[donavanm]

FYI, youre underplaying the migration aspect. For NSW, and I believe other states, their migration was a byproduct of habitat loss/pressure. Their native habitat is riverine and marsh lands, like macquarie marshes. As ag and surface water “reclamation” impacted those areas the birds were forced to migrate. As an example before the 1980s there were huge flocks in macqaurie and none recorded in sydney. By 2000s theyre functionally absent from macqaurie and only surviving in (sub)urban areas with easy food and water access.

This riverine habitat loss is why you unfortunately see them nesting in palms in the city. It resembles the reedy habitat theycome from and keeps them safe-ish from urban cats, rats, etc. The downside is theyre not arborial birds and they lose tons of chicks and fledglings to falling out of the trees and dying. Same with appearing “dirty” because they dont have proper water access to clean and preen.

In short, we destroyed their habitat and theyre hanging on where they still can. Welcome to the lucky country.

[hilbert42]

Very interesting. Come to think of it I can remember a time when ibises were never about (this was a time of sparrows before miners took over the city). Anyway, one year ibises suddenly appeared as if out of nowhere. (When I first saw them I thought they were some exotic bird that had escaped captivity.)

We may have destroyed their natural habitat but I reckon they're more than just hanging on—they seem to have adapted to our city environment extremely well.

Thanks, you've answered a question I posed above before reading your post when I said they're the dirtiest scruffiest birds I've seen and wondered how clean they'd be in a natural environment.

[donavanm]

Interesting indeed! Im definitely not authoritative, but my partner did some biology research and field work in this general area. My slightly vaguer recollection is that yes for Sydney there was a big mass migration year when the marshes and murray darling were particularly stuffed up.