Fig. 3. Distributions of rates of attraction to (A) dimethyl sulfide (DMS) and (B) cod liver oil compared with distributions predicted by relative Poisson processes. These graphs compare the observed distributions of approach rates (black bars) to distributions predicted if birds were approaching the platforms at random (gray bars). The approach rate (approaches min^–1) was calculated by taking the total number of approaches recorded in a 5-min observation period and dividing by five. We then tallied the frequency of occurrence of each rate to generate the curves for DMS (N=12) and cod liver oil (N=11). The distribution of approach rates departed significantly from a Poisson distribution for DMS but not for cod liver oil presentations; approaches to DMS were clustered, whereas approaches to cod liver oil occurred at random (Zar, 1996).

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