Sitting on a California beach, you see a flock of birds flying just above the cresting waves in perfect V-formation. As they scan the waters below for fish, the leader glides upward, then turns and dives into the surf below. In quick succession, the rest of the flock shoots into the water, resurfacing moments later.

In what might have been an uncommon sight only a few decades ago, these birds, the California subspecies of the brown pelican (Pelecanus occidentalis californicus), have recovered from the brink of extinction.

Their success story is tied to the life and work of one of nature’s most passionate protectors, biologist Rachel Carson.

In the 1940s and 1950s, scientists thought they had finally found the solution to one of the biggest problems to plague humanity—mosquitoes. The insect with the incessant buzz does more than just annoy you and leave the occasional itchy red bump on your arm. Mosquitoes and other insects carry diseases, including malaria, that cripple and kill thousands of people every year. Other insects kill crops and devastate agricultural yields. Chemical advances in the early 20th century provided new and powerful insecticides to battle against these pests.

One insecticide widely used on everything from forests to parks, beaches to bedrooms, was DDT (dichlorodiphenyltrichloroethane). DDT was purported to be safe, without any side effects. Over time, this was shown to be untrue. DDT bioaccumulates, or builds up, in the fatty tissues of creatures that come into contact with it, either in their environment or their food.

As it progresses up the food chain, DDT biomagnifies, resulting in higher predators having greater amounts of the chemical in their tissues. In birds in particular, this biomagnification had dire consequences. It caused a thinning of their eggshells. Parent birds crushed their eggs while incubating them.

The loss of songbirds and other species was brought to the attention of Carson, who had worked for the U.S. Fish and Wildlife Service. She was upset about this phenomenon and motivated to inform the public about what was happening to our wildlife.

With the 1962 publication of Carson’s book Silent Spring, the issue of thinning eggshells and the loss of birds was brought to the attention of the public in a major way.

By this time, however, the populations of many species had already been drastically reduced. Due to biomagnification, top predatory birds like hawks, eagles, and pelicans were devastated. The brown pelican was becoming increasingly rare throughout its North American range.

Larry Schweiger, the president and CEO of the National Wildlife Federation, believes Carson’s work was a turning point for birds, including the brown pelican.

“My personal view is that Rachel Carson's book really woke up the public to what scientists had been saying for some time, and that was the decline of certain bird species including the California brown pelican,” he says.

Schweiger says Silent Spring helped influence the creation of the Environmental Protection Agency in 1970, the Endangered Species Act in 1973, and the ban on DDT in 1972. The Endangered Species Act ordered the creation of a Species Recovery Plan and extreme protection of any species listed. The brown pelican was one of the first species to be protected.

“What [Carson] did do was she sparked an awakening that swept across America, and that awakening triggered an upwelling that really took several years after her death [in 1964] to come to fruition,” Schweiger says.

As a result of the DDT ban, careful species management, and protection, the brown pelican has recovered. In 2009, the U.S. Fish and Wildlife Service removed the brown pelican from the federal list of endangered species, and the California Fish and Game Commission removed the subspecies from the state’s list.

Today, the U.S. Fish and Wildlife Service estimates that 650,000 brown pelicans exist globally, and a healthy breeding population of more than 140,000 birds thrives along the Pacific coast.