The cacophony of screeches, whistles and tweets heard from outside Lyn John's home crescendo to a deafening pitch the closer you approach.

Inside the unassuming house in Hammondville in Sydney's south-west, Ms John is a foster mum to 60 birds.

Her back patio is lined with large enclosures, while two of her rooms have been turned into aviaries and are stacked to the ceiling with cages.

"They're my alarm birds ... they knew a stranger was here," Ms John said as a way of explaining the noise.

"I am going deaf.

"I have some hearing loss but I am used to it, and when I'm working I'll tune out the noise."

Lyn John helped set up a parrot alert website to report injured and missing birds. ( ABC Sydney: Amanda Hoh )

Formerly an animal rescue worker, Ms John set up the avian foster service six years ago.

She has 12 volunteer carers around Sydney who also house birds and has in total about 100 birds on her books.

There's a range of species including a love bird, cockatoos, galahs, lorikeets, eclectus parrots, Indian ring-necks, conures and a couple of rare and sought-after Amazon species.

Lola, a doubled-headed Amazon, which is an endangered species to Mexico and South America, is a bright yellow and green and is accustomed to talking and singing to Ms John throughout the day.

The other, a beautiful blue-fronted Amazon named Marley, has taken some time to recover after being found in a dumpster.

Injured birds are nursed back to health. ( ABC Radio Syndey: Amanda Hoh )

The majority of birds are given to Ms John by vets, while others are handed in after being found injured or because their owners had died and the family was unable to take over its care.

Surprisingly, there are no complaints from Ms John's neighbours nor the local council.

"I've got really good neighbours actually. One neighbour has canaries and quails also," she said.

"Because [the birds] aren't permanent, it doesn't break any laws."

A full-time job

Ms John rarely has time for herself and said she and her husband hadn't had a holiday in years.

Her day starts at 5:30am cleaning the cages, refreshing water bowls, and preparing a "gourmet" salad mix that included sweet potato, kale, bok choy, carrot, cauliflower, red cabbage, silverbeet, chia, quinoa flakes, rolled oats, capsicum and squash.

"They also get fruits like passionfruit, pomegranate, apples, apricots," she said.

"I get up at 4:30am every Saturday to go to Flemington markets and do a weekly shop for them."

Ms John believes there should be stricter rules and regulations for bird owners. ( ABC Sydney: Amanda Hoh )

Ms John keeps the birds for at least a year before putting them up for adoption.

Her main goal, however, is to reconnect the birds with their owners.

Recently, she was able to return a galah to its owners, two years after it had gone missing.

"If we can't find their owners after a year, two years, we put them up for adoption, reluctantly in most cases, because we get very attached to them," Ms John said.

"I cry when they go. I am a big sook."

Fending off interested parties

There can be a dark side to the foster care experience.

Some birds, like the Amazons, can fetch up to $5,000, while others like the New Zealand kakariki or ring-necks are worth between $60 and $250.

Ms John lets the birds stretch their wings one at a time. ( ABC Radio Sydney: Amanda Hoh )

Ms John said she'd had people enquire about different birds and purported to be their owners with the intention of reselling them.

"Unfortunately it happens a lot," she said.

"We don't flick the birds on like the RSPCA who get them in, hold on to them for three or four days, then sell them.

"We try and get them home.

"We're not in it to make money on the birds — we're here to look after them, keep them safe until we can find their owners."