North Yorkshire Police said it has received "worrying" reports of possible squirrel poisoning near Harrogate.
The reports have come from the Burton Leonard area, between Harrogate and Ripon.
Officers have said that checks with vets have not identified any diseases or illnesses likely to be the cause.
A police spokesperson said:
“It is illegal to set poison for squirrels and any control attempts should be requested through council or approved pest control.
“Deceased animals should be disposed of in a way that prevents other pets or wildlife being able to access remains.”
Officers urged anyone with information about the reports to call 101.

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