Research overview: range residency versus drift diagnostics

Before estimating a home range, one must verify that the animal actually has one, that its movement is range-resident rather than dispersing, migrating, or nomadic. This overview describes diagnostic tools, especially the semi-variance function or variogram, which plots how the variance of displacement grows with time lag. A variogram that reaches a plateau indicates bounded, range-resident movement, whereas one that keeps rising signals ongoing drift or migration, in which case a home-range estimate would be meaningless. For species like snow leopards, where residency versus nomadism is genuinely uncertain, such diagnostics are decisive. The overview frames variogram analysis as a mandatory first step in continuous-time movement modeling, guarding against the error of fitting a home range to an animal that does not have one.