Is this so? I still seem to keep getting those mice and birds. Or maybe it's just my area.
There certainly still are many of those, but i see many more pokemon that usually used to be less frequent. Still basic and common, but some of these are nice, and they all increased in frequency, which implies that pidgey and rattata actually got less common.
I am talking about stuff like spearow, jigglypuff, oddish, paras, venonat, meowth, slowpoke, magnemite, shellder, krabby, voltorb, horsea, goldeen, eevee.
Weedle is now the most common one i see, it used to be third place, it is now followed by pidgey and rattata. And the next tier of pokemon all appears to be more common now.
I also got some randomly appearing pikachu and squirtle and bulbasaur, certainly more than before.
So its clear to me, they took those 3 down a notch and filled it with other pokemon, probarbly a good chunk of them being weedles and spearows, but all the rest quite clearly moved up a bit. More diversity. There still are enough pidgeys, caterpies and weedles to pick 11-candy evolutions for experience.