Sally, a rare Montagu's harrier, has gone missing from her Norfolk breeding site leading to fears that she may have been killed.

Eastern Daily Press: Sally, the rare Montagus harrier that is feared dead. Picture: RSPBSally, the rare Montagus harrier that is feared dead. Picture: RSPB (Image: Archant)

She was last seen near her nesting site on August 6 before her satellite tracker went dead.

The Royal Society for the Protection of Birds (RSPB) said it was 'a major blow for this species in the UK'.

Sally and her mate Roger were the only pair of Montagu's harriers left in eastern England and one of only four pairs in the country.

They had bred at Bircham Tofts for the past two seasons, raising a total of five juveniles, the RSPB said.

Eastern Daily Press: Sally, the rare Montagus harrier that is feared dead. Picture: RSPBSally, the rare Montagus harrier that is feared dead. Picture: RSPB (Image: Archant)

Due to the rarity of the birds, the society had been closely monitoring Sally with the aid of satellite tracking.

But since she went missing, only Roger has been seen at the nest site.

Mark Thomas, a senior investigations officer for the RSPB, said the signal should still transmit for several days after a bird dies until the battery failed.

He said: 'We know she roosted just north of Bircham Tofts on August 5 as we have several precise data points during the evening. She was then reliably seen by birdwatcher at mid-day on August 6 near her nest site.'

Eastern Daily Press: Sally with TV presenter Martin Hughes Games and scientist Raymond Klaassen of the Dutch Montagus Harrier Foundation. Picture: RSPBSally with TV presenter Martin Hughes Games and scientist Raymond Klaassen of the Dutch Montagus Harrier Foundation. Picture: RSPB (Image: Archant)

He said they had received data from her tag that morning and expected further transmissions in the evening that never came.

'We have checked the predicted satellite passes and we should have had quite a few over the proceeding days even if she had died naturally - we have had nothing from Sally.

'Something very serious has happened to the tag, and most likely the bird. It is highly suspicious.'

Birdwatcher Mark Batten is believed to be the last to have seen Sally.

He said: 'We had gone to the area to look at the youngsters and saw Roger. We also saw Sally very briefly and thought nothing more of it. We returned later that evening but did not see either bird.'

Mr Batten said he had posted the sighting on social media. 'The next thing I knew I got a message from Mark Thomas asking to talk to me.'

A Norfolk police spokesperson said: 'Anyone who knows the whereabouts of the bird, or the satellite tag, or who has any other information, should contact Norfolk Police on 101 quoting incident number 128 of 15 August.'

Satellite tagging technology

Satellite tags provide conservationists with valuable information on the migratory patterns of birds.

Mark Thomas, a senior investigations officer for the RSPB, said Sally had amazed everyone last winter by travelling the furthest south of any tagged Montagu's harrier when she wintered in Ghana.

'This year she timed her return migration to perfection, arriving back in Norfolk at the exact time as Roger and they met up once more over last year's breeding field. Her satellite tag has been very reliable giving us a daily window into her life.'

He said satellite tags would continue transmitting signals even when a bird is dead, so long as the tag is in daylight.

'This enables you to locate the body and tag. In fact, the Dutch Montagu's' Harrier Foundation recently located a tag on a dead Montagu's harrier in Senegal, Africa over a year after the bird died, as the tag had reliably been transmitting a signal every day.'

Montagu's harrier

The RSPB describes Montagu's harrier as a slim, medium-sized, long-winged bird of prey.

It has a long tail, is smaller than a buzzard, and has more pointed wings than the similar hen harrier.

The male is grey above and the female dark brown.

In flight, it shows black wingtips and a black stripe across the inner wing.

It is an extremely rare breeding bird in the UK, and its status is precarious.

Each pair needs special protection.

Sally was was paired with Roger and together bred successfully in Norfolk for the past two seasons raising a total of five juveniles.

The birds seem increasingly to be nesting on arable farmland rather than on marshes.

They are summer visitors, and migrate to Africa to spend the winter.

Nest sites are generally kept secret to protect them from egg collectors and other unwitting disturbance.