Anthropogenic Triple Jeopardy: Exploring the effects of multiple stressors on waterbirds

© 2021 Kajanka Jehan MathiaparanamUrbanisation is occurring at unprecedented rates, exposing animals to many anthropogenic stressors. Noise, light and chemical pollution are three major sensory pollutants that often co-occur, and this simultaneous exposure to the mixture of all three could be considered an ‘anthropogenic triple jeopardy’. Yet, the combined effects of these stressors on animals are not well understood. In this thesis, I addressed three important, but previously understudied questions related to the effects of noise, light and chemical pollution on urban waterbirds. First, I reviewed the current state of knowledge and focus of work on the three stressors through a systematic review, to examine the frequency with which these stressors are studied independently or in combination. I compared the results of this literature review to a case study I conducted examining the likelihood of habitats in Greater Melbourne in south-eastern Australia being exposed to one or more stressors at levels likely to cause biological impacts. Melbourne would provide a conservative estimation given that it is relatively less urbanised than many urban centres elsewhere (i.e., 90% of the metropolitan cities have a higher population density than Melbourne). I found that while less than 4% of the research focused on multiple stressors, animals were likely to be exposed to multiple stressors at 33-46% of the habitats around Melbourne, highlighting a mismatch between the research focus and the realistic likelihood that animals are exposed to multiple stressors. This lack of multiple stressor focus was true across a range of biological endpoints, even though individual stressor studies showed that most endpoints were impacted by more than one stressor. Secondly, I tested for individual and interactive effects of noise and artificial light at night (ALAN) on the abundance of a common and widely distributed waterbird, the Eurasian coot (Fulica atra) around Melbourne. I found that coot abundance was individually and interactively negatively impacted by noise and ALAN. There was a detrimental synergistic effect of noise and ALAN on coot abundance, with coots predicted to be absent at the sites with highest noise and ALAN. Thirdly, I explored the interactive effects of noise and ALAN at the community level, testing how the abundance of 30 species varied in relation to the two stressors, and the degree to which foraging and nesting habitat use and behaviour might explain variability in effects. Abundances of 50% of the species (n=15) were impacted by noise or ALAN in isolation, and 60% of those (n=9) were impacted by interactive effects, indicating possible shifts in community composition driven by noise and ALAN. Yet, community parameters (species richness, Shannon-Weiner index, or Simpson’s index) did not capture this change, suggesting the importance of monitoring community effects at a species-level to detect changes by anthropogenic stressors. Predictions based on foraging and nesting habitats did not consistently align with the observed trends, hinting at a myriad of other factors that may influence how species are impacted by noise and ALAN. My thesis provides insight into the interactive effects of noise and ALAN on abundance of birds and demonstrates potential detrimental outcomes on the distribution of individual species as well as community composition through shifts in individual species abundances. My findings also highlight that most current research is not being optimally directed towards the anthropogenic threats and complex forms of exposure that urban animals currently experience