Distance within eBird should be the distance you covered along a trail, road or waterbody, whether on foot, bike, car, kayak, elephant or some more novel means of moving across the landscape. If you cover the same section of trail out-and-back we encourage you to submit a checklist for the trip in, and another for the trip out. This will provide us with extremely valuable information how detectable different species are under different conditions. Shorter distance checklists are strongly preferred, ideally 1 kilometer or less, but do your best to keep it under 7 kilometers.
If you want to submit a single checklist for out and back, only report the one-way distance. You should only record the distance traveling in one direction, but you should record the total time you spent traveling both out and back on the trail as long as it's on one checklist. Only record birds on the return trip if you suspect that they are new. Be conservative!
The most accurate way to report your location is using eBird Mobile, which automatically records a track of your travel and the distance you covered. Please check the track before submitting. If you notice that the track made errors in terms of jumping around off of the route you walked, do your best to reduce the total distance to what you actually covered. If you do submit a single checklist for a trail that is out-and-back, we encourage you to reduce the checklist distance to only the one-way distance. This is a recommended best practice to remain consistent with how out-and-back distances are gathered on non-track lists.