Apologies for being a bit late in on this thread, I plead guilty of not noticing it earlier. Anyway, just a couple of further thoughts. Like Jill I've also noticed from time to time some apparent concern about "too many images" of some of the more common and/or more popular species, but I personally don't share this concern for reasons I'll try and explain.
I think that any issue with this is related to the dual-purpose nature of the site: on the one hand it has a goal to assemble a comprehensive photographic reference database of all Australian bird species, and in this regard there may be some perceived disadvantage in having too many images of certain species; but on the other hand it also has an equally important role as a website dedicated to excellence in bird photography, and in this regard it shouldn't matter what species is the subject of the latest submission if it just so happens to be one of the best photographic images on the site. Because of this latter point, I don't think members should be overly discouraged from submitting new images of the most commonly uploaded species, or indeed be discouraged from photographing them. As Jill has suggested, set yourself the challenge of going out and getting the best-yet image of a Superb Fairy-wren or a PBD (both very photogenic birds) - but first look through the existing database to judge what you have to beat!
If for database reasons it ever came to a need to limit further expansion of image numbers of a particular species, I would be more in favour of culling some of the lower-quality existing images than limiting submission of new ones - thereby allowing for improvement of the database.
Cheers, David