1. Barrett & Lowen (1998) and Waser (1976) attempted to explain the net mon
thly and yearly displacements of Grey-Cheeked Mangabeys using observed shor
t-term step lengths and assuming a random walk, with and without boundaries
. This paper reanalyses their data.
2. Analytic approaches require the root-mean-square step length, not the me
an. However, a more flexible approach to making and testing predictions is
Monte-Carlo simulation. With a random walk long-term displacements have a l
arge variance, so a single observation is unlikely to disprove this null hy
pothesis.
3. Restricting movement to a square lattice is a reasonable approximation e
ven when rectangular boundaries are incorporated. Describing the boundary c
onfiguration accurately is more important.
4. The observed non-uniformity in turning angles should have been incorpora
ted as it has a large effect on predicted net displacements, unless the are
na is tightly constricted. Randomness of movement within a day can be disti
nguished from that between days. For Waser's population it makes sense to p
redict long-term displacements using only long-distance daily displacements
.
5. There are better approaches to establish both whether boundaries exist a
nd whether movements follow a random walk.