Seabirds fly toward the light, get run over by cars

You shouldn’t litter. Everybody knows that rule, perhaps thanks to grisly images seabirds with six-pack soda rings around their necks. But not all pollution is made of trash. Birds can suffer from another, far more pervasive, far more subtle form of pollution. Instead of being made of paper and plastic, this form of pollution is made of photons.

Because most people visit wildlife parks and preserves during the daytime, it’s easy to forget about light pollution. But for the vast majority of time that life has existed on our planet, the nighttime has been dark, save for the faint glow of the moonlight and the stars. And during that time, life on our planet evolved to take advantage both of the cover of darkness, of the location of the moon and stars in the sky for the purpose of navigation, and even of the moon’s phase to mark the passing of time. All of that gets too easily disrupted by our artificial lights.

As a group, seabirds are at the greatest risk of all birds, and the petrels are at the greatest risk of all seabirds. That’s why it’s so worrisome that shearwaters and storm-petrels can be so severely impacted by artificial lights. These are nocturnally active species (during breeding season), and fledglings leave the nest only at night. They didn’t evolve to account for our lights. “Worldwide, thousands of birds are attracted to lights every year during their first fledges from their nests to the open ocean, a phenomenon called fallout,” explains Australian researcher Airam Rodriguez in a recent paper in the journal PLOS ONE. “Some fledglings may actually reach the ocean successfully but are attracted by the coastal lighting back onto the land. Fledglings are vulnerable to injury or death by collisions with human infrastructure and once grounded, to predation or become road casualties.”

It’s not exactly clear just how and why fledglings become so disoriented by our lights, so Rodriguez, together with colleagues from Phillip Island Nature Parks and Spain’s Estación Biológica de Doñana, looked at 15 years (1999-2013) data gathered during short-tailed shearwater rescue campaigns conducted at Phillip Island, Victoria, Australia. Phillip Island is an “Important Bird Area,” since it’s home to more than 1% of world’s short-tailed shearwaters and little penguins. The island’s main tourist attraction is (no surprise) the penguins, and that ecotourism means lots of lights. Lights from cars, lights from roads, lights from the bridge that connects the island to Melbourne. To the fallout data the researchers added information regarding the date, lunar phase, wind speed and direction, number of tourists, and whether it was a holiday or not.

They recorded a total of 8,871 birds collected during the rescue campaigns between 1999 and 2013. It’s perhaps heartwarming to know that’s actually less than 1% of the fledglings produced each year. Of the nearly 9,000 birds rescued by the group, nearly 40% were found dead or dying, and that proportion remained fixed over time.

As expected, there were more grounded fledglings on overcast and rainy nights. The researchers suspect that could be because of the confluence of bad weather and the way in which precipitation and clouds increase light pollution on any given night. In addition, they found that nights with faster winds had the largest numbers of grounded birds. Shearwaters require a long runway, they explain, especially for fledglings who are not experienced with flight. That’s especially true on flat islands like Phillip Island, where the birds can’t take advantage of mountain winds or high cliffs.

It may seem heartening that so few fledglings appear to be affected by artificial light, but of those who are, a whopping 40% die. Curiously, that’s a rate some four to eight times higher than estimates involving other seabird species on other islands. Rodriguez suspects that could be because rescue campaigns on most other islands are opportunistic, requiring the public to notify authorities. And most of the public wouldn’t bother alerting wildlie rescuers about birds who had already died. The rescue efforts on Phillip Island, in contrast, were more intentional, with park workers looking for both live and dead birds. Therefore, fallout estimates elsewhere may be systematically under-estimated.

Once the birds were grounded, their main source of mortality was collisions with vehicles. While the number of tourists didn’t seem to impact their mortality, the increased traffic during holidays did seem to result in more mortalities. “Thus,” the researchers concluded, “two threats interact in a fatal combination: light pollution disorients birds until they get stranded and later traffic kills them.”

Finally, to demonstrate that the lights were indeed to blame, the researchers arranged to have the lights turned off on the bridge during certain days of the breeding season. And on those nights, there were fewer grounded birds, both alive and dead.

While the weather can’t be controlled, light pollution and traffic can at least be mitigated. Lights can be turned off during critical parts of the fledging season, for example. And the researchers also saw reduced mortalities by reducing speed limits and by installing signs that said “Drive Safely! Birds on the Road!” on parts of the roads where the birds were particularly prone to grounding.

Ecotourism is an important means of maintaining conservation interests while recognizing the needs of local economies. However, the tourists’ activities must be carefully monitored, and they must be explicitly educated about the possible impacts of their behavior on wildlife, if it is to remain a viable tool in the conservationists’ toolbox. – Jason G. Goldman | 17 October 2014

Source: Rodriguez A., Burgan G., Dann P., Jessop R., Negro J.J. & Chiaradia A. (2014). Fatal Attraction of Short-Tailed Shearwaters to Artificial Lights, PLOS ONE, 9 (10) e110114. DOI: 10.1371/journal.pone.0110114

Header image: JJ Harrison/Wikimedia Commons.