Does tourism revenue help birds in protected areas?

How much does tourism help fund bird conservation? Given the continuing boom of the "avitourism" industry, this sounds like the sort of question to which both environmentalists and entrepreneurs should know the answer. However, while researchers have performed calculations investigating the availability of tourism revenues for mammal and frog conservation efforts, nobody has explored similar trends in other taxa--or, to be more accurate, nobody had explored those trends until a group of Australian scientists recently decided to crunch the relevant numbers. The results of their analyses were reported earlier this month in the journal PLoS ONE.

(Grey-crowned crane living in the Kenya's Solio Game Preserve)

To make their study question a bit more manageable, the researchers focused on only a subset of all the 10,000-some extant bird species in the world and on only a portion of all the habitats in which these animals live. First of all, the researchers explored statistics relating only to the 562 species currently classified as Critically Endangered (CE; 190 species) or Endangered (EN; 372) on the IUCN Red List of Threatened Species. They also only counted tourism revenue generated by activity in one of the 120,000 or so protected areas (or 13% of all terrestrial habitats) established around the world. Cumulatively, these techniques should result in a conservative estimate--or a worst-case scenario--of how much the tourism industry actually contributes to avian conservation.

Revenue data were obtained from a variety of financial records published by individual parks and agencies. These allowed the researchers to calculate R, the proportion of park funding generated by tourism activity. This value was calculated across entire countries to account for the fact that conservation agencies often distribute funds to multiple different locations. However, the scientists also calculated what proportion of each individual park's revenue was generated by tourism. This was entered into a relatively simple equation (also incorporating data on the size of birds' global populations and the size of their populations within protected areas) that yielded T, the proportion of each bird species' global population that is protected by tourist activities.

(Flamingos feeding in Lake Nakuru, Kenya)

The financial contributions of tourist activities varied hugely between protected areas. Some sites received no revenue from tourism, while other sites were completely funded by visitors; R values generally fell somewhere between 5 and 80%. Private reserves were particularly likely to earn a substantial portion of their income from tourists. Protected areas in African countries had the greatest tourism support (36-81%), while those in the most developed countries had the least (generally <15%). The low R values calculated in more developed areas likely reflects the fact that the governments of these nations tend to subsidize conservation work with earnings from federal taxes, while developing countries tend to be much more reliant on tourism earnings.

Population data were not available for all 562 CE and EN bird species originally selected for the study, but the authors were still able to investigate trends associated with 131 local subpopulations of 91 species. Calculations revealed that tourist activities helped support the protection of anywhere from 0-64% of each species' global population. A handful of species were at either end of the tourism support spectrum, receiving either no help from visitor revenue (n = 9) or having over a fifth of their global population supported by tourism (n = 8); the bulk of species (n = 50), however, fell somewhere in between these two extremes. Notably, T was significantly greater for CE species than EN species, indicating that tourism revenues are extremely valuable for helping preserve the most at-risk birds.

 (Speckled mousebirds on Mount Kenya)

Overall, the study reveals a number of surprisingly low R and T values. While it may be tempting to interpret these as an indication that tourism revenue is not generally that significant, it is important to note that the researchers identified 41 species for whom >10% of the entire global population relies on tourism revenue; decreases in visitor spending could have catastrophic impacts on the protection of these birds. Perhaps even more importantly, the countries with the highest R values are developing nations that likely do not have alternative sources of funding to devote to conservation efforts. In these nations, tourism revenue is probably a lifeline not only to threatened bird species, but also the locals who make a living by catering to visitors. It is also important to keep in mind that ecotourism is still a growing industry, suggesting that, in some areas at least, R (and maybe also T) will continue to increase over time.

