Attempts to fit simple mathematical models-of animal movement to obser
ved distributions of movements have been extremely successful. However
, the extent to which these results were influenced by use of potentia
lly distance-weighted sampling methods has not been evaluated. Of the
15 field studies used to test model fits, 13 used methods that sample
unevenly over distance. We use a simple Monte-Carlo simulation model t
o evaluate the effects of unequal sampling over distance on results ob
tained from simple mathematical models of animal movement. For three d
ata sets that provide detailed maps of observation sites, the effects
of unequal sampling are profound. Prior to sampling, data simulated by
our model follow a uniform distribution, but a geometric model adequa
tely fits the ''sampled'' simulated data. Following corrections to the
field data to mitigate the effects of distance-weighted sampling, in
only one of five studies do simple mathematical models adequately fit
the observed distribution of movements.