Meeting Abstract
Despite numerous species co-occurring with humans in urban environments, no study has documented the effects of human-made light pollution on free-ranging wild terrestrial mammals. This research examines the role of artificial light on reproductive activation in the Tammar wallaby (Macropus eugenii) from two populations with differing levels of light pollution on Garden Island, Western Australia. Change in day length is an important cue for reproductive activation in the Tammar wallaby to ensure optimal timing of greatest maternal investment with favorable environmental conditions. We collected reproductive data over a 5-year period to calculate birth schedules and blood samples for measurement of melatonin levels. Using micro-light loggers attached to GPS collars, we measured habitat use and light intensity experienced by wallabies at night in the two populations. The distributions of birth dates are significantly different between urbanized and natural populations (Kolmogorov-Smirnov two sample test; D=0.351, P=0.001). The median birth date for pouch young in the urbanized population was February 28th, while the natural population was February 1st. Wallabies from the urbanized population are subject to highly variable and significantly greater artificial light levels (t-test; t=-2.31, P=0.04) and attempt to avoid nighttime light but are restricted in their ability to do so. The shifts in birth dates are a result of suppression of melatonin production by light pollution at night and hence a delay in reproductive activation. Future work will employ manipulative experimentation (e.g. changes to light wavelengths) to isolate the mechanistic drivers of reproductive activation.
