Scores of cockerels are being given up or abandoned after a surge in people getting chicks during 2020.
One charity in Dorset said it took in 11 of the birds in three days, mainly from people who hatched eggs at home.
Margaret Green Animal Rescue said some people had tried raising their own hens amid an egg shortage during lockdown but ended up with male birds instead.
But the noisy nature of the now-adult birds and new bird flu regulations mean many owners can no longer keep them.
Margaret Green Animal Rescue said during the first coronavirus lockdown it was "inundated" with enquiries for ex-caged hens, often from people attempting to secure an alternative supply of eggs.
But now it has no more space at its Church Knowle centre in Wareham and is unable to accept new arrivals or re-home them, except in an emergency, because of the latest lockdown measures.
Charity spokeswoman Jazmin House said: "A lot of people bought eggs during lockdown and are now at the stage where the boys are starting to crow and make a lot of noise.
"We were asked to take in 11 over a three-day period and we are expecting that to increase.
"Now the weather is getting worse and bird flu restrictions are in force, people are not wanting to continue caring for them."
In November and December, the government imposed measures to help slow the spread of bird flu, requiring keepers of all types of birds to keep them inside and to follow strict biosecurity requirements.
The RSPCA said it had already rescued a number of cockerels that had been dumped, including one found in a lay-by near Christchurch on 17 November and another found straying in a garden in Poole on 2 December.