Background Information
Because raptors are at the top of the food chain, they are especially vulnerable to changes in their habitat and act as indicators of environmental health. When raptor populations go down, it means something has changed, usually for the worse. For example, when peregrine falcon populations were nearly extinct in this country, the decline was linked to the use of the pesticide DDT. But how do you know if raptor populations are increasing or decreasing? You study them. Each year biologists, researchers, and college students study many aspects of the raptors that live in the Snake River Birds of Prey National Conservation Area (NCA).
Researchers are trying to find out why the numbers of some raptors in the NCA are declining.
Part of their research involves monitoring golden eagle territories and nesting sites. Many golden eagle nests are not exactly easy to reach, so helicopters come in handy.
A golden eagle female sits on her eggs in a cliffside nest. After about a 45-day incubation period, golden eagle chicks are born, covered at first in downy white feathers
Although Larry does not have a degree in biology, he has made it part of his job to assist the biologists and researchers with some of the counting, trapping, banding, and monitoring of the NCA's raptors. This not only helps the researchers accomplish their work but also teaches him more about these magnificent birds. In turn, Larry’s new knowledge helps him when giving presentations and educating others about raptors.
In order to track the NCA’s golden eagle population, researchers many years ago identified all of the known nesting areas (territories). Each year they monitor the nests to see if they are occupied and to see which ones are successful. In other words, which nests have young eaglets in them? On the surface this sounds like a pretty simple task. But the golden eagles that nest along the Snake River canyon will generally protect a territory that’s about five-to-six kilometers (three-to-four miles) long from other eagles. There are also a number of eagles that nest in cliff areas outside the canyon or on powerline towers. Many of the nests are in very remote locations and usually a hundred or more meters (several hundred feet) up on a sheer, basalt cliff. This means that if you want to try and count the number of golden eagle nest sites that are occupied each year, not only do you have to cover a very large area, but you also have to get to areas that are not exactly easy to reach. That’s where helicopters come in handy.
Golden eagles build their nests not only in the cliffs by the river, but also on powerline towers that run through the area. In fact, the power company actually installs nest structures on some of its towers to help the eagles.
Attaching leg bands enables scientists to track the movements of individual birds. This ferruginous hawk chick is receiving a leg band–a completely painless process, despite the look on its face. Note the sharp beak and talons (claws) typical of all raptors.
During a few of the NCA’s annual Spring Hikes, members of the public travel with biologists and assist with counting and putting leg bands on some of the raptors. Leg bands will help scientists keep track of these ferruginous hawk chicks.
Each spring NCA researchers make an initial helicopter flight to all the historic eagle territories to determine whether an eagle pair is using a territory. If so, they also need to find out which nest is being used, since each territory may have three or more nests. A second flight is made approximately two months later to determine which of the occupied nests have chicks and, if so, how many. For several years, Larry has accompanied researchers on these flights. Great care is taken to minimize the disturbance to the nesting birds. A territory is approached from downwind and the nest used the previous year is checked first. Once an eagle is seen on a nest, there is a quick exit so as not to further disturb the eagle.
But not all eagle nests require a helicopter to check on them. Larry has “adopted” one of the powerline tower nest sites that is fairly easy to reach. This nest structure was put on the tower in 1983 and the first eagle pair used the nest the following year. Each year the eagles bring new nest material and place it on the nest. Over the last twenty years this nest has grown to almost two meters (six feet) high and one meter (about four feet) across. The same pair tends to use the same territory from year to year and, in this case, the same nest.
For Larry, checking this nest has become like visiting old friends. Each year in late winter he starts watching for the pair. Usually by early March the female is sitting on her eggs while the male is keeping a close watch circling high above. By May the downy chicks are moving around wanting plenty of food from mom and dad. Late June arrives and the eaglets are getting ready to test their wings. In the heat of July and August, if he’s lucky, Larry will see the adults showing their young the best places to hunt and find shade. Next spring the cycle will start all over.
In addition to counting nesting eagle pairs, Larry helps in trapping and banding raptors for identification. By banding birds for identification, researchers can track the movements of individual birds and learn a great deal about their habits.
Scientists think that recent wildfires have contributed to the decline of golden eagle and prairie falcon populations in the NCA. Such fires can spread rapidly through many acres of sagebrush and other native plants.
Sagebrush provides cover for black-tailed jackrabbits, an important food source for golden eagles.
Scientists hope that golden eagles, prairie falcons, and other raptors will continue to nest in and fly high over the Snake River Birds of Prey NCA.
With all these studies of raptors over the years, what have scientists learned about them and about the environment of the NCA? For one thing, there’s been a significant decline in the populations of two raptor species–golden eagles and prairie falcons. Now, this is where researchers have to put on their detective hats and try to identify what has changed in the last 20 years that could be affecting the raptor populations. Identifying the cause is only the first step, of course. Fixing the problem is what’s really important. After all, the main reason the National Conservation Area was established by Congress was to “protect and enhance raptor populations and their habitat.”
Research from around the West has shown that the size and frequency of wildfires on western rangelands have increased dramatically during the last 20 years, transforming vast areas of native sagebrush and bunchgrass into annual grasslands. The Snake River Birds of Prey National Conservation Area is no exception. Since 1979, wildfires have consumed more than 140,000 hectares (350,000 acres) of wildlife habitat in the NCA. Shrubs that provided food and shelter for many animals have been replaced by annual grasses. Is there a link between the type of vegetation in the area and the raptor populations?
