Monday, 31 October 2011

Does conservation status put threatened cats at risk?

Hunters and conservationists have long debated the impacts of trophy hunting. Hunters tend to argue that the practice targets such a small number of individuals that it does not have negative impacts on quarry species. In fact, they say, hunters can contribute to conservation by supporting habitat protection efforts, reducing the market for poachers, and buying expensive permits--the profits from which can be used for preservation efforts. On the other hand, conservationists often argue against trophy hunting not only on the grounds that it is unethical, but also because it may have detrimental impacts on animal populations, lead to corruption, and foster the growth of an industry that is not as profitable as alternatives (for instance, photographic tourism.

Scientific studies have found evidence to support both arguments, leaving the two sides in a stalemate. However, recent research efforts begun to report some interesting trends that may settle the debate. For lions and several types of ungulate, attractiveness to hunters appears to be closely related to conservation threat status (e.g., "least concern," "vulnerable," "threatened," "endangered"). Specifically, the higher the conservation threat, the more attractive the quarry. This is not entirely surprising, given the number of studies showing the value of rarity--in zoos, for exotic pet collections, in luxury good consumption, and for ecotourism. Overall, these patterns suggest that the very conservation action that was taken to protect the animals might, in some ways, have put them more in harm's way.

(A male African lion, Panthera leo. This species is listed as "vulnerable"--a status that was caused, in large part, by high levels of hunting.)

To investigate whether this pattern was true for felid species, researchers from the Université Paris-Sud and the Université Lyon collected hunting data on 10 types of cat: the caracal (Caracal caracal), the African wild cat (Felis silvestris libyca), the serval (Leptailurus serval), the Canada lynx (Lynx canadensis), the bobcat (Lynx rufus), the cheetah (Acinonyx jubatus), the African lion (Panthera leo), the European lynx (Lynx lynx), the cougar (Puma concolor), and the leopard (Panthera pardus). Data on trophy takes, quarry mass, conservation status, and illegal takes (determined from confiscated trophies, skins, and skulls) between 1975 and 2008 were collected from the Safari Club International database, the CRC handbook of mammalian body mass, the International Union for the Conservation of Nature (IUCN) red list, and the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) database.

(A serval, Leptailurus serval. This species has a conservation status of "least concern." Among exotic pets, these appear to be fairly common--despite the fact that full-grown adults can weigh up to 40 pounds (18 kg) and have a shoulder height of just over 2 feet (66 cm)).

For 7/10 species, the number of individuals killed rose markedly over the study period, and for 6 of these species, the increase was exponential. The increase in trophy hunting was generally most noticeable for species that were most threatened--including lions, cheetahs, and leopards. For these animals, hunting efforts doubled every 7.2 years rather than every 11.7 years, as observed in other, less threatened, species. Illegal takes also increased (linearly) throughout the study period, indicating that there is a good market for felid trophies. This is troubling since the rise in illegal activity is concomitant with dwindling populations sizes of all 4 species of conservation concern. An analysis of monetary values of trophies revealed that near threatened and vulnerable species are worth more, regardless of body mass or trophy size. Among those species whose statuses were upgraded from "least concern" to "near threatened," there was a small but noticeable increase in trophy numbers; among those upgraded to "vulnerable," the increase was even more obvious. A downgrading of status, on the other hand, resulted in a reduction in exploitation. None of these relationships is statistically significant (though they are close), and none clearly shows a cause-and-effect relationship between conservation status and quarry popularity. However, the consistency of the results strongly suggests that "vulnerability to extinction makes felid species more hunted."

(A bobcat, Lynx rufus. This species has a conservation status of "least concern.")

Given the similarity between these findings and those recently obtained from a study of ungulates, it appears that the patterns observed here are probably descriptive of the effects of hunting on a broad range of species--not just felids, but other groups as well. Overall, these findings put conservationists in a bit of a bind. Conservation statuses can be used to obtain different levels of protection for the animals that need them, but then again they may make species more susceptible to trophy hunting and poaching. The authors suggest that one of the draws of rare cats is that their extremely low densities offer a challenge that has been taken out of other hunting endeavors with the advent of modern technology (including all-terrain vehicles, advanced weaponry, electronic tracking and surveillance gadgets); in other words, rarity may put some of the thrill back in the chase.

