Survival rates for hen harriers reared and released through an innovative scheme to help the recovery of the species are better than for wild birds, it has been reported, as the trial enters its final year.
Data from satellite-tagged hen harriers given a boost in the Brood Management Scheme trial shows the survival rate from fledging through the difficult winter months to the following May is 44 per cent, compared with 24 per cent for wild birds.
Fledging success of the trial to date has been nearly 100% – higher than observed in similar captive rearing programmes and in the wild.
The reasons for the improved survival rate are not fully understood, but a full formal investigation into the effects of the Brood Management Trial is underway.
Hen Harriers suffer high mortality rates, particularly in their first year of life. The hen harrier population in England is now at a 200-year high, with 141 chicks fledging successfully in 2023.
Since the first broods were managed in 2019, 58 chicks have been taken, safely reared and released back into the wild population.
The Moorland Association is a partner in the Brood Management Scheme trial and has helped satellite tag birds in each of the five years the trial has been operating. Thanks to this tracking technology, the researchers know that some of the birds from the cohort tagged in 2020, for example, are nesting and breeding successfully, adding further chicks to the increasing population.
Wet, cold and cloudy winter weather is not only a challenge for the young birds but also for their tracking devices which rely on solar powered batteries.
This year nine birds were tagged of which four are still transmitting regularly. It is hoped that the signals may return with some better weather, but the lack of signal from some is being treated as suspicious and is currently under police investigation.
Among the birds that epitomise the importance of the brood management trial is a male tagged in 2020 by the Moorland Association, who has fathered chicks three years in succession to date, favouring the grouse moors of the North Pennines, thus boosting biodiversity targets.
The most celebrated of the satellite-tagged wild birds in England is probably Frank, who was fitted with a tag by Natural England in August 2018 and who has gone on to father at least 21 chicks. Frank was not originally a brood-managed bird but some of his chicks have been taken into the scheme. Frank continues to be seen in the skies above Nidderdale and Coverdale in North Yorkshire and making use of the winter roost at Swinton, sometimes joined by up to 12 other adult and juvenile hen harriers, which can be seen from the estate bird hide.
Posted On: 22/11/2023