A Dunedin woman who saw a sparrow plummet to the floor in Pak'nSave and begin to die a prolonged death says she was horrified to learn the supermarket poisoned birds.

Pak'nSave owner Foodstuffs NZ defended the practice as necessary to prevent the spread of disease, but said it was looking into alternatives.

The woman, who requested anonymity, said she was shopping in the South Dunedin supermarket on Friday when she saw the sparrow fall from the air and land with a thud on the ground.

"I went up and it was obviously dying in one of the aisles." She scooped up the young bird before taking it to the customer service desk.

"I asked the lady there, 'are you poisoning your birds?"' The staff member was not aware of the practice, but after making a phone call to a manager she confirmed the store had laid poison.

The woman made her objections clear as the bird continued to languish.

"I said to her, 'that's not on, it's cruel and distressing to see'.

"And she said, 'yeah, it upsets me as well'." Leaving her shopping in the store, and by this point distraught and crying, the woman took the ailing bird to a nearby vet to be euthanised.

"I just wanted it to be assisted to pass on as quickly as possible. I was very upset ... distraught and crying on the street.

"It's just sad to see an animal suffer."

A self-described animal-lover, the woman suggested the store should invest in traps where birds can be caught before being set free.

Foodstuffs NZ spokeswoman Antoinette Laird said birds loose in supermarkets could spread disease via droppings, "hence the need to remove them".

Asked why traps were not used instead of poison, Laird cited health and safety.

"While our stores endeavour to use the quickest and most humane solutions available for pest control, we also have to look out for the safety of our team.

"Traps in lofty ceiling spots are potentially difficult and dangerous to manage."

However, Laird said the Hillside Rd store had advised it was "looking into alternatives".

She would not be drawn on the type of poison employed.