Three puppies dumped in a recycling box in woodland were saved when a passing dog sniffed them out and raised the alarm.
The two males and one female, about eight weeks old, were found shivering in the green plastic box in woods in Failand, Bristol, on Sunday.
They were discovered by a dog being walked in the woods, who ran over to them and barked repeatedly until her owner came.
The owner took the puppies to Holly Hedge Animal Sanctuary in Barrow Gurney, Bristol, where they are being looked after.
A vet will check the puppies, believed to be collie or collie cross breeds, and they will live in foster homes while awaiting adoption.
Staff at the centre, which is caring for 40 dogs and up to 70 cats, have named them Tosca, Carlos and Mabel.
Sarah Schranz, kennel and cattery manager for the charity, said the puppies may have died if it had not been found.
"They are really sweet and very friendly," she said.
"There was a dog walker out walking the dog and it ran off into the woodland and was barking.
"The owner went over and found these three puppies shivering in the bottom of a green recycling box with a little blanket in there.
"It was a Lassie-style rescue.
"We don't know how long they had been there before they were found but it was the afternoon.
"They were in quite an isolated spot where if they had been left for the night they would not have survived.
"They would have struggled to survive in there with no warmth and no mother."
The dog walker brought the puppies to Holly Hedge, where they were checked in and spent the night with managers.
Those looking to adopt the puppies are asked to come into the centre and fill out an application form.
Potential owners should be home most of the time and have knowledge of active dogs.
"It is so sad," Ms Schranz added.
"It beggars belief that in this day and age, with a rescue centre down the road, that someone would leave them there.
"We would never turn away a puppy and they didn't even ask, we had no calls.
"We don't know where they came from. My gut feeling is that these are unsold dogs that were left over from a litter.
"They were going to need vaccinating, worming and flea treatment. They do not have microchips."
The charity has "queues" of foster homes and managers on site at all times, she added.
It is urging those looking to rehome a dog to go directly to rescue centres, rather than posting on sites such as Gumtree and Facebook.
To donate to Holly Hedge visit: http://www.hollyhedge.org.uk.