Nothing spells Australia quite like the iconic sound of a kookaburra laughing. It’s a raucous cackle, loud and distinctive, and one can’t help smiling.

Their laugh is known as the “bushman’s clock”, announcing the start and the close of each day.

Ironically, the main purpose of its laugh is to announce its territory and warn others not to intrude.

Aussies overseas will almost be brought to tears of homesickness if they watch an Australian film with the sounds of kookaburras. It’s the unique sound of the Australian bush. It’s the sound of home.

Songs have been written about them, and the Indigenous Australians have stories and legends about kookaburras – their name even derives from the Wiradjuri word “guuguubarra”.

Sporting teams such as the Australian Men’s Field Hockey team, carry their name of Kookaburras with pride. Kookaburras have been featured on postage stamps and coins, and they were one of the mascots for the Sydney Olympics. They have the honour of being the state bird emblem for New South Wales.

However, kookaburras have a nasty little secret.

Kookaburras are native to Australia and New Guinea, the latter having the rufous-bellied and the spangled kookaburra, which both sound like dogs yapping. The blue-winged kookaburra, found mostly in northern regions of Australia greets the new day with a laugh that finishes like a choking cough, as if it has forgotten its own joke.

However, all three are very closely related to the popular “laughing jackasses” found particularly along the eastern coast states and introduced to the southwest areas of Western Australia. These are the ones we know and love best.

They officially belong to the terrestrial tree kingfisher family – but they rarely eat fish, preferring a diet of worms, beetles and other insects, lizards, and frogs, along with mice and snakes. What could be more delicious?

With increasing degradation of bushland to make way for housing, the presence of kookaburras in suburbia has diminished. Regrettably, we don’t hear their cheerful sound as frequently as in the past.

However, on Tuesday I heard kookaburras laughing merrily, and two were sitting on branches outside my son’s living room. His large property on the far fringes of suburbia has tall eucalyptus trees, and slopes down to a creek. There are doubtless snakes near the creek, (my son had to snake-proof his chicken run) so his backyard offers a promising environment for kookaburras to enjoy life, and a regular source of protein. They were kind enough to pose for photos.

But they too probably have a nasty little secret.

Are they aggressive? Their prey would say yes! They don’t stand a chance when kookaburras swoop. Sometimes “kookas” will bash their catch against a rock to kill and soften it before eating.

However, they are not usually aggressive towards humans unless they perceive a direct threat, in which case they may defend themselves.

Kookaburras often attend picnics and outdoor barbecues, uninvited, where they hope that friendly humans might offer them a piece of sausage or steak. In general, they are quite tame and social, and in urban and suburban areas where they are used to people, they will give a loud chorus of laughter to announce their presence, and then come down from their perch to eat scraps of meat straight from humans’ hands.

We are warned not to feed them – as the birds then have expectations which are not appreciated by other picnickers, and secondly because human food is not designed for their digestive systems.

Of course, occasionally they don’t wait to be offered – they simply swoop down and snatch their chosen delicacy from a human hand halfway between plate and lips. That is quite simply bad manners, not their little secret.

Kookaburras measure around 46 cm (18 inches), and have mostly greyish-brown and white feathers, with a creamy belly area, good for camouflage. Their bodies are solid, and their legs are short but strong. They have a short neck and a long wide bill with a pointed tip.

They can live for up to twenty years and choose a partner for life. During the breeding season, which is mostly the spring months of October and November, (if unsuccessful they will continue into summer), the female lays three (or sometimes four) white eggs in their nest at two-day intervals. Nests are created in a suitable tree hollow, and after twenty-four to twenty-eight days of incubation by both parents, and sometimes older siblings, the chicks are born, blind and naked – totally without feathers, and very vulnerable. The surviving chicks are then cared for by all family members.

But not all do survive. The chicks are responsible for what is called siblicide – they frequently kill their siblings. That’s their nasty little secret.

Kookaburra chicks are very aggressive. They have a small weapon – a special hook on their beaks, and they jab their siblings’ heads. The first two chicks to hatch often peck subsequent ones to death. Their plan B for killing a sibling is to grab all the insects and worms brought back to the nest by their parents and other carers, so that other nestlings starve to death. These attacks are more common when food is scarce. Deaths of chicks are far more frequently caused by siblings than by other predators. Not a very likeable characteristic, and they keep this nasty little secret to themselves. It’s not widely known.

If the chicks are fortunate enough to be survivors, they remain in the nest for about a month, after which they can fly. Somewhere during this maturing process in the nest before they fledge, they lose their hook weapon and then grow up to become nurturing and very helpful.

They remain within the family circle until they are fully independent and can manage for themselves, at around four years of age. During this period, these juveniles also act as helpers during the following breeding season, incubating and finding food for the next generation – often supplying new chicks with half their food. Kookaburras therefore are social, preferring to be in groups rather than just pairs. Interestingly, the name for a group of kookaburras is “a riot of kookaburras”.

In the end these aggressive new-borns turn out to be fine, sociable, and upright members of the bush community, giving pleasure to all who hear their wonderful contagious laughter.