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The bird species Saltator grossus (the slate-colored grosbeak), which weighs about 45 grams, and Microbates collaris (the collared gnatwren), which weighs about 10 grams, share territory in French Guiana with Thamnomanes caesius (the cinereous antshrike), which emits a loud alarm call when it detects predators. Biologist Ari Martinez and colleagues, who studied the ecological community these species share, hypothesized that since there is an inverse relationship between body size and vulnerability to predation, there will also be an inverse relationship between body size and sensitivity to predator warning signals from neighboring species.