WALKERS on the heather moorlands of Upper Wharfedale are being asked to keep an eye out for hen harriers.

The moorlands are the natural habitat for the country's most threatened bird of prey, which last year only managed four successful breeding pairs.

In an effort to find out where the birds may be breeding, the RSPB is asking people to contact its Hen Harrier Hotline with any sightings.

If any breeding pairs are located, they will be protected round the clock by RSPB volunteers and information used towards their continued survival.

“Sadly, hen harriers are a much rarer sight in the Yorkshire uplands than they should be," said Amanda Miller, conservation manager for the RSPB in Northern England. "But if you are lucky enough to see one, it’s an experience you won’t forget in a hurry. The male’s courting ritual is a particularly stunning spectacle; a series of breathtaking swoops and somersaults that earns it the name Skydancer.”

Hen harriers are in trouble largely because of ongoing illegal persecution, says the charity.

In addition to their diet of small birds and mammals, hen harriers sometimes eat grouse, which brings them into conflict with the driven grouse shooting community.

This type of shooting requires huge numbers of gamebirds and some game managers feel they need to illegally kill or disturb harriers to protect their business.

A government-commissioned scientific report, published in 2011, found that illegal persecution continues to be the biggest single factor preventing the hen harrier’s recovery in England.

“Breeding hen harriers are so rare that any sighting is extremely important," added Ms Miller.

"We have dedicated staff and volunteers ready to protect nests around the clock but we can only do so if we know where they are.

"I would urge anyone who spends time in our beautiful uplands to keep an eye out for these stunning birds and get in touch with us if they see one.”

Male hen harriers are an ash-grey colour with black wing tips and a wingspan of just less than a metre. They are sometimes known as “ghostbirds” because of the pale colour of their plumage.

Female hen harriers are slightly larger, owl-like in appearance, and have a mottled brown plumage, which camouflages them when they nest on the ground. They have obvious horizontal stripes on their tails, giving them the nickname “ringtail” and a patch of white just above, on the rump.

The Hen Harrier Hotline is part of Skydancer, a four-year RSPB project aimed at protecting and conserving nesting hen harriers in the English uplands.

It is funded by the Heritage Lottery Fund and United Utilities, with additional support from the Forestry Commission.

This year, Skydancer’s monitoring and protection work will be getting an extra boost from the RSPB’s new European-funded Hen Harrier LIFE Project, an ambitious, five-year project, which aims to expand on hen harrier conservation work across northern England, and southern and eastern Scotland.

The hotline number is 0845 4600121, and calls are charged at a local rate. Reports of sightings, including the time, date and exact location, with grid reference if possible, can also be e-mailed to henharriers@rspb.org.uk.