Walkers in the Pembrokeshire Coast National Park are being asked to be on the lookout for armed trespassers.
Police and park officials say there have been instances of individuals going on to private farmland in the Newport and Moylegrove areas and shooting wildlife.
An authority spokesman said: "The widespread killing of vulnerable wildlife is totally unacceptable. We will make every effort to work with the Police and the landowners to end this illegal activity."
Dyfed-Powys Police said: "Trespass with firearms is a serious offence and those involved face arrest and up to three months in prison, a fine or both.
"Anyone with any information is urged to contact Dyfed-Powys Police on 0845 330 2000 immediately."