Food-niche relationships of sympatric mallards and green-winged teals

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Abstract
Diets of juvenile green-winged teals (Anas crecca) and mallards (A. platyrhynchos) in August and September were studied with respect to (i) the proportion of animal and plant matter. (ii) prey size. (iii) prey diversity, and (iv) the vertical distribution of invertebrate prey in the water column. The size distribution of prey in the diets of the ducks was also compared with that in the environment. Teal diets contained a larger and more variable fraction of invertebrates than did mallard diets. Teals used more small food items than did mallards; however, both used a wide spectrum of sizes. Teals ate more invertebrates that live in the water column or above the water surface, whereas mallards ate more benthic animals. These results contradict earlier studies that had classified teals, on the basis of digestive tract morphology, as more herbivorous than mallards. Therefore, inferences about differences in diet based on morphology alone should be made with some caution. I also suggest, contrary to some earlier studies, that both teals and mallards are generalist foragers, the teal being probably even more plastic when different modes of aquatic feeding are considered.

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