The chance of the character locating a bird in flight will be 100% within 50 miles of land, once per day. For each reduction of 10 mi. from this distance, the number of 'sightings' will treble, so that within 20 mi., birds will be spotted a little better than every hour and within 10 mi., every fifteen minutes. Closer that this and bird sightings will more or less be continuous.
Conversely, for every 100 mi. increase from any land, sightings will diminish by two-thirds. At 150 miles, the chance of seeing a bird on any given day will be 1 in 3; at 250 miles, 1 in 9; and at 350 miles, 1 in 25 (adjusted from 27 to produce a simpler number). Thereafter, the chance will diminish by half for every additional 200 miles, so that at 550 miles distance from land the chances of spotting a bird will be 1 in 50; at 750 miles from land, 1 in 100 and so on. There are few parts of the globe where it is possible to be more than 750 miles from any land.
The DM will take note of the correct cardinal direction of land. If the direction of land was ESE, for example, then the character will guess randomly with the result of either E, ESE or SE, rolling a d3. With each sighting of a bird, the random roll is made. Note that at a very great distance, even a correct guess may mean failing to sail directly towards land - the skill should give, at best, a general bearing and no better.
While the ability will enable the character to spot birds on land, it will confer no special ability to find a bird's roost or nest; this is a skill offered under bird tracking (placeholder for content).