The rules state:
Wing-Clipped: The flight of wing-clipped strix is weaker than normal,
whether from deformity or injury. Their fly speed is 20 feet (poor)
instead of the normal fly speed, and they must make a DC 30 Fly check
to fly upward. Ostracized by their tribes and forced to deal with
other races, these strix compensate for their weakness by gaining a +2
racial bonus on Bluff, Climb, and Diplomacy checks.
Looks like normal flight rules apply:
You generally need only make a Fly check when you are attempting a
complex maneuver. Without making a check, a flying creature can remain
flying at the end of its turn so long as it moves a distance greater
than half its speed. It can also turn up to 45 degrees by sacrificing
5 feet of movement, can rise at half speed at an angle of 45 degrees1,
and can descend at any angle at normal speed. Note that these
restrictions only apply to movement taken during your current turn. At
the beginning of the next turn, you can move in a different direction
than you did the previous turn without making a check. Taking any
action that violates these rules requires a Fly check. The difficulty
of these maneuvers varies depending upon the maneuver you are
attempting, as noted on the following chart.
Aside from the poor flight (which manifests itself as a -4 to all Fly skill checks), it looks like the only problem the strix will face is when he wants to gain elevation.
- gliding - no problem (assuming he travels at least half his speed)
- flying - makes a fly check (DC 30) each time they want to gain elevation, otherwise no problem.
- fly 100ft - At 20 feet per turn, will take 5 rounds assuming a straight path.
Note: DC 30 is a hard check to make for Fly, nearly impossible at low levels, so the strix will likely never get higher off the ground then they can jump.
Assuming they max the fly skill each level their fly check is:
1d20 + Level + Dex mod - Armor check penalty + 3 (for being a trained class skill) - 4 (poor flight).
At level 1, if they roll a 20 have a + 4 Dex mod(18 dex), and no check penalty they still only get 24 on their fly check and would not gain any vertical flight. Using the same formula and assumptions, it is not until level 7 where they get a 5% chance to get some vertical flight (an additional 5% chance per level).
The acrobatic feat can provide a +2 bonus to their Fly check, reducing the minimum level to gain vertical flight to level 5.