Foraging-patch use and within-patch diet selectivity in Mourning Doves, Zenaida macroura

Abstract

Past studies of foraging-patch exploitation among granivorous animals largely have focused on mammals, so we sought to test patch-use strategies in an avian granivore, the Mourning Dove (Zenaida macroura). Based on available experimental evidence and existing food habits/selection information, we hypothesized that Mourning Doves use a fixed-time patch departure strategy and an expanding specialist within-patch diet-selection strategy (specialization at high resource densities but generalization at low densities). We tested predictions based on these hypotheses and selected alternatives in three outdoor aviary experiments. Mourning Doves failed to equalize food giving-up densities (GUDs; food densities at the point of patch departure) between rich and poor patches, and no indirect interactions took place between multiple foods in patches. The ratio of GUDs between rich and poor patches equaled the ratio of initial food densities. Neither selectivity among, nor ratio of GUDs between, multiple foods varied with degree of patch exploitation. Results of all experiments supported a fixed-time patch-departure strategy among Mourning Doves; this may be a general pattern among open area-foraging avian granivores. A fixed-time strategy in this guild may indicate inability to assess patch resource density, possibly due to lack of olfactory capabilities or to a constant rate of seed intake at most seed densities. Results did not completely support an expanding specialist diet-selection strategy, but this strategy seems a more likely cause of partial diet preferences than does an alternative mechanism, a generalist strategy with unequal encounter rates.