One of Nova Scotia's leading environmental groups is encouraging cat owners to keep their pets indoors to keep more birds alive.

"When it comes to birds, we don't necessarily think about it but  there's a large number of birds that are killed by cats every year," said Mark Butler, the bird conservation co-ordinator at the Ecology Action Centre.

"The estimate in Canada is about 100 million birds a year are killed by cats."

The Ecology Action Centre and the Hope for Wildlife Society have teamed up to create the Allied Cats program and spread the message.

"As a cat owner you don't want to think of your pet as the one that's causing any destruction because they're like family and you don't want that to be the case," said Veronica Sherwood, the owner of two male cats and part of the Allied Cats program.

"I was hearing more and more from friends of mine in the birding community that we were losing a lot of songbirds as a result of cat predation and feral cat colonies and cats being outside, taking the birds."

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Cat owners are being encouraged to keep their pets indoors to keep more birds alive. (CBC)

Sherwood said one of the last times she let her cats out into her backyard unsupervised, they killed a downy woodpecker she had been observing.

"I was mortified. I was heartbroken and I just said, 'No, there's something I have to do about this.' It's wrong," she said.

Sherwood put up chicken wire in her backyard so her cats could no longer jump over the fence and her pets are always supervised when they're outside. She also took down her bird feeder to attract fewer birds to her backyard.

"A lot of people feel, 'Well the cats have to go out and hunt because that is natural.' But in the fact the cats are brought over here and domesticated so a domesticated cat does not have to go outside," Sherwood said.

"The reality is, they're healthier and safer in the indoors from cars, from getting in fights with other animals, attacked by dogs, different diseases."