The researchers suggest that, if trophy hunting of threatened animals is to continue, it will be vital to create a better, scientifically-based quota system. This will require accurately assessing species' population sizes, measuring their growth capacity, and identifying any density-dependent mechanisms (trends that are only seen once populations shrink to a certain size). Additionally, any quota system should be combined with protection methods to ensure that only licensed hunters--and not poachers--are killing the animals. 

For supplementary images associated with this post, please visit the Anthrophysis pin board at Pinterest.

Palazy, L., Bonenfant, C., Gaillard, J.-M., Courchamp, F. 2011. Cat dilemma: too protected to escape trophy hunting? PLoS ONE 6(7):e22424.

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Sunday, 30 October 2011

British swans: protected, but still hunted

National and international laws have been put in place to protect many species of wildfowl from the population declines, and even extinctions, that can be caused by unsustainable hunting. Despite this, there are regular sightings of pellet-ridden birds; however, few studies investigate the prevalence of this type of anthropogenic damage or its long-term impacts. These are likely to be particularly problematic for long-lived species such as migratory whooper (Cygnus cygnus) and Bewick's (Cygnus columbianus bewickii) swans. These birds produce few young per year and do not start breeding until they are several years old; thus, the health of swan populations could be seriously impacted by decreases in adult condition and increases in adult mortality.

(Whooper swan, Cygnus cygnus)

In the UK, these Bewick's and whooper swans have been protected since 1976 and 1954, respectively. Despite this, many of the birds carry shotgun pellets in their flesh, which indicates that the animals are being hunted illegally. Researchers at the Wildfowl & Wetlands Trust recently conducted a study to measure just how many birds were shooting victims, whether particular characteristics made some birds more susceptible than others, and whether there are any consequences of living with embedded pellets. They achieved this by taking live X-rays of swans caught in "swan pipes" at 4 sites; they also analyzed postmortem data from swans that had been collected between 1970 and 2009.

 (Bewick's swan, Cygnus columbianus bewickii)

Overall, the scientists considered 1,492 X-rays from 1,132 birds. Nearly a third of Bewick's swans carried pellets (43.2% of all adults), while this was true of only about a tenth of whooper swans (16.3% of all adults). Although most shot birds had 1-3 pellets, up to 30 were recorded within a single Bewick's swan, and up to 11 were found within individual whooper swans. Males and females were equally likely to have been shot, but older birds generally carried more pellets than younger ones. For Bewick's swans, more pellets were also found in larger birds--perhaps because they offered a bigger target that was easier to hit.

Over 200 birds were captured multiple times, allowing the researchers to look for changes in pellet load over time. Between the two species, 50 of these birds were found to have more pellets at the second capture. Since the birds had remained on their wintering grounds between the two X-ray periods, this result roughly pinpoints locations where the birds were shot--Slimbridge, for the Bewick's swans, and Caerlaverock, for the whoopers. On the up side, the percentage of recaptured birds with an increased pellet load decreased over time for both species, indicating that, while illegal hunting continues, it is at lower levels now than it was in the past.

(Wintering waterfowl at Caerlaverock)

The presence of pellets did not appear to have a statistically significant impact on body condition--although the relationship between pellet count and condition did trend towards significant in Bewick's swans. Among dead birds collected for analysis, 8.4% of Bewick's swans and 3.1% of whooper swans appeared to have died from gunshot wounds. However, the proportion of deaths varied over the years; again, the evidence indicated that illegal hunting is still a problem, but less of one now than in previous decades.

While the presence of protective laws seems to have reduced swan shootings, it doesn't appear to have prevented them altogether. Bewick's swans are particularly susceptible, carrying pellet levels similar to those observed in huntable species such as the pink-footed goose (Anser brachyrhynchus). Differences between the two swan species may result from differences in their habitats and migration routes. Bewick's swans breed on the arctic tundra of European Russia, then winter in the northwestern portion of Europe, staging in Estonia and the Gulf of Finland along the way. Their long route puts them into much longer, and more frequent, contact with humans than that experienced by British whooper swans, which breed in Iceland and then fly east across the ocean to winter in the UK. An added burden of the longer, more overland, migration route of the Bewick's swans is that it is more difficult to adequately and effectively police hunting activities in so many countries.

