Here's why kookaburra numbers are declining in Australian cities

The kookaburra is an Australian icon: the birds are a symbol of Australia’s avian wildlife, known to children as 'king of the bush; from the nursery rhyme 'Kookaburra Sits in the Old Gum Tree'.

But a recent study has found kookaburra populations are in sharp decline. 

The study was published in the peer-reviewed journal Biological Conservation and used citizen science data to examine the diversity of bird species across Greater Sydney, Greater Melbourne, Greater Perth and Greater Brisbane, which included the Gold Coast. 

Griffith University ecologist Carly Campbell said: "We have found that a lot of these species that we consider 'common' might not necessarily be as common as we thought anymore.

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"Iconic species such as the galah and kookaburra have declined in prevalence in urban areas." 

Campbell, the study's lead author, said that there is also an increase in aggressive birds—like the noisy miner—which flourish in urban areas.

"[These] are often implicated in driving down the prevalence of other species because they are so aggressive," Campbell said.

Among the reasons for the decline in kookaburras are that diminishing habitat options reduce their nesting options and food sources. 

Sparse backyards with limited trees and plants, on the other hand, allow the aggressive, noisy miner to keep a better eye on their territory—chasing other species out.

Ms Campbell said people and communities could play a key role in keeping a diversity of bird species in their city's suburbs. 

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She said: "Think about our backyards and the spaces we look after as a place for wildlife as well.

"Often that comes down to picking the right species of plants for our backyard and that's making sure we have a variety of different types of plants…not just the ones that have beautiful showy flowers, but ones that can also provide a habitat for smaller birds as well, such as some dense shrubs and structural complexity."

Beyond the individual, she also said state governments and local councils should be preserving native vegetation or else risk moving towards a homogenised set of species. 

"It's so important that we do keep that amazing diversity in our cities and suburbs. We want to avoid our cities all ending up looking the same in terms of what species we see," she said.