Commensalism in the Little Blue Heron

Abstract

Abstract Little Blue Herons feed in association with White Ibis by using the ibis's movements to increase foraging effectiveness. When feeding near a White Ibis, a heron increased the number of prey caught without increasing its energetic costs of foraging. The strike rate of a bird was higher when feeding commensally than when feeding alone, but its success per strike did not increase because of the commensal association. This increased energy return when feeding commensally resulted from greater opportunity for commensal herons to observe and attempt to catch prey rather than from an increased probability of their catching a prey item after it had been observed. The results of this study of a non-obvious commensal relationship suggest that many previously reported associations among water birds are also commensal. It also supports the hypothesis that multispecies aggregations of ciconiiforms may be characterized by cryptic forms of commensalism.