A man has been sentenced to three months' jail for his role in the slaughter of a mother bear and her two cubs in their den in Alaska — actions that were caught by a research camera.

Key points: A motion-activated camera set up as part of a bear study recorded the carnage

A motion-activated camera set up as part of a bear study recorded the carnage It showed the younger man firing two shots at the sleeping mother bear, before the father killed the cubs

It showed the younger man firing two shots at the sleeping mother bear, before the father killed the cubs The two butchered the mother bear and placed the remains in game bags before skiing away

Andrew Renner received the sentence while his son Owen Renner received 30 days of suspended time for the April 2018 killings.

Prosecutors said the father and son skied to the site on Esther Island in Prince William Sound, and that the son killed the mother bear in front of her two cubs and then the older man turned his rifle on the shrieking newborns.

A motion-activated camera, set up outside the den as part of a bear study by the US Forest Service and the Alaska Department of Fish and Game, captured the carnage.

The men pleaded guilty to multiple misdemeanour counts, including the illegal killing of the bears.

Aaron Peterson, an assistant attorney-general who prosecuted the case, said jail time in wildlife cases was unusual.

"My office believes and argued for active jail time in this case because of the egregious nature of it, and the necessity of letting the public know Alaska will not tolerate poaching," he said.

'They'll never be able to link it to us'

Andrew Renner's attorney, Scott Sterling, declined to comment. An attorney for Owen Renner did not immediately respond to a request for comment.

At their sentencing, the 41-year-old father was ordered to pay a $US9,000 ($12,498) fine, forfeit a pickup truck, boat and trailer, weapons, skies and cell phones. His hunting licence was revoked for 10 years.

Owen Renner, 18, was ordered to take a hunters' safety course and his hunting licence was suspended for two years. Mr Peterson said the younger man was seen as less culpable in the crimes.

Video showed the men approaching the den and noticing the female bear, according to court documents. The younger Renner fired at least two shots, causing the cubs to shriek.

The men eventually realised the sounds were coming from the cubs, not their dead mother. Andrew Renner then shot the cubs.

The camera then catches the elder Renner saying: "It doesn't matter. Bear down."

They then realised the mother bear had a Fish and Game collar after dragging it from the den.

Andrew Renner then tossed the cubs' carcasses onto the snow outside the den. In another video clip, the younger Renner said the collar was removed.

"They'll never be able to link it to us," he said, before the two butchered the mother bear and placed the remains in game bags before skiing away.

Subsequent video showed them returning two days later. They retrieved the collar, picked up the shell casings, and placed the cubs' bodies in a bag and skied away.

Authorities said Andrew Renner also falsified documentation about killing the animal when it was his son who did so and failed to note the number of bears illegally killed.

AP