Artificial Lighting -- Impacts on Research Paper

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The authors explain that "Large-scale habitat loss and fragmentation…" that results from urban sprawl is a major cause of the lack of biodiversity within the insect species (Acharya, 1999, 27). Even the building of a new road, or street lights, in places where previously there were no roads or lights, what the authors call "undisturbed areas," has an impact on insect biodiversity, Acharya explains. Meanwhile, moths, which are known to be drawn to light, have trigger mechanisms that detect the echolocation signals of bats; and on the other hand bats feed "…heavily" on moths, Acharya continues; in fact many bat species use moths as their "main food item" (Acharya, 27).

The point of that information (and of this study) in this peer-reviewed piece is that if "…eared moths" exhibit behaviors that allow them to avoid bat attacks, they would not be caught as often by bats and hence this would have an effect on bat feeding (28). The authors "deafened" some moths as an experiment to determine of the moths would still be evasive to the echolocation abilities of bats. The authors released 33 "deafened" moths and 80 "eared" moths and none of the deafened moths exhibited evasive behaviors when bats attacked while 47.5% of the moths that could "hear" bats' echolocation did attempt evasive behaviors. And so, while lighting changes bat behaviors and causes bats to alter their normal paths, lighting also interferes with "…a moth's ability to respond to echolocation calls" and hence moths "…suffer a selective disadvantage around lights" -- which ironically is to the advantage of bats (Acharya, 32).

Light dependent shift in the anti-predator response of a pyralid moth

Another research paper dealing with moths and bats is published in the journal Oikos; in this case the authors demonstrated that moths are actually able to "…switch between defensive strategies from insectivorous birds [in the daytime] to bats in the evening" (Svensson, et al., 2003, 239). Moreover, this research places emphasis on what Acharya was explaining in the previous research article: that is, a moth's ability to dive away from a bat -- "a spiral flight towards the ground" which is set in motion by the detection of a bat's echolocation signal -- is "inhibited when the moth flies close to a mercury-vapour streetlamp" (Svensson, 239). This in turn, can explain why bats (in this Swedish study they observed the pyralid moth's behaviors) "are successful when hunting moths around streetlights" (Svensson, 239-240).

Again, the irony in these research articles is that while light pollution has a negative impact on bat mortality, a streetlight can also be the bats' friend because it draws in moths. That said, the ultimate goal of Svensson's paper is to prove that moths seem to adapt to avian attacks differently in the daytime than they do at night. In daylight moths seem to understand that birds are their enemies, and hence moths perform "erratic flight patterns" to defence against birds. But at night, moths seem to know their predators are bats, and in response moths land on water or in vegetation "…then remain motionless for a few seconds" (until the threat is gone) (Svensson, 245).

Contradiction to the previously referenced upside of streetlights for bats

According to the book, Fighting Light Pollution: Smart Lighting Solutions for Individuals and Communities, written by the International Dark-Sky Association (IDSA), long-eared bats (including horseshoe and mouse-eared bats) are "…repelled by light," which makes it problematic for bats to "…procure [food] when insects swarm around lights" (IDSA, 2012, 29). That contradicts Svensson's research, which was conducted in Sweden. But on the other hand the IDSA's research echoing what Stone's research paper suggested: the IDSA explains that recent studies in the UK of the "…endangered lesser horseshoe bat show that the species will take a longer route to feeding grounds in order to avoid lighted areas" (29).

In turn, the longer commute for bats (that are reportedly repelled by streetlights) means the bat "…expends more energy, is exposed to predators longer, and has a shorter time to feed" (IDSA, 29). Hence, because moths are a "favorite food of lesser horseshoe bats," when moths are drawn to "…the very light sources these bats avoid" moths are therefore not a "viable pray" for the food-focused mammals (IDSA, 29). And so, according to the authors, the decreasing source of food (moths) for bats, along with a combination of loss of habitat and "life-cycle disruption," can be considered contributing factors in the "overall decline in many bat populations" (29).

