I've not managed to prove beyond doubt that there was nothing in between those two quotes, but I think you've definitely got most, if not all of it, in your post.

In your second source - as in a few similar sources - there is an ellipsis between two parts, but they are usually missing the first sentence from your first source:

The owls in the Harry Potter books, which deliver the mail by magical means, were never intended to portray the true behaviour or preferences of real owls.

Here is a source from the time that presents the text you have as a single quote.

Other than that, I've found the following "meta discussions" about her change on the 1st Feb:

1. An entry on the HP Lexicon timeline of her website mentioning she rewrote the post on that day:

Jo rewrites and changes the Owls entry in ExtraStuff – Miscellaneous posted the previous day.

2. This thread from CoSForums:

Oh wow, JKR updated the Owls section of the Extra Stuff page. Yesterday it just talked about how you shouldn't keep owls as pets, but now it has a whole lot of other info about Owls in it too. Cool! [Post link]

3. This thread on HPLF Forums - I'm quoting all the relevant posts but I don't think I can link them individually. They're from a mix of posters with a fair bit of back and forth.

There is also an update in the extra stuff on owls!

I am happy to see the item about the owls. It's a very important message to get out. Glad to see she cares. (As if there was any doubt!)

The Owls entry has been updated. When I checked this morning it was merely saying that she's not in favor of the trend of keeping owls as pets and rather encouraged people to just sponsor bird sanctuaries if they wish to own owl pets. Now, there's the Athena connection and there's mention of Pig, Errol, and Hedwig.

I re-read the owl entry this morning. It indeed has more than was there last night. I especially found the information on Hedwig interesting.

I wonder why she took out the adoptive part though?

What "adoptive" part did JKR take out of the "owls" update? I didn't see both versions, only the new edited one.

Before the update, she said that owls did not make good pets, and she suggested that people who have become fond of owls because of the HP books should consider "adopting" an owl at a wildlife refuge or zoo, rather than try to get one as a pet. I think that's more or less the gist of it, I only read it once, and then it was updated.

on the first update about owls (on the extra stuff page)all it stated was about JKR being against owning owls as pets. Then she gave us further information about some of the owls in the books. And people keep saying that she took the other part out, she didn't you just have to scroll down, at least I can still see it.

[Same poster as previous] I just checked it again, and I was a tad bit wrong, it doesn't mention the adopting owls at a sanctuary, but it does say that she doesn't think anyone should keep them as pets

I wonder why she took it out though, maybe because she was afraid there would be a run on owl adopting? I can't see how that could be a bad thing?

I think she may have taken out the adopt-an-owl suggestion because someone pointed out to her that you can't, really. She'd said (I only read it once, so this is vague) something about visiting your adopted owl in a sanctuary, and I don't think that would be possible. Perhaps someone told her so, and she deleted it on that account.

Also, her original post, even the part about simply not having owls as pets, seemed to me much stronger than it is now. My suspicion is that she decided that the whole thing was a bit intemperate, and toned it way down, then added the information about the owls in HP to fill it up a bit.

I wonder if it was deliberate leaving that bit about adopting an owl up for such a short period. Long enough to encourage people into thinking about it, but short enough so that zoo's and animal sanctuary's don't get swamped with would be adopters. In other words, her original suggestion lives on in the forums and bulletin boards of her devoted fans and not the general public.

As an aside, it's really frustrating trying to find info about owls on long threads that reference Rowling and knowledge a lot >.<

Hope that gets you somewhere!