But Worthing Borough Council has defended the work, saying it applied for the licences needed to do this and worked within the law.
Dan Fagan, of Stanhope Road, said he had seen herring gulls nesting on the derelict site for three years, so when demolition works began earlier this year, he informed the council.
On May 12, he spotted two nests: one on top of the old car garage alongside Teville Road and one on top of the multi-storey car park.
On Monday, May 14, the 32-year-old claimed he told the council and site foreman about the nests. But the next day, he claimed demolition continued and the nest on the multi-storey car park was destroyed.
Mr Fagan, who has worked in conservation for 12 years, said: “It was heartbreaking, because I saw the gulls building the nests.
“So to see it being ripped out from under them in such a destructive manner with the pinchers of a crane, I was completely horrified.”
He said he reported the destruction of the nests to the police under the Wildlife and Countryside Act 1981, which protects all gull species.
However, the council emailed him days later to say it had a licence to destroy the nests on health and safety grounds because high winds on the half-demolished building posed a safety risk, he said.
On Friday, May 18, the second nest was destroyed.
Mr Fagan said he was happy the ‘eyesore’ was finally being demolished but felt Teville Gate’s renovation should not come at the expense of wildlife. He said: “Seagulls are our iconic seaside bird and we should be celebrating the fact they are here breeding, even though they might steal your chips.
“We need to change that thought that they are vermin because they are becoming increasingly under threat – especially if the council destroys their nests.”
A Worthing Borough Council spokesman said: “We have correctly applied for and received a GL05 licence for the works from the Environment Agency.”
Sussex Police confirmed it is a criminal offence to disturb a herring gull’s nest under the Wildlife Act, but could not find a record of Mr Fagan’s report.