Variation in the visually observable behavior of groups of Galapagos spermwhales

The behavior of groups of female and immature sperm whales (Physeter macroc ephalus) was measured on 117 d within an 11-yr period off the Galapagos Isl ands, Ecuador. On each day, up to 18 measures of visually observable behavi or were calculated. These concerned speeds, headings, movement patterns, di ving synchrony, foraging formations, time spent socializing, and aerial beh avior. The measured behavior of the sperm whales was considerably more vari able when they were socializing than when foraging. None of the measures sh owed much correlation with sea-surface temperature, and only measures of co nsistency of movement were significantly correlated with defecation rate, a n indicator of feeding success. However, month-long time periods accounted for over 50% of the variance in eight of eighteen measures, and, in the cas es of surface speed and dive synchrony, the effects were statistically sign ificant. In contrast, there was no autocorrelation with lag of one day in t he residuals of any of the measures. Thus, behavior may be tracking substan tial temporal variation in the whales environment over scales of about seve ral months. Groups of whales had significantly different travel patterns, b ut there was little other evidence for group-specific behavior, perhaps bec ause tests of group-specific effects were not of adequate statistical power . Variation in sperm whale behavior, especially over time scales of a few m onths or longer and spatial scales of a few hundred kilometers or larger, s hould be considered when estimating densities from sighting surveys.