The bird of prey used to widespread across the UK but there are now only about 800 breeding pairs, mostly in Scotland. In England there are only around a dozen pairs, predominantly in the northern uplands.
The RSPB and Natural England have been trying to boost numbers through the Hen Harrier Breeding Project since 2002. However this year the project recorded the poorest breeding season on record. Only six nests were successful in total in England from 12 attempts, resulting in just 15 chicks. Even in Bowland in Lancashire, where most of the successful breeding attempts have been in the past, only four nests successfully fledged.
The cold winter, with heavy snows and temperatures falling to minus 10 degrees C, has been blamed for the poor breeding season. By spring, when hen harriers need extra food to feed their chicks, many of the small birds, mammals and insects that they rely on for prey had died out.
Hen harriers take a few years to mature and many of the chicks will not survive.
Dr Mark Avery, the RSPB’s Director of Conservation, feared hen harriers will be lost from England for ever unless the birds can breed more successfully.
“We always feared that with hen harrier numbers kept so low, the English population was extremely vulnerable to a bad year like this," he said.
While there is no evidence of illegal killing or nest destruction associated with this year’s breeding failures, hen harriers have been killed in the past by gamekeepers on grouse moors.
John Swift, Chief Executive of the British Association for Shooting and Conservation, said landowners and gamekeepers must help to protect the bird.
“A bad winter has left the hen harrier population even more vulnerable than before – this means that everybody must concentrate on doing what they can to ensure that the moorland habitat continues to be well managed and that persecution is confined to history," he said.
“It is imperative that we find a solution to the conflict between grouse shooting and birds of prey and those who manage grouse moors must continue to be vigilant against persecution of harriers.”