The Evolution of Avian Food-Storing Behavior

Abstract

Food-storing bird species reside in environments with seasonal pulses of durable particulate food items, followed by periods of relative food scarcity. They have generalized diets and foraging repertoires, and show behavior (including territoriality) that helps storing individuals retain possession of stored items. Storing species occur in few families: woodpeckers, corvids, parids, and nuthatches. Less well developed storing occurs in shrikes and some predators because its evolution is constrained by rapid food item deterioration. Species in other families lack an ability to defend or retain cached food, do not feed on storable items, or lack sufficiently dense supplies of potential stored food. Storing increases food availability during periods of food scarcity, evolutionary leading to increased survival, longer life, and possibly to augmentation of a trend toward kin-selected social organizations. Storing species developed the trait in accord with the principle of economic defendability. A strategic analysis of the socioecological behavior of melanerpine woodpeckers and jays of the United States and Canada confirms expectations from an evolutionary model by showing that species utilize a single optimal strategy involving assessment of storable food availability. Individuals remain on a site and store food in favorable circumstances; in unfavorable conditions the selected behavior includes abandoning otherwise favorable habitat and opportunistically wintering where storable food is more abundant. Resident storers only opt for abandonment in very poor years, apparently because of benefits attending long-term residence. Fugitive storers only choose to remain when conditions in breeding areas are exceptionally favorable, i.e., when there is abundant storable food.