Happy news about animals
Bald eagle populations plummeted in the mid-20th Century, the result of mass poisoning by DDT, and long-term effects of human predation, harassment and development. Today, the resurgence of the Pacific Northwest bald eagle population rewards efforts of conservationists.
“From a biological standpoint, they are not an endangered species anymore, there are enough individuals for the population to maintain. The population needs a good distribution to sustain,” said Frank Isaacs, a senior faculty research assistant at Oregon State University who works with the Oregon Cooperative Fish and Wildlife Research Unit at the Department of Fisheries and Wildlife. He said bald eagles are highly adaptable, but prefer forested areas with mature trees, for habitat, which provide adequate platforms for nests and some security from the elements. Such sites, not currently supporting resident bald eagles, are still found along Oregon’s north and central coast.
A study tracking nesting populations of bald eagles was initiated in 1978, and Isaacs began work on the project in 1979. At that time, approximately 100 known nesting pairs of bald eagles remained in Oregon. Today the number of known nesting pairs in Oregon approaches 500.
Less protection for habitat will be the most dramatic consequence of delisting the species from the Endangered Species Act, said Isaacs, noting part of success during this resurgence has been concerted habitat protection. He said Oregon’s undeveloped public lands will, in theory, enable the population. Bald eagle resurgence is the result of protection measures, including banning use of the pesticide DDT in the late 60s, coupled with the momentum of population growth. Isaacs said, while suitable habitat remains, and in the absence of new poisons, it is likely the bald eagle will continue to thrive. “They’re very plastic in their ability to use different habitats and eat different kinds of food and put up with different human activities.”
Current generations haven’t been harassed or hunted by humans, as preceding generations had been. “The birds we follow nowadays seem to be a lot more tolerant of human activity than the birds were 25 years ago,” said Isaacs, “and I think that’s because of generational changes in both people and eagles. They are used to human activity, and are much more apt to nest in proximity to human activity.”
In addition to resident nesters, Isaacs explained, “Oregon is a kind of crossroads, or mixing grounds, for eagles moving up and down the western flyways: the Pacific and the inter-mountain flyways,” said Isaacs, “And birds from far north come south into Oregon during the winter. And birds from the south, such as southern California and Arizona, come north into Oregon after their nesting season.”
Isaacs said the first bird book written for Oregon was completed in the late 1800s, “and there is a mention in there of 10 pairs of bald eagles around Yaquina Bay. Today we know of about five or so. If that late 1800s report is an indication of the population of eagles before the country was settled, then we may still see an increase in eagle numbers in that area.”
David Pitkin, wildlife biologist with the Oregon Coast National Wildlife Refuges Complex, a division of the United States Fish and Wildlife Service, said the resurgence of bald eagles is taxing populations of common murres on the north and central Oregon coasts, with several effects.
Every year the FWS surveys a subset of seabird colonies, with the entire seabird population on the Oregon coast counted only periodically. In 1988 a full count showed more than 400,000 nesting murres supported on Oregon’s north and central coast colonies. Currently, a full count is being compiled for 2006. Though the data has not been quantified, Pitkin said, “we know there have been major effects by bald eagles. Our assumption is, there will be a lot fewer than 400,000 murres, in these colonies, after were are through counting.”
Pitkin explained, when an eagle goes out to a seabird colony, three things can happen, and sometimes all three:
* Direct take of seabirds on a colony; whereby an eagle seizes a murre, or two, and takes them away to eat somewhere else;
* Secondary predation of seabird colonies by gulls, ravens and crows, which come in after an eagle scatters seabirds, leaving eggs and nestlings exposed; and
* Complete abandonment of seabird colonies caused by eagles habitually perching within traditional seabird colony sites. This perching behavior is especially characteristic of young, usually non-breeding eagles. (An example of a rock abandoned by common murres is Gull Rock, off Otter Crest).
Bald eagles started to hunt common murres on Gull Rock, off Otter Crest, in the mid-90s – and have had several effects. At the time the bald eagle predation began, 15 to 30 thousand common murres nested on Colony Rock, approximately 5 miles south of Gull Rock, off Yaquina Head. Since the mid-90s, the numbers of common murres on Colony Rock have increased, and this year more than 70,000 common murres attempted to breed there. Pitkin said it is believed the increase represents common murres which abandoned Gull Rock.
“Colony Rock may be the densest murre colony in the world now,” said Pitkin, “When a murre comes into Colony Rock now, usually it has to land on top of other murres, and filter down to the rock … Like standing in a crowded elevator … there might be up to 50 murres per square meter on that rock.” On the margins Brandt’s cormorants, a bigger bird, find the nesting space they can.
An entire generation of common murres has now passed since the 50s and 60s, and the new generations are subject to an abundance of aerial predators without prior habituation. Pitkin said common murres on Colony Rock have habituated to eagles coming out and attacking directly, by scattering only nearby the snatching spot, rather than across the whole rock, as would previously have been considered commonplace. “It behooves them to do that, because every time they flee in panic, they’re open to predation from gulls, ravens and crows, around all the time and always waiting for an opportunity to go in there and steal eggs and chicks.”
Pitkin said when adult bald eagles snag their prey they typically return to feed at their nests; whereas non-breeders will remain perched in the midst of colonies to devour their kill. Bald eagles don’t perch on Colony Rock, and Pitkin said it’s been surmised the proximity of the lighthouse and attendant visitors might dissuade them.
Interestingly, where peregrine falcons have established territories, fewer eagle attacks are recorded on common murres resident of pelagic mounts therein.
“We don’t have a very good idea, along the Oregon coast, what the natural equilibrium was, between the nesting seabirds and bald eagles and human predators. We know the natives that lived along the coast used the seabird colonies as very valuable food resources,” said Pitkin, “We don’t know what those effects were, and we know before the big crash in the bald eagle population there were a heck of a lot of eagles along the coast.”
Pitkin said he would guess, interactions observed between bald eagles and common murres today, are returning toward a more historically characteristic equilibrium. Noting a lack of human predation, and the abysmal numbers of bald eagles in recent decades, Pitkin said, “My assumption is common murre numbers along the north and central Oregon coast have increased quite a bit over the last 40 or 50 years compared to what they were historically, and now they’re beginning to decline with the resurgence of natural predation by bald eagles, occurring along the north and central Oregon coast.”
Endangered Species Act
It seems likely the FWS will remove the bald eagle from the Endangered Species Act, the federal list of threatened and endangered species. It was recently announced the decision will be postponed, to be resolved no later than June 29, 2007. The FWS had been under a court ordered deadline of Feb. 16, 2007 to make a final decision on bald eagle status due to a pending lawsuit brought by Minnesota developer who had issues with a few bald eagles’ nests and sued the FWS to make a decision on whether or not to take the bird off the list. The developer cited the 1999 FWS proposal to delist the bald eagle, which was not acted upon. The court approved the extension until June 29.
The FWS reports the additional four months will be time to complete additional analyses related to the final rule and put in place management guidelines and procedures that will make it easier for the public to understand ongoing protections of the Bald and Golden Eagle Act, ensuring the bald eagle continues to thrive once delisted.
Once delisted from the Endangered Species Act, bald eagles will continue to be protected by the Bald and Golden Eagle Protection Act (BGEPA) and the Migratory Bird Treaty Act (MBTA). Both acts protect bald eagles by prohibiting killing, selling or otherwise harming eagles, their nests or eggs. The BGEPA also protects eagles from disturbance.