(Trumpeter swan, Cygnus buccinator, injured by illegal shooting; luckily, it was spotted by bird-lovers, patched up by a veterinarian, and released back into the wild)

It would be useful to evaluate the actual rate of deaths per shooting event, and to understand how hunting injuries may interact with normal levels of disease and exhaustion to hamper the birds during migration. Further, additional studies would be needed to directly measured how pellet loads impact animal health and survival, and whether these effects go on to influence the health of swan populations. However, these data are not easy to collect. It is also difficult to pinpoint where poaching occurs and why it happens. The authors suggest that partnerships with hunting organizations might be effective in providing hunters with proper identification, identifying at-risk areas, and uncovering more information on why swans continue to be persecuted. They stress that regulation should not occur on a country-by-country basis, but rather should be pursued at the flyway level--offering protection to these migratory birds throughout their entire trip, rather than at just a portion of their pit stops along the way.

For supplementary images associated with this post, please visit the Anthrophysis pin board at Pinterest.

Newth, J.L., Brown, M.J., and Rees, E.C. 2011. Incidence of embedded shotgun pellets in Bewick's swans Cygnus columbianus bewickii and whooper swans Cygnus cygnus wintering in the UK. Biological Conservation 144:1630-1637.

Thanks to the following websites for providing the images used in this post:

Saturday, 29 October 2011

What we can learn from the West Nile Virus epidemic

The U.S. has seen its fair share of invasive pathogens over the years, resulting in major economic and ecological costs associated with harm to humans, livestock, and wildlife. One recent example is West Nile Virus (WNV), a pathogen that was first isolated in Uganda in 1937 and made its way to North America in 1999, probably by way of the Middle East.

(Schematic showing transmission of West Nile Virus. Click on the image for a larger view.)

Writing in the latest issue of Science, infectious disease ecologist Dr. A. Marm Kilpatrick (University of California--Santa Cruz) says that there is much to learn from the history of WNV. In particular, he emphasizes the relationship between globalization, urbanization, and infection, and suggests that a better understanding of the interrelatedness of these factors could help us pinpoint important areas for future research, as well as develop more effective prevention plans for other pathogens that might appear in the future.

Historically, Kilpatrick writes, many historical pathogenic invasions have occurred as a result of trade and travel--including malaria, dengue, HIV/AIDS, anthrax, rinderpest, rabies, chestnut blight, potato blight, and sudden oak death, to name a few. Modern levels of globalization, and the connectedness it brings, only serve to increase the likelihood of future invasions. Although a majority of pathogens have followed an East-to-West trajectory, there is no reason to think that New World diseases won't one day cause more problems in the Old World.

 (Potato affected by the potato blight (aka "late blight"), caused by the protist Phytophthora infestans, which traveled from the Old World to the New in the mid 19th century)

Where it is present in the tropics, WNV is associated with longer transmission seasons and, occasionally, increased transmission intensity. This, Kilpatrick says, is related to the fact that the virus is spread by mosquitoes (the viral vector), which develop faster and, cumulatively, bite more often in tropical areas. Similar trends have been found for other vector-borne diseases in the tropics, indicating that introduction of invasive pathogens to these areas could be quite damaging. Strangely, though, reports of sickness and death are not as high in tropical regions as elsewhere--an intriguing pattern that awaits explanation. A better understanding of these issues would be useful for predicting the potential impacts of climate change on both the spread and impact of diseases.

Throughout the range where WNV is currently found--it is endemic to tropical Africa, southern Asia, and northern Australia, is episodically transmitted in Europe, and, of course, is now found in North America--there are a variety of mosquitoes (Culex spp.) that act as vectors. Where these overlap in range, some are more effective vectors than others, and this is is not always related to abundance of the insects or the frequency of their interactions with the animals that eventually become ill. For instance, Culex pipiens and Culex restuans appear to be responsible for the majority of human infections in many regions of the U.S. despite the fact that these mosquitoes generally prefer to feed on the blood of non-humans. In order to develop effective prevention and mitigation plans, it will be critical to understand the respective impacts of different vector and host species. To achieve this, Kilpatrick suggests that scientists will need to simultaneously collect data on mosquito feeding patterns and host abundance from the same place and time; similar data are needed for other invasive pathogens. Unsurprisingly, this information can be difficult to obtain, particularly in the case of diseases whose transmission routes are not yet well understood. 

