I'd like to estimate the distance at which the bird is singing from the point of recording, to then finally get the source level from one microphone.
I've seen studies, and heard from colleagues use visual guesstimates and laser range finders. Guesstimation is good, though errors when the bird is nearby (a distance of 1 m instead of 0.5 m makes a big difference to the estimated source level). The laser range finder I have at least doesn't really work well during the day (it's also not a low-end model...Bosch GLM 50).
What are some of the ways I can estimate distance to the bird accurately (or any other diurnal vocalising animal) during daylight?
Post-script: The question was initially ambiguous about the number of microphones in play. It has now been edited to specify that Nmics=1.