How might you estimate the population size for a species of bird?

As birds are a motile organism, we would use the mark-release-recapture method. First, capture a sample of individuals (possibly through mist netting), mark them (e.g. a wing tag or leg ring) and release. Then leave sufficient time for the marked individuals to mix evenly back into the population, before capturing another sample. To calculate the population size, we can then use the following equation:P=(S1xS2)/RWhere:P = Size of the population S1 = Number of individuals captured, and subsequently marked, in the first sample S2 = Number of individuals captured in the second sample R = Number of marked individuals captured in the second sample