"The flight of the Brown Pelican, though to appearance heavy, is remarkably well sustained, that bird being able not only to remain many hours at a time on wing, but also to mount to a great height in the air to perform its beautiful evolutions. Their ordinary manner of proceeding, either when single or in flocks, is by easy flappings and sailings alternating at distances of from twenty to thirty yards, when they glide along with great speed. They move in an undulated line, passing at one time high, at another low, over the water or land, for they do not deviate from their course on coming upon a key or a point of land. When the waves run high, you may see them "troughing," as the sailors say, or directing their course along the hollows. While on wing they draw in their head between their shoulders, stretch out their broad webbed feet to their whole extent, and proceed in perfect silence."
Brown pelicans fly in formation as the sun peeks through dense fog, San Francisco
Passage of the Migratory Bird Treaty Act in 1918 curtailed these forms of collection. Yet surveys conducted in 1970 showed that brown pelicans had all but disappeared from California. Only a small nesting population remained on one of the Channel Islands, off the coast near Ventura. The birds' killer this time was almost invisible—carried on the wind and in water, hidden in the tissues of fish which the pelicans consumed. It was dichlorodiphenyl-trichloroethane—better known as DDT.
First synthesized in 1873, DDT was virtually forgotten until the 1930s when Swiss chemist Paul Müller discovered its effectiveness as an insecticide. In World War II DDT was applied to protect Allied troops from diseases spread by mosquitoes and lice. Dr. Müller won the Nobel Prize in Chemistry for his work, which was seen as a life-saving advancement in the fight against insect-borne diseases. After the war, and through the 1960s, DDT was widely used in agriculture and advertised as a safe treatment for household pests. Human health risks from the chemical were not immediately apparent, but evidence of environmental hazards soon began to mount. DDT has a long life in the environment, as do the products of its chemical breakdown, DDE and DDD. These chlorinated hydrocarbon chemicals move up the food chain from microscopic organisms to fish and thus to pelicans and other piscivorous birds. They accumulate in fatty tissues over time, so that larger and longer-lived animals—such as pelicans—accumulate proportionately greater chemical loads than smaller, shorter-lived species. Humans are also affected by this process, called biomagnification.
Biologist Rachel Carson reported the effects of DDT in her ground-breaking book, Silent Spring, published in 1962. She wrote about the sudden decline among populations of American robins and other ground-feeding birds after DDT was used to treat Dutch elm disease in many communities during the 1950s. Direct exposure to the insecticide caused many of these small birds to die immediately. But Carson was also concerned about long-term effects. She noted that for many years DDT had been sprayed along the Atlantic coast to combat marsh mosquitoes, and knew the effects on marine species, and reported the situation in Silent Spring:
"Fishes and crabs were killed in enormous numbers. Laboratory analyses of their tissues revealed high concentrations of DDT—as much as 46 parts per million."
Carson knew that fish make up a significant part of the bald eagle's diet, and extrapolated that by virtue of their long lifespan eagles and other fish-eating birds would store proportionately larger concentrations of DDT than small, shorter-lived marine animals. As a consequence, she wrote, "they are less and less able to produce young and to preserve the continuity of their race. (Carson 122)" Declines in the rate of bald eagle reproduction had already been observed. Carson felt certain DDT was to blame, though she could not explain how the chemical caused physiological damage.
Research in the late 1960s revealed the mechanism by which DDT affects bird reproduction. Calcium carbonate is the primary mineral component of eggshells, and serves as a crucial source of calcium for embryonic skeletal development. Calcium carbonate is secreted by the bird's shell glands during egg formation. It is apparently blocked by the presence of DDE, a chemical that results from the metabolic breakdown of DDT. By the late 1960s, brown pelicans nationwide produced eggshells that were, on average, 20 percent thinner than in years prior to DDT use. Some populations of California brown pelicans were found to have shells only half as thick as normal. Brown pelicans build a stick nest on the ground or in a tree. The male and female of each pair take turns on nest duty, sitting on the edge of the platform and incubating the eggs beneath large, webbed feet. DDE-thinned eggs were delicate and susceptible to cracking under pressure, making pelican reproduction an abysmal failure.
Brown pelicans might have gone the way of their ancient dinosaurian kin. But thanks to a 1972 ban on DDT and protections under the U.S. Endangered Species Act, extinction of the species was averted. The intervening decades have seen a slow but sustainable recovery of brown pelican populations, significant enough to lead the U.S. Fish and Wildlife Service in 2008 to propose delisting of all brown pelican populations from the Endangered Species list. That process was finalized on 17 November 2009.
On your next visit to San Francisco, tear your eyes from that big, beautiful bridge for just a few minutes. Watch instead the narrow valleys between cresting whitecaps, and look to the sky at hilltop level. Better yet, wend your way westward and south through city neighborhoods to China Beach, Lands End, or Fort Funston. It won't be long before an undulating line of pelicans drifts in, skimming silently across the water or plunging-and-plundering in search of fish. Don't be embarrassed if your heart starts to beat a little faster. It's appropriate to be thrilled when you witness a miracle.