The Western Australia Department of Agriculture and Food is reporting that a man who spotted what he thought was an odd-looking bird ended up helping prevent the establishment of an invasive species in WA. The man reported the finding to his local DAF office, and when biosecurity officers went out to the site, they were surprised to discover a tree sparrow (Passer montanus). The bird, which was captured and removed, is thought to have arrived in WA on a ship at a nearby port. Tree sparrows (.pdf) are native to Eurasia, and while discoveries of individuals in Western Australia are not infrequent, the species has not yet established any feral populations there.
Thanks to Sandy L. for sending this story in to the ALIENS-L listserver.