Light reflectance patterns of decayed wood with implications for the visual ecology of woodpeckers
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Birds rely on eyesight for many aspects of their behavior and ecology, and a majority of diurnal species have thus evolved complex visual systems that include sensitivity to near ultraviolet (UV; 300-399 nm) wavelengths. The benefits of UV sensitivity to birds have been linked primarily to foraging and signaling. Behavioral studies of UV sensitivity have been conducted largely with passerine test subjects. Woodpeckers are a globally distributed avian subfamily (Picinae) that is ecologically and economically important. They are considered keystone taxa because the cavities that they excavate are utilized by dozens of other species of birds, mammals, and reptiles. Additionally, woodpeckers are responsible for millions of dollars in damage to anthropogenic structures annually. Despite their importance both as primary cavity excavators and nuisance animals, little work on their visual systems has been published. We developed a novel foraging-based behavioral assay designed to test UV sensitivity in woodpeckers, using the Pileated Woodpecker (Dryocopus pileatus) as a model organism. We acclimated 21 wild-caught D. pileatus to foraging for frozen mealworms within 1.2 m sections of peeled cedar (Thuja spp.) poles. We then tested the functional significance of multiple UV-reflective cues by placing frozen mealworms behind increased UV covers (0.07% MgCO3, wt/wt), decreased UV covers (0.07% MgCO3 + UV Killer[copyright] or UV Killer), or decayed red pine substrates within the same 1.2 m poles in independent experiments.
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