Bald eagle numbers are soaring across America. Here’s where

The bald eagle was on the brink of extinction in the second half of the 20th century, but for decades its population has rebounded thanks to one of the most successful conservation efforts in history.

Recent data collected in New Jersey revealed that the state’s eagle population is reaching new heights: Nearly 250 active nests were identified last year.

This is more than double the number counted a decade earlier, and in stark contrast to 1970, when the state had just a pair of breeding eagles.

Throughout the 1970s there were fewer than 1,000 breeding pairs in the US, mostly due to the prevalence of a toxic pesticide, DDT, which thinned the shell of their eggs and reduced the probability of hatching.

But after a federal ban on DDT was imposed in 1972, the eagle population experienced a gradual resurgence. And in 2007, the government was finally able to remove the bald eagle from its endangered species list.

According to the most recent national count, conducted by the US Fish and Wildlife Service in 2021, there are now more than 315,000 individual bald eagles in the US.

Tom Wittig, the US Fish and Wildlife Service’s eagle coordinator for the Northeast, said numbers are likely to rise further.

“The population has almost certainly continued to grow in the four to five years since those data were collected,” he said. “In most states, the number of nests continues to increase, which is a sign that the population is continuing to increase.”

There are several ways to measure population. Ornithologists and conservationists often like to think in terms of “breeding pairs.”

A breeding pair describes a male and female eagle pair that has begun building a nest to incubate eggs.

“Historically, there has been a lot of attention paid to the number of breading pairs because of how DDT affected eagles. We know it affected their ability to raise young, which became a major factor in their recovery,” Witttig said.

Bald eagles also have a unique migratory behavior, making it difficult to attribute populations to specific states. Therefore, monitoring of active nests is much more feasible.

‘Different populations [of bald eagle] in the United States and Canada they will have different migratory patterns,’ he said. “For birds in general, migration is driven by the availability of food. In particular climates, rivers will freeze and limit access to food.’

Bald eagles in North America are considered ‘partial’ migrants as some live ‘year-round’ in one location, while others migrate during the winter to escape those extremely cold conditions.

“Individual eagles likely have a general preference and consistent behavior, but it can vary from year to year. If you have a harsher winter, they may be more inclined to go,” he said. “Everything is a calculation, at a certain point it makes more sense to stay than to travel.”

Many migratory bald eagles breed in northern Canada during the summer before heading south to the US to avoid a cold winter with little food.

Illinois is a unique state in that it is only home to about 40 bald eagle nests, but it sees a large number of migratory birds in the winter, more than 3,000 at some times of the year.

The Midwestern states close to Canada, including Wisconsin, Ohio, Minnesota, and Michigan, are home to some of the largest numbers of breeding bald eagles.

In the northwestern states, including Oregon and Washington, there are also many nesting eagles. Florida stands out as one of the few southern states with more than 1,000 breeding pairs year-round.

While the DDT ban was partly the cause of the increase in eagle populations, conservationists took other steps to help increase their numbers.

‘The eagles were translocated from healthy populations in Alaska and Canada and the upper Midwest. As populations started to recover, some of that was attributed to these reintroduced birds,” he said.

While the bald eagle population in the US continues to increase, the trend is not expected to last indefinitely.

‘Eventually it will result in a plateau, it’s a law of ecology, but it’s hard to guess when that will happen. There is a strong case that the Chesapeake Bay and Maine are getting closer to that point,” Wittig said.

‘Bald eagles are starting to run out of real estate and have to compete with each other. Now they can reach six or seven without procreating.

That means more ‘hovering’ eagles are also taking to the skies. Those eagles fly, they migrate between states, but they don’t settle in one particular place.

“For almost the entire second half of the 20th century, any healthy adult bald eagle would probably end up reproducing,” he said. “Interestingly, we’re seeing a trend in recent years that reaching that age doesn’t guarantee that a bald eagle will be able to claim territory.”

More recently, younger adult birds are unable to establish a territory on their own and are therefore unable to breed. Some of those pairs will desperately build nests in the wrong places and at the wrong time of year.

In the most recent 2021 Fish and Wildlife Service report, the total bald eagle population was divided among several “lanes.”

We call them migratory routes. Bald eagles will almost always stick to their flight path; it’s relatively rare for a bird to move dramatically east or west,” Wittig said.

“Once in a while the bird’s compass goes bad, that’s how you get rare birds in new places,” he said.

Of the nearly 320,000 bald eagles in the lower 48 US states, around 40,000 were found to be on the westernmost ‘Pacific Flyway’, 30,000 were on the ‘Central Flyway’ just to the east. East of that is the ‘Mississippi Flyway’ with the most eagles – 160,000. Finally, on the easternmost ‘Atlantic Flyway’ there were around 85,000 birds.

The following table approximates the number of bald eagle breeding pairs in each US state, based on the latest data from different state sources: