The brown pelican (Pelecanus occidentalis) is a large seabird that inhabits coastal areas in North and South America. In the 1960s and 1970s, brown pelican populations plummeted due to the effects of pesticides like DDT and dieldrin. By 1970, the brown pelican was declared endangered under the Endangered Species Conservation Act. After decades of conservation efforts, populations recovered enough that the brown pelican was removed from the endangered species list in 2009. However, there are still threats facing brown pelicans today.
What are brown pelicans?
Brown pelicans are large seabirds in the genus Pelecanus. There are seven living species of pelicans worldwide, and the brown pelican is the smallest of them. Brown pelicans live along coastlines in the Americas, ranging from the United States and Mexico down through Central America and South America to Chile and southern Brazil. They are also found in the West Indies.
Brown pelicans have a wingspan of over 7 feet wide. Their bodies are big and bulky, with a very large throat pouch that they use to capture fish. Their feathers are mostly brown, with white heads and dark bills and legs. The heads of adult pelicans turn from brown to white in the breeding season. Young pelicans start off with gray-brown plumage and gradually turn more white as they mature over the course of several years.
Brown pelicans mainly eat fish that they capture by plunge diving from the air into the water. They work together to herd small fish into compact groups before scooping them up in their throat pouches. The pouches can hold up to 3 gallons of water and fish. Once the pouch is filled, the pelican squeezes the water out before swallowing the fish. Brown pelicans also occasionally eat amphibians and crustaceans.
What caused brown pelican populations to plummet?
Brown pelican populations declined dramatically between the 1950s and 1970s due to contamination from pesticides like DDT. DDT (dichlorodiphenyltrichloroethane) was widely used at the time to control mosquitoes and agricultural pests. However, DDT and its byproducts accumulated in the environment. The chemicals worked their way up the food chain, becoming increasingly concentrated in predators. Birds that consumed contaminated fish were severely affected.
One of the effects of DDT exposure is that it interferes with birds’ calcium metabolism. The thin shells of brown pelican eggs cracked under the weight of incubating parents. Nesting success plummeted, with crushing mortality rates of 90-95% in some areas. DDT also caused birth defects and organ damage. Adult birds sickened and died. Entire colonies collapsed as reproduction failed.
In addition, the pesticide dieldrin contributed to the declines. Dieldrin was widely applied to control terrestrial insects and also accumulated in fish. The combined effects of DDT and dieldrin contamination caused brown pelican populations to crash in several states including Louisiana, Texas, and California. In 1970, the brown pelican was officially declared endangered under the Endangered Species Conservation Act.
Brown Pelican Population Trends
Year | Population Estimate |
---|---|
1950s (pre-decline) | 150,000-200,000 |
1970 (endangered) | 1,000-2,000 |
1980 | 6,500 |
1990 | 19,000 |
2009 (delisted) | 650,000 |
Why did brown pelican populations recover?
After the threats from DDT and dieldrin were recognized, bans on the use of these chemicals allowed brown pelican populations to start recovering. The use of DDT was banned in the United States in 1972. Though DDT residues persisted for years, the levels gradually declined. With less exposure, birds’ breeding success improved. Conservation programs also helped by protecting nesting colonies and rehabilitating and releasing sick birds.
By the 1980s, brown pelican numbers were increasing again, though at different rates in different parts of their range. Populations rebounded more quickly on the Atlantic and Gulf coasts, where contamination was less severe. The recovery was slower on the Pacific Coast, which had suffered the most from DDT disasters in the 1960s. Still, nesting pairs on the West Coast increased from just 150 in the 1970s to over 6,000 by 2005.
Improved breeding success and colony protection efforts allowed brown pelican populations to grow and recolonize old territories. Over several decades, numbers reached healthy levels again throughout most of their range. By 1985, brown pelicans no longer met the criteria to be listed as endangered. In 2009, with over 650,000 birds counted across North and South America, the brown pelican was finally removed from the U.S. endangered species list.
What threats do brown pelicans still face?
Though brown pelican populations have recovered significantly, there are still ongoing threats to their survival. These include:
Habitat loss
Coastal development, shoreline armoring, and disturbance of nesting islands for recreation reduces habitat available to brown pelicans. Loss of mangroves and natural shorelines removes important habitat.
Human disturbance
Brown pelicans are very sensitive to disturbance at their nesting colonies. Human activity near breeding sites may cause nest abandonment and colony failure.
Environmental contaminants
While DDT and dieldrin are now banned, brown pelicans remain vulnerable to other pesticides, oil spills, chemical pollution, and discarded fishing tackle. Contaminants get passed up the food chain and concentrated in fish-eating birds.
Climate change
Sea level rise, storms, altered fish distributions, and changes in prey availability due to climate change may all impact brown pelican populations in the future.
Incidental capture in fishing gear
Drowning in fishing nets and injuries from swallowed or entangling fishing tackle are ongoing problems, especially where fisheries operate near colonies.
To protect brown pelicans into the future, conservation efforts aim to reduce these threats. Protecting habitat, limiting human disturbance, reducing pollution, responding to climate change impacts, and modifying dangerous fishing gear can all help keep brown pelican populations healthy. Though no longer endangered, they still need continued monitoring and management.
Conclusion
Brown pelican populations crashed between the 1950s and 1970s due to reproductive failures from pesticide contamination. Widespread DDT and dieldrin use contaminated the pelicans’ fish prey. With bans on these harmful chemicals, populations recovered gradually over the following decades. Conservation efforts also helped by protecting colonies and rehabilitating sick birds. Though now delisted, brown pelicans still face threats from habitat loss, pollution, climate change, and fishing bycatch impacts. Continued management is needed to protect the recovery of this iconic coastal seabird.