Artificial light at night (or ALAN) is a relatively new phenomenon on the Earth. It’s only been around for the past 120 years or so, since humans developed widespread electric lights. While light at night can cause many problems for natural organisms (higher risk of predation, disruption of sleep, etc.), some organisms can take advantage of it. And in some situations, anoles, the subject of most of my current research, fall into this group. While usually diurnal (or active during daylight hours), when presented with artificial lighting, some anoles will extend their activity into nighttime hours, often camping out near lights and wolfing down the insects that are attracted to them.
The benefits of using this “night light niche” (like a bug buffet) might outweigh the costs (using extra energy, getting eaten by nocturnal predators). However, we have very little information on how animals use ALAN. In anoles, anecdotal reports suggest that >20 different species have been seen using lights at night (!), but these are isolated observations. I was recently asked by Andy Maurer, a PhD student at NC State, to collaborate on a project examining how anoles in Antigua make use of the opportunity that light at night presents to them.
While working on his main PhD project looking at reproduction of nesting sea turtles in Antigua, Andy decided to make good use of the night hours when he wasn’t messing about with turtles by tracking how the anoles at his research station used the external lights. Andy tracked individual anoles, the times that they used the lights, their sex and size, and other observational data.
Andy observed both Watts’ anoles (Anolis wattsi) and Leach’s anoles (Anolis leachii) eating arthropods attracted to light. When we crunched the numbers, we found that there was a clustering of anole activity around light in the early morning hours before dawn, not in the early night hours after sunset. This was a surprise because most previous observations of anoles using lights have been made from about 8 pm to midnight, perhaps corresponding to when many herpetologists are returning from field work (or having a drink on a porch!). Andy’s data suggest that anoles may be using lights before dawn even more, but perhaps herpetologists have been too “busy” sleeping to notice.
Andy’s data also show that ALAN is mainly used for foraging by male anoles. No females were observed doing so in this study. This pattern has been suggested by other reports, but the reasons for it remain unclear. Hopefully future work can provide some illumination!
This was a great project to work on despite the fact that I did not have the opportunity to conduct fieldwork on anoles in Antigua (I’ll have to save that for some future project!). I was also happy to work with the other coauthors, including Alex Fireman, director of the Jumby Bay Hawksbill Project; regular collaborator James Stroud, a postdoc in the Losos Lab at Washington University in St. Louis; and Sean Giery, a postdoc at Penn State University. This work was recently published in Herpetological Conservation and Biology.
Maurer, A.S., C.J. Thawley, A.L. Fireman, S.T. Giery, J.T. Stroud. 2019. Nocturnal activity of Antiguan lizards under artificial light. Herpetological Conservation and Biology. 14:105-110. [PDF]