Street lighting, moths and predatory bats

This study caught my eye last week: Light-emitting diode street lights reduce last-ditch evasive manoeuvres by moths to bat echolocation calls. It's a paper published early this month in the Royal Society Open Science journal by researchers at the University of Bristol (Wakefield et al 2015). It got my attention for two reasons: firstly, obviously, I love moths and so any research concerning them tends to catch my interest, and secondly, the impacts of artificial lighting is an area I find fascinating and is the topic I conducted my undergraduate research project on. 

Lighting technology is rapidly developing, with policies in many developed countries aiming to increase efficiency to reach emission targets. Light emitting diode (LED) is one such energy efficient lighting type and it's use is certainly growing; it is thought it will constitute 70% of generaly lighting by 2020 (Peters 2011). In 2009 LED street lights were being rolled out across the UK, with little research having been conducted on the potential impacts of this change for wildlife or human health. Research into the impacts of LED lighting has therefore been retrospective which probably isn't that ideal.

Lighting type has an influence on wildlife responses due to differing spectrums being covered by differing lighting varieties. Moths are for example generally more attracted to light with shorter wavelengths. A study by researchers at the University of Exeter in 2013 (paper here) for example showed  significantly larger catches at whiter, short-wave length lights than the yellowish longer wave-length, with this pattern being driven by the attraction of moths from the noctuid family, whilst geometrids showed no significant preference between lighting types (Somers-Yeats et al 2013). A study in New Zealand also demonstrates an affect of white lighting on invertebrates: LED lights attracted 48% more flying insects than high pressure sodium lamps (Pawson & Bader 2014).

This recent study (Wakefield et al 2015) was looking at much finer scale impacts than merely numbers attracted, and was infact looking at behavioural responses of moths, and subsequent impacts for predation events by bats. Predator avoidance responses of moths include a power dive (a straight down drop), zig zag flight and a spiral drop flight.  Using artificial lighting, bat feed buzz playbacks and camera footage, this study found that moths were significantly less likely to exhibit power dives in LED lighting treatments compared to no lighting, reducing their ability to evade predation by bats. 

Whilst I liked this study and think they found some really interesting results, I think it would have been cool to compare moth behaviour between differing lighting types, rather than just LED and no lighting at all. Obviously research is always constrained by time and funding, so maybe that is just a cool area for future study!

Find the original paper here. For more information on research being conducted by the University of Bristol bats and lighting research group, click here.

Photo by Tom Lee.