How the urban bird gets the worm

Foraging habits of the Australian White Ibis revealed in science journal PLOS ONE today.

12 April 2018, Sydney, Australia: Despite their proven predilection for carbohydrates, when the weather changes, so does the diet of inner-city ibis. Research published today in the science journal PLOS ONE demonstrates that the Australian White Ibis, fondly known as the ‘Bin Chicken’ engages in complex foraging decisions mediated by rainfall.

Researchers from University of Wollongong, Royal Botanic Gardens, Sydney and Australian Museum quantified Ibis density, bin density, food dumping and picnicking in Sydney’s parks. They found that Belmore Park, adjacent to Sydney’s Central Station, was the stand-out in terms of fast food volume.

In dry weather, Australian White Ibis congregate in Belmore Park at a density that is 10 times higher than other parks, including Hyde Park and the Domain – the central Sydney parks.

But after rainfall, ibis numbers drop in Belmore, a pattern consistent with 7 years of survey data. No such decline was apparent in the other parks, in fact some increased their Ibis populations after rain.

Dr. Richard Major, Principal Research Scientist, Terrestrial Vertebrates, Australian Museum said, “My Eureka moment was when I emptied my home-brew steriliser on my lawn and observed a handful of earthworms wriggling out of the soil.”

Building on this discovery, University of Wollongong Honours student, Matt Chard, took up his mentors’ challenge and systematically dosed 1 m2 quadrats of city parks with the new-found skin-irritant, both before and after rainfall. “The carboy-cleaner was the perfect brew”, said Chard. “Not only did it demonstrate that worms were 80% more abundant after rain than in dry periods, but we found six times as many worms in the Domain as in Belmore Park”.

In between rummaging in bins and feeding on sandwiches, the researchers found that Ibis spend a large proportion of their day picking around for natural foods. They suspect that the high density of Ibis in Belmore Park has depleted its worm population.

When the rain comes, many birds, use their foraging memory to spread out from Belmore Park and head for greener pastures. There, they exploit the worm windfall that moves up in the soil profile. Indeed, the rate of worm consumption by Ibis was four times higher in wet weather than dry weather.

“Humans have complex interactions with wildlife and it is accentuated in landscapes where human impacts are high,” concluded Chard. Importantly, no earthworms suffered long-term harm from this research. “All worms were counted, rinsed in water and returned to irritant-free ground where they soon reburied – unless they were discovered by an opportunistic ibis.” Chard said.

Paper is available on 12 April, 2018 at:
http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0194484

For interview opportunities or further details please contact:

• Claire Vince, media advisor, Australian Museum: claire.vince@austmus.gov.au / 0468 726 910
• Victoria Bogovac, publicist, University of Wollongong; vdimise@uow.edu.au