Functional visual sensitivity to ultraviolet wavelengths in the Pileated Woodpecker (Dryocopus pileatus), and its influence on foraging substrate selection

Abstract

Most diurnal birds are presumed visually sensitive to near ultraviolet (UV) wavelengths, however, controlled behavioral studies investigating UV sensitivity remain few. Although woodpeckers are important as primary cavity excavators and nuisance animals, published work on their visual systems is limited. We developed a novel foraging-based behavioral assay designed to test UV sensitivity in the Pileated Woodpecker (Dryocopus pileatus). We acclimated 21 wild-caught woodpeckers to foraging for frozen mealworms within 1.2 m sections of peeled cedar (Thuja spp.) poles. We then tested the functional significance of UV cues by placing frozen mealworms behind UV-reflective covers, UV-absorptive covers, or decayed red pine substrates within the same 1.2 m poles in independent experiments. Behavioral responses were greater toward both UV-reflective and UV-absorptive substrates in three experiments. Study subjects therefore reliably differentiated and attended to two distinct UV conditions of a foraging substrate. Cue-naïve subjects showed a preference for UV-absorptive substrates, suggesting that woodpeckers may be pre-disposed to foraging from such substrates. Behavioral responses were greater toward decayed pine substrates (UV-reflective) than sound pine substrates suggesting that decayed pine can be a useful foraging cue. The finding that cue-naïve subjects selected UV-absorbing foraging substrates has implications for ecological interactions of woodpeckers with fungi. Woodpeckers transport fungal spores, and communication methods analogous to those of plant-pollinator mutualisms (i.e. UV-absorbing patterns) may have evolved to support woodpecker-fungus mutualisms.Published by Elsevier Inc.

A larval aggregation pheromone as foraging cue for insectivorous birds

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Visual cues for woodpeckers: light reflectance of decayed wood varies by decay fungus

“…These results are relevant because both fungi are known to be associated with woodpecker cavities (Jackson and Jackson 2004), and woodpecker detection by the use of external basidiocarps (conks) is unlikely for these 2 fungi (Connor et al 1976, Rudolph et al 1995. Additionally, Pileated Woodpeckers successfully discriminated between P. pini wafers and control red pine wafers in captive behavioral trials (DS ¼ 2.4, average VS model;O'Daniels et al 2017).…”

Assessing kea perception of cereal baits using modelling of spectral reflectance

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