The Abundance and Movements of the Australian White Ibis Threskiornis molucca in an Urban Environment

The Australian White Ibis Threskiornis molucca has established large, permanent populations in many urbanised areas of coastal eastern Australia, and many agencies aim to reduce its numbers. This study investigates daily and seasonal trends in the abundance and movements of ibis in Centennial Park (a large inner-city park of Sydney, NSW) from autumn to mid-winter (non-breeding to breeding season). Abundances fluctuated daily and seasonally. Highest numbers of ibis were observed during early mornings and evenings, while numbers were lowest during late morning and midday. Most ibis travel daily to a feeding site and only used the park for roosting. Ibis movements into and out of the study area were significantly orientated toward the same main direction throughout the study. Key temporal trends in ibis movements to and from the roost were identified, with approximately 50 per cent of all morning departures occurring within 40 minutes of first light and over 50 per cent of all evening arrivals occurring between 40 and 10 minutes before darkness. Abundances also fluctuated seasonally with lowest numbers recorded during March (autumn) and highest numbers recorded during July (mid winter, start of breeding period). The ibis population of Centennial Park, and possibly the entire Sydney ibis population, may consist of a permanently present, sedentary subpopulation as well as a mobile subpopulation that spends the non-breeding period outside Sydney and migrates to Sydney for the breeding period. This is consistent with knowledge on ibis colonies throughout Sydney and other urban areas along the east coast of Australia.

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