In a perfect world, conservation would simply be a matter of identifying species at risk, passing policies to prevent harm to the organisms and their habitats, and watching their numbers rebound accordingly. Unfortunately (and in case you haven’t noticed…), ours is anything but a perfect world. The political and social squabbles about conservation are a topic that can/have/will be batted around endlessly, but nature itself presents complications as well, as a recent case in Maine illustrates.
Apparently Great cormorants (Phalacrocorax carbo_), which are not classified as endangered yet, are on the downslide in New England. The number of breeding pairs remaining in in Maine is down to less than a third of the number found there 15 in 1995. There are, as usual, multiple reasons for their decline, but apparently one significant factor is that they suffer high mortality in the claws of bald eagles (_Haliaeetus leucocephalus), which have been progressively rebounding from near-extinction several decades ago.
While bald eagles are no longer on the U.S. Endangered Species List (removed in 2007), they are covered by both the Bald and Golden Eagle Protection Act and the Migratory Bird Treaty Act, which means it is illegal to kill, period.
This is where the conundrum comes in. We have the cormorants facing serious declines. One of the key reasons their populations in Maine are crashing is predation by eagles. Unfortunately, the cormorants lack any legal protection, but the eagles-which have had increasingly healthy populations for years now-are covered under multiple articles protective legislation, and are essentially untouchable. What to do?
This isn’t the first time that successful eagle conservation has caused problems. Years ago, studies showed that golden eagles (Aquila chrysaetos_) were causing massive declines in the populations of island foxes (_Urocyon littoralis) in the Channel Islands. The foxes faced extinction, but there was almost no way to control the populations of eagles on the islands. Again, what to do?
It should be noted that the eagles are not the villains in these stories. In both cases, the eagles were forced to change their typical hunting strategies due to human disturbances. Bald eagles are fish specialists, but the coasts of New England have become so over-harvested that the birds cannot find enough fish to sustain themselves, and must resort to preying on other birds.
Golden eagles are more likely to prey on mammals, but historically did not inhabit the Channel Islands in large numbers, until humans introduced pigs to the islands. The eagles moved in shortly after, and populations grew up around the tasty supply of pork. Once the birds had exhausted the pig supply, they had become established in breeding territories, and so instead of leaving the islands, they switched to foxes as their primary food source.
In the Channel Islands case, human intervention was required. Instead of killing the eagles, translocation efforts were made, and golden eagles were shifted from the islands to the mainland. At the same time, bald eagles were moved from mainland to the islands, to restore the original ecological balance. (Bald eagles used to inhabit the islands, until DDT pollution caused massive declines in the mid-20th century). Baldies are fish specialists, so pressure on foxes was relieved while maintaining a healthy population of raptors.
The recent bald eagle situation is trickier, though. It is not limited to Maine: there are reports of eagles decimating seabird populations in Alaska, consuming blue heron chicks in the midwest, and ransacking flocks of waterfowl on their migratory routes. On the surface, this may seem like a Big Bad Bird issue, with the eagles gaining numbers and bullying other species. Brad Allen, who works with the Main Department of Inland Fisheries and Wildlife, has said “They’re like thugs. They’re like gang members.” In reality, though, it’s about the fish. Most of our conservation legislation covers habitat and the organisms themselves, but all species are parts of complex webs of interactions within their ecosystems, and effective conservation involves their prey base, their predators, their prey base’s resources, on and on . . . in nature, the multitude of connections makes it very hard to know quite where to draw a line around what should (or, more importantly, what can) be covered by a program.
For example, the eagles in Alaska are killing seabirds because fish populations are dropping due to disappearing kelp beds. Kelp forests are decreasing due to over predation by sea urchins. Urchin populations are growing due to decreasing predation by sea otters, which are facing severe declines due to increasing populations of orca whales. So, more whales means more eagles, which means less seabirds. Orcas and eagles must be the criminals, should we just cull them and let everyone else recover? And open up all kinds of loop holes for people of questionable intentions to start killing whales and eagles? My head is starting to hurt, how about yours?
The unfortunate reality about conservation is that, well, it exists in reality. This means that hard decisions must be made and compromises are unavoidable. One of the take-home messages about the cases above is that it is much, much harder to restore a system once it is out of whack than it is to simply not let it become profoundly disturbed in the first place. That, however, would require both foresight, concern, and proactive problem solving from many different aspects of the government, economy, and society….
Further reading:
Bald eagles running off bird populations
Reisewitz, S. E., J. A. Estes, and C. A. Simenstad. 2006. Indirect food web interactions: sea otters and kelp forest fishes in the Aleutian archipelago. Oecologia 623-631.
Roemer, G. W., c. J. Donlan, and F. Courchamps. 2002. Golden eagles, feral pigs, and insular carnivores: how exotic species turn native predators into prey. PNAS 99: 791-796.
