I'm sure others, like Kent McFarland, could answer your eBird concerns
better than I can, but I would say that you are worrying too much about the
1. Counting birds: The eBird website has advice for reporting numbers as
opposed to X for "present" where they stress that a best guess estimate is
better than an X. When numbers and trends are studied in bulk, the
difference between 130 vs 131 snow buntings (or even 140) is insignificant.
If a large flock of birds flies overhead, it's difficult for most people
(without a lot of practice) to get within 20% of the actual number. Even
getting an exact count on a group of chickadees is difficult when they keep
moving around and all are not visible at the same time. I think a best guess
is OK. Two people walking the same trail at the same time could get
different counts on many birds depending on their hearing, eyesight, optics,
and identification abilities (both by eye and ear). The inexactness of
"citizen science" is offset by shear volume of data. When aggregating
hundreds of lists and thousands of birds, the errors cancel out to some
extent, and a guess is better than no data at all.
2. Location: The difference between one end or the other of a mile-long
road or trail is insignificant when analyzing data by county, for instance.
After all, most birds could fly that distance in a short time and could be
counted at one end of the road one time and at the other end an hour later.
It doesn't make a bit of difference. However, if it matters to you which
end of the road you saw a bird, you can enter it as two points for your
records, but that's a personal choice. For example, two of the trails at
Missisquoi National Wildlife Refuge are right across the road from each
other. I have entered these trails as 2 locations on eBird, and even if I
birds both trails on the same day, I report them separately. Other people
might report everything they see on the whole refuge (all 6500 acres) as one
location. I think either way is OK. It's up to the eBirder.
Disclaimer: These are my opinions only. I can't speak for the scientific
community using the data. I hope Kent McFarland will respond with his