 (Mosquito taking a blood meal from a human)

Although mosquitoes are the vectors of WNV, the predominant carriers of the disease are birds, millions of which died following introduction of the virus to North America. In some areas, this had a significant impact on avian populations--many of which have yet to rebound. Further observations will be needed to document how long it takes for the birds to recover, if they ever do. These data will be useful for understanding the timescale over which not just WNV in particular, but also invasive pathogens, in general, are capable of reshaping wildlife assemblages and, potentially, impacting ecosystem function.

During the early stages of the North American WNV epidemic, crows and house sparrows (Passer domesticus) were frequently identified as the most infectious animals--not unsurprising given the importance of these animals during WNV outbreaks in the pathogen's native range. However, Kilpatrick reports that recent work has found that the American robin (Turdus migratorius) is an important vector despite the fact that it is neither as abundant nor as widespread as the other two types birds; what it lacks in presence, it makes up for in attractiveness to mosquitoes. Robins are currently 50-100% more common now than they were just 25 years ago, thanks to the fact that they thrive in (increasingly common) urban areas. This raises the question, would WNV have spread as easily and/or as quickly in the absence of land use changes associated with human development? Further, in what other ways might anthropogenic changes impact pathogen invasion--and what other pathogens might be aided? Answers to these questions could facilitate "ecologically based land-use planning," which could minimize the threat of dangerous pathogens.

 (American robin, Turdus migratorius, an important carrier of West Nile Virus)

A locally evolved WNV genotype appeared within 2 years of the pathogen's arrival in the US, and after only 4 more years it had become the dominant strain; the new genotype did so well because it improved transmission efficiency. Pathogen evolution is a well-documented phenomenon common to many infectious diseases, but what is less well studied is any potential evolution of resistance to WNV in North American birds. Kilpatrick advocates a better understanding of these dynamics in order to improve the accuracy of predictions about the long-term effects of WNV on wildlife populations.

Perhaps one of the biggest remaining questions about WNV is whether we're in the clear, or whether a new, and potentially worse, epidemic might arise in the future. With WNV, as with other pathogens, it is difficult--if not impossible--to guess when an outbreak will occur, where and when it will happen, and how far it will spread. However, Kilpatrick writes, in-depth studies of individual outbreaks may increase our ability to model disease spread and, therefore, predict what will happen when future epidemics emerge. Disease models might be particularly useful for improving urban design and travel and trade practices--thus minimizing the transmission and spread of new and dangerous pathogens.

For supplementary images associated with this post, please visit the Anthrophysis pin board at Pinterest.

Kilpatrick, A.M. 2011. Globalization, land use, and the invasion of West Nile Virus. Science 334:323-327.

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Thursday, 27 October 2011

Vineyards help conservation efforts: I'll drink to that!

It's not often that agriculture and conservation go hand-in-hand, but a recent study by biologists at New Zealand's University of Canterbury suggests not only that vineyards can provide habitat for an endangered bird species, but also that the birds earn their keep once introduced there.

The study took advantage of a conservation project called Falcons for Grapes, which was begun in 2005 to help revive populations of the threatened New Zealand falcon--the country's only remaining endemic bird of prey. Juvenile falcons (Falco novaseelandiae) are relocated from their natal grounds in the mountains to vineyards in Marlborough, New Zealand's largest wine-growing region. The researchers hypothesized that, once there, the falcons might help minimize damage to grape (Vitis vinifera) crops by preying on and/or scaring off pest birds. This includes 3 invasive species that eat grapes whole--the blackbird (Turdus merula), the song thrush (Trudus philomelos), and the starling (Sturnus vulgaris)--and one native species (the silvereye, Zosterops lateralis) that pecks holes into the grapes and makes them susceptible to fungal infections.

(New Zealand falcon, Falco novaseelandiae, a bird that has been described as "utterly fearless.")

During the 2-year study, the researchers surveyed 6 vineyards where falcons were introduced, and 6 where they were absent. Falcons are not native to the Marlborough area, so the researchers did not expect any of these birds to be sighted at their control sites. But, just to be sure, they trained field workers to identify the New Zealand falcon and asked them to report any that were observed during the study period; none were. At the introduction sites, the scientists performed bird surveys on a weekly basis in order to identify which pest species were present. They also measured grape damage and removal, estimating not only how many grapes were impacted, but also what these losses cost the viticulturists. Finally, the researchers used a 0-5 scale to quantify the non-falcon-related bird-scaring methods (including visual and auditory deterrents and hunting) used by the farmers to keep pest animals away from their grapes.