Consider this: Golden eagles in the NCA feed heavily on black-tailed jackrabbits. The jackrabbits need tall stands of sagebrush for food and cover. Wildfires have removed large areas of sagebrush, which means these areas can no longer support jackrabbit populations. With fewer jackrabbits, the eagles must find other prey or relocate to a place where jackrabbits are still abundant. A similar case holds for the prairie falcon and its primary prey, the Paiute ground squirrel.
So, has this change in vegetation caused the golden eagle and prairie falcon populations to decline? There may well be a link, but it is hard to say for sure. There could be other factors that have not been considered. Are there other reasons the jackrabbit population has decreased? Why, in years when ground squirrel populations were up, didn’t prairie falcon numbers go back up, too? Maybe there are other factors affecting the raptor population that are completely unrelated to vegetation or prey animals. All these unanswered questions keep Larry and many others at the NCA busy. In fact, such unanswered questions provide a good reason for all of us to keep exploring our world and to keep asking “why.”
Background InformationBecause raptors are at the top of the food chain, they are especially vulnerable to changes in their habitat and act as indicators of environmental health. When raptor populations go down, it means something has changed, usually for the worse. For example, when peregrine falcon populations were nearly extinct in this country, the decline was linked to the use of the pesticide DDT. But how do you know if raptor populations are increasing or decreasing? You study them. Each year biologists, researchers, and college students study many aspects of the raptors that live in the Snake River Birds of Prey National Conservation Area (NCA).
Although Larry does not have a degree in biology, he has made it part of his job to assist the biologists and researchers with some of the counting, trapping, banding, and monitoring of the NCA's raptors. This not only helps the researchers accomplish their work but also teaches him more about these magnificent birds. In turn, Larry’s new knowledge helps him when giving presentations and educating others about raptors.
Each spring NCA researchers make an initial helicopter flight to all the historic eagle territories to determine whether an eagle pair is using a territory. If so, they also need to find out which nest is being used, since each territory may have three or more nests. A second flight is made approximately two months later to determine which of the occupied nests have chicks and, if so, how many. For several years, Larry has accompanied researchers on these flights. Great care is taken to minimize the disturbance to the nesting birds. A territory is approached from downwind and the nest used the previous year is checked first. Once an eagle is seen on a nest, there is a quick exit so as not to further disturb the eagle. But not all eagle nests require a helicopter to check on them. Larry has “adopted” one of the powerline tower nest sites that is fairly easy to reach. This nest structure was put on the tower in 1983 and the first eagle pair used the nest the following year. Each year the eagles bring new nest material and place it on the nest. Over the last twenty years this nest has grown to almost two meters (six feet) high and one meter (about four feet) across. The same pair tends to use the same territory from year to year and, in this case, the same nest. For Larry, checking this nest has become like visiting old friends. Each year in late winter he starts watching for the pair. Usually by early March the female is sitting on her eggs while the male is keeping a close watch circling high above. By May the downy chicks are moving around wanting plenty of food from mom and dad. Late June arrives and the eaglets are getting ready to test their wings. In the heat of July and August, if he’s lucky, Larry will see the adults showing their young the best places to hunt and find shade. Next spring the cycle will start all over. In addition to counting nesting eagle pairs, Larry helps in trapping and banding raptors for identification. By banding birds for identification, researchers can track the movements of individual birds and learn a great deal about their habits.
With all these studies of raptors over the years, what have scientists learned about them and about the environment of the NCA? For one thing, there’s been a significant decline in the populations of two raptor species–golden eagles and prairie falcons. Now, this is where researchers have to put on their detective hats and try to identify what has changed in the last 20 years that could be affecting the raptor populations. Identifying the cause is only the first step, of course. Fixing the problem is what’s really important. After all, the main reason the National Conservation Area was established by Congress was to “protect and enhance raptor populations and their habitat.” Research from around the West has shown that the size and frequency of wildfires on western rangelands have increased dramatically during the last 20 years, transforming vast areas of native sagebrush and bunchgrass into annual grasslands. The Snake River Birds of Prey National Conservation Area is no exception. Since 1979, wildfires have consumed more than 140,000 hectares (350,000 acres) of wildlife habitat in the NCA. Shrubs that provided food and shelter for many animals have been replaced by annual grasses. Is there a link between the type of vegetation in the area and the raptor populations? Consider this: Golden eagles in the NCA feed heavily on black-tailed jackrabbits. The jackrabbits need tall stands of sagebrush for food and cover. Wildfires have removed large areas of sagebrush, which means these areas can no longer support jackrabbit populations. With fewer jackrabbits, the eagles must find other prey or relocate to a place where jackrabbits are still abundant. A similar case holds for the prairie falcon and its primary prey, the Paiute ground squirrel. So, has this change in vegetation caused the golden eagle and prairie falcon populations to decline? There may well be a link, but it is hard to say for sure. There could be other factors that have not been considered. Are there other reasons the jackrabbit population has decreased? Why, in years when ground squirrel populations were up, didn’t prairie falcon numbers go back up, too? Maybe there are other factors affecting the raptor population that are completely unrelated to vegetation or prey animals. All these unanswered questions keep Larry and many others at the NCA busy. In fact, such unanswered questions provide a good reason for all of us to keep exploring our world and to keep asking “why.” |
