By Matthew Cimitile and Aaron Dalley
They soar over coastlines, rural countryside and lakes in search of prey. They rear their young in pine trees and manmade structures in parks or urban neighborhoods. They are a national treasure often seen soaring the skies over the Tampa Bay region, particularly during the fall and winter months when they nest here.
Once on the endangered species list, the bald eagle has made a remarkable comeback both nationally and in Florida. In 1973, there were 88 eagle nests across the entire state. Last year, more than 1,300 active nests were counted in Florida, making it the nation’s third-largest concentration of bald eagles behind only Alaska and Minnesota.
The state’s long coastline and abundance of lakes make it prime habitat for the raptor, said Ulgonda Kirkpatrick, an eagle biologist with the U.S. Fish and Wildlife Service (FWS). “All that water makes for a lot of really good foraging areas and we have a fair amount of habitat for nesting.”
Water is critical to bald eagles, adds Michelle van Deventer, bald eagle management coordinator for Florida Fish and Wildlife Conservation Commission (FWC). “Most bald eagle nests in Florida are within 1.8 miles of water, so an area like Tampa Bay has the appropriate habitat for eagles.”
The FWC’s Eagle Nest Locator (https://public.myfwc.com/FWRI/EagleNests/nestlocator.aspx) website finds nearly 100 nesting sites within a 25-mile radius of downtown Tampa. While those numbers are probably significantly lower than they were before World War II, they’re considerably higher than some people may have ever expected to see them.
The American bald eagle plays a central role in our country’s history. Upon declaring the bald eagle America’s symbol in 1782, the Second Continental Congress cited the bird’s power, bravery, and perseverance as worthy
attributes to represent the new nation. (Famously, Ben Franklin saw the eagle as an animal with “bad morale character,” favoring the turkey as the nation’s symbol.)
Once numbering in the hundreds of thousands, eagle populations began to dwindle as the fledgling United States grew. Their preferred habitat – forests located near waterways and coastlines – appealed to settlers hungry for land. As large tracts of forests were converted to farmland, populations of waterfowl, shorebirds, and other animals the eagles hunted also plummeted. Eagles also had to contend with direct assault from hunters and farmers, who considered them a threat to their livestock.
By the mid 1950s, a hidden but deadlier adversary emerged for the bald eagle: dichlorodiphenyltrichloroethane, more commonly known as DDT. The pesticide, seen as a miracle cure for insect control, was extremely effective at protecting crops and killing mosquitoes. However, it also seeped into nearby water, infiltrating the food chain and eventually bioaccumulating in the fat tissues of fish and other animals. As top predators, eagles consumed high levels of toxins from the bodies of their prey.
DDT was in widespread use throughout the 1940s and 50s on farms, in coastal wetlands, even in neighborhoods. “When I was a kid growing up you bought powdered DDT to spread around the foundation of your house to keep bugs out, and you used to run behind fogging trucks that were spraying for mosquitoes to cool you down in the summer heat,” recalls Gabe Vargo, a professor emeritus of biological oceanography at the University of South Florida College of Marine Science and head of the birds of prey aviary at Boyd Hill Nature Center in St. Petersburg.
Raptor populations, including bald eagles, were declining rapidly – bad news for both the birds and the ecosystems where they lived. “As top predators, raptors are sentinel organisms,” said Vargo. “When they are not doing well ecologically, then there is usually something wrong with the larger environment. Their role in the ecosystem is to maintain populations of organisms below them in the food chain at reasonable levels and maintain a healthy prey population by easily removing sick or weak individuals that may carry disease.”
The far-reaching impact of DDT was largely unknown so scientists were both alarmed and puzzled by the declining numbers. The effects of DDT and decades of habitat loss and predation struck home when the U.S. Fish and Wildlife Service estimated that there were less than 500 pairs of eagles nesting in the lower 48 states by 1963.
One of the first researchers to document the decline in eagle populations was Charles Broley, a retired Canadian banker who spent his winters in St. Petersburg. He was fascinated by raptors so a friend and member of the National Audubon Society suggested that he begin banding eagles. At the time, no one knew how many lived in the Tampa Bay region – or where they went during hot summer months.
