Reintroduced juvenile white-tailed eagles on the Isle of Wight have been tucking into a varied diet of hares, rabbits, fish and even a marine invertebrate - despite fears they would go after lambs, a study from Forestry England has found.
In addition to revealing the prey items of the birds, the study, thanks to its direct observations, also showed how what they eat changes as the juveniles matured. Younger birds focused mainly on mammals and birds, whilst those a few years older were eating a much higher proportion of fish.
“The change in age is one of the most interesting things we found,” says Steve Edgerton-Read, the White-tailed Eagle Project Officer at Forestry England. “That change from mammals and birds being dominant in the diet, to fish.”
These direct observations also revealed some surprising prey items, including one white-tailed eagle stealing a water vole from a marsh harrier, and the older juveniles learning to catch common cuttlefish, a common marine invertebrate in the Solent.
“It’s not a diet item that we know of anywhere else in Europe – I’m sure it does occur, but it’s not something we found in the literature,” adds Edgerton-Read. “So, this ability to exploit this super common resource, here on the south coast of England during those spring and summer months, is really impressive.”
The study required innovation from the project as the diets of white-tailed eagles are normally studied by examining the prey remains found in nests at the end of a breeding season. However, white-tailed eagles typically reproduce at four or five years old, and the reintroduced birds are still relatively young.
One pair has fledged a chick – unexpectedly doing so as the two birds were only three years old – producing the first white-tailed eagle chick in England in 240 years.
Instead, the study involved thousands of hours of directly observing the eagles out in the field, monitoring what they were feeding on.
The nature of the study meant the observers could also note down the strategy used by the eagles in obtaining their food, and how frequency of the strategies changed as the eagles matured. These included hunting feeding on carrion (favoured by the younger eagles), catching live prey and pirated from another bird.
Main image © Dan Sayers
