Ornamental colouration as an indicator of environmental pollution with application to the tree swallow (Tachycineta bicolour)

• Author / Creator

  Lifshitz, Natalia

• Anthropogenic pollution causes habitat degradation for many species, but its effects on individuals can be difficult to detect until they result in the decline or disappearance of populations. Current techniques to monitor the effects of pollution on wildlife usually include invasive sampling of expendable species, but measuring colouration of ornamental traits may provide an alternative that is non-invasive and suitable for species of conservation concern. As products of sexual selection, ornamental traits are sensitive to environmental conditions, thereby providing honest information about the health and condition of their bearers as ready-made biomarkers. The objectives of my thesis are (1) to review the literature on the effects of various pollutants on ornamental colouration of fish and birds; (2) determine whether colouration of wild tree swallows (Tachycineta bicolour) is sensitive to environmental metal pollution; and (3) compare colour metrics of tree swallows obtained via spectrophotometry and digital photography, while also determining if remote photography is precise enough to detect changes in colouration. For objective 1, I conducted a literature search and reviewed the documented effects of several classes of pollutants on ornamental colouration of fish and birds. I found that several types of pollutants, including pharmaceuticals, pesticides, industry-related compounds and metals, impede the expression of carotenoid- and brown melanin-based ornamental colouration, enhance traits coloured by black melanin, and have opposing effects on different metrics of structural colouration. I concluded that by finding suitable model species and comparative colour metrics, it could be possible to lay a foundation for pollution monitoring that is less invasive and more generalizable than existing standards. For objective 2, I studied tree swallows nesting in boxes at four sites surrounded by a different degree of urbanization. I estimated pollution exposure for each brood via feces produced by chicks and compared these values to the feather and health (measured via oxidative stress) and colouration of provisioning parents. I further compared parental colour to reproductive success (measured by number of young fledged). I found that plumage colour shifter from bluer to greener, while feather brightness increased, with increasing exposure to copper and zinc. Both patterns would be expected from changes in the microstructure of the feathers. Unexpectedly, increasing exposure to these metals correlated with increased apparent health (lower oxidative stress) in female swallows, but not males. Number of young fledged decreased slightly with exposure to metals but did not vary with the colour of parents.For objective 3, I compared colour information obtained from digital photographs of birds in-hand to the differences in colour that I obtained using reflectance spectrophotometry on the same individuals. With different individuals, I calibrated digital photographs of tree swallows perched on their nest boxes with colour reference cards that had previously been attached to the boxes using three measures of colour: hue, saturation and brightness. I found that hue of tree swallows was highly correlated between techniques, and saturation and brightness were uncorrelated. Additionally, hue values measured using photography at a distance fell within the range of plumage hue reported for tree swallows, and the colour reference panels showed a very low variation between the photographs, even when taken on different days and under different environmental and illumination conditions.In combination, my results suggest that ornamental colouration of birds can be a reliable tool for monitoring environmental pollution. For tree swallows, colouration seems to be sensitive to metal pollution, although more work will be needed to understand the complex relationships among ornamental colour, health, and fitness metrics. My results suggest that hue of iridescent plumage can be measured as effectively with photography as with spectrophotometry, and that calibrated remote photography may provide a reliable measure of it. These results support the suggestions by several previous authors that ornamental colouration could provide a non-invasive tool for assessing pollution exposure in birds while advancing tools for achieving that goal.

• Subjects / Keywords

  • monitoring
  • ornamental colour
  • tree swallow
  • pollution
  • early-indicator

• Graduation date

  Spring 2019

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/r3-f1j0-pq28

• License

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