Many pointed out that there are many species of owls related to ground, also it doesn't need to lose it's wings to become Grass/Groud, the Ground type just needs to be more suitable than the flying one (which Imho implies that Rowlet will get a bulkier evolution ), just like Blaziken which fits both the Fighting and the Flying type (it learns many flying moves including brave bird) but fits more the Fighting type than the Flying one...

That beeing said I'm 99% shure that those types aren't related to the final evolutions because they simply don't fit these starters, Litten is 99% going to be a Fire/Poison, but if they happen to be related to the final evolutions then the types will certainly be Grass/Ground, Fire and Water/Fighting...

Water/fighthing is cool, but I read somewhere else that popplio could be water/fairy which would be pretty awesome.

So it looks like Popplio is gonna be cool after all.
I just hope Rowlet evolves into something that is not grass/flying. That's a terrible type combo.

If Popplio ends up Water Fighting when fully evolved, he is def gonna be my starter 100%.

Gen IV did that already.

What are these many species and in what way are they more related to the ground than flying? And yes it kinda does actually since otherwise there's no way Ground typing makes more sense on something with wings that flies and lives high up, let alone suddenly going from Flying to Ground, two polar opposite types. Your Blaziken example doesn't work since he never had another secondary typing and he doesn't have wings but hands so fighting only makes sense. The only Pokemon I can think of that changed dual types after evolving is Surskit to Masquerin, which while stupid and no one liked, atleast it made sense since Masquerin no longer skates on water but flies in the air.

Obviously they're gonna be related to the final evolutions as they almost always are. No one could really tell what Gen 6 starter's secondary types would be on the first evolutions alone. Also how can you still be 99% sure while we have likely proof otherwise? Then again you believe the color black means Poison instead of Dark, and that an already flying type Owl suddenly becoming ground type while the Fire starter gets shafted is certainty, something Gamefreak knows would only piss everyone off.

I'll be extremely disappointed if that's how listen will end up looking like

I don't understand why everybody thinks a Pokemon staying monotype is a bad thing. A diverse and expansive movepool is better than having two types.

The Burrowing Owl just to make an example is an Owl used to set into burrows underground making it a prime candidate for a possible Grass/Ground evolution for Rowlet, if GF decides to make it partially underground (see diglett) or simply stand on the land because it becomes fat to rappresent it's bulk it can easily mantain it wings while shifting from Grass/Flying to Grass/Ground. I think they are 99% likely to not be related to the final typings because they could simply be there for another reason, say Rowlet's final evo is Grass/Flying, then on his page as a description they might underline how it's typing is immune to ground, same could go for Popplio if it became Fairy saying that it's attacks are supereffective against fighting types. I NEVER said that the color black means poison, I said that the Pokédex description and that the Sulfur sign on Litten's head point in the direction of him beeing a Fire/Poison. I'm shure that Fire type fans (like me) would prefer a regular Fire type with only 3 weakneses over a Grass/Flying or Grass/Ground with plenty of other weakneses (and the Ice one beeing x4)

http://www.dailymail.co.uk/sciencetech/article-2303809/The-underground-owls-Florida-make-burrows-instead-living-trees.html

It makes more sense than dozens of type combinations already out there.

"The burrowing owls who live underground instead of in trees"

"The owls nest in holes rather than in trees, and are active during the day"

Now, they do fly, but so does Golurk and Garchomp. Both of those are still Ground type.

Also, we have no idea what it will be in its final form. We have too many examples of Pokemon that start as one kind of animal and turn into something completely different (Cyndaquil line, Oshawott line, Spheal line right off the top of my head), and we have too many examples of Pokemon that start primarily resembling a species of an animal, then evolve into a different species of the same animal. It's not a stretch to believe Rowlet will eventually become a burrowing owl that spends a lot of time underground.

Just because a starter has never gone from one dual typing to another doesn't mean that it can't happen. There's no rule against it, and it will probably wind up better from a competitive standpoint if it happens: fewer weaknesses, access to two STABs and plenty of flying moves because of its former typing. I just hate that it's still going to be 2x weak to Ice.

Tell that to Serperior! I guess it's not necessarily a bad thing, but dual-types are just more interesting naturally.

Alright, there is that, but I don't see what makes it a prime canidate over other types of owls. And yes that's what I mean, it'd require a drastic and (going by your examples) silly inferior change in appearance to make sense. That's simply unlikely, especially for a starter. Even more unlikely and outlandish is your reasoning for those images being on the site. They're with and numbered the same as the starter type images, and there's only two of them. Common sense from there. Granted, while odds are extremely slim, I can't say your reasoning is flat out impossible, but you're clinging to the most unlikely scenarios. Also you said 99% it'll be Poison, which means you're saying there's basically no chance of it being anything else.