I went through the “Public Gallery” pages just now, and compiled this count of the number of photos taken and identified for each species. In ascending count order, they are:
| bird | count |
|---|---|
| bald eagle* | 1 |
| golden-crowned sparrow | 2 |
| song sparrow | 10 |
| lesser goldfinch | 10 |
| pygmy nuthatch | 52 |
| mourning dove | 56 |
| rock pigeon | 57 |
| anna’s hummingbird | 72 |
| american robin | 88 |
| chestnut-backed chickadee | 91 |
| squirrel* | 134 |
| house finch | 222 |
| dark-eyed junco | 340 |
| black-headed grosbeak | 410 |
| no bird* | 410 |
| wesetern scrub-jay | 672 |
| house sparrow | 1054 |
* not actually a bird ID (though in the case of the “bald eagle”, the system thinks it is).
So, that gives you an idea of the relative rarity of the various species, at least in terms of the photos taken and identified so far.