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Nearby Morro Bay is known for its abundant migratory shorebirds, but I don't know if early Sept is a good time, or not. There are little water taxis that will take you to the sand spit and other areas good for photography. There should be raptors on the drive between Paso and Morro.
Check the on-line site for elephant seals in the Cambria area. This is not the mating/pupping season, but it might be moulting season, when they also come ashore.
To the east, the Carrizo Plain is a special spot for pronghorns, elk, and snakes, plus elusive kit foxes. However, all these animals may be no-shows, plus it will be hot there. (Not that an Arizonan would be bothered by heat....)
All these places have on-line sources to contact for the latest information. I'll be interested to know what you found...
Paso Robles is also prime wine country, so if the photo places fail....