The RSPB has been accused of acting like a “corporate monstrosity” for attempting to impose parking charges at one of north Wales’ most scenic birdwatching locations.

The Royal Society for the Protection of Birds plans to charge £5 a day for peak season visits to the South Stack reserve in Anglesey, despite renting the 780 acres of public land for just £7.

Parking at the reserve – home to puffins, guillemots, peregrines and razorbills – has been free for the last 41 years.

Locals argue the new charge would price the community out of enjoying their own land. Anglesey is one of the UK’s poorest regions, ranking last in government statistics for the strength of the economy out of the 173 economic regions in the UK.

The RSPB has taken its fight to the planning inspectorate, launching an appeal after councillors on the Isle of Anglesey county council twice rejected its bid to impose the charges.

At one of their meetings with the RSPB prior to their appeal, local councillors accused the charity of losing their way. “How much more money does the RSPB seriously need? … This isn’t a charity, you’ve become a corporation,” councillor Robin Williams said.

Councillor Trefor Hughes accused the RSPB of being “an organisation which wishes to make money on those locals who cannot afford the fee”.

Councillor Dafydd Rhys Thomas said it “feels like David versus Goliath with this very rich charity trying to tax our historic right to roam”.

Lewis James, RSPB Cymru head of reserves said: “It is increasingly challenging for conservation organisations to raise the funds needed to manage special places that are hugely important to wildlife, especially at a time when species across Wales are in decline and many are being pushed towards extinction.

“As a site of special scientific interest there is a legal duty on the Isle of Anglesey county council to protect the special features of the area. Every year the RSPB invests almost £250,000 in managing over 300 hectares of land at South Stack. The RSPB has held the lease for this land on behalf of the local authority for over 40 years and incurs costs that would otherwise fall to the taxpayer.

“We want as many people as possible to come and discover places like South Stack so have avoided having parking charges when other places have introduced them. However, we must now seek other means of securing the funding necessary to protect sites like South Stack. We have listened to a wide a range of views expressed about our charging proposals and we’ve responded to the public’s opinion by changing the pricing the structure, which means there will be a trial concession at a rate of £20 for Anglesey residents.”

The RSPB wants to use the income from the new charges to help fund a £840,000 visitors’ centre.

The charity, which earns £140m a year and has received over half a million pounds in public grants since 2016, says the income from parking is an essential part of the business case for financing eight local staff for the centre.

Neither the concession of extending the £20 annual pass to Anglesey residents, nor a proposed staged fee of £2 an hour has been enough to quell support for a petition against the parking charges, which has gained about 6,130 signatures.

But Keith Moore, who runs Anglesey Social Media, a Twitter page with more than 44,000 followers, says residents are unconvinced: “This monstrosity of a corporation wants to build this useless centre off the back of this extortionate charge. A real charity is about the community as well and our council has huge funding pressures”.