Still another research article referencing moths and bats

Kelvin Conrad and colleagues write in the peer-reviewed journal Biological Conservation that of the myriad insect populations -- which comprise "more than two-thirds of terrestrial species" -- marco-moths in England are in serious decline (Conrad, et al., 2006, 279).

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Of the 337 species of moths, the authors explain that 71 (including marco-moths) of those are threatened. That, in turn, offers "worrying implications" for bats, Conrad continues.

Using sophisticated traps (RIS light-traps), the authors have been counting marco-moths over the years from 100 traps; they have discovered "…alarming declines in the overall abundance of wide-spread marco moths. In the thirty-five years of trapping and sampling, marco-moths have declined by 31% (Conrad, 281). The greatest decline in the marco-moth population has occurred in southern England, which has also been the site of the decline of various butterfly populations.

What does it mean to the larger ecosystem when a species of moths suffers serious declines? Conrad asserts that this decline in moth populations signals "…strong impacts on the wider ecosystem and at higher trophic levels such as predacious insects, insectivorous spiders, birds and bats" (284). This deterioration in the population of moths in England signals a "…biodiversity crisis for Britain" and is an indicator that insects (and hence, bats) may be facing great losses in other countries and temperate-zone industrialized countries in particular (Conrad, 284).

Some bat species swarm around mercury street lights

Bob Mizon is co-coordinator for the British Astronomical Association's "Campaign for Dark Skies," and in his 2012 book he asserts that -- like previous research presented -- the presence of "exterior lighting" changes and sometimes shortens bats' "foraging paths" (Mizon, 2012). Indeed floodlighting often deters bats from their normal foraging spots; and in particular when lighting is near river corridors, or near woodland edges and hedgerows, studies show that lighting in these areas is harmful to bats (Mizon). Lighting along roads "…creates barriers which bats cannot cross"; indeed, Daubenton's bats "…move their flight path to avoid street lamps" (Mizon). However, other bat species, like Leisler's, serotine, and pipistrelle bats, "…swarm around white mercury street lights feeding on insects" (Jones, 2000). Jones' article ("Impact of Lighting on Bats") adds that slower bats like Plecotus, Myotis and Rhinolophus (lesser horseshoe bats) "avoid streetlights" altogether.

Jones' assertions are verified by authors Travis Longcore and Catherine Rich in the peer-reviewed journal Frontiers in Ecology and the Environment; "Many bat species are attracted to insects that congregate around light sources" (Longcore, et al., 2004, 195). The slower flying bats tend to avoid lights, Longcore explains in concert with Jones; but "…faster-flying species of bats congregate around lights to feed on insects" (195). Mercury vapor lights, in particular, "disrupt the interaction between bats and tympanate moths by interfering with moth detection of ultrasonic chirps used by bats in echolocation," a fact and concept discussed earlier in great detail in this paper (Longcore, 196). Without the ability to detect those ultrasonic chirps bats make, the moths cannot take their typical actions to avoid being snatched out of the air by bats, Longcore explains (196).

The Longcore article takes the time to admit that scientists' understanding of the "full range of ecological consequences of artificial night lighting is still limited"; that said, Longcore suggests that this field offers "many opportunities for basic and applied research" (196). In time the research into "…the influence of stray light on ecosystems will expand in geographic scope and intensity," but for now Longcore asserts that many ecologists "…have neglected to consider artificial night lighting as a relevant environmental factor" (196). Moreover, the writer continues, conservationists have "certainly neglected to include the nighttime environment in reserve and corridor design" (196).

Conclusion

Travis Longcore and Catherine Rich, with the Urban Wildlands Group in Los Angeles, and authors of an article on the ecological effects of light pollution, believe much more research should go into the impacts on wildlife of night light pollution. In order for successful investigations to be completed, the authors explain, there will have to be "…collaboration with physical scientists and engineers" so that equipment can be developed that will accurately measure light "characteristics at ecologically relevant levels under diverse field conditions" (197).

If addition empirical research is conducted -- of the kind that Longcore and Rich have describe -- no doubt the plight of bats, slow flying and fast-flying bats, will be taken into consideration. Not included in this paper is the terrible disease (the….....

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