Predictability Of Behavior

Measures of uncertainty can be a valuable tool in assessing the predictability of responses of individuals to others. Again, we explore an example from our work on wood mice (Stopka and Macdonald, unpublished data). For example, all combinations of five male and four female wood mice kept under video surveillance in an enclosure with abundant nest boxes sometimes denned communally, although there was no thermoregulatory need to huddle. It was therefore surprising that cohabitants were often agonistic to each other. One of the most common categories of interaction was approach and nose-to-nose contact, categorized by Bovet (1972a, 1972b) as amicable, but lag sequential analysis revealed that although this (nose-to-nose) behavior pattern was indeed sometimes a precursor to flank-to-flank or nasoanal contact, on other occasions it was followed by attacking or chasing. Therefore, nose-to-nose encounters are defined by their context within a sequence. Sequential analysis revealed that nose-to-nose contact was sometimes the prelude to an amicable encounter and sometimes to an aggressive one (figure 10.10).

The crucial question is how to recognize mixed categories. Haccou and

Meelis (1992) recommend: performing a global inspection of bar plots to ensure stationarity, testing the bout lengths of all acts in the ethogram for exponentiality (e.g., Darling's test), using cumulative bout length plots and the likelihood ratio change point test to reveal deviations from exponentiality attributable to lack of stationarity, and devising a rational basis (in the case of nose-to-nose in wood mice, lag sequential analysis) on which to split problematic categories into new robust categories. Other methods of splitting the behavior according to the bouts are based on fitting a nonlinear curve to the logarithm of the observed frequencies of gap lengths (Sibly et al. 1990) and on the use of likelihood ratio tests in helping to determine whether the data occur in bouts (Langton et al. 1995).

However, it is important that the statistical procedure does not obscure biological insight, so the new, split categories must make sense. For example, it is clearly sensible to split the instances of follow-B (individual B) that were preceded by fight from those preceded by copulation or intromission because both new categories of follow (A, B) have different contextual functions and, it turns out, different bout lengths. Splitting of the category nose-to-nose contact did not make sense because it was equally likely to precede a fight or nasoanal contact. However, on further exploration, the probability that nose-to-nose contact would lead to one or other of these categories depended heavily on the sex of interactant. Such sex-dependent sequences may even resolve

AP - approach N-N - nose-to-nose N-A - naso-anal F-F - flank-to-flank GR - groom opposite Fl - fight AV - avoid

Figure 10.10 The flow diagram (state-space representation) of the sex-dependent nose-to-nose interaction. Lines between behavioral elements represent the tendency of switching from one behavioral element to another, based on a maximum-likelihood estimator.

puzzles in video surveillance by allowing inference of the sex of an unmarked individual.

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