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Fig. 7. Revisits to previously emptied feeders in comparison to revisit frequency
expected under random choice of feeders. (A) Between-trials: revisits during
successive trials of the experiment. The drop within the first three trials
indicates the transition from a brief win-stay to a win-shift strategy. For
calculations, see text. Revisits expected under random choice (line symbol)
are a function of the number of feeders emptied during a trial; this number
increases (from trials 1–3 to trials 11–20) as more feeders are
emptied within a trial. Error bars are 95% confidence intervals of the
difference (paired t-test) between measured revisits and revisits
expected assuming random choice of feeders. Differences were significant for
trials 1–3 (t=5.3, d.f.=14, P<0.001) and trials
11–20 (t=–2.8, d.f.=15, P=0.014) but not for
trials 4–10 (t=0.5, d.f.=15, P>0.05). Data shown
are means of the individual values for N=16 individuals (one
individual with less than 20 visits during each of trials 1–3 was
excluded from this specific analysis). (B) Within-trials: ratio of revisits to
revisits expected under random choice within a trial. Data are for successive
blocks of five visits within trials (based on trials 11–20,
N=16 individuals, for calculation, see text). Data shown are the
means of individual values (±S.E.M.). Frequency of revisits
differed significantly from random expectation up to the 20–25th visit
during a trial (Wilcoxon test, Z>2.1, N=16,
P<0.05).
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