Mabry & Stamps, 2008. Decision making by Dispersing Brush Mice

Ref: Mabry, K. E., & Stamps, J. (2008). Searching for a new home: Decision making by dispersing brush mice. The American Naturalist, 172, 625-634.

Natal dispersal: Young animals leave the area where they were born and search for a new place to settle.

They looked at the mate search literature and asked whether there are similarities between habitat search and mate search using radiotelemetry.
Finding: Search behavior by juveniles was most often consistent with comparative decision rules (best of n and comparative Bayes), suggesting that the decision-making processes involved in searching for a place to settle and searching for a mate may be quite similar.

3 main decision rules in mate search literature. Good and fuller descriptions found in Luttbeg (2002).

Threshold (T): Items are sequentially sampled until one that exceeds a preset quality threshold is reached, at which time that one is selected. There can be a fixed threshold or a flexible threshold (in which the threshold declines with time). Only fixed is considered here.

Best of n (BN): Individual samples a fixed number n of alternatives and returns and picks the best one. Determining this n may be difficult.

Comparative Bayes (CB): Individuals assess the option that maximizes their expected future fitness, and if the cost of assessment exceeds the expected fitness benefit of assessment, an individual should choose the option with the highest associated expected fitness. Individuals must have prior estimates of the quality of each available option. Options are weighed only on how they will affect decisions at the next time step. Since signals may not be fully informative, individuals may revisit sites to gather more information. Thus, BN and CB are distinguished by the extent to which individuals return to previously sampled items.

Results: They tracked the animals on sequential nights of exploration. More animals seemed to use the CB rule (61%) than the BN rule (19%), meaning that they visited previously seen spots and settled on a previously seen place. This fits in with theory suggesting that CB outperforms both T and BN when either search time or the number of suitable options is limited and when searchers have difficulty evaluating the quality of the items they encounter during search (Luttbeg, 2002).

Further Discussion:
Relatively small number of novel areas that juvenile brush mice investigated before settling at a new site. One possible reason is that small mammals such as brush mice are quite vulnerable to predation and therefore that examining a limited amount of unfamiliar space may provide some measure of safety.

Not explicitly said, but the implication is that these animals are using a time of area-restricted search (ARS; Hills, 2006).

Lots of individual variation: brush mice from the same locality varied with respect to their search behavior during the dispersal period. For example, some mice were extremely sedentary and never left their natal home range, while others ranged widely on a nightly basis. They list a bunch of possible contributing factors, including sex, population density, physical condition, and personality.