Course:CONS200/Recovery of bird populations in Great Britain

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A Case Study of Peregrine Falcons, Golden Eagles, Osprey, White-tailed Eagles and Red Kites


An adult and a juvenile white-tailed eagle (Haliaeetus albicilla) fighting. By Andreas Weith via Wikimedia Commons. CC BY-SA 4.0

Over the past centuries, predators have on average declined significantly, and sometimes drastically, with negative effects on the biosphere[1]. However, that isn’t to say that the field of predator conservation lacks success stories. One of the West’s most prominent is that of the recovery of birds of prey populations in Europe, but above all in the United Kingdom[2]. With the British Isles having been extremely human-modified environments for millennia, raptors in Great Britain have experienced extra negative pressures from people for centuries[2]. However, the apex predators found themselves beset on all sides starting in the 19th century, starting declines, and in some cases extirpations, that continued well into the 20th century[2]. The factors that precipitate these declines were as diverse as direct human persecution, habitat loss, and pesticide pollution in the environment[2]

However, all was not lost. In the last century, most bird of prey populations across the United Kingdom have recovered significantly[2][3]. With a decline in persecution later strengthened by legal protections of raptors, the reduction and then subsequent banning of the organochloride pesticides harming reproduction, and concerted human help in the form of reintroductions and habitat increases, populations have, and continue to, bounce back[2]. Particularly, a strong case study can look at the decline and subsequent recovery of the Peregrine Falcon (Falco peregrinus), the Osprey (Pandion haliaetus), the Golden Eagle (Aquila chrysaetos), the White-tailed Eagle (Haliaeetus albicilla), and the Red Kite (Milvus milvus). An analysis of their threats (both past and present), their causes, and the actions taken (both past and present) can offer conclusions about their current prospects as well as solutions for other recovering species and their habitats.


Historic Presence

The birds of prey of the British Isles have experienced large reductions in their ranges associated with each species declines.

Osprey

Osprey. By NASA via Wikimedia Commons. Public Domain.

The osprey is a wide-spread raptor that is found in many habitats worldwide, and the UK is no exception. Prior to their decline, they probably used to breed throughout the UK, though because they disrupted medieval fish farming they were persecuted starting relatively early, leading to a slightly unclear historical range[2]. Because of this, P. haliaetus was extirpated from England in 1840 and from Scotland, its last home in the British Isles, in 1916[4]. However, natural dispersal from Scandinavia caused them to reappear in 1954, and are now dispersing through Scotland in addition to being found at select sites in Northern and Central England as well as Central Wales[2][4].

Golden Eagles

Golden eagles were once widespread over the uplands of Great Britain, including areas such as the Scottish Highlands, and the Pennines[2][5]. However, they declined to their low point of 80-100 pairs in the 1870s, surviving only in a few choice areas of Scotland[2]. They have since increased, though they are still restricted to mainly the Scottish Highlands, with a few pairs residing in the Southern Scottish Hills- meaning none occupy their original territory outside of the UK’s northernmost country[6]

Peregrine Falcons

Peregrine Falcon with Kill. By Will Mayall via Wikimedia Commons. CC BY-SA 4.0

Similar to Golden Eagles, peregrine falcons were originally found all over the United Kingdom anywhere that offered suitable nesting habitat, generally cliffs, including sea cliffs and uplands escarpments[7]. However, due to persecution and the effects of DDT, their numbers had plummeted and their range contracted, with the low point being 1963[2]. Luckily, with measures to combat the factors leading to their decline, the falcons have recovered and are now found throughout their original range[2][7]. In fact, peregrine falcons are now expanding their range into new areas of the British Isles, the lowlands, due to man-made structures being suitable roosts, and are now found virtually anywhere in the archipelago[7].

White-tailed Eagles

White-tailed eagles have been gone from much of the British Isles for hundreds of years, leading to uncertainty over their exact original ranges[8]. However, it is thought that they occupied much of the coast, from Scotland all the way down to Southern England, as well as Ireland[8]. Today, however, they occupy only a sliver of that former range, with the main population in western coastal Scotland and a small population in Eastern Scotland due to reintroduction[2].

