Interview with Mike McGrady about Golden Eagles in Great BritainDate of the interview: 14 June 2010 In this interview, eagle researcher Mike McGrady talks about the current situation of Golden Eagles in Great Britain.
Mike McGrady radiotracking golden eagles in Scotland.
© Mike McGrady
Mike McGrady: Currently there are about 430 pairs of golden eagles in the UK, and these are found in Scotland only. There are unpaired eagles in England. Golden eagles are less widely distributed in the UK than they could be. Of course, there used to be eagles in England, Wales and Northern Ireland. Even in Scotland there are fewer than 4 pairs south of the urban belt of Glasgow and Edinburgh. In other places in the Highlands of Scotland eagles are absent from appropriate habitat, most likely due to consistent, concerted persecution. Markus Jais: How has the population developed during the last decades?
Mike McGrady: Golden Eagles were heavily persecuted in many areas in the late 19th and early part of the 20th centuries. The World Wars took gamekeepers off the land for some time and so there was some respite during those years. After the 2nd World War keepers returned in lower numbers, but it was at this time that persistent organochlorine pesticides came into use, and these may have had some effect on eagle productivity. Egg collecting was a popular pastime during Victorian times, but has had an ever smaller following. The population has been largely stable over the past 30 years or so, though there have been losses of pairs and that means large areas of appropriate habiats are now eagle-less.
© Mike McGrady
Mike McGrady: Probably the main threat to golden eagles in the UK is persecution, but habitat loss and badly located windfarm developments are also problems. I have it in my mind that lead poisoning may be a bigger threat than we suspect. I could be wrong on this, but many deer are shot and either lost or their organs are left on the hill. These are a potential sources for lead. Eagles can die from lead poisoning and deaths may be difficult to document. I understand that the Forestry Commission and the RSPB now use lead-free ammunition in the forests and reserves they manage. Markus Jais: How does illegal persecution affect the distribution of the species?
Mike McGrady: Persecution affects the distribution of the species by removing some pairs, and when non-breeders are killed reducing the pool of potential recruits that could fill in gaps in the population and contribute to the population's expansion into new areas. Markus Jais: What habitat do Golden Eagle prefer in the UK and how is the habitat affected by forestry, development and wind farms?
Mike McGrady: Golden eagles in the UK, like almost everywhere else in the world, need open areas in which to hunt. When they hunt in forests they are forests that have wide spacing between trees. When considering the golden eagle in the UK one has to remember that the landscape, for all its apparent "wildness", is very artificial. So, for example, hundreds of years ago Scotland was more wooded, but trees were felled and sheep were put out on the hills, and this has maintained the open character of many areas. It also provided carrion in the form of sheep carcasses. Also, gaming estates, especially for grouse, were established and have been managed to provide a hyper abundance of these birds so they could be hunted by humans. During the 20th century, many areas of upland UK were planted with commercial forests, mostly of exotic species. This had the effect of closing off areas to eagles for hunting (habitat loss) and probably reducing overall prey abundance and availability. Habitat loss due to commercial forestry was a threat, but the expansion of this type of development has slowed. Today more areas are being planted with native species and so the landscape is becoming more like what it was before the tree felling. This may have an effect on eagles and cause change. It may be that the development of a more natural land cover of trees results in fewer eagles, but it should also support a healthy eagle population, with fewer pairs that may be more productive. Expanding the extent of native forests should also have other biodiversity benefits. Windfarms also present a potential threat. What little data exist suggest that territorial eagles avoid windfarms. So, although they may not be killed by collision with the turbines, territorial eagles may essentially lose habitat. Of course if too much habitat or particularly important habitat is lost then territories can become unviable: a negative effect on eagles. Even fewer data exist on how windfarms affect juvenile and sub adult eagles. This portion of the population generally wanders the landscape hunting in open upland areas not occupied by territorial eagles. These are exactly the places that are being identified for potential windfarm development. Again, there is so far no indication that eagles are being killed in large numbers at windfarms (no eagles yet found dead due to collisions), but habitat loss may be just as problematic to the health of the population as it needs a steady stream of recruits to occupy places in the breeding population. Although no cases of eagles being killed by wind turbines have been documented in Scotland, this does not mean it does not happen. Golden eagles are killed in other countries by wind turbines.
