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Stable isotopes reveal biodiversity in the manakin diet that may be key to their future survival A quick glance at someone else’s shopping cart at the grocery store can convey a great deal about a person’s diet. All health judgments aside, a vegetarian may have veggies, tofu, and nuts; while an omnivore might skip the tofu and add a steak. A pregnant mom may be loading up on protein, a young athlete piling on carbs, and an elderly shopper buying less food altogether. Humans and animals don’t always have the luxury of choice when it comes to their diets, but when they do, it can be illuminating to see what they choose. Because you are what you eat, these choices impact the detailed composition of your body. But it’s not just about choice. Food selection for many animals is more about survival than personal preference; if a species relies too heavily on one food source, and that food becomes threatened by environmental changes or dis- ease, the species may become threatened as well. Dietary habits may also play an important role in an ecosystem, such as by dispersing seeds or cleaning up debris. Variety in diet can translate into a better chance for survival for that species as well as those dependent upon it in the food chain. Since scientists can’t ask animals about their diets, they instead have to rely on observations of animal behavior, coupled with analysis of animal excrement, to determine what the subjects have eaten. This method is fairly reliable, but also limited because fecal samples are only representative of what was consumed recently. Gaining popularity as an indicator of diet is the analysis of stable (nonradioactive) carbon and nitrogen isotopes assimilated into animal tissue. In all organisms, some food is consumed for energy, and some is broken down and used as building blocks for new growth. Stable isotopes help uncover clues about the latter. Scientists at Los Alamos recently applied their expertise in stable isotopes to analyze bird feathers from Ecuadorian mana- kins, small, fruit-loving birds who distribute seeds in their Amazon habitat— a key ecosystem service. Using a specialized algorithm developed to incorporate uncertainty in the isotopic concentrations from 18 1663 April 2014