Patterns of food abundance for breeding waterbirds in the San Luis Valley of Colorado

Abstract

We measured the amount and distribution of macroinvertebrates and seeds in four wetland habitats (short emergent, seasonal open water, semipermanent/permanent open water, and saltgrass [ Distichlis spicata ]) used by breeding ducks and shorebirds at a wetland complex in the San Luis Valley, Colorado, USA. Density of macroinvertebrates did not differ among habitats or sampling periods ( P =0.45), but dry mass, crude protein, and gross energy production were greater ( P <0.05) in short emergent than in other habitats. These differences were largely due to the greater dry mass of gastropods in short emergent than in other habitats. Total seed density, dry mass, crude protein, and gross energy differed among habitats and periods with interaction effects ( P <0.01). Although seed abundance varied among habitats and sampling periods, abundance was greatest in short emergent during all sampling periods. Breeding waterbirds consumed a variety of macroinvertebrates and seeds on the study area. Patterns of abundance among habitats of macroinvertebrates and seeds consumed by six waterbird species were not consistent with patterns of foraging habitat use by most ducks and shorebirds at this wetland complex. Our results indicate that estimates of food or nutrient abundance are useful in assessing the functional role of broad habitat types, but factors other than food abundance also influence avian selection of wetland foraging habitats.