(A vineyard in scenic Marlborough, New Zealand)

In comparison to control vineyards, falcon vineyards had significantly fewer song thrushes and blackbirds (78.4% and 82.5% less, respectively), and markedly fewer (79.2%) starlings. Among interior vines, song thrushes and silvereyes were significantly less common (70.5% and 95.2%, respectively). However, starlings were significantly more common (57.7%); this is probably related to this species' tendency to prefer open areas during times of uncertainty, since these spaces allow the flock to look out for predators and other signs of danger.

(A silvereye, Zosteros lateralis, which damages vineyard grapes by pecking holes into them)

At both the edge and interior of vineyards, there was significantly less grape tampering: Fewer grapes were removed from bunches, and fewer grapes were pecked. Among edge vines with Sauvignon Blanc grapes, for example, removal rates were 0.6% at control vineyards, but 0.03% at falcon vineyards; peck rates were 2.3% at control vineyards, but only 1.0% at falcon vineyards. Overall, viticulturists at control sites lost approximately $819/ha across both their Sauvignon Blanc and Pinot Noir crops combined; on the other hand, cumulative losses only amounted to $259 at falcon vineyards.

 (A blackbird, Turdus merula--one of several songbird species that steal grapes at vineyards)

Because of the relatively small size of the Falcons for Grapes program, the researchers were not able to sample many vineyards. However, they surveyed several vineyards where the raptors were present in one year and absent in the other; shifts in damage/removal rates echoed the patterns observed across the rest of their study, indicating that the birds really do help keep out pest species. This is probably due to direct predation--eating the offending animals--as well as simply scaring them off by making the whole neighborhood a more dangerous, and therefore undesirable, place to spend time.

Interestingly, the authors did not find a significant relationship between grape removal/damage levels and the traditional forms of bird-scaring strategies. This is likely because the pest birds quickly habituate to these stimuli, which (with the exception of hunting) generally cause them no harm. Falcons, on the other hand, are always a threat. Although more studies are needed to examine the long-term viability of the Falcons for Grapes initiative for both the raptors and their human hosts, it would appear that this is a win-win scenario--with benefits that spread all the way to your wine cellar.

For supplementary photos associated with this post, please visit the Anthrophysis pin board at Pinterest.

Kross, S.M., Tylianakis, J.M., Nelson, X.J. 2011. Effects of introducing threatened falcons into vineyards on abundance of Passeriformes and bird damage to grapes. Conservation Biology, online advance publication.

Thanks to the following websites for providing the images used in this post:

Wednesday, 26 October 2011

Are we living in the Anthropocene?

Human influence on the environment is undeniable. Among other things, we introduce chemicals into, and change the pH of, the water; we fragment and reduce habitat; we persecute species to the point that they go extinct; and we introduce invasive species that reconfigure local ecosystems. As a result of all these things and more, many scientists have begun calling our current epoch the "Anthropocene," or the time of humans. The popularity of the term is such that geologists are not debating whether this is an accurate designation, but rather when, exactly, this era began.

However, not everyone is on board with this concept--in terms of both its accuracy and its usefulness. In an essay in the scientific journal Conservation Biology, collaborators from two departments at the University of California--Davis (the Department of Wildlife, Fish, and Conservation Biology, and the Department of Animal Science) argue that it is wrong to believe that there are no longer any places on earth that are "natural"--or, in other words, untouched and/or unaltered by humans. They acknowledge that humans are "undoubtedly" the dominant species on Earth, but stress that there are many specific regions/ecosystems that are still intact. These are areas in which the majority of native species are still present and active in the same functional role they performed prior to the appearance of humans, where nutrient flows have not been drastically altered by pollution, and where there are not many human residents. The authors classify these into 5 broad categories: places that are unexploited by humans, wilderness areas, ecoregions with little or no human presence, local sites little influenced by human activity, and biodiversity hotspots.

 (The Cameroon mountains, listed by the authors as a relatively untouched "site of extraordinary species richness.)