Of course, there are some drawbacks to relying on ecotourism to sustain conservation efforts. For one thing, an increased number of visitors can lead to a decreased quality of life for endangered animals, to the point that the gains in revenue may not actually lead to improvements in species numbers. Another issue is the unpredictable and volatile nature of the tourism market, which can be influenced by uncontrollable factors such as weather. In the future, the researchers hope to utilize more detailed and sensitive calculations that might potentially allow them to take these sorts of trade-offs into account in their models.

(Guillemots and razorbills in the Isles of Scilly, UK)

Perhaps a more important thing to focus on right now, though, is the authors' finding that 43% of their 562 focal species seem to exist wholly outside the boundaries of protected areas, and thus may receive no real conservation help at all. Of the species that are found in protected areas, there are a number that live in only a single preserve. Together, these results suggest that avian conservation efforts could be vastly improved, regardless of how they are funded. As we set out to rectify this problem, we might consider focusing on island habitats and wilderness areas found in South America; these are the two types of environment in which there appears to be the greatest need for increased habitat protection. As the authors point out, the large number of threatened animals living outside of formally protected areas also emphasizes the importance of generalized efforts to increase biodiversity, rather than action plans that are focused only on particular tracts of land.

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Steven, R., Castley, J.G., and Buckley, R. 2013. Tourism as a conservation tool for threatened birds in protected areas. PLoS ONE 8(5):e62598.

All photos by me; more can be seen on my flickr photostream.

Could roadways actually be good for wildlife?

You might interpret roadkill as a sign that highways are bad for wildlife, but it's possible these carcasses actually indicate that roadsides are attractive habitats that can support a large number of individuals. That's one interpretation, anyway, of a new study investigating small mammal populations living along highways in central Spain.

(Roadside verge. Image courtesy of Flickr user hedgerowmobile.)

The study was performed by a trio of Spanish researchers who counted the abundance of three small mammal species--wood mice, greater white-toothed shrews, and Algerian mice--living along a busy roadway in an area classified as a Site of Community Importance. Over a period of two years, the scientists logged an impressive 8,640 trap-nights, using bits of fried bread to entice animals into captivity. Traps were distributed in 50-m bands located at three distances from the road: 0-50 m away, 500-550 m away, and 1000-1050 m away. The researchers also performed habitat surveys in 5-m circles centered on each trap. They classified habitats by type (e.g., bare ground vs. woodland), and then measured the height of any vegetation located in the circle.

Over the course of the study, the research team captured a total of 1,004 individuals, the vast majority (94.4%) of which were wood mice. Because of this skew, several of the further analyses were only performed on wood mouse data. Contrary to what you might expect, more mammals were captured nearer the road (in the 0-50 m band) than farther away. This was true in both years of the study even though an apparent population crash caused overall mammal numbers to drop in the second year. One interesting result of this crash was that it highlighted just how common the animals were near the highway: During the first year of the study, the ratio of mammals captured in the 0-50 m band relative to the other two bands was 3:2; during the second year, it jumped to a whopping 9:2. Cumulatively, these results suggest that the road verge acts as a refuge for the animals.

(Wood mouse, Apodemus sylvaticus. Image courtesy of Wikipedia.)

This pattern held true regardless of vegetation characteristics, though mice were particularly common in areas with dense scrub cover and higher grass and trees--areas, in other words, where the animals felt relatively safe and sheltered. These microhabitat effects are some of the first documented in the context of road-effects studies; they are also the only patterns measured in woodland areas rather than extremely human-disturbed areas or in deserts. In the future, it should be interesting to collect similar data in other types of habitats in order to see whether road effects vary across the landscape.

As for the current study, the authors believe that the most parsimonious explanation of their results is that predation pressures are lower near roads, thus allowing local populations to become more dense. Support for this is provided by the high proportion of roadside juveniles: This age class is one of the most susceptible to predators, so the commonness of young mice in verges indicates that less predation is occurring there. A road-mediated increase in survivorship could have beneficial cascading effects on the entire ecosystem--for example, by increasing the dispersal of seeds or the consumption of pest insects. The authors further suggest that we might even think about deliberately attracting small mammals to verges by manipulating the density and height of vegetation near roads.