Red Kites

Red kites, like most of the other raptors in the UK, were originally widespread[2][9]. Yet, by 1968-1972 there were less than 100 breeding pairs, all found in central Wales[2]. Today, the species has bounced back thanks to protections in addition to reintroductions in England and Scotland, meaning they are found almost everywhere, with locations in all four of the UK’s constituent countries[9].



Decline

Bird of prey populations in the United Kingdom have faced rapid declines in population size and overall health since the mid 20th century. The various causes of their studied decline are due to changes in ecosystem, climate, and human-developments.

Human Interference

Haliaeetus albicilla (Svolvær, 2012). By Yathin S Krishnappa via Wikimedia Commons. CC BY-SA 3.0

Human persecution towards raptor species have increased their decline. During the 19th and early 20th centuries, falconry, game hunting and illegal trading were at large, which drove the white-tailed eagle, peregrine falcon and osprey to near extinction. Landowners took advantage of game hunting by allowing them to indulge in the ecosystem service of hunting on their land in exchange for payment[2].The illegal trade of falcons within the United Kingdom led to their mistreatment and dangerous training routines of inexperienced handlers and separated pairs of peregrine falcons that led to their inability to mate and reproduce[10].

Habitat and Food Loss

A large cause of raptor decline is shown in the loss of habitat and food sources due to agriculture and urban development. Intensive agricultural development in the past 50 years has wiped out forest, wild fields and mating regions that predatory birds rely on to live, nest and mate. Farmers continuously cut back the surrounding land around their farmed fields to expand their agricultural space, which continuously harms the habitat[2]. Since 2003, field birds have declined to 13% and woodland birds to 17%, which act as vital food sources for raptor species[11]. They naturally have a long-life expectancy, lay few eggs, and have slow breeding rates, and therefor cannot repopulate at a fast-enough rate in comparison to the speed at which they are dying off [12].

Great Britain. By Cnbrb via Wikimedia Commons. Public Domain.

Climate Change

Another major factor toward predatory bird decline in the UK is the impacts of climate change. Global temperature rises are already causing ecological effects, such as shifts in species distribution and alternate migration patterns[12]. The 2016 Statistical data sets from the UK department of Environment presented that the all-species index showed a long-term decline of 8% from 1970 to 20155. This decline is the result of average UK temperatures increasing by 1 degree since 1980 and sea level rise along the UK coast to rise 14 centimeters. The Breeding Bird Survey 2016, surveying 5,000 nesting locations around the UK, exhibits the impact of a warmer climate on the decline of predatory birds as seen in late migration periods resulting in shorter mating seasons, limited intertidal habitats, and less coastal, farmland, and woodland birds available for raptor species to hunt[11].

Pesticide Use

Pesticides application. By Zeynel Cebeci via Wikimedia Commons. CC BY-SA 4.0

The largest cause of the decline of birds of prey populations in the UK is the exposure of environmental contamination in the form of agricultural pesticides and industrial chemicals. Organochlorine pesticides, including Dichlorodiphenyltrichloroethane (DDT), and other neurotoxic chemicals were introduced to the UK after the Second World War and were widely used in agriculture throughout the 1950s and 60s to proposedly protect crops from insect infestation and disease. Though, the use of such pesticides directly correlates with the decline of predatory birds due to chemical poisoning [13]. these chemicals are not biodegradable and only about 6% is absorbed by crops, while the other 94% is attained into the soil and waterways. Environmental Scientist, Rachel Carson’s 1962 text “Silent Spring” detailed her findings of the environmental impact of agricultural chemicals, which led to a surge of studies to take place over the rest of the century[14]. The main types of chemicals that cause these devastating effects on birds of prey species are these organophosphate pesticides (mainly DDT), petroleum hydrocarbons, and polychlorinated biphenyls[14]. Studies conducted by groups such as the US National Institute of Health, and British Toxicologist David Peakall’s 1985 study of DDT on predatory birds, found that physiological and behavioural effects occurred in birds of prey after environmental contamination that including direct effects on both adults and embryos[13]. Direct impacts to adult raptor species are reproduction difficulties, inability to fly, and complications in catching and digesting food. Organochlorine chemicals are soluble in fat and therefore stay in the both the raptor’s and their prey’s internal system, allowing the chemicals to be passed along the food chain, ultimately leading to adult and chick mortality. The effects of pesticides on raptor embryos include reduced hatchability, egg shell thinning due to the inability to inhibit calcium, and teratological impacts producing skeletal abnormalities and impaired reproductive and nervous system mechanisms[14]. Agricultural pesticides and industrial chemicals are especially dangerous because their residue persists in ecosystems and could lead to unnatural behavioural changes as the toxins alter nature and the animals’ structure[13]. Due to their status at the top of the food chain, their health can notion the state of the ecosystem as a whole. Naturally, raptor species have a long-life span, slow breeding rates, and lay few eggs, so they are unable to repopulate at a pace as fast as they are dying off. The dramatic decline of their populations in the UK show the truly detrimental effects of these pesticides[2].