Using these areas as evidence, the scientists argue that, despite popular belief, humans have not changed everything. For instance, there are "gaps" in the human footprint (a blanket concept covering population density, land-cover and land-use changes, accessibility to humans, and the availability of electrical power) at equatorial, subtropical, temperate, and palearctic latitudes. In other words, the bulk of human disturbance is concentrated within particular geographic areas, leaving other regions intact--or, at least, under less pressure. Further, the authors state that, while climate change has led to overall increases in global temperature, locally, these have been recorded mostly in the northern and southern latitudes and at high elevations, leaving the lowland tropics--where most of the world's species occur--in a much more "natural" condition. Finally, the scientists point to the fact that there are many areas where humans do not live, or only live at low densities. In these places, there are many ecological elements--species diversity, the presence and activity of top predators, food webs, nutrient cycles, and overall ecosystem function--that have not been dramatically altered by the rise of humans.

(Greenland--one of the 4 ecoregions identified by the authors as having "virtually no human presence")

All of these points are not advanced purely as a rhetorical and philosophical exercise, however. The authors stress that the intact regions listed in their paper should immediately receive management support so that we can ensure their continued ecological health. Further, the scientists worry that acceptance of the Anthropocene concept will lead to the adoption of unhealthy and dangerous attitudes towards wildlife and conservation. For instance, people may be tempted to "open the floodgates to human manipulation of species assemblages," falsely believing that the only way to preserve wildlife is to engage in potentially damaging (and currently controversial) practices such as assisted migration and Pleistocene rewilding. In order to set more appropriate conservation goals, it is important to have intact areas that can be used as baselines and targets; if we fail to recognize the existence of such "natural" areas, it will be very difficult to understand how humans have impacted ecosystems, or to create logical and useful conservation goals. In fact, people may be less inclined to support conservation efforts at all--monetarily, emotionally, or with contributions of time and effort--if they feel that they are only fighting a losing battle. At that point, the authors argue, a defeatist attitude may lead people to feel that they might as well do even greater damage--such as building more dams, exploring for oil in new locations, razing forests for lumber--rather than continuing to seek sustainable methods of coexisting with wildlife.

(Gran Chaco, also known as the "last frontier in South America." It was identified by the authors as one of several intact "wilderness areas.")

Overall, the scientists state, we have a duty to future generations to consider these scientific, practical, public relations, and ethical reasons against the Anthropocene mindset. They feel that if we wish to preserve the environment for ourselves and our descendants--a decision that will enhance quality of life "by providing...the opportunity to observe the wonders of nature"--we should focus on developing appropriate conservation and restoration objectives. Rather than advocating the idea that "humans have altered everything," we should believe that humans can achieve anything--even those conservation goals that may, at first, seem unobtainable.

For supplementary images associated with this post, please visit the Anthrophysis pin board at Pinterest.

Caro, T., Darwin, J., Forrester, T., Ledoux-Bloom, C., Wells, C. 2011. Conservation in the Anthropocene. Conservation Biology, online advance publication.

Thanks to the following websites for providing the images used in this post:

Tuesday, 25 October 2011

Impacts of roadways on dragonflies

Anyone who has washed a car after a road trip knows that insects often don't survive their encounters with traffic. For many flying invertebrate populations, this is not a problem (at least in the conservation sense), since adults breed shortly after emerging from their larval form and have therefore already reproduced by the time they collide with vehicles. This is not true for longer-lived species such as beetles and dragonflies, however, which breed over an extended period of time. For populations of these animals, which may encounter many roads during their travels through the habitat, traffic could have a serious impact by reducing the number of individuals available to breed.

Since 277 of 441 dragonfly species in the U.S. have been categorized as "species of greatest conservation need" in at least part of their range, there has been increasing interest in documenting all of the environmental factors that may be contributing to these animals' declines. This is important not just for preserving or restoring dragonfly populations, but also for maintaining the health of wetland ecosystems, where dragonflies can be a top predator in aquatic food webs. Previous studies have reported some intriguing trends for dragonfly-vehicle encounters. One survey in India found that dragonflies made up 61% of insect deaths along roadways, while research in Michigan indicated that up to 256 dragonflies are killed per kilometer of driving.

(A common whitetail, Plathemis lydia)

In order to characterize traffic-dragonfly interactions more fully, collaborators from The University of South Dakota, The Nature Conservancy, and Iowa State University teamed up to perform a combination of observations and experiments along roadways in the Des Plaines River Valley near Joilet, Illinois. They selected 4 stretches of road that each differed in the amount of traffic they saw each day (ranging from <10 vehicles to 25,500 vehicles per day). The researchers conducted roadside surveys in order to count how many dragonfly carcasses accumulated over a 24-hour period; this allowed them to calculate mean daily mortality rate per kilometer for each site. Since dragonfly bodies are both light-weight and attractive to hungry scavengers, the scientists also performed an experiment in which they counted how many deliberately-planted bodies disappeared over a 24-hour period. This allowed them to estimate whether their survey data were underrepresenting actual dragonfly deaths along the roadways.