(Zones with reduced speed limits might help protect animals living in roadside verges. Image courtesy of TRL.)

That, of course, still leaves the issue of roadkill, which will probably always be a negative side effect of roadways--even if it is not one that puts populations at risk of local extinction. As previous studies have suggested, it might be a good idea to consider mitigation techniques such as reduced speed limits, wider shoulders, and even fences in order to add further protection to roadside dwellers.

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Ruiz-Capillas, Pablo, Mata Cristina, and Juan E. Malo. 2013. Road verges are refuges for small mammal populations in extensively managed Mediterranean landscapes. Biological Conservation 158:223-229.

Ecological gardening: beautiful and good for biodiversity

You may not think of private gardens as wildlife refugia, but an increasing body of scientific evidence suggests that these habitats can host a variety of species and act as stepping stones across landscapes that are otherwise dominated by human structures. To increase the effectiveness of gardens as havens for wildlife, many researchers have touted a management technique variously known as "wildlife gardening," "ecological gardening," and "naturalistic gardening." Whatever you call it, this method involves avoiding pesticides and mowing, using organic compost instead of industrial fertilizers, and providing habitat structures, such as ponds or wood piles, that provide food, water, and places where animals can take shelter.

(Example of a garden that has been ecologically managed. Photo courtesy of The Canadian and its primer on ecological gardening.)

Ecologically managed gardens often look more unkempt than those tended using traditional methods, and therein lies the problem...maybe. A pair of researchers from Europe recently explored whether gardeners might avoid ecological management techniques because they dislike the resulting appearance, or even because they are worried that their neighbors might frown upon an untidy lawn. The scientists also investigated whether ecological management directly impacts biodiversity and, if so, whether this can be detected by people who see the garden. Cumulatively, the answers to these study questions should help researchers better understand the psychological aspects of wildlife appreciation, thereby potentially allowing them to improve conservation practices.

The researchers conducted their study on a set of 36 focal gardens distributed across the canton of Zurich. Management regimes spanned the conventional-to-ecological spectrum--something that was specifically assessed using questionnaires asking garden owners to describe frequency of mowing and weeding, use of artificial fertilizers and pesticides, and presence/absence of beneficial "features" such as ponds, nesting structures, wood piles, and flower meadows. The questionnaires also collected more general information about the gardeners' psyches; for example, respondents were asked how ecologically-minded they considered themselves to be, and how much they cared about how others perceived their gardens.

(More traditionally managed gardens tend to be closely mown and frequently weeded, and may also be treated with artificial chemicals. Image courtesy of Garden Visit.)

All gardens were subjected to a 75-minute-long census during which researchers counted all native wild species that could be identified without the use of trapping or catching techniques; once the surveys were complete, the scientists also photographed the gardens. These images were later displayed to volunteers who were asked to rate each garden on a scale from "very ugly" to "very beautiful." The volunteers were also asked to select which of the following descriptors applied to each photograph: "species-rich," "species-poor," "colorful," "neat," "normal," "boring," "natural," "wild," "exotic," "special," "artificial," and "chaotic.

Across all focal sites, the ecological gardening index ranged from 0-11; however, the mean was 3.5, suggesting that the bulk of gardens tended to be fairly traditionally managed. Results from the gardener survey indicated that many people felt that ecological gardening was actually easier and less time-consuming than conventional gardening, though they wished they had more background information on this practice. People also indicated that they viewed gardens as important wildlife habitats, and that they would not mind the presence of a "wild" garden in their neighborhood. These are encouraging results given that the scientists found significantly more wildlife species in gardens that scored higher on the ecological management index; the presence of beneficial features (the most common of which were bird boxes and wood piles) was also significantly associated with higher species richness.

(Woodpiles like this one can act as miniature nature reserves; the BBC advocates woodpile construction as one of several outdoor activities that can both promote biodiversity and improve the quality of human interactions with wildlife. Image courtesy of Wikimedia Commons.)

People who viewed photographs of the gardens were generally very positive about their aesthetics, regardless of management regime. That said, there was a significant positive relationship between degree of ecological management and overall aesthetic rating. This appears to have been driven by the presence of particular features (ponds, for instance) rather than actual management regime. Gardens that received the highest aesthetic ratings were described as "species-rich, colorful, and natural." The surveys performed on these same gardens found that there were, indeed, high levels of richness, suggesting that viewers may have been responding, on some level at least, to the diverse array of wildlife shown in the photographs. Indeed, when asked to do so directly, respondents were generally able to identify which gardens were species-rich and species-poor; they could also determine which gardens had been subjected to ecological management regimes. Encouragingly, viewers frequently indicated that they recognized gardens as important habitats, and generally had no bias against the "wild, chaotic, and not neat" appearance of the gardens that had been most heavily ecologically managed.

Cumulatively, these results suggest that it is possible for habitats to simultaneously offer both ecological and aesthetic value, suggesting that it may not be hard to help wildlife by encouraging more gardeners to use ecological management techniques. Currently, though, these regimes are not common across Switzerland, prompting the study's authors to wonder whether people have a "not in my backyard" mentality, or perhaps have simply not yet learned enough about ecological management to think about using this technique on their property.

(Garden ponds can provide breeding habitat for invertebrates and amphibians, and also supply mammals and birds water for drinking and bathing. Image courtesy of Wikimedia Commons.)

Previous work has found that gardeners often mimic their neighbors--a phenomenon known as "garden contagion." This suggests that a few ecological management pioneers might be all that is needed to help this technique catch on, not just in Switzerland, but even across Europe. Increased popularity of ecological management would be good news for humans and wildlife alike: Lightly managed gardens could make significant contributions to the conservation and preservation of a variety of species, while humans could benefit from increased opportunities to see wildlife and experience the many health benefits associated with spending time in green spaces.

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Lindemann-Matthies, Petra and Marty, Thomas. 2013. Does ecological gardening increase species richness and aesthetic quality of a garden? Biological Conservation 159:37-44.

Urban ecosystems: the final frontier?

This month's volume of Frontiers in Ecology and the Environment features a Trails and Tribulations essay that will likely hit close to home for any biologist who has worked in urban areas or places with high levels of human traffic. Titled "Trials of the Urban Ecologist," the piece is written by a group of researchers from the Center for Urban Ecology at Butler University (Indianapolis, IN, USA).

Image courtesy of the Urban Ecology Collaborative

The authors' interest in urban locations--which they refer to collectively as "one of the final frontiers of ecological exploration"--stems both from the fascinating ecological complexities of these sites and from practicality. As they point out, over half of all people now live in cities, making the continued health and stability of these environments a necessity. Traditionally, scientists were more interested in replicating studies from "natural" areas within city limits in order to compare the two and verify the universality of certain ecological principles; modern research, however, is increasingly geared towards appreciating and characterizing the novel ecology of highly anthropogenically disturbed areas. There is, of course, an added bonus for scientists whose institutions are located in or near cities (and for metropolitan residents who are keen to keep in touch with nature): Urban areas offer easily accessible places in which to observe wildlife.

All research sites offer their own difficulties, but, write Dolan et al., scientists who cut their teeth performing studies in remote wildernesses may require a period of adjustment when making the transition to urban areas. There, they may face novel difficulties including feral animals such as cats, dogs, and rats; theft of equipment and other research materials; habitat destruction by residents, developers, or caretakers; and even the release of animals captured for examination.