Impact on Vulnerable Bird of Prey Species

Osprey prepare to mate in their nest. By Matt edmonds via Wikimedia Commons. GNU Free Documentation License.

The five-major bird of prey populations that have faced detrimental decline is the osprey, golden eagle, white tailed eagle, peregrine falcon, and red kite. Ospreys historically bred throughout the UK but human persecution nearly brought them to extinction by 1916. Fish make up 99% and therefore the species was captured to assist the fish farming industry from the medieval to industrial revolution period[12]. Following extensive protection, including Operation Osprey, a 24-hour watch at the RSPB’s Loch Garten site, numbers in Scotland rose to exceed 200 pairs by 2003, but had difficulty regaining its population size in England due to the slow rate of their reproduction[2].

The peregrine falcon faced a decline in the UK in the 1800s and early 1900s. Their early population decrease was due to persecution, illegal egg collecting, falconers, and specimen hunting as the peregrine was a rare bird in most of England[10]. Climate change and an increase in rainfall in the UK led to a loss of habitat as many nests were destroyed in storms[15]. Peregrines were reduced to 360 pairs in Britain by 1963, largely owing to organochlorine pesticide poisoning from the increase in agricultural pesticides. populations suffered due to the greater areas of agricultural land and so more widespread use of organochlorines, with only 30-50 territories in the country [16].

Juvenile white-tailed eagle (Haliaeetus albicilla) in flight. By Andreas Weith via Wikimedia Commons. CC BY-SA 4.0

Golden eagles were a relatively numerous species before 1800 but by 1870, they were reduced to between 80 and 100 pairs. Decline resulted from a combination of human population expansion in rural areas, habitat alterations, ill treatment. Wildlife crime experts at the Royal Society for the Protection of Birds (RSPB), a partner in the project, say many birds of prey are struggling to survive in northern England because of systematic poisoning, shooting and nest disturbance by gamekeepers to protect commercial red grouse and pheasant shoots[17]. Even where golden eagles attempt to nest, persecution can be a major cause of failure. A long-term study, in north-east Scotland, showed that on Scottish grouse moors between 58 and 75% of breeding attempts failed because of persecution, compared with 15% on deer estates, where golden eagles bred over five times more successfully[18].

White-tailed eagles numbered more than 200 pairs in 1701. They faced persecution and by 1916, were nearly extinct. Habitat loss, and human harm such as egg collecting and deliberate killing, posed a threat to their recovery[2]. White tailed eagles also have a slow natural population growth which remains a threat to their recovery.

Red kites, formerly widespread in Britain and Ireland, were reduced to just 10 pairs in Wales by the 1930s[2]. Pesticide poisoning remains a threat to these raptors, which is the leading cause of their mortality[13].

Recovery to Date

Recovery success in the 20th century

By the beginning of the 20th century, the status of many populations of Bird of Prey in the United Kingdom was grim. Many factors contributed to the total loss of several large raptor species, and the severe endangerment of many others. The downfall of these populations was a result of human interference, both direct and indirect. Many species, such as Red Kites, who were not driven to local extinction, were reduced to just several reproducing pairs. The Red Kite population was observed to only included 10 viable pairs in 1930[2]. By mid-century, the significance of this collapse became clear, and conservation programs were created to help recover these populations to stable levels. The initiatives, legal measures, and reintroduction efforts achieved incredible success, and have resulted in near, to full, recoveries of Bird of Prey populations across the United Kingdom[2]. According to an annual report compiled on behalf of the Royal Society for the Protection of Birds (RSPB), outlining the state of birds in the UK, species such as the Peregrine, Red Kite, Goshawk, and Golden Eagle have been designated green indicating low conservation concern[11] (2016). Other Bird of Prey species including the Osprey still maintain a yellow designation, however, the overall scale of recovery has proven a resounding success[11]. Work still must be done in the recovery of these species, as the observed numerical recovery has not been accompanied by a full restoration of historic range. The population recovery has however, provided a strong and healthy template onto which these birds will continue to populate and spread across the UK, eventually restoring their past presence.

Reintroduction

A hands-on approach to population recovery began in earnest in the 1970’s, when several species previously extinct to the UK were reintroduced. These reintroduction efforts focused on the relocation of young birds from Scandinavian countries such as Sweden and Norway. One of the first modern examples of a reintroduction program for a large raptor occurred between 1975 and 1985, when the White-Tailed Eagle, a large Raptor which had been extinct to the area since 1917[19], was reintroduced to several Scottish islands[20]. With high non-native juvenile mortality rates, and long reproductive cycling[20], this reintroduction was slow and tedious. However, a recovering White-Tailed Eagle population base was eventually established with 36 pairs observed in 2006[2], and a further 55 pairs by 2011[20]. Research commissioned on behalf of Scottish National Heritage (SNH) predicts that the numbers of these large raptors could rise to as many as 221 by 2025[19]. A second extremely successful reintroduction program began soon after, with Red Kites, a species near extinction, which had been reduced to a small area of Wales. This effort began in 1989, and is regarded by some as the “greatest conservation success story of the past 20 years” (The Field, 2010)[21]. The work has enabled a prolific comeback of the species to Scotland, Ireland, and the rest the UK. Red Kites have become so numerous in Great Britain that the region has become an exporter: providing young birds to other European areas seeking to reintroduce, or boost, populations[22].

Ban of Organochlorine Pesticides

Already struggling, Bird of Prey populations faced a new and fatal pressure following the Second World War when Organochlorine pesticides, such as DDT, emerged and gained popularity. On its introduction, DDT was widely praised for its low cost, high efficiency, and ability to combat insects carrying disease such as malaria and typhoid[23]. Swiss chemist Paul Hermann Müller was awarded the Nobel Prize for medicine in 1948[24] for his discovery of the insecticidal qualities of DDT. Following its wartime introduction and the aforementioned discovery, it became a very common agricultural pesticide and disease fighting tool. Soon after; however, evidence of its harmful effects emerged. A book published by marine biologist and nature writer Rachel Carson in 1962, titled Silent Spring, raised a large public awareness to the dangers of DDT and its ability to bioaccumulate to high concentrations in tertiary species. Some of the main victims of DDT, outlined in this book, were birds. The chemical caused severe eggshell thinning, leading to an extremely high infant mortality rate[2][23]. DDT continued to wreak havoc on bird populations through the 50’s and 60’s until its ban in America in 1972[25], and its eventual ban in the UK in 1982[2]. The ban has been controversial on many levels. The scientific merit of “proof” offered on its harmful effects has been questioned and contrasted with the chemical’s history and lifesaving reputation in combatting malaria[23]. Various opinions on the ban aside, the positive effects on bird populations were clear. Following the slow removal and disappearance of DDT[20], reproductive health was restored to many species, and eggshell thickness returned to healthy levels. Phasing out these chemical pesticides was one of the last major contributing factors to recovery of Birds of Prey in Great Britain observed during the 1990’s and early 2000’s[2].

