Bird Forum Kindness
As all the above people who kindly replied to your query said, the Tasmanian form of the Silvereye has these rich chestnut flanks which you noticed. The Silvereye (all forms) is Zosterops lateralis. The Tasmanian subspecies you are asking about is Zosterops lateralis lateralis. According to my guide, they migrate as far north as Caloundra, Queensland in the autumn (and they might be resident in Melbourne for all I know). There are several other subspecies which lack this chestnut colour.
I am replying to this thread because I have been to Australia recently, and people there were helpful to me, as people here at Bird Forum have been helpful to me in identifying problem birds when I got back (and in the past about other birds). But before asking the question, I identified the birds I could from a field guide - I identified about 115 out of 128, asked a bird park host in Australia about the remainder, and asked about the most difficult few here.
The three people who took the trouble to reply to your query all gave the correct answer: this is the normal form in a certain area of Australia; and they told you what form it is, the race or subspecies 'lateralis'.
In the case of this common bird, the field guide I bought, the 'Slater Field Guide to Australian Birds', gives a clear description and clear pictures of the silvereye, even though the book is not so good (being compact) on birds which are more difficult to identify. I (politely) suggest that you get a guide such as this if you become really interested in birds. It will make looking around much more fun.
My experience of this forum has been that people who are extraordinarily expert on birds are willing to help people who are more or less beginners (such as me recently on my first trip to Australia). They are also happy to repeatedly answer the same question about common birds from any number of people. This site is one of the ones that makes you say, 'This is what the Internet is for'. Sometimes people make an educated guess at an identification, and are wrong. But, if three people here give you the same answer, then I think you should believe them unless you have done some serious research so you have reason to think they are wrong.
