A supermarket has been criticised on social media for putting up netting to stop swallows from nesting.
Tesco erected the nets above its trolley park at its Ipswich Road store in Norwich after complaints about bird droppings on the trolleys.
Concerns have been expressed that the migratory birds will get caught in the mesh and die, and the move has been branded unacceptable by many.
Tesco said it had left the back of the store clear so they could nest there.
However, according to Chris Skinner, a Norfolk farmer and conservationist who has been monitoring the swallows at the Harford Bridge shop since they arrived about six years ago, the birds would try to return to the same spot - where they would be greeted by the netting.
There had been "complaints about swallow poo on the trolley handles and the little seats which children sit in", he said.
The birds had flown from South Africa - a 5,000-mile journey - and not being able to access [the former nesting site] meant they would not breed there this year, he said.
Seriously @Tesco ?!? Netting off swallow nesting sites in trolley shelters in Norwich. Experts say returning swallows will get caught and die. Take them down!!!!! @BBCNews @ChrisGPackham @katehumble @BBCNorfolk https://t.co/houQVgDyDv— Jake Humphrey (@mrjakehumphrey) March 15, 2019
Mr Skinner said it was not illegal to install netting as long as it was not done within the nesting season, which is "two or three weeks' away".
The simple alternative was to put boarding underneath the nesting site, he added.
Conservationist and writer Kate Blincoe described the netting as "not acceptable at all".
Others on social media said the netting was "horrendous" and "disgusting".
A spokesman for the supermarket chain said the netting was installed following customer complaints.
"We needed to take steps to address the risk presented by bird droppings to our trolleys," he said.
"Following advice from experts, we are installing netting at the front of the store.
"This is designed to encourage birds to the back of our store which has purposefully been left open so that they can nest here instead."
The RSPB tweeted to say it was aware of the netting and was discussing the situation with Tesco.
We're aware of the situation at @Tesco Norwich re netting the building where swallows traditionally nest. We're currently in discussions to provide advice to support returning swallows & find ways to accommodate them. We'll advise once we have further detail.— RSPB (@Natures_Voice) March 15, 2019