How many golden eagles are there?
(PHYSorg.com Biology)

For conservation efforts to be effective, wildlife managers need to know how many individuals of a species are out there. When species are spread out over large areas and occur at low densities, as is the case with the Golden Eagle, figuring this out can be tricky. However, a new study from The Condor: Ornithological Applications applies an old technique called `mark-recapture` in a novel way, eliminating the need to actually capture and mark eagles but instead, using math that allows scientists to turn individual observations into population estimates.