Although his friend suggested that he hire a younger helper to climb trees to the eagle nests, Broley did it himself with a homemade rope ladder. One biographer describes the process: “He would spring, spiderlike, on a web of fragile ropes, 100 feet above the earth, until he could secure a death grip on a jungle of sticks and heave himself into a nest of protesting – and sometimes threatening – birds.”
Once in the nest, he would hold one wing down with his leg then attach an aluminum band to its left foot. Between 1939 and 1958, Broley banded well over a 1,000 eagles, making the Tampa Bay eagles the most intensively studied population in North America, according to Rachel Carson’s Silent Spring.
Broley’s annual banding revealed two important discoveries. First, young bald eagles migrated out of Florida as far north as Canada, generally not returning until they reached adulthood at the age of five. Second and more importantly, the number of eagles being banded in Florida each year was diminishing at an extremely rapid pace. At first, Broley found and banded about 150 eaglets per year. By 1958, he found only one eaglet to band within a 100-mile range and just 10 adults.
Broley concluded that that DDT was the likely culprit but he died in 1959, three years before Carson’s book was published and clearly linked the decline of our national symbol with the indiscriminate use of DDT. Carson showed that the egg shells of predators became thinner when parents were eating fish with high doses of DDT, so thin in fact, that the shells would break when their parents sat on them to keep them warm.
“By going to egg collections that were held at Smithsonian and other museums, ornithologists eventually discovered that the thickness of the current bald eagle egg shells were much thinner than what the shells had been in the past,” said Vargo.
The publication of Silent Spring, along with the dwindling numbers of raptors and the overall degradation of our ecosystems, is generally credited with spurring the modernday environmental movement. The creation of the Endangered Species Preservation Act, later expanded to the Endangered Species Act, and the banning of DDT in 1972 laid the foundation for the eagles’ recovery.
“The combination of regulations that ban DDT and smarter habitat management were key to the survival of the species,” said Kirkpatrick. “We no longer completely clear-cut forests, we regulate in a manner that protects eagles. Through greater education, we’re helping more people understand that this is both our nation’s symbol and an important species in the ecosystem.”
For many people, the bald eagle is the poster child for the Endangered Species List. That first class inducted in 1967 included charismatic animals like the Florida panther, grizzly bear and whooping crane, but listing our national symbol as an endangered species clearly illustrated the severity of the crisis.
Of the nearly 2,000 species identified as endangered, only 21 have been de-listed, indicating that populations have reached a sustainable level and they no longer need federal protection. The eagle’s remarkable resurgence was assisted by its status as the nation’s symbol, increasing awareness of its plight. And unlike other endangered species, breeding populations of bald eagles remained in Canada and Alaska and could be used to help bring back eagles to the lower 48.
“Bald eagles from Canada and Alaska were used in a captive breeding program to raise young for reintroduction throughout the nation, including Florida,” said Vargo. “Once they started reestablishing themselves, there was enough food out in the wild to support a higher population since there were so few eagles at the time.”
By 1995 the U.S. Fish and Wildlife Service changed their classification from endangered to threatened, then removed eagles from the list in 2007.
Although no longer protected as an endangered species, bald eagles still retain federal and state protections. In fact, the first government protection for bald eagles actually preceded the list by 30 years. Congress passed the Bald Eagle Protection Act in 1940 that prohibited killing, selling and possessing the species. It was later amended to include the golden eagle and remains in effect as the Bald and Golden Eagle Protection Act. Another federal law, the Migratory Bird Treaty Act, prevents the taking of migratory birds, eggs, feathers and nests.
Additionally, Florida has its own bald eagle rule that protects the state’s population, and a Bald Eagle Management Plan designed to maintain or increase the population of eagles throughout the state. The plan focuses on minimizing activity near nests to reduce potential disturbances, said van Deventer.
“The last call I received pertained to eagles nesting in a cell tower that needed to have repairs done to it,” she said. “The climber doing the repair called to see when would be the best time to conduct the work so as not to disturb the nest and our guidance was to conduct the repairs outside of the nesting season.”
