Up to 1,800 "vulnerable" day-old chicks have been abandoned in a field in Lincolnshire, sparking an RSPCA investigation.
Officers of the animal welfare charity were called after the chicks were left in a field near Crowland on Friday.
Insp Justin Stubbs of the RSPCA said: "I have never seen anything like it; it was just a sea of yellow. And the noise was unbelievable."
He said some birds were dead but most "did not appear to be suffering".
"For someone to dump these vulnerable chicks is unbelievable," he added.
There were between 1,500 and 1,800 chicks dumped, of which about 30 were dead or dying, the RSPCA said.
Some of the birds had to be humanely put down.
Insp Stubbs said: "These chicks were just all huddled together, just a mass, a writhing mass of cheeping yellow fluffy balls, where they shouldn't be, in conditions they should not be out in.
"The sick ones sadly had to be put to sleep. They were literally dying of exposure.
"I've never known anything so ridiculous. We get a lot of animals dumped in a lot of numbers, 80 here, 100 there, of mice, guinea pigs, rabbits.
"But 1,800 chicks, I'm never going to get over the number and the vulnerability of these particular animals."
It is not yet known if the chicks came from a nearby commercial producer or if they were abandoned by someone else.
People in the area helped round up the birds into boxes and a breeder collected the survivors and took them back to his unit.
The RSPCA said the chick producer was co-operating with its investigation.