Age Differences in Foraging Efficiency of American Avocets Recurvirostra americana

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Abstract
We examined the foraging efficiency, measured by the time interval required to capture 10 successive prey items, in adult and young American Avocets feeding in a tidal slough and mudflat of San Francisco Bay at Palo Alto, California [USA]. We examined two habitats, two distinct feeding methods and three tidal stages. For both adults and young, food items were obtained significantly more quickly by pecking rather than by the sideways motion called scytheing, on mudflats rather than in channels, and in the rapidly moving incoming tide rather than in slow moving or slack water. Adults performed significantly better than young for all combinations of independent variables. Success was influenced by habitat and age and the interaction between these two factors. For the Avocet for which delayed maturity is documented, this foraging efficiency difference may be of major importance selecting against breeding at one year of age.