FWC guidelines call for a buffer zone of 660 feet around an occupied eagle’s nest to minimize impacts. Activity outside this area is not likely to disturb the eagles. The buffer zone is critical, regulators stress, because disturbances could result in decreased productivity during breeding season. Eagles typically return to the same nest throughout their life, sometimes for 15 to 20 years, if not disturbed.
“Activities like building a new home, clearing trees, putting in a new highway or building a retention pond can be noisy and disruptive and cause eagles to abandon their nest. These activities should be delayed until outside the nesting season,” said van Deventer.
As the region continues to grow, land-use issues are likely to become more challenging.
For instance, a parcel of land with development rights for 16 homes is owned by the Morton Plant Mease Foundation in the East Lake area of St. Petersburg. Unable to sell the property to a developer due to eagles’ presence, the foundation is trying to sell the land to budget-strapped local governments as a preserve.
But it is possible to work around an active eagle’s nest, van Deventer stresses. The city of Pinellas Park had planned to demolish and rebuild a recreation center before they discovered eagles in a nearby cell tower. Working with van Deventer, the city rescheduled the construction for summer months when the eagles were not nesting. “The city was able to plan to complete the work without disturbing the eagles or needing a permit, the eagles were unaffected by the work and park goers continued to enjoy their eagle watching,” she said.
In Sarasota, eagle eggs were removed from a nest in a light fixture at the newly renovated Baltimore Orioles spring training stadium. Those eagles, however, had decided to build their nest in the midst of an ongoing construction site rather than the construction beginning after they laid their eggs, van Deventer said. “It’s the only time I’ve ever heard of eagles nesting in an ongoing construction site – usually they avoid that kind of activity.”
The goal, says Kirkpatrick, is to work with land owners to ensure that, if necessary, permits are issued for activities around eagle nests while providing for conservation of the species.
“We don't want people to be fearful of having nests on their property, thinking that they may lose their property rights,” Kirkpatrick said. “This is certainly not the case. We work with them through the permitting process to ensure that they are able to meet their land management or development needs, while minimizing impacts to eagles and avoid liability by obtaining a permit.”
Over the last three to four years eagle populations in Florida have remained relatively stable, said Vargo. “That would indicate we are at ecological carrying capacity or maximum population level.” The limiting factor, however, is appropriate nesting sites, not food, he added. Eagles in urban areas like Pinellas County nest in cell phone towers or stadium light fixtures but they’re more likely to be exposed to human-related threats, such as vehicle collision, indirect poisoning, or overly aggressive photographers and bird watchers.
Unlike ospreys, eagles prefer more covered locations than open nests on power poles – although there is a pair nesting in a man-made structure along Interstate 4 near Orlando, he said. One option that needs additional exploration might be building nesting platforms near trees that may not be strong enough to support an eagle’s nest but can still provide cover.
Across the state, about 95% of eagles nest in natural settings, but the percentage of birds nesting in man-made structures is much higher in the Tampa Bay region – probably because Pinellas County has the most dense population of humans in the state. FWC researchers are reviewing data from multiple years of statewide monitoring which may help shed light on some of the questions about eagle nesting on artificial structures.
“We know there are some issues like collisions with power lines and electrocution. There are also risks to fledglings learning to fly above concrete surfaces and busy roads, so it’s a situation we are trying to understand better,” van Deventer said.
Residents of Tampa Bay can help. Eagle Watch, a program of the Florida AudubonSociety, uses trained volunteers to help acquiredata on eagles in the state. The citizen- scientist initiative locates and observes bald eagle nests and collects information on productivity. It also fills in gaps of knowledge regarding how many eagles are nesting in Florida each year. Additionally, residents can contact the 24 hour Wildlife Alert Line at 888-430-3922 if they see any activities that may disturb eagles nesting nearby.
Matthew Cimitile is a writer working for the U.S. Geological Survey’s Coastal and Marine Science Center in St. Petersburg. Aaron Daily is a USF student interning in science communications at the USGS.