Does Seasonality, Tidal Cycle, and Plumage Color Influence Feeding Behavior and Efficiency of Western Reef Heron (Egretta gularis)?

Abstract

Polymorphic traits may evolve in many species of birds, often driven by multiple environmental factors. It is hypothesized that polymorphic traits in herons could be influenced by feeding behavior. Most of the Western Reef Herons (Egretta egularis) (more than 70%) are of the dark morph in the United Arab Emirates (UAE). Feeding behavior and efficiency in the dimorphic Western Reef Heron was characterized in a shoreline habitat of Al-Zora Protected Area, Ajman, UAE in relation to season, tidal cycle, and color morphs. Foraging behavioral observations were made using standard focal birds during summer and winter seasons spanning entire tidal cycles. Western Reef Herons used 13 feeding behavior types with difference in their utilization between seasons and age groups. Stand and wait and slowly walking were the two most commonly used techniques in both morphs. Feeding behavioral diversity was higher in both morphs in summer, probably because summers are harsh and abundance of food is lower. Feeding behavioral diversity was higher in dark morphs in general and was even higher in summer during falling tides. Foraging efficiency, however, did not vary between seasons or morphs. Feeding behavioral diversity and foraging efficiency was significantly higher during lag periods of rising tides in both morphs. Thus, it appears that dark morphs could be disadvantaged in summer months and therefore be utilizing a wider variety of behaviors to acquire adequate food. This does not explain why there are more dark morphed birds (70%) in the population. We suggest that dark morphed birds compensate for lower feeding efficiency by increasing feeding behavioral diversity and feeding efficiency during the rising tides. Further studies are needed to evaluate the influence of prey avoidance and the choice of predators that attack herons, to better understand factors influencing the numerical dominance of dark morphs.