Differential preference for ultraviolet light among captive birds from three ecological habitats

With receptors for red, blue, green, and ultraviolet-A light, birds have tetrachromatic vision. For birds, ultraviolet (UV) light is important for a number of their behaviors, including mate selection, foraging, and nesting. Many captive birds, however, are housed indoors without access to natural light and without UV-supplemented lighting; a practice which may negatively impact their welfare. Understanding how birds use UV light, and assessing its relative importance, is necessary to provide optimal care in captive settings. Accordingly, we tested the preference for UV light shown by 67 birds housed at Lincoln Park Zoo, Chicago, USA, and its impact on their behavior. We tested 18 species which represented three natural ecologies typified by different natural light levels: high light dwellers (e.g., birds that live in savannas or seashores), patchy light dwellers (e.g., birds that live in forested areas), and circumpolar dwellers (e.g., birds that live near the poles). Experiment 1 investigated the birds’ lighting preferences through simultaneous presentation of areas of their exhibit lit with supplemental ultraviolet light (UV+ zone) and with standard artificial light. Experiment 2 investigated the impact of supplemental UV light on these birds’ behavioral repertoire. Birds from high light and circumpolar environments showed a preference for the side of their enclosure to which UV light was added. High light birds were recorded in the UV+ zone during 64% trials and, similarly, circumpolar birds were observed in this UV+ zone for 61% of trials; a significant preference for UV+ zone, P < 0.001 for both. Perhaps mimicking their natural habitat of part-sun and part-shade, in Experiment 1 birds from patchy light environments split their time evenly within their enclosure (they were recorded in the UV+ zone for 54% of trials). When in an environment with added UV light, birds from patchy light habitats were more sociable: the percentage of their observation trials spent in proximity and in contact with other birds increased from 5% to 11% (P = 0.026). Although certain birds showed a preference for the added UV light, none showed changes in their behavioral repertoire beyond the sociability measure. We discuss this preference for UV-supplemented environments and the management implications for zoos and other captive facilities which house birds indoors.