Reduced Persecution

Persecution was one of the earliest anthropogenic stresses for Raptor populations and a leading catalyst for their great decline. These birds came under attack by humans in the early 1800’s for a variety of reasons, including game shooting, cultural egg poaching, and control due to livestock predation[20]. Many of these practices were reduced in the early 20th century as a result of societal shifts; however, persecution remained an enormous problem for Bird of Prey populations. As numbers dropped to unsustainable levels, governments in the UK introduced legal measures to give birds protection both within the UK, and throughout Europe. Initiatives such as the Wild Bird Directive (WBD) have been included in European Union legislation and represent the UK’s commitment to the protection of vulnerable Aves[2][26]. Birds of Prey gained legal protection in the UK in 1954[2] through the Protection of Birds Act, rendering nearly all forms of persecution involving birds, their eggs, and their nesting sites, illegal [20]. The implementation of this legal protection was coupled with another important piece of British legislation which sought to implement and adhere to provisions outlined in the WBD: The Wildlife and Countryside Act. This act, passed in 1981, provided enhanced protections to Birds of Prey within Great Britain, and also strengthened existing protections[2][20][27]. The act uses a tiered system to classify birds based on their vulnerability, and enforces tighter regulations on birds listed on Schedule 11 including Raptors such as Osprey, Golden Eagle, and Peregrine[20]. With this designation, such species are protected against harassment in or around their nest. These various pieces of legislation give Birds of Prey in Great Britain legal protection against persecution, and have helped facilitate their recovery.

The Issue of Climate Change and Future Recovery

Effects on Vulnerable Species

While Birds of Prey populations have been assisted in making remarkable recoveries, there are still many factors that lead to the uncertainty in their future health, including climate change impacts. Model projections indicate that there will be potential changes in over 50% of the 124 widespread bird species populations due to decreases in climatic stability, most of which are already considered of conservation concern[28]. Climate change has been recorded to affect bird populations biologically in many ways, including migration, reproductive success and interactions with other species[29][30]. Evidence has shown that as birds change physiologically due to increasing mean temperatures, their breeding pattern no longer coincides with the instant of maximum food abundance, resulting in higher chick mortality rates and changes in ecosystem functioning[31][32]. Since Great Britain has been predicted to receive more extreme weather events, the effects on breeding patterns and migration would be even more detrimental to the already at-risk bird populations[33]. Model analyses of the effects of climate change on all of the species discussed showed that the strength of the relationship between climate change impacts and species distributions does not weaken when comparing trophic levels, which implies that each of the species would show the same impacts as plants and other organisms in their ecosystem[34]. Bird populations and their attenuations due to climate change are a fairly new topic and more in-depth studies will be required to accurately predict future populations and the direct and indirect impacts on bird species. For the specific species, there have been similar trends for all of the modelled projections and the current data that indicate instability due to climate changes[34].

Counteracting the Threats

In order to successfully assist birds in their population recoveries further, adequate research and conservation efforts will be required. The methods of captive breeding, reintroduction and ensuring habitat wellbeing can help the populations to maintain or increase their numbers, however, most species will suffer due to a lack of resources from conservation teams[28]. Targeting species that are vulnerable and ensuring that their numbers return to historic values will improve their response to climate change. The raptors discussed will have impacts that could lead to either an increase or decrease in abundances and further climate models should be developed to assess the impacts on their future populations[35]. Studies have shown that some species of birds predicted to go extinct are not even considered threatened currently so it appears all species are at some risk[36]. Habitat restoration is one of the most prevalent solutions for managing the bird populations since it is more successful than relocating birds to regions that do not have the same conditions, even if ideally the conditions would be better[36]. As well, establishing new conservation or protected areas to promote new species migration to the areas controlled for habitat health may be effective.

Conclusion

Birds of Prey in Great Britain showed great declines in abundance and distribution in the last few centuries. While the Birds of Prey populations faced many opposing factors that hindered their recovery, following the reintroduction programs, banning of damaging pesticides and reduction in persecution through hunting and egg-collecting, there was significant increases in their populations that rivalled historic population sizes. Though there was a successful recovery story overall, the birds are still very much vulnerable to impending and current climate change impacts like migration alterations, earlier egg laying and extreme weather event mortality. In order to ensure the raptor populations continue to increase, conservation efforts in the form of current habitat restoration and establishment of healthy habitats for birds to migrate to should be considered, as well as the continued enforcement of reducing persecution against raptors. Policies involving the protection of raptors and their ecosystems should be introduced or maintained and the public should be informed of the situations so that they may assist wherever necessary.

References

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