The number of barn owls in Suffolk has dramatically declined due to the cold and prolonged winter and spring, wildlife chiefs have said.

News that barn owl mortality rates in the county have soared was revealed after a barn owl chick is believed to have been stolen from a north Suffolk nature reserve on Sunday night.

The chick, which was ringed by the Suffolk Wildlife Trust about 10 days ago, went missing from its box at the trust's Carlton Marshes reserve, near Lowestoft, after two males were seen interfering with its nest. A neighbouring barn owl box was also damaged.

The reserve's two barn owl boxes are part of a network of more than 1,400 boxes set up in the county since 2007 by the Suffolk Community Barn Owl Project to help boost the declining numbers of the birds.

Revealing the impact of the bad weather on the barn population Matt Gooch, the trust's broads reserves warden, said: 'Both barn owl boxes had their doors ripped off, then the little chick we had ringed only last week is gone. Not surprisingly there is now no sign of the parent birds.

'It is particularly worrying as due to the cold and prolonged winter and spring this year, barn owl mortality has been extremely high. In 2012 we had more than 30pc occupancy of the barn owl boxes, but due to high casualties sustained this year we are down to 5pc.

'If these vulnerable creatures also have to contend with vandalism and chick theft then their recovery in the county will be seriously impeded.'

In April, Suffolk Wildlife Trust revealed that mainly because of the box project the number of breeding pairs of barn owls in Suffolk had risen from 108 in 2007 to 427 last year – the highest number of birds recorded since 1932.

However, barn owl numbers have fallen over the winter and spring due to flooding of river valleys, very cold weather and overgrazing by livestock all leading to a fall in voles on which barn owls feed. But there are hopes that the barn owl boxes will provide a lifeline to the species.

Steve Piotrowski, who leads the trust's barn owl work, says the recent population loss has been 'devastating' and has left bird numbers 'even more vulnerable'.

Mr Piotrowski said: 'It was good news when barn owl box monitors noted 437 occupied breeding sites in Suffolk in 2012. This has helped this declining species build its populations to a sustainable level which will hopefully help them through this awful period.

'Sadly, without this intervention (the bird boxes) this recent harsh weather would have had a far greater impact and I fear the barn owl could have been lost to Suffolk altogether.'

Anyone with information on the damage to the barn owl boxes and the possible theft of the chick, which happened at about 9pm on Sunday, should call Suffolk police on 101.