Image courtesy of Landscape Architecture Daily

While working in Indianapolis, the authors have experienced a number of frustrating setbacks that they appear to have taken in stride--and from which they have learned a great deal about the hazards of working in an urban environment. During one project, for example, a study site was bulldozed; during another, landscapers frequently mowed patches that were supposed to be left untreated. These sorts of situations highlight the necessity of good communication, diplomacy, and patience--all of which are especially important (and challenging) during projects that involve multiple stakeholders.

In fact, Dolan et al. say that one of the most important outcomes of their work in urban ecology is the development of "a deeper appreciation of what it means to be teachers, as [they] share [their] research directly and indirectly with urban residents." Educational moments may happen on a small scale, such as when researchers explain what they are doing to curious passersby, or on a much larger scale, such as when media coverage of urban studies provides residents with the knowledge and drive required to influence local management practices.

Image courtesy of Radix Ecological Sustainability Center

"Trials of the Urban Ecologist" is a timely essay, given the increasing popularity of urban ecology over the last several years (and decades). It reminds readers that anthropogenic habitats are just as interesting and important as those that are more "natural" and "wild"--and stresses how urban studies can have long-lasting and far-reaching implications for conservation, management, and sustainability.

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Dolan RW, Carter T, Ryan T, Salsbury C, Dolan TE, and Hennessy M. 2013. Trials of the urban ecologist. Frontiers in Ecology and the Environment 11: 163–164.

Bioremediation of used motor oil

What happens to used motor oil after it leaves our cars? That's a question that many of us don't stop to ask, but hopefully the answer is that it is taken to a recycler to be cleaned for future reuse. However, even if the oil handled in the most responsible way possible, chances are that a bit gets dribbled on the ground during the transfer from car to container. Places such as car dealerships and body shops will likely see a number of these dribbles over the years, potentially leading to an unhealthy buildup of oil residues in nearby soils. Some of this buildup may remain local, but some can dissolve in water and make its way into the tissues of plants and animals--where the heavy metals it contains can wreak havoc on their health and fitness.

(Changing motor oil. Image courtesy of Motorcycles Online.)

There are a number of options available for cleaning up oils before they can do too much damage, but these may have drawbacks: Some are quite expensive, others may have negative ecological side effects, and still others may simply remove oil from one location to another. One of the most promising genres of treatment is bioremediation, or the use of microorganisms that metabolize pollutants and release harmless end products in their place. This process can be facilitated by encouraging the growth of indigenous bacterial species (biostimulation), adding new species to the contaminated site (bioaugmentation), and/or altering environmental conditions to speed the growth of bacterial colonies. Although this sounds fairly straightforward, it is still necessary to identify the conditions under which microorganisms can most efficiently clean contaminated soils.

This was the goal of a team of Nigerian researchers who recently utilized aerobic fixed bed bioreactors to investigate the efficacy of six different bioremediation techniques. Their findings, published in the most recent edition of Bioremediation & Biodegradation, indicate that biostimulation may be the way forward--though they admit that further work will be necessary to hone their "recipe" and develop a larger-scale system for decontaminating large amounts of soil.

(Bacillus subtilis, a microorganism commonly found in oil-contaminated soil. Image courtesy of Wikipedia.)

The team's research utilized samples collected from a Nigerian auto repair shop--one of several locations surveyed in a preliminary study exploring the "similarities and major differences in physicochemical and microbiological characteristics" of polluted soils. All samples were moistened with water, but other aspects of their preparation differed markedly. Some were subjected to heat sterilization in order to kill off endogenous (Bacillus subtilis and Micrococcus leteus) bacteria, others were given a dose of exogenous bacteria (B. subtilis and Pseudomonas aeruginosa), some received nutrient-rich fertilizers, and others experienced some mixture of these treatments.

The researchers prepared a total of six samples, all of which were placed in separate aerobic fixed bed bioreactors--or, in other words, oxygen-containing containers that remained stationary for the duration of the 70-day experiment. Every 10 days, the team collected measurements reflecting soil conditions, bacterial activity, and success of the bioremediation effort. While readings on temperature, moisture content, and pH were all useful for confirming that the bioreactors were facilitating the optimal environment for bioremediation (26-32 C, 10-20% w/w, and 5.5-8.5), perhaps the most exciting results were those indicating the extent to which the bacteria actually removed oil from the soil.

