Thousands of Californian hens have escaped being gassed after an anonymous donor provided $50,000 for some of them to be flown across the US on a charter flight to a happy retirement on the east coast.

The hens, who have reached the end of their egg-laying life, were due to be killed – a common practice in the US.

But after an approach from the Animal Place sanctuary in northern California, 3,000 of them will enjoy a comfortable retirement instead. Thanks to an unnamed benefactor, 1,150 of them will be flown to New York to be distributed to sanctuaries in the eastern US.

"It's certainly the first time this many adult birds have been flown across the country," said Marji Beach, education director at Animal Place.

Commercial airlines would not accept the 1,150-chicken load, which is why the group had to turn to a private jet company. Beach said the jet company did not seem shocked by the request.

Beach said she was also surprised that the egg farm allowed it to rescue the hens. "The big battery-cage operations – where the hens are crammed into cages so small they can't even flap their wings – we just didn't think they would ever be open to an animal rights organization going to their property and pulling hens, but this person was," said Beach.

This batch of two-year-old rescued hens is expected to live two to four more years on these farms.

Animal Place has saved 12,000 birds since it started in late 2010, the largest rescue operation it has saved 4,460 hens.

"If you met a chicken, they have unique personalities like dogs and cats and we think they deserve the same amount of compassion and respect that we give to dogs and cats – I promise we're not crazy," said Beach.

An employee from Sasha sanctuary in Manchester, Michigan will make the eight to nine hour drive to New York to pick up one hundred birds to join the sanctuary's collection of cows, pigs and other farm animals.

"It's going to be a challenge, it's going to cost us a lot of money, but we're glad to do it, these birds deserve a chance, unfortunately we can only take a small proportion," said Sasha director Dorothy Davies, who started the sanctuary in 1981.

Davies said the last time she remembers any rescue animals being flown across the country was after hurricane Katrina, when shelters took in displaced dogs. She said that it was an uncommon sight and that hens raised to lay eggs are "almost never" rescued. "I don't know how they pulled it off," said Davies.

Chickens raised to lay eggs have a different genetic makeup than birds raised to be used as meat. Once the egg-laying birds lose their ability to produce a profitable amount of eggs they serve no commercial use.

"It's not your all-purpose bird that grandma had in the backyard – got a couple eggs, had them for sunday dinner – it's not like that anymore," said Davies.

At the sanctuaries, the birds will be kept separate from other chickens to be screened for health and monitor their adjustment to farm life.

"They have not walked around, they've been in cages, they've never seen the sky before so it's going to be quite an adjustment for them, hopefully they will adapt and be happy," said Davies.