Seasonal resource tracking by Amazonian hummingbirds

Abstract

Many ecological theories predict a close match between food resources and the number and diversity of consumers but comparatively few empirical studies have simultaneously quantified seasonal variation in an entire assemblage and its resource base. Hummingbirds provide an excellent model system to examine this relationship because their primary food resource is conspicuous and easily quantified. Over a 2‐year period I used mist‐netting and direct observation of birds feeding at flowering plants to record the abundance of 16 species of hummingbird in lowland Amazonian rainforest. Although there was very little annual variation in temperature and daylength, both rainfall and river level showed significant seasonal variation. At the study site this resulted in an annual flood lasting for over 5 months, inundating much of the area to a depth of 2 m. I recorded marked seasonal patterns in flowering phenology and arthropod abundance, which correlated with river level and rainfall, respectively. In turn, these seasonal fluctuations in resource abundance correlated very closely with variation in hummingbird species richness, hummingbird abundance and the total biomass of hummingbirds in the assemblage. This study is the first to demonstrate tracking of seasonal resource variation in equatorial rainforest and provides evidence that hummingbirds are sensitive to resource availability at spatial and temporal scales much greater than previously documented.