The Hazards Associated with Australian White Ibis, An Emerging Urban Scavenger (IMCG)

Jon Epstein, Hume Field, Phil Shaw and Jeff McKee

In South-Eastern Australia urban populations of Australian white ibis (Threskiornis molucca) (AWI) have increased exponentially since 1983. This population increase is related to coastal redistribution of flocks in response to inland drought and the availability of novel artificial food sources in urban areas. AWI have adapted to scavenging food scraps in open landfills and human recreation areas. The ready availability of these non-seasonal food sources has lead to increased fecundity, an extended breeding season and decreased emigration, which have in turn accelerated the population increase. Three main problems have been identified with the increase in urban AWI: Firstly, there is observed environmental damage to remnant urban vegetation due to overburdening by large AWI roosting and nesting colonies – in one remnant rainforest patch there was a marked resurgence in numbers of the endangered Richmond Birdwing Butterfly after 800 AWI nests were cleared from the site. Secondly there is an increased air navigation hazard associated with AWI flocks transiting and feeding around regional airports. – on the eastern seaboard in the last three years, there has been two reported in-flight engine failures in commercial jetliners resulting from ibis ingestion. Removal of colonies proximal to one airport has resulted in an 80% decrease in the numbers of AWI foraging in the airport environs and a marked reduction in air navigation hazard. Thirdly there is a perceived increased risk of disease transfer from ibis to humans and production animal species. The assessment of ‘increased disease risk’ is qualitative and has come about from a number of generic and specific observations. The rapid change in the population dynamics and behaviour of AWI has been accompanied by desensitisation to human presence and observed frequent close interactions between AWI and people in recreation areas, providing theoretical opportunities for disease transfer. These include begging and aggressive scavenging, contamination of eating areas with faeces and nasal secretions, physical contact and minor injury, mainly to young children. There are observed increases in AWI flocks feeding in association with cattle feedlots, piggeries and poultry enterprises in para-urban areas, again providing opportunities (as yet ill-defined) for direct or indirect disease transfer. High densities of AWI on landfills (up to 2000 at a time) increase the possibility of exposure to and recombination involving human pathogens and provide novel opportunities for interspecies mixing with other urban scavengers such as rodents, corvids and kites. Previous surveys on small numbers of AWI ( n=35 & n= 50) demonstrated that 5% of birds carried Salmonellla typhimurium, 5% carried Vibrio cholerae, and 30% carried avian haemoprotozoa. Comparison between surveys 2 years apart showed an increase in sero-prevalence of Newcastle disease virus (NDV) from 5% to 30 % and in Avian Influenza (AI) from 5% to 40%. The NDV strains and AI HN types were not determined, although some high titres to NDV appeared inconsistent with infection with lentogenic strains. The semi–nomadic and semi-aquatic habits of AWI make them potential reservoirs and distributors of flavivirus such as Australian encephalitis virus (AEV) and Japanese-B virus (JBE). Similarly human disease caused by an emerging alphavirus, Barmah Forest Virus (BFV) is increasing in prevalence in the area but as yet reservoir hosts for BFV and its ecology have not been well defined. Prior surveys showed AWI negative for AEV and JBE but showed 15% positive for generic flavivirus. This has yet to be followed up and given the apparent southward spread of JBE serial surveys are indicated. Prior surveys have not included testing for BFV. In the last few years several large AWI colonies have been observed co-roosting with flying foxes Pteropus spp. which carry Hendra virus (HEV) and Australian bat lyssavirus (ABL). The intimate association between the two species raises the possibility that AWI may be exposed to both these zoonotic agents. Water birds are reported as asymptomatic carriers of lyssaviruses elsewhere, and although initial serosurveys of AWI did not demonstrate evidence of infection with HEV, the ecology of HEV is yet to be fully elucidated. ABL has not been tested for in AWI. Co-roosting behavior between AWI and Pteropus appears to be a recent phenomenon associated with the contemporary flux and urbanisation of both taxa. Hence it may be worthwhile to proactively monitor for cross–host transmission.. An ongoing AWI population management plan, first instigated by South East Queensland regional consortium (IMCG) in 1995, has ameliorated some of the ecological, public nuisance, disease and air navigation problems at a local level as alluded to above. Their mitigation procedures. while locally effective, have redistributed rather than reduced urban AWI numbers. Urban AWI populations are still increasing and the primary problem of unrestricted access to artificial food sources has yet to be adequately addressed by local authorities.