Doctor of Philosophy
School of of Biological Sciences
Martin, John, Investigations into the ecology and management of a nuisance native bird in urban environments: the Australian white ibis, Doctor of Philosophy thesis, School of of Biological Sciences, University of Wollongong, 2012. https://ro.uow.edu.au/theses/3845
Urbanisation is a major global trend that presents a novel environment for wildlife to colonise. This novel environment offers an abundance of anthropogenic resources (food, water, habitat), which has occasionally resulted in wildlife encroaching upon humans. Human–wildlife conflicts may be the result of increases in wildlife populations or encroachment on human assets (e.g. dwellings, infrastructure, flight paths); the Australian white ibis (Threskiornis molucca) is culpable in both instances. Ibis in urban settings are commonly considered a nuisance and have been lethally managed for over 20 years. There is a paucity of information, however, regarding the ecology of ibis in the natural or urban environment, and the effectiveness and consequences of the lethal management actions.
To address this information gap I aimed to investigate key attributes concerning ibis behaviour to inform their management and conservation. In urban areas ibis commonly nest within close proximity to humans and are consequently viewed as a pest. Actions to deter nesting include the destruction of nests and eggs or the removal of nesting habitat (i.e. vegetation). These actions are also implemented within some of the larger breeding colonies to reduce the overall reproductive success. At the larger colonies, actions to reduce the reproductive success are conducted to appease residents under the guise that it will slow the growth of the urban population, which is viewed as an issue. These management actions can result in colony displacement, which from a regional management perspective is an undesirable outcome at the larger colonies. Consequently, I assessed a population control technique involving the application of vegetable oil as a method to prevent eggs hatching whilst not destroying the nest and leaving the unviable eggs to be incubated. This method resulted in reduced reproductive success whilst not causing the breeding birds to abandon their nests or the colony.
To address a gap in knowledge about the size of the ibis population in urban areas, I conducted monthly population surveys of the Sydney region over the three years and confirmed that the ibis population varied annually and seasonally. The peak population of 8900 ibis was associated with the peak in the breeding season. Following the breeding season, adult and juvenile ibis were observed to disperse within and outside the Sydney region, with the population dropping to 3000. On average 40% of the ibis population was located within landfills each month, which are a major anthropogenic foraging resource.
While the location of ibis within the Sydney region had been identified through the regional population surveys, the daily movement behaviour of ibis had not been assessed. To address this I fitted radio transmitters (n = 82) to ibis at an urban park, a breeding colony and a landfill foraging site to assess the foraging preferences, roost fidelity and the distance ibis travelled during daily foraging movements. Ibis were recorded moving up to 72 km from their roost during a day’s foraging at multiple locations. Landfills were identified as a major foraging resource with 63% (n = 82) of birds located therein. Ibis were located at up to nine foraging and seven roost sites indicating the connectedness of the regional population. Lastly, the site-fidelity of adult ibis was assessed within an urban park that provides both breeding and foraging opportunities. The first year resighting rate for females was 89% (n = 59) and 76% for males (n = 34); this decreased to 41% of females and 21% of males in the fourth year. Over the four years 77% of females and 70% of males were resighted at additional sites within the study region (~50 km). Females showed greater site-fidelity than males in each of the four survey years suggesting there are greater selective pressures on males to find breeding opportunities.
The results of my research indicate that the management of ibis within urban areas requires a three-pronged focus: 1. reducing access to foraging resources across the focal region, particularly management of landfill sites, 2. establishing refuge colonies where breeding can occur undisturbed, and 3. management of undesirable colonies. Implementing these actions should reduce the frequency of human–wildlife conflicts without negatively impacting the species reproductive success, specifically as the non-urban ibis population has declined in association with natural habitats over the last 30 years.