But should their age determine their right to a chance at finding a new home?

The RSPCA ACT is offering half-price adoptions for around 90 adult animals for one week, as the Weston shelter nears capacity.

These great and small creatures include dogs (16), cats (10), rabbits (25), guinea pigs (2) and a range of birds including roosters (5), budgies (23), cockatiels (11) and a galah.

Until next Wednesday, it would cost $162.50 to adopt a dog, $97.50 for a cat and $40 to take a rabbit home, providing they are all more than six months old.

During this period, ducks and guinea pigs cost $15, birds start at $10 and roosters are free.

The RSPCA had adopted over 200 animals in the past two weeks while some adult animals had remained there for more than 100 days.

Staff are becoming increasingly strained, RSPCA ACT director of animal welfare Jane Gregor said.

"We cannot accept new animals, we have been unable to take on new dog surrenders for over one month," Ms Gregor said.

"The older animals sometimes get overlooked when they are many puppies and kittens in the shelter."

Overpopulation also makes it harder to control diseases.

Ms Gregor said there are many advantages in opting for an older pet.

Some of them have been trained to sit and walk well on a lead, owners can know their personality, nature, and full size, and all adult cats and dogs are desexed, microchipped, vet checked and behaviourally assessed.

"We are currently in the middle of kitten season so we will see many more kittens come into care over the next few months," Ms Gregor said.

"But many people do not realise that we also re-home many different types of animals."