Predator–prey size relationships in North American dabbling ducks

Abstract

Diets of dabbling ducks (Anas: Anatidae) usually have been recorded only with respect to taxonomic composition and not prey size. Interspecific diet overlap thus has been termed large. However, using published taxonomic diet lists for seven species of ducks, measurements of bill morphology from museum specimens, and "handbook" data on the sizes and caloric density of invertebrates, prey size distributions were found to differ among species (P < 0.001). Also, the sizes of prey in each species' diet differed from that found in the environment. The number of lamellae per centimetre of bill negatively correlated with mean prey size (P < 0.001); body size and bill length did not. Based on the similarity of environmental and dietary prey size distributions, species were classified as specialist or generalist foragers. This classification corresponded well with one generated from analyses of foraging behaviour alone. An explanation for the diminuitive sizes of ducks on islands was advanced: if interspecific competition for food selects for niche divergence among coexisting dabbling ducks along a prey size niche dimension, then in the absence of competition from small species on islands, large solitary species have evolved to a smaller size which may be optimal for the distribution of energy among prey size classes in the environment.

Remedial Investigation Report: White Phosphorus Contamination of Salt Marsh Sediments at Eagle River Flats, Alaska

“…Most of the particles isolated were greater than 0.5 mm in length ( Fig. IV-6), and thus are in the size range of food items (Nudds and Bowlby 1984) or gizzard mattial selected by ducks. The smallest particles isolated were around 0.25 mm in length.…”

“…The majority of sediment samples that tested positive for WP have very low concentrations or mass of WP, and although ingestion of a large number of very small particles could poison a duck, a 1-g particle about 0.082 mm in diameter is smaller than food items usually selected (Nudds and Bowlby 1984). Contaminated sediments probably contain many small particles and a very few large WP particles so that when a duck processes large amounts of contaminated sediments, the ingestion of a large particle is likely.…”

Remedial Investigation Report: White Phosphorus Contamination of Salt Marsh Sediments at Eagle River Flats, Alaska

“…IV-6), and thus are in the size range of food items (Nudds and Bowlby 1984) to relative humidity and wind speed. Smoke clouds were generated by the controlled burning of WP in a combustion chamber, and the products were passed into a wind tunnel, where various measurements were made.…”

“…The majority of sediment samples that tested positive for WP have very low concentrations or mass of WP, and although ingestion of a large number of very small particles could poison a duck, a 1-jg particle about 0.082 mm in diameter is smaller than food items usually selected (Nudds and Bowlby 1984). Contaminated sediments probably contain many small particles and a very few large WP particles so that when a duck processes large amounts of contaminated sediments, the ingestion of a large particle is likely.…”

“…WP particles ingested by waterfowl should be in the size range of other food items selected by dabbling ducks (Nudds and Bowlby 1984). We also hypothesized that the source of these particles is WP-containing incendiary munitions fired into ERF.…”