In addition to conducting body counts, the researchers also performed almost 2,000 observations of dragonflies near roadways. This allowed them to assess relative abundances of different species and record dragonfly behavior. In particular, the scientists were interested in evaluating how often the dragonflies flew across the road and, when they did, how high they flew. By surveying cars in a large parking lot, the researchers determined that the average height of vehicles is 1.8 m; thus, dragonflies that fly above this height are less likely to be killed during a road crossing than dragonflies that fly below it.

(A widow skimmer, Libellula luctuosa)

A total of 49 dragonfly bodies were collected during 36 roadway surveys. However, the carcass removal experiment indicated that about two-thirds of dead dragonflies disappeared from the roadside within a 24-hour period. Thus, the researchers multiplied their results by 3.12 in order to determine the real number of bodies that likely accumulated during a day's worth of traffic. This revealed that daily mortality per kilometer was anything from 2.1 to 34.6, depending on the roadway. Nine species of dragonflies were identified from the carcass sampling; the three most common species (making up 71% of all samples collected) were the common whitetail (Plathemis lydia), the widow skimmer (Libellula luctuosa), and the green darner (Anax junius). Interestingly, none of these was the species most commonly seen during the behavioral observations; that was the black saddlebags (Tramea lacerata), which accounted for almost a quarter of all identified dragonflies.

During the behavioral observations, over half (~58%) of all flying dragonflies were seen over the roadway; just under one half (~47%) were seen crossing to the other side. Species at the busiest site were significantly less likely to cross the road, indicating that the dragonflies were aware that commuting conditions were less than ideal for them at that particular roadway. Species identity also influenced the likelihood of road crossings; widow skimmers and black saddlebags crossed the road more and less frequently, respectively, than expected by chance. Further, while widow skimmers, Eastern pondhawks (Erythemis simplicicollis), and blue dashers (Pachydiplax longipennis) spent 79% of their flight time in the danger zone below 1.8 m, the Eastern amberwing (Perithemis tenera) and green darner spent the majority of their time above this height.

 (Mating green darners, Anax junius)

Cumulatively, these data allowed the researchers to construct a model comparing predicted and expected mortality for different species; this could then be used to determine which factors were most closely associated with dragonfly deaths along roadways. The models were not strongly associated with relative abundance of different species, minimum flight height, or percent observed crossing the road. However, when models were explored on a site-specific basis--with busier roads considered separately from those with less traffic--the number of dragonflies observed over the road was highly correlated with both death rates and volume of traffic. Thus, unsurprisingly, dragonflies are more likely to end up as roadkill if they live near busy roads and position themselves near passing vehicles. 

These findings indicate that the presence of roads can have significant impacts on dragonfly mortality. Thus, it will be important to consider the potential impacts of these anthropogenic corridors when deciding whether one should be installed in a nature preserve or an area where threatened dragonfly species are known to live. Roads may have different impacts on different species, since not all dragonflies flew at the same height or ventured over or across busy roadways. Clearly, more work is needed to provide additional details of how the dragonflies perceive the traffic and adjust (or fail to adjust) their behavior accordingly.

More research is also needed to understand which roadway attributes are most dangerous--is it purely number of vehicles, or do other characteristics such as number of lanes, speed of traffic, and type of vehicle also have an impact on dragonfly mortality? It will also be important to investigate whether these individual dragonfly deaths have a longer-term, broader-scale impact. For instance, does the death of potential breeders reduce population size and act as a constraint on conservation efforts to preserve or restore dragonflies? Further, how does the reduction of top predator numbers impact food web dynamics and ecosystem function in wetlands? These are questions that will need to be answered in order to develop appropriate conservation plans for species like the endangered Hine's emerald dragonfly (Somatochlora hineana) and the habitats in which it lives.

For supplementary images associated with this post, please visit the Anthrophysis pin board at Pinterest.

Soluk, D.A., Zercher, D.S., Worthington, A.M. 2011. Influence of roadways on patterns of mortality and flight behavior of adult dragonflies near wetland areas. Biological Conservation 144:1638-1643.

Thanks to the following websites for providing the images used in this post: