Efficient Use of Food Patches At Different Distances From a Breeding Colony in Black-Billed Gulls

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Abstract
A probability model is developed and tested to examine the hypothesis, derived from optimal foraging theory, that black-billed gulls utilize foraging sites efficiently by foraging at sites close to the colony when these are available. One hundred and nine inland foraging sites were located. Only 17 (20 % ) of 86 sites measured were used for more than 3 consecutive days. Use of 46 foraging sites by birds from the main study colony was documented by direct observations of foragers commuting between the colony and foraging sites. For these sites, the distance from the colony ranged up to 11.9 km (mean = 4.7 km). The daily pattern of foraging site use in relation to distance from the colony correlated with the pattern predicted by the optimality model, but differences in detail were evident. Departures from predicted foraging distances appeared to relate more to errors in the main assumptions of the model as applied to a field context, rather than to any obvious failure on the part of the gulls to utilize food sites efficiently.