Vine already seeing declines after Instagram video release
On Android, if you look at the installs for the last 30 days chart that Google provides, Vine has been on a steady decline since its initial release anyway, so Instagram's arrival didn't change all that much. But, on iOS, Vine has seen noticeable slippage. On the U.S. iPhone download chart of free apps, Vine slipped from #2 to #7 between Thursday and Sunday. In Mexico, Vine fell from #3 to #10 in that same span. And, in the United Kingdom, which has been a European stronghold for the app, Vine fell out of the top 10 completely, going from #5 to #12.
Around the world, Vine had been on the top 10 iPhone download charts in 34 countries last Thursday, but by Sunday that number had fallen all the way to 11 countries.
Vine still has passionate supporters, but the fact that Instagram video suddenly went live to 130 million users gives the app a big step up on Twitter's Vine. That probably explains why Twitter started sending out promo e-mails so soon after the announcement.