A popular nesting area for skylarks has been destroyed after council contractors brought their mowers out three weeks early.
Now residents fear the number of skylarks on Beacon Hill will decline and possibly disappear for good.
The hill, between St Dunstan's at Ovingdean and the Rottingdean windmill, has for years been a popular nesting ground for skylarks, with protected flowers and wildlife, It is an offence under the Wildlife and Countryside Act to kill and destroy protected birds, animals and plants.
Numbers in Britain are declining.
A special management plan has been drawn up because of the sensitivity of Beacon Hill. It involves environmental experts, Rottingdean Parish Council, Brighton and Hove Council and council contractors Ecovert.
Ecovert, following complaints about the way Beacon Hill has been managed by contractors, found it did not have the expertise to deal with the land, and sub-contracted the upkeep of the hill.
Last week the new contractors cut the land and tidied up the western side of the hill and some of the nesting grounds of the skylarks were destroyed.
Rottingdean Tory councillor Lynda Hyde had several calls from worried residents about the mowing.
She said: " We have a proper management plan for this hill and something has gone wrong.
"The western side of the hill should not have been cut until the skylarks had finished nesting, which is not until the end of the month."
Andrew South, public affairs officer for the Royal Society for the Protection of Birds, said: "The nesting season for skylarks is between March and July.
"There are skylarks on the hill as they like short and sparse vegetation which gives them some sort of cover. They also like areas where there is a plentiful supply of insects.
"To ensure they are not disturbed, we would advise no cutting before the end of July."
A spokeswoman for Brighton and Hove Council said: "We were asked to cut the grass by Rottingdean Parish Council because it was getting too long.
"One-third has been mown and we have left the rest. The majority of skylarks are nesting in the remaining two-thirds, but some skylarks may have been disturbed."
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