Bermuda?s local birds are increasingly under threat as more and more of their natural homes are replaced by man-made developments, wildlife lovers warn.

Less than half the birds on the Island are now local or migrant species, according to the latest Christmas bird count by the Bermuda Audubon Society.

Experts say many species ? such as bluebirds, white-eyed vireos, longtails and cardinals ? are struggling to survive as grassland, open space and wildlife which used to provide their habitat continues to disappear.

Invasive species ? starlings, kiskadees and sparrows ? are more aggressive and able to out-compete local birds for habitat which remains. As a result, these birds made up 52 percent of the 7,000 birds recorded in the count earlier this month.

Environmental change in the Americas has also impacted on the number of migrant birds, which land on the Island as they fly across the Atlantic.

Andrew Dobson, who co-ordinated the Christmas bird count, said he was disappointed at the numbers of local birds. Mr. Dobson said: ?Bermuda has become far more urbanised in recent years and breeds have to compete for an increasingly small amount of natural habitat.

?The growing number of buildings will affect our local birds. If you have less space, then you have less habitat for our local breeds. This affects everything from longtail nesting sites to green grassland areas for bluebirds.

?Barn owls are now becoming very rare because they don?t have the space in which to hunt.?

Starlings were originally introduced to Central Perk in New York and spread to Bermuda around the 1950s while kiskadees were introduced to the Island at about the same time as an attempted biological control on lizards. Sparrows were also imported to North America from Europe.

Mr. Dobson said the bird count underlined how they all posed a threat to local birds.

?Fifty two percent of all birds were starlings, kiskadees or sparrows ? all invasive species which shouldn?t really be in Bermuda ? and they have certainly had an impact on our local birds,? he said.

?They are more successful than the local birds. Invasive species like starlings will be aggressive towards the local birds and can take over nest holes. Kiskadees are very aggressive and territorial, and house sparrows will take bluebirds? nest boxes.?

Mr. Dobson said numbers of migrant warblers had reduced due to the disappearance of habitat in Canadian and American forests, and deforestation in Central and South America.

?The low numbers of migrant warblers continues a depressing downward trend in the population of these species,? he said.

?If their habitat is gone in North America and less are being bred, it will affect the number that pass through to Bermuda on migration.?

Exactly 100 species of birds were recorded by 20 members of the Bermuda Audubon Society, who carried out their count in a 24-hour period. Unusual species included a grey heron at Tucker?s Town Bay, a bird that is common on the other side of the Atlantic.

Meanwhile, a northern mockingbird, a species rife in North America but rarely seen in Bermuda, was found on Boaz Island.

Other unusual finds included a snow goose on Belmont golf course, a hummingbird in St. David?s and a surf scoter on Mangrove Lake.

Two species of globally endangered species were spotted: Bermuda?s national bird, the cahow, and the piping plover, a small shorebird which breeds in the eastern US and Canada.

The Christmas bird count is carried out by more than 50,000 observers across the Americas, and its results are compiled into the longest-running database in ornithology.

It aims to monitor the status and distribution of bird populations across the western hemisphere. Organisers hope to use the information to identify local trends in bird populations which can indicate environmental threats to wildlife.