Release of a territorial adult golden eagle after fitting with a transmitter
© Mike McGrady
Mike McGrady: Persecution needs to be tackled. Eagles of all ages are shot, poisoned and trapped. Nests and their contents are destroyed and removed. Nest disturbance forces eagles to abandon their nesting attempts. This annual loss of individuals and reduction of fledgling production due to persecution are the main impediments to secure the future of golden eagles in the UK. In parallel to tackling the problem of persecution, one should look into trying to expand the population into areas that could accommodate them. There is really no good reason why some eagles should not be found in southern Scotland, parts of England, Wales and Northern Ireland. Of course, the Republic of Ireland has demonstrated that eagles can be restored to their former areas (though the future of that population is not yet secure). Reintroduction or supplementation of local populations are potential tools for expanding populations, but these are generally pretty expensive. Also, developments of any type should be considered very carefully. This, I think, is particularly true when it comes to windfarms, and in general a precautionary principal should be applied. The responsibility for the decision as to whether a development gets permission or not lies with government. The problem here is that we lack data to even apply a precautionary principal except in a fairly coarse way. Although there is a very big debate going on about whether windfarms are the best way to address human induced global warming, most would agree that climate change is the single greatest threat to the environment, and this must include the eagles that live in that environment. I think more research is needed and data on eagles that have been collected for the many windfarms that exist should be released to be analysed together. Again, it is important to remember that the UK is a very artificial landscape. The hand of man is everywhere. Natural habitats have, on the whole, been in decline for centuries, and this has had a generally negative affect on eagles. With this as background it may be difficult to understand why efforts to restore the natural condition in the UK, may not all be strictly "eagle friendly". By restoring a natural forest you might reduce the number of pairs of eagles from two to one by reducing the area of open ground that eagles use to hunt, but you might gain new areas of rare plants, extend the distribution of black grouse or capercaille, etc. While golden eagles are a component of biodiversity, it is important to remember that achieving overall beneficial biodiversity goals may result in lower numbers of eagles. Markus Jais: What is the main prey of Golden Eagles in the UK?
Mike McGrady: Golden eagles can take a wide variety of prey from earthworms to deer. In Scotland, especially during the winter, carrion (sheep and deer) is important. In the summer live prey is generally more important. Being such generalists one can say: where eagles occur with rabbits, they take them; where eagles occur with hares, they take them; where eagles occur with seabirds, they take them. If there is any unifying principal here it is that eagles prefer to take live prey of the 1-2 kg weight range. In Scotland eagles in the west generally have a more varied diet than birds in the east. Markus Jais: What is the effect of Golden Eagles on Red and Black Grouse and Mountain Hares?
Mike McGrady: Certainly eagles take red and black grouse and mountain hares. As far as I am aware there is no direct evidence that the number taken by eagles actually affects population numbers on anything other than the local scale. Other raptors (e.g. hen harriers and sparrowhawks) can affect the populations of their prey in certain situations, and this might suggest to some that eagles could reduce red and black grouse and hares. However, this has not been proven. Part of the difficulty in proving this lies in the fact that other forces seem to be having negative impacts on these populations. So, red grouse numbers are declining in places where raptors are not present, hares have been lost from areas of Scotland where there are no eagles, and black grouse are in general decline in many places across Europe.
Territorial adult golden eagle trapped as part of a study into the effects of plantation forest cover on eagle ranging
© Mike McGrady
Mike McGrady: These vary. In general where prey availability is high, home range sizes are small and vice versa. However, in eastern Scotland (where pairs are more successful) densities of eagles are lower. These two statements seem to contradict one another, but might be a result of less carrion being available in the east and persecution being more prevalent there. Most home ranges fall into about the 30-50 square km range. Markus Jais: How many pairs do breed in cliffs and how many on trees or other platforms?
Mike McGrady: More than 90% of nests are on cliffs. This was probably not the case hundreds of years ago when native forest cover was more common. Current forest cover consists of more exotic species (like Sitka spruce) whose limb structure is not as good as say native Scots pine for accommodating large eagle nests. Also, trees in commercial forests are generally close together, and this impedes eagle flight through the forest. Markus Jais: Is there an exchange with populations from Scandinavia or other parts in Europe?
