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Tips for urban Ibis colonies


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There is a lot of research into ibis at the University of Technology Sydney (UTS) in the Environmental Sciences Department and Dr Andrew Smith completed his doctorate which looked mainly at the population dynamics.    
In particular, Andrew was looking at breeding to determine whether the birds had moved here or whether they had bred in such numbers that caused the population to be more than 9,000. When the ibis first arrived in Sydney they tended to take up residence on islands, preferring to be surrounded by water. Later, they graduated to using even structures such as water fountains and now it seems these Sydney dwellers have lost their connection to water and will inhabit palm trees which they use a base for their feeding travels to local tips.

Andrew studied three main breeding colonies, marking each nest with a tag, as well as all the eggs in each nest. When the chicks hatched they were weighed and their morphological characteristics were measured providing growth curves. This was quite an operation given there are about three eggs per nest and, as on one island at Woy Woy, over 2,000 eggs to be marked.

Great care was taken to protect the nests which were left in their natural state after the measurements were taken. Measurements were repeated on the growing birds and each was fitted with coloured and numbered leg bands making long term individual identification possible. Banding allowed examination of relationships between breeding colonies and the landfill sites they used for feeding.

At Woy Woy, for instance, the birds at the island colony were counted when roosting at night and those feeding at the landfill sites were counted during the day and on average there was a 77% match between the two sets of sightings. By contrast however in Sydney, there were birds from different colonies at landfill sites, with one bird being tracked to all of them.
For Sydney-based and other urban ibis, the clutch sizes and the actual eggs have been found to be smaller than in their natural, rural habitats. There were also less hatchlings per nest in the urban environments compared to the inland breeding places like the Narran Lakes. The success of the urban fledglings, however, was high and in some cases doubled the survival rate in the wild.
Young birds tend only to remain for a relatively short time with their colony. It is thought they head north as far as Papua New Guinea and may later return to large urban breeding colonies such as in Sydney and the Gold Coast.

The management of ibis is problematic as it is council based and not every council has a colony (or wants one).
If a colony is moved by a council from one location, then the birds will simply join another colony - probably in another council area. Some of the complaints levelled at ibis, such as they carry disease, have never been substantiated. However, the main concerns from people are really about aesthetics. Their large colonies do smell, the breeding colonies are noisy and the birds will boldly frequent parks where they are seen by some to be menacing.

As a result of their foraging on tips, the urban ibis tend to have elevated levels of lead and dioxins in their systems which may be a long term problem developing for their predators such as ravens and sea eagles.

Since it is already known, that some of the urban chicks are born with usually very rare deformities, this is an area worthy of further for research.

There is a circular irony about urban ibis. The diversion of inland water to grow food for our nonproducing city folk, caused the ibis to move to Sydney where they feed off our vast food waste in landfill sites.
What goes around comes around.

Text: V.B. March 2010
Images from Andrew Smith

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