Twelve little penguins found dumped in a garbage bin on the northern Tasmanian coast were probably killed by a dog, a post-mortem examination has found.

A member of the public alerted authorities to the dead birds, which were discovered at the Low Head Coastal Reserve, last Wednesday.

Rangers from the Department of Primary Industries, Parks, Water and Environment (DPIPWE) have been conducting extra patrols in the area and contacting local dog owners.

"We'll be ramping up our efforts in specific penguin colonies, certainly around the Low Head area, and any dogs found at large could be subject to penalties," ranger Adam Scurrah said.

Mr Scurrah said dog owners needed to ensure their dogs did not leave their properties at night.

"Dogs can get out and come back home without people knowing," he said.

"They have a tendency to seek out these locations where penguins are and can use them just as a toy, thinking it's a great game."

The department is warning dog owners they face penalties if their pets attack wildlife like penguins.

"Dog owners could face fines and in some cases the dog may be destroyed if found to be responsible for taking wildlife," DPIPWE said in a statement.

Anybody with information or knowledge about the death of the penguins is urged to contact the DPIPWE's Wildlife Operations Branch on 0427 437 020 or Police Crime Stoppers on 1800 333 000.