Group Effects and Background Color Patterns Affect the Exploratory Behavior of Tree Sparrows

摘要

Exploratory behavior serves the function of acquiring information when facing environmental uncertainty, thus plays an important role for animals living on patchy or ephemeral resources. Our study tested the hypothesis that exploratory behavior is affected by ecological factors associated with the risk of predation. We conducted experiments to examine exploration behavior of wild-caught Eurasian tree sparrows (Passer montanus) under the influences of background color patterns (white or camouflaged) and group sizes (single vs. five sparrows). We further conducted two-pattern choice experiments and offered sparrows backgrounds combining those two color patterns. In comparisons with single sparrows, flocking sparrows had shorter landing latencies, started exploring sand patches earlier, spent less total time on the ground before pecking at the first patch and nearly successfully located and pecked all patches. In contrast, sparrows responded nearly indifferently to the two single-pattern backgrounds; yet when given a choice, sparrows still favored the camouflaged portion in the two-pattern backgrounds and first landed more frequently there. Twice as many patches were left untouched on the two-pattern backgrounds, mostly by single sparrows, than on both types of single-pattern backgrounds. In tests of flocks, sparrows that first landed on the ground to initiate exploration had a higher chance to also first explore a sand patch than random expectation on single-pattern backgrounds, but not necessarily on two-pattern backgrounds. Our results demonstrate context-specific effects of social exploration, suggest possible influence of individual variation and offer evidence for advantages of group living in situations where explorers have to cope with environmental uncertainty.