John Reinhold Forster did not deserve this bird. 

Forster was one of the naturalists on board the Resolution during Cook’s second Pacific voyage in the 1770s. The botanist Joseph Banks, who had accompanied Cook on the Endeavour, had planned a repeat trip, but Cook couldn’t accommodate Banks in the style to which he felt entitled, and Banks called it off. A mutual friend recommended Forster as a substitute, and he joined the expedition with his 17-year-old son George.  

The elder Forster was a Prussian minister who had lost his church and attempted to make a secular living first in Russia, then in England by publishing pamphlets on zoology and botany. Cook could have used a Darwin or a Huxley, but that wasn’t what he got.  

Cook’s biographer J. C. Beaglehole describes Forster as “dogmatic, humourless, suspicious, censorious, pretentious, contentious, demanding.” He didn’t get on with Cook, who once had to throw him out of his cabin; with Cook’s lieutenant Charles Clerke, who threatened him with arrest; with the master’s mate, who knocked him down on one occasion; or with the crew. Forster was always muttering about complaining to the King; the men mocked him. 

George Forster, on the other hand, seems to have been a nice guy, perhaps trying to compensate for his difficult father. But it was the father after whom Thomas Nuttall named the tern, in recognition of John Forster’s treatise on the birds of Hudson Bay, which, as far as I can tell, Forster had never visited.  

The tern has another dubious distinction that’s a bit more serious than being named for an unpleasant man. Forster’s terns in San Francisco Bay have been found to have higher levels of polybrominated diphenyl ethers—PDBEs—in their tissues than any other wildlife species sampled, anywhere in the world.  

PDBEs have been in use as chemical flame retardants for about 30 years. They’re in children’s pajamas, computers, hair driers, coffee makers, building materials, and polyurethane foam carpet padding.  

The North American market demand for the stuff in 2001 was 33,100 metric tons. California’s flame retardant standards are the strictest in the US, and the state presumably leads the nation in PDBE use. Health effects are still being explored, but PDBEs appear to harm the brain and reproductive organs during development, and have been shown to disrupt the thyroid and estrogen hormone systems in rodents. 

Like other problematic chemicals, PDBEs bioaccumulate in fatty tissues, and biomagnify. Tiny planktonic creatures take in small quantities, fish eat the plankton, birds, marine mammals, and humans eat the fish, and PDBE levels increase as you go up the food web. By the time you get to the Forster’s tern, the concentration, as measured in tern eggs, is 63 parts per million. That tops the previous record holder, the peregrine falcon, with 39 ppm. 

The tern’s diet has not been studied as intensively as that of the endangered California least tern and the larger Caspian tern, which has an unfortunate taste for salmon and steelhead. One study in Monterey Bay found shiner perch, anchovy, and arrow goby to be the predominant prey species. All three are abundant in San Francisco Bay. 

How do PDBEs get into the bay? Municipal wastewater appears to be a major source. Landfill leaching, storm drains, and industrial effluent discharges also contribute. PDBEs are likely to be with us for a while, joining the array of what pollution-control folks call “legacy pollutants.” So far, concentrations are highest in the lower South Bay. 

That’s also the part of the Bay that has historically had the largest Forster’s tern nesting colonies. (History in this instance goes only as far back as 1948, when the terns were first detected breeding inside the bay. They had previously nested in freshwater marshes in the Central Valley and on the Modoc Plateau.) The birds’ numbers have declined in recent years, and various culprits have been suggested: disruption of nest sites by California gulls, whose population has burgeoned; predation by introduced red foxes and feral cats; fluctuating water levels within the South Bay salt ponds; disturbance during levee maintenance. But since PDBEs are hormone disruptors, you have to wonder if the terns’ chemical load is affecting their reproductive success. 

This isn’t just about the birds, of course. The researchers—toxicologist Jianwen She and colleagues—who reported the elevated PDBE concentrations in tern eggs had another disturbing finding: women in the Bay Area have some of the highest PDBE levels ever reported in humans. I am reluctant to drag that overworked canary through the coal mine one more time, but it does serve to reinforce that we’re all in this together. 




Photograph by Ron Sullivan 

What’s in that fish? A young Forster’s tern (left) accepts dinner from its parent.