What Pokemon are regional for each region?

Question

Well I know Birds Regional Pokemon are Pidgy, Sparrow, Hootoot, tailow, pidove, and Fletching.

what are the regional rodents, snakes, bugs, and others

Answer 1

Regional birds
Kanto: Pidgey / Spearow
Johto: Hoothoot
Hoenn: Taillow / Wingull
Sinnoh: Starly
Unova: Pidove
Kalos: Fletchling
Alola: Pikipek
Galar: Rookidee
Paldea: Wattrell

Regional rodents (or early Normal-types)
Kanto: Rattata
Johto: Sentret
Hoenn: Zigzagoon
Sinnoh: Bidoof
Unova: Patrat
Kalos: Bunnelby
Alola: Yungoos
Galar: Skwovet
Paldea: Lechonk

Regional bugs
Kanto: Caterpie / Weedle
Johto: Ledyba / Spinarak
Hoenn: Wurmple
Sinnoh: Kricketot
Unova: Sewaddle / Venipede
Kalos: Scatterbug
Alola: Grubbin
Galar: Blipbug
Paldea: Tarountula / Nymble

Regional Pikachu clone
Kanto: Pikachu
Johto: Pichu
Hoenn: Plusle / Minun
Sinnoh: Pachirisu
Unova: Emolga
Kalos: Dedenne
Alola: Togedemaru
Galar: Morpeko
Paldea: Pawmi

Regional pseudo-legendary
Kanto: Dragonite
Johto: Tyranitar
Hoenn: Salamence / Metagross
Sinnoh: Garchomp
Unova: Hydreigon
Kalos: Goodra
Alola: Kommo-o
Galar: Dragapult
Paldea: Baxcalibur

Comments

"Lechonk is very obviously the intended addition here. Zigzagoon and Yungoos aren't rodents either."

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I don't think dogs should be a category here. All the other categories share either a type or a base stat total, so the dogs pattern looks a lot weaker and is more likely to be a coincidence.

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OK I'll remove the dogs.

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According to this Appendix on Bulbapedia, it states that Tandemaus is recognized as a Regional Rodent.
https://m.bulbapedia.bulbagarden.net/wiki/Appendix:Fan_terminology#Early-route_Pok.C3.A9mon

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I think Tandemaus should be excluded because:
1. Its BST is considerably higher than the others.
2. It is substantially less abundant in its region compared to the others.
3. Lechonk fits the brief without either of the aforementioned problems.
4. I don't think it's a match design-wise either.

I think the Bulbapedia page casts a very wide net considering it includes Lillipup and Wooloo. I call these coincidences, but if somebody else with editing powers feels strongly about this then go right ahead.