In the latest blog from our white-tailed eagle project officer Steve Egerton-Read, we explore what we’ve learnt so far about the birds' behaviour and look at their diet since release.
It’s now been almost 2 years since the reintroduction of white-tailed eagles to England began. The five year programme to reintroduce this incredible species started in the summer of 2019 when six birds were released on the Isle of Wight, followed by a further seven birds in 2020.
During lockdowns last year, many people got in touch as they spotted the eagles flying over their gardens or local countryside. The birds covered enormous distances during this time reaching Norfolk, the North York Moors and even the Lammermuir Hills in Scotland. Only one bird (G274) remained relatively local, making several explorations of the south-east and south-west coast, but always returning to the Isle of Wight.
These exploratory flights are an important part of behaviour for young eagles as they enable them learn about the landscape. This was shown by the presence of four or five juvenile eagles from continental Europe during that time, likely also on their first exploratory flights.
Coming home
As fascinating as all these journeys have been, even more striking is that all of the birds recognise the south coast of England as home. Bird G318 spent nearly a year in the north-east of England before returning. Bird G393 spent a staggering 17 months away, leaving the Isle of Wight in September 2019 to travel around much of the country during 2020, then came back to the Isle of Wight in February 2021.
On 20 March this year all four surviving birds released in 2019 were on the Isle of Wight, the first time they have all been present since September 2019. Importantly, this is the age we expect to see these birds behaving in this way. White-tailed eagles typically return to within 50 kilometres of their natal site at around two to three years old. This is really positive as it suggests these birds may set up breeding territories on the south coast in the not-too-distant future.
With the establishment of territories comes a change in behaviour: a lessened tolerance for other eagles. G393, despite returning to the island twice, has been chased off by G274 in the first evidence of territorial disputes between the 2019 birds. Bird G274 has also shown little tolerance for the 2020 males, with both G408 and G461 returning but quickly ousted! It’ll be interesting to see how this behaviour develops and represents the beginnings of an exciting new phase for the project.
Eagle explorations
The young birds released last summer have started to make some incredible flights of their own. All six of the surviving 2020 cohort have travelled away from the Isle of Wight. We’ve received a lot of sightings and photos this year already, and these journeys are well detailed on the Roy Dennis Wildlife Foundation website. We expect these birds will return after a year or two of roaming, like the 2019 birds have already.
Some of the 2020 cohort have been visiting other white-tailed eagle populations, which is very exciting. Male G463 made a staggering journey across the English Channel and then travelled north through France, Belgium, the Netherlands and Germany. The young male then went on to explore the Danish Wadden Sea coast. White-tailed eagles recolonised Denmark in the mid-1990s and there are now approximately 100 breeding pairs, and so G463 will be encountering other eagles on his travels. Equally exciting, female G466 has flown to northern Scotland close to where she originated. This demonstrates how a south coast population could help reconnect the population in the British Isles with the expanding population in Europe.
Understanding diet
All of the birds are closely monitored, and we are learning a lot about their behaviour. Perhaps one of the most important elements for the project to learn about is their diet.
We monitor what the birds eat in a couple of ways. One way is by observing them in the wild. However, finding good vantage points without disturbing the birds is difficult and white-tailed eagles spend about 90-95% of their day perched, so you can spend a long time waiting for something to happen! The other is to check roost sites for pellets. Like owls, eagles regurgitate undigested remains, so it’s possible to identify prey from bones, feathers or fur. However, this doesn’t tell us how the bird acquired its meal. So it’s best to use both approaches when possible to get a complete picture of how the birds are using the landscape.
Observations suggest rabbits are one of the first prey species these birds can catch. White-tailed eagles tend to adopt a sit-and-wait strategy when it comes to hunting, so it’s easy for them to drop out of a tree to capture this prey. The team find rabbit remains in pellets quite regularly and rabbits have been an important part of these birds’ diets across the country throughout the year. The team have also seen the eagles catching brown hares and brown rats, which also appear in their diet on the continent.
Catching prey
Perhaps what white-tailed eagles are best known for is catching fish! Fish remains their preferred choice of prey, but seldom turn up in their pellets because the birds can digest the bones quite well. It takes a lot more patience and time to understand how fish fits into their diets, but it certainly means you get to witness some really exciting moments.
In their first spring, G274 and G324 spent many days catching grey mullet in the estuaries around the Isle of Wight. As the summer progressed, G274 became adept at catching cuttlefish from the Solent. Encouragingly, both G324 and G274 continued to hunt off the coast of the Isle of Wight through the winter months, when fish is less readily available. It’ll be fascinating to see whether cuttlefish remains important in the bird's diet, now they have returned to spawn this summer.
The greatest diversity of species in their diet is birds. Gull, corvid and pigeon remains are frequently found at roost sites. Gulls are the easiest to catch and feature throughout the year. White-tailed eagles aren’t particularly agile but can pursue injured or weakened individuals in the air. Often they test flocks of gulls to identify potential targets, but breeding gull colonies are avoided as they put up a vociferous defence!
In the Netherlands, coots are an important prey species and G274 has been seen catching these, hovering over reedy pools like an enormous marsh harrier to catch them. Other potential prey include injured Canada or greylag geese. G274 caught an injured adult Canada goose in late February and another in late March. Evidence from Europe indicates that eagles can be important in controlling populations of these birds, especially where they don’t have other natural predators.
Pirates!
Catching live prey, or even finding carrion, isn’t always the easiest way for an eagle to get a meal. White-tailed eagles are no strangers to ‘pirating’ food from others. Birds such as red kites, ravens and buzzards are adept at finding carrion in the countryside and so the much larger white-tailed eagles are happy to intimidate them and force the birds to give up their hard-earned find.
Equally, white-tailed eagles are happy to steal fish off birds, including grey herons or cormorants. One of the most remarkable recent observations was of G324 pirating a Mediterranean gull from a female marsh harrier, which itself had only just stolen it from a peregrine falcon! This behaviour also extends to stealing meals from other white-tailed eagles.
Planning ahead
We hope later this year to be able to release the next group of young eagles in this project, so watch this space. They will join those already thriving across the English landscape, as we continue to learn more about these truly incredible birds.
Blog written by white-tailed eagle project officer Steve Egerton-Read
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