Can I be jealous you are seeing shiny Ponyta and Cubone? Between my and my kids accounts we have looked at over 200 and none shiny. Got plenty of shiny Pinsir but this Ponyta/Cubone thing is nuts!
I do get your frustration, my son was thrilled a pidgey showed up at the house so he could get his challenge done. More so than the Chansey! :)
Niantic logic.
So, Niantic have released shiny Pinsir, Pontya and Cubone recently. All are fairly rare spawns normally. I've caught a few shinies, wahey.
Throughout these days, i have not seen a single pidgey, anywhere. I have to bin the evolve 2 pidgey tasks cos i see no pidgeys. Normally i consider it a sin binning any task for a potential shiny, but this is an exceptional case.
Only Niantic could create a scenario where we're more likely to catch a shiny than to even see a pidgey. Only Niantic :D
Answers
I've caught 3 shiny pinsir, and today I caught a shiny ponyta and cubone. Not sure if I'll find more but both shinies of an event in just 1 hour lol. And yes, pidgey has become pretty rare. But then again if I remember right, caterpie can nest, so people will eventually get more chances of finding a shiny there. Plus caterpie spawns in some parks quite often.
What gets me is that since this game's inception Pidgey had been one of the single most common encounters to the point of annoyance - for a period I stopped tapping on them outright because they had become such an infestation. Now that they're in the process of releasing a fourth generation and revamping spawns to become more diversified and exciting they make Pidgey relevant despite it becoming rather uncommon after the previously mentioned reworks. My area's chat legitimately had people calling out Pidgey spawns to one another.
It seems like for every step forward they take with the game there's always a step to the side that leaves me scratching my head.
Normally, I catch/evolve/transfer pidgeys. They are still coming up, just nowhere near as frequently as normal. So now I catch them, wait until I want to evolve two of them for a quest or three, and then transfer them. Not really a problem, just stock up on them, and double or triple the evolve pidgeys quest.