Rare birds of prey reintroduced to Wharfedale over the past eleven years have continued to thrive this year, but more have fallen victim to poisoning.

The Yorkshire Red Kite Project says the monitoring of breeding pairs of kites got off to a difficult start in 2010, and the hard winter may have accounting for some pairs vanishing from their old nest sites.

More breeding pairs were spotted in West Yorkshire this year than in 2009, and at least 85 chicks were raised. Another 46 young kites were successfully raised in North Yorkshire, an increase of seven on those recorded last year.

But the kites have continued to be poisoned, prompting those leading the project to call on people to report these incidents to the police.

Six birds were poisoned in North Yorkshire this year, and a suspected of case of poisoning in West Yorkshire this month is under investigation.

The large carrion-eating birds became extinct in England and Scotland around 150 to 200 years ago and re-introduced kites today are protected by the Wildlife and Countryside Act 1981.

From 1999 onwards, the Yorkshire Red Kite Project, based on the Harewood Estate, began releasing kites into the wild.

The birds have since become a familiar sight in the skies over the Bramhope area, Menston and Burley-in-Wharfedale, and in the Washburn Valley.

They are easy to recognise by their distinctive forked tail, rusty coloured plumage and habit of soaring with angled wings.

The project revealed earlier this year that since the kites project began, several birds killed by poison had been found in the Washburn Valley, and one in Clifton, near Otley.

The kites projects’ latest newsletter has revealed that a total of 17 birds were found dead in Yorkshire this year. Four are thought to have died after feeding on poisoned bait, while another two are believed to have died as a result of eating dead rats or other creatures which have themselves been poisoned.

The death toll included kite chicks in a nest in North Yorkshire.

A bird released in 2003 was found dead of suspected poisoning in West Yorkshire this month. Test results are awaited.

The Yorkshire Red Kite project said the widespread intensive use of anti-coagulent rodenticides represented the ‘greatest single threat’ to kites and other wild scavengers in the UK.

The project team said: “It is imperative that manufacturers’ instructions are followed. Rats poisoned by rodenticides should be regularly collected up and safely disposed of to prevent them entering the food chains of kites and other scavenging species.”

A further kite was shot in Cumbria, one of the first 30 birds released in the county in a new project.

More birds have been found dead or injured in North and West Yorkshire in 2010, including some found dead on roads, one of their favourite places to search for carrion.