In a centuries-old tradition you can still see men around Hong Kong taking their pet bird for a walk in the park. 'Birds have always been popular in Hong Kong,' says veterinary surgeon Tony Matthews, of Acorn Veterinary Hospital in Sai Ying Pun. With nearly 500 varieties in the city, Matthews adds the most common pet birds are cockatiels, budgies, lovebirds and large parrots, such as cockatoos and African Greys. If you are thinking about becoming a pet bird owner, the vet advises carefully considering the undertaking before flying into ownership. 'Birds are the most difficult and challenging of pets to keep responsibly. It really is a welfare issue, and it's extremely important to give them the correct diet and environment, a large area and proper stimulation,' he says. Matthews recommends the best size for a birdcage is the biggest you can accommodate. 'Having a small cage for their whole lives is not acceptable. It'll be your fault if the cage is too small, and then you shouldn't really keep birds,' he says. While some owners may believe two birds are better than one, some can be aggressive towards each other if they are of the same gender. It's difficult to determine the bird's gender as sexual organs are internal. A common mistake is many people forget birds come from a tropical climate and need not only exposure to ultraviolet light. 'They need full spectrum light for their vision, about two to three hours a day. If they don't have the right frequency, it can almost send them mad,' he says. In the wild, natural daylight in the tropics is limited, so approximately 10 hours a day of light is sufficient, Matthews says. While birds love eating seeds, too many can lead to obesity, or a deficiency in calcium or vitamin A. 'Birds tend to pick out certain seeds like sunflowers that are very fattening and, as a result, give themselves an unbalanced diet,' he explains. Seeds that have been sitting around in warehouses or store shelves can also become old and mouldy, causing respiratory diseases. The best feed for birds, Matthews says, is a pellet diet. These contain all the nutrients, calcium and vitamins a bird needs. In addition to pellets, owners should vary the diet with fruit, such as grapes, slices of apple, pear or orange, leafy greens, and nuts. Inside the cage, Matthews advises natural wood for chewing and stripping the bark should be provided to help with beak care and prevent it becoming overgrown. Over the years, the vet has treated a number of birds injured in preventable accidents. 'If you allow your bird out of the cage, you need to bird-proof your flat. They can electrocute themselves by chewing wires or break their necks trying to fly out of the window when they don't see the glass,' he says. 'Put mosquito netting or crosses over the windows so the bird knows the glass is there.' Matthews says some birds easily mask an illness, particularly parrots. Look out for signs such as loss of appetite, abnormal diarrhoea, losing weight or discharge around the eyes or nose. One of the most common diseases is psittacosis, also known as parrot disease or parrot fever, with symptoms including sneezing, drooping on the perch and general lethargy. Psittacosis is an infectious disease and can be transmitted to humans. Matthews says many vets will routinely check for the disease through a faecal sample. Another major illness that can develop is psychological problems. 'Birds are extremely intelligent and in their natural tropical environment there are lots of colours and sounds,' Matthews says. 'But if they are stuck in a cage in the corner without any toys, company, a varied diet, branches to strip and chew on, sights, sounds or smells they will become bored and depressed.'