Abstract
BackgroundGeneralist herbivores are challenged not only by the low nitrogen and high indigestibility of their plant foods, but also by physical and chemical defenses of plants. This study investigated the foods of wild parrots in the Peruvian Amazon and asked whether these foods contain dietary components that are limiting for generalist herbivores (protein, lipids, minerals) and in what quantity; whether parrots chose foods based on nutrient content; and whether parrots avoid plants that are chemically defended.Methodology/Principal FindingsWe made 224 field observations of free-ranging parrots of 17 species in 8 genera foraging on 102 species of trees in an undisturbed tropical rainforest, in two dry seasons (July-August 1992–1993) and one wet season (January-February1994). We performed laboratory analyses of parts of plants eaten and not eaten by parrots and brine shrimp assays of toxicity as a proxy for vertebrates. Parrots ate seeds, fruits, flowers, leaves, bark, and insect larvae, but up to 70% of their diet comprised seeds of many species of tropical trees, in various stages of ripeness. Plant parts eaten by parrots were rich in protein, lipid, and essential minerals, as well as potentially toxic chemicals. Seeds were higher than other plant materials in protein and lipid and lower in fiber. Large macaws of three species ate foods higher in protein and lipids and lower in fiber compared to plant parts available but not eaten. Macaws ate foods that were lower in phenolic compounds than foods they avoided. Nevertheless, foods eaten by macaws contained measurable levels of toxicity. Macaws did not appear to make dietary selections based on mineral content.Conclusions/SignificanceParrots represent a remarkable example of a generalist herbivore that consumes seeds destructively despite plant chemical defenses. With the ability to eat toxic foods, rainforest-dwelling parrots exploited a diversity of nutritious foods, even in the dry season when food was scarce for other frugivores and granivores.
Highlights
The ecological role of parrots in tropical forests may yet be underestimated, but a growing number of recent studies have described the feeding ecology and diets of wild parrots
Often classified as frugivores, most parrots eat seeds in various stages of ripeness as the primary component of their diets, with larger parrots eating a higher proportion of seeds relative to fruit pulp than do smaller parrots [6,7,9,14,15,18,19]
As part of a broader study of parrots in the Peruvian Amazon of Manu National Park [28,29,30], we investigated the foods eaten by 17 species of parrots
Summary
The ecological role of parrots in tropical forests may yet be underestimated, but a growing number of recent studies have described the feeding ecology and diets of wild parrots (in the neotropics alone: [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17]). Often classified as frugivores, most parrots eat seeds in various stages of ripeness as the primary component of their diets, with larger parrots eating a higher proportion of seeds relative to fruit pulp than do smaller parrots [6,7,9,14,15,18,19]. Most of these recent studies classify parrots as pre-dispersal seed predators, regardless of geographic region or habitat type. This study investigated the foods of wild parrots in the Peruvian Amazon and asked whether these foods contain dietary components that are limiting for generalist herbivores (protein, lipids, minerals) and in what quantity; whether parrots chose foods based on nutrient content; and whether parrots avoid plants that are chemically defended
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