In a new study conducted in Australia, researchers have determined that the over-abundance of artificial light disrupts the reproductive cycle of wallabies. The miniature cousins of kangaroos, wallabies are found in the plains and forests of Australia, New Guinea and one of New Zealand’s islands. Their reproductive patterns are generally very time-specific and this new research shows how artificial light can mess with those cycles.
Wallabies mate in October, but the female’s body relies on the sun for cues as to when to deliver her babies. She holds the embryo dormant until after the summer solstice, which occurs in December down under.
Essentially, the natural, predictable shortening of days and the decreasing daylight triggers the female’s body to create and produce melatonin. This hormone regulates sleep and wakefulness. The production of melatonin thereafter increases progesterone levels, which signals the embryo to develop into a fetus.
Once the fetus develops, wallabies deliver their babies exactly six weeks after the summer solstice, when day length and temperatures are perfect.
Up until now, most studies on the effects that light pollution has on mammals have taken place in controlled laboratory environments or on field observations of behavior alone. The researchers of this new study, consisting of Australian and German scientists, actually observed wallabies in their natural environments as well as obtaining biological measurements.
The researchers placed small collars on five females. The collars measured near constant light levels and GPS coordinates of the marsupials. The team also collected several blood samples which they measured for levels of melatonin. They also recorded the birth schedules of approximately 300 babies delivered over a five-year period.
Importantly, the researchers studied two different populations of wallabies. One population lived in a bush environment that was far away from artificial lighting. The other population was located in the grasses near a naval base that had tons of artificial light glowing at all hours of the night.
The observations of researchers indicate that the presence of artificial light definitely alters the reproductive timing of female wallabies. Females located near the naval base had a more difficult time responding to shortening days (because the artificial lighting masked natural lighting.) They therefore developed less melatonin than the females located in the bush (which enjoyed natural light and darkness.) Less melatonin means delayed development of the fetus.
The study concluded that for the naval base mothers, the lighting caused biological changes that affected their bodies as well their babies. On average, the mothers delivered their babies a whole month after the bush mothers delivered their young.
The researchers note that the problem of the abundance of artificial light is not going away any time soon for wallabies, as well as all kinds of wildlife. Artificial light pollution is constantly increasing, growing at a rate of about 6% annually.