Making a murderer

Soaring through the air, eyes glinting as it searches out its next meal. It’s not necessary for them to flap their wings because they’re adapted to gliding on existing wind currents, which makes for a pleasant aerial view to seek out unsuspecting prey below. It may be dramatic to call them murderers, but they would take it as a compliment. Their sharp talons are evolved to be killer weapons as they grab their prey in the head or neck, immobilizing them almost immediately. With that said, they’re not picky– they’ll take an easy kill if there is a weak or injured (or already dead) animal available. It’s a low calorie kill, after all.

Take a look at some of the key differences between our two native eagle species.

Besides their rather glorious appearance, the value of Bald Eagles extends beyond their good looks. Eagles are a keystone species– a species that has a disproportionate effect on the surrounding environment. Think of it as a rock arch. If you pull the stone at the top, the entire structure will collapse. Salmon are also keystone species, even though they fill an entirely different role in the food chain compared to eagles. One of the reasons we know they fall into this category is because of their near disappearance (we’ll get to that later). The species is considered an indicator of ecosystem health, which means their presence in an ecosystem is a mark of a healthy ecosystem. The absence of the species can spark a bit of concern for biologists, as evidenced by the challenging but worthwhile conservation battle that many of us remember. 

As one of the largest birds of prey in the country, the sight of a bald eagle in the sky is one that many people stop to observe. So when we stopped seeing eagles soaring, people quickly took notice (at least, more so than if we were talking about a species of mouse). By the 1950s, the population of bald eagles had plummeted to just over 400 nesting pairs in the continental U.S. In addition to hunting, the biggest threat to bald eagles at the time was DDT. Thanks to the Migratory Bird Act, these high flyers gained some protections, but that didn’t address the pesticide that was decimating their ability to reproduce. Once DDT was in the bird’s system, it affected the strength of the eggs that they laid– leading to high chick mortality. As we all know, reproduction is the key to a species’ success.

From building the nest to caring for the young, bald eagles are dedicated co-parents.

Wondering how DDT was making its way into eagles? Bioaccumulation is the short answer– but what is that? Essentially, it means that the pollutant concentration grew as it went up the food chain. So, if a mouse eats some corn that had DDT sprayed on it, it eats a small portion of that toxin. A bunny would eat dozens of mice, and the concentration of toxin in their body would increase accordingly. An eagle may eat a combination of mice and bunnies and, therefore, they would absorb all the toxins that came from those creatures. None of these animals are equipped to filter out this human-made pollutant, so it stays in their systems until they die (and/or get eaten by something else). 

Let’s take a look at the timeline:

For conservationists, this marked a huge win. Not only was it good for the eagle, but it showed that the listing process and following efforts were successful. Bringing back a species from the brink of extinction is not something that has been done too many times. This is one of those stories that gives us hope. If we get enough people to care and make changes, we can help at least some species rebound– species like salmon.

It’s easy to draw parallels between eagles and salmon struggles. When eagle populations declined, we (the scientific community) identified the problem, took steps to eliminate the threat, and gained enough public support to implement programs that led to the recovery of populations. Now, we have identified the leading threats to salmon, we have started the work of restoring their habitats, but we still have work to do. The “solution” isn’t quite as obvious as banning DDT, and it’s going to take public support and buy-in to remove fish passage barriers, restore habitat, protect water quality, and keep rivers pumping cold water. The further we get from a time when salmon were packed in our rivers, the harder it will be to make the changes that are needed.

Conservationists have long known that people consider the environmental conditions of their youth as “normal.” There’s even a name for this: shifting baseline syndrome. That is a dangerous precedent. If people can’t imagine a world where a species did exist (or existed at a greater frequency) then they have no motivation to solve the problem. In truth, they don’t even see it as a problem. So, while the story of eagles can give us hope, it’s also a reminder that we have to look at historic conditions and do everything we can to restore the conditions that wildlife need to survive. If not, more and more species will fall into the category that we can’t solve: extinction.