Photographing animals has been a lifelong passion for veteran lensman Rick Stevens, affectionately called "The Rat" by his colleagues.

Stevens first visited Sydney's Taronga Zoo as a cadet in the early 1960s. He was attracted to photographing animals because of the challenges involved in getting a frame that has impact and holds the viewer.

As he explains, "Animals don't complain about bad hair days, they're not self-conscious, but on the other hand you can't tell a group of chimps to move closer together. In many ways there are similarities between animals and humans. There is not much difference between a group of young chimps playing and a group of young children playing; they misbehave much the same and get scolded by their parents much the same way."

At zoos and wildlife parks around the world, photo calls are typically held for newly born arrivals and cute, furry imports, high in the "ooh, ahh" factor. Here, Stevens celebrates the senior citizens of Sydney's Taronga Zoo.

The life span of animals in captivity varies from species to species, but generally it is longer than their wild relatives due to easy access to food, lack of competition and expert medical care.