Simple answer: No. However some Scottish eagles are being sent to Ireland for their reintroduction efforts. Does that count? Markus Jais: When the White-tailed Eagle was reintroduced to Scotland, some people feared it might displace the Golden Eagles from certain areas. How is the relationship between the two species? Is there competition and do they fight each other?
Mike McGrady: There is some overlap between diets of golden and white tailed eagles. Also, there is some overlap in their distribution. So, there is probably competition in a broad sense. Currently, there seem to be no effects of competition on either population. If one looks at the sea eagle population alone, it seems to be growing and new territories are established in most years. Both species are territorial near the nest against other eagles, and so will drive intruders away. That said, white tailed eagles and golden eagles nest in fairly close proximity to one another on the island of Mull (in particular). Markus Jais: How is the relationship between the Golden Eagles and other raptors beside the White-tailed Eagle? Do Golden Eagles compete with other raptors? Do they take them as prey?
Mike McGrady: Golden eagles do not really compete with other raptors in the UK. From an ecological standpoint the buzzard may be the species that has the most similar diet. However, prey items taken by buzzard are, as you might expect, generally smaller than those taken by eagles. Also, buzzards occupy areas at generally lower elevations than eagles. So, despite the apparent potential overlap, there is a good deal of niche separation between these two species. Golden eagles can prey on most other raptors. Personally I have found the remains of short eared owl, long eared owl, barn owl, buzzard, kestrel, hen harrier and sparrowhawk in the nests of golden eagle in Scotland. Markus Jais: With Golden Eagles, the second born chick is often killed by the larger siblings. How often do two or even three young fledge in the UK? What affects the survival of the 2nd (or 3rd) chick?
Mike McGrady: It is hard to say what percentage of siblings remain intact in Scotland. Maybe 10-20%. It is probably less than 1% that raise triplets. Although the link between survival of both chicks and food supply has not been absolutely confirmed, siblings are most likely to survive in territories with sufficient food. Also, no link has been made between the sex of the eldest chick (females are generally larger than males, but male chicks develop more quickly). It has also been hypothesized that weather plays a role in sibling survival, but that has not been proven. Markus Jais: The Golden Eagles is better studied than most other eagle species in the world. What gaps in our knowledge of the species do still exist? Where should research focus in the coming years?
Mike McGrady: Currently, the main gaps that exist are related to the ecology of non-breeding birds. This is an important segment of the population because it contributes new recruits to the population. In places where eagles are migrant then information on winter ecology is also lacking. In global terms the golden eagle is a wide spread, relatively common, generalist eagle. Just as studies of the common buzzard, kestrel and sparrowhawks provided information that could be applied to rarer and more specialized species of Buteo, Falco and Accipiter, I think that studies of the golden eagle could provide insight into large eagle ecology that could be applied to rarer species. Markus Jais: You run a company called Natural Research. What does Natural Research do with Golden Eagles and other eagle species? On what Golden Eagle projects are you currently working on?
Mike McGrady: The biologists at Natural Research are interested in understanding the ecology of K selected species like golden eagle. K species are large bodied, long lived, often have delayed maturity, low annual productivity and relatively hihg parental investment in young. So, in the bird world, eagles are a good example of a K selected species. Our research on eagles includes generally ecology, movement and ranging, recruitment, diet and impacts of human development including forestry activities and windfarms. We use a variety of tools including DNA analyses, VHF and satellite radio tracking, ringing, and the more mundane: direct observations. Currently we have projects on golden eagle, white tailed eagle and Steller's sea eagle. Markus Jais: What was your most amazing experience with Golden Eagles?
Mike McGrady: For one study I needed to catch adult breeding golden eagles to radio track them. We had an eagle that had failed on eggs, but was still incubating the infertile eggs. So, this offered an opportunity to try to catch the bird without causing the nest to fail (since it already had failed and she would abandon her futile incubation attempt soon). I camouflaged myself and buried myself in the nest as much as I could and sat to wait. The nest was not very deep, so my knees were sticking out the top of the nest and the nest itself sat in my lap and covered me to my lower chest. After about 2 hrs an eagle came in and perched on my knee. My hands were in a position such that I would have needed to backhand the eagle's legs to catch her. In the split second it took me to consider my options, she flew away. I think she heard my heart beating! Markus Jais: Mike, thank you very much for the interview.