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An Experimental Assessment Of Polarized Light’s Role In Avian Behavior Toward Water: Implications For Collisions With Pv Solar Panels
John Swaddle
John Swaddle
Abstract
The number of solar panel installations in the United States has grown quickly in the past decade and is expected to continue rising. While solar power is an important component of our energy portfolio, there are some ecological concerns associated with increasing commercial sites. Bird mortality at solar panel sights has been observed and recently begun to be investigated. This phenomenon is still poorly investigated, and many questions remain to be answered, including what attracts birds to solar sites. The “lake effect” hypothesis is that birds collide with solar panels as they mistake for water because both surfaces reflect polarized light. Birds may be attracted to linear polarization (hereafter “polarization,”) which is created in high levels by both solar panels and water. There is some evidence that birds use environmental polarization as a decision-making cue. For example, migrating birds appear to use skylight polarization to help them orient during takeoff and recent research suggests that birds are more attracted to small water sources (bird baths) with higher polarization. There are no studies that have directly addressed whether polarization might drive solar panels collisions. To test whether polarization might be used by birds to direct them toward water, we created an operant conditioning experiment where domesticated zebra finches (Taeniopygia guttata) were trained via both positive and negative reinforcement to move towards water. Birds were trained in a testing arena with two choices, a bowl of water and an empty bowl. Once trained, as assessed by a success rate of 80%, we tested birds with an unreinforced version of the training stimuli, as well as with two more sets of polarization stimuli: a set of water bowls where one produced higher polarization, as modified by a set of films; and a set of light sources where one had higher polarization. The objective was to assess whether: 1. Birds preferred water with higher polarization, and 2. Whether this preference carried over to non-water sources of polarization. Although birds passed through the training criteria, they did not perform better than chance when tested with the training stimuli. These results suggest that operant conditioning training was not successful, possibly because reinforcement was not compelling enough. Birds also did not show a preference for higher polarization in either of the subsequent tests. As training was not successful, these results of these tests can be considered in the context of having no previous exposure to these polarization stimuli. The results of this study are contradicted by other studies, that showed a preference for higher polarization when making foraging decisions. It could suggest that polarization vision is highly context dependent, taxonomically contingent or used only in conjunction with related cues. Few studies and conflicting evidence suggest that there is still much to be learned in how birds use environmental polarization, particularly as it could have important ecological consequences in the form of solar panel collisions.
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2024-01-01
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Biology
DOI
https://dx.doi.org/10.21220/s2-hfrz-mz11