In Heidelberg, Germany, a flock of feral Swan Geese (Anser cygnoides) and Eurasian Coots (Fulica atra) feed together on a lawn during winter. It was investigated whether the presence of geese provided benefits to coots in terms of reduced vigilance and whether the association incurs costs, e.g., by reduced foraging success. Further, the hypothesis was tested whether a decrease in vigilance rate is mirrored by an increase in feeding rate. A digital video camera was used to record behavior of the same individual. Head-up movements were considered to have vigilant function when the bill was raised up from the foraging position to a position nearly parallel with the horizontal line, or when raised to a position higher than the body (“high-cost vigilance”). Coot feeding in the presence of geese showed a significantly lower scan rate. Steps per minute did not differ between the coot with and without geese, but the time taken for 30 pecks was significantly shorter in the presence of geese. There was a significant negative correlation between feeding and scan rate, suggesting that scanning decreased peck rate. Further, scan rate was inversely correlated with total flock size (number of coot and geese), suggesting that coot recognized the geese as flock mates. Coot benefited from feeding in the proximity to geese by a lower scan rate and a higher peck rate, but they did not encounter costs in terms of reduced food quality as measured by step rate.
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