(Example of a bioreactor. Image courtesy of Wikipedia.)

Petroleum hydrocarbon levels decreased in all six treatment groups, from a range of 169-326 down to 54-129 mg/kg dry weight; this represents a change of 49-72%. The greatest decreases were seen in treatment group 3 (soil + heat sterilization + water + exogenous bacteria) and treatment group 6 (soil + water + two different fertilizers), while the least amount of change was observed in the control group (soil + water + heat sterilization). Motor oil can have fairly low levels of petroleum hydrocarbons, and so a better measure of bioremediation success is change in oil and grease content. When the researchers examined this metric, they again found that treatment group 6 was a top performer, experiencing a 75% reduction (38,592 to 9,830 mg/kg dry weight) over the course of the study. For all soil samples, speed of removal was highest during the first five weeks of the study, after which it slowed markedly.

Based on their findings, the research team concluded that a full-scale bioremediation technology should involve the conditions found in their sixth treatment group. However, they also suggest that they might be able to further optimize their method by adjusting moisture content and, especially, experimenting with different types of fertilizer; while they dosed their samples with NPK and KH2PO4, alternative varieties might improve the efficiency of hydrocarbon removal.

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Abdulsalam S., Adefila S.S., Bugaje I.M., and Ibrahim S. 2013. Bioremediation of soil contaminated with used motor oil in a closed system. Bioremediation & Biodegradation 3(12):1000172.

Cigarettes can be healthy...for birds

The negative impacts of cigarettes, on both smokers and those around them, are widely known. While some effects may only be cosmetic (wrinkling, yellowing of the skin), others, such as cancer, can be fatal. According to a team of Mexican researchers, however, cigarette smoking can be beneficial to at least one group: urban birds. The benefit, unsurprisingly, does not come from actually smoking the cigarettes, but instead from incorporating discarded butts into nests. There, chemical residues in the cigarette fibers appear to act as repellents that keep parasites away from vulnerable nestlings

(Male house sparrow, Passer domesticus. Image courtesy of Redbridge Birdwatching.)

These unusual and surprising findings, published in the journal Biology Letters, were the result of an undergraduate research project conducted on the campus of the National University of Mexico in Mexico City. The project was undertaken after researchers noted the presence of cigarette butts in nests of urban-dwelling house finches (Carpodacus mexicanus) and house sparrows (Passer domesticus). Similar patterns have also been reported in other species and locations, prompting the scientists to wonder whether the inclusion of the butts was deliberate. This seemed particularly likely given the fact that nicotine, one of the dominant chemicals in cigarettes, is known to repel ectoparasites—parasites that live on the surface of the body. In fact, both poultry and rabbit farmers use nicotine as an organic method of parasite control.

To investigate whether the urban birds had also begun to employ nicotine as a pesticide, the researchers performed both experimental and observational work. For the experimental portion of the study, nests of both species were located and fitted with thermal traps designed to attract ectoparasites by mimicking the heat signatures of potential hosts. Cellulose cigarette fibers—from either smoked or unsmoked cigarettes—were attached to the heating component of each nest, and a strip of adhesive was placed next to the heaters in order to capture all approaching parasites. The researchers hypothesized that they would find fewer parasites near the heaters fitted with smoked cigarette fibers, since these materials contained a higher proportion of pesticidal chemicals. Indeed, they found that parasites were not only more scarce at these nicotine-treated sites, but, in some cases, were nearly 6 times less likely to appear.

(House finch, Carpodacus mexicanus. Image courtesy of Wikimedia.)

Once the experiments were complete, the research team waited until the birds had finished breeding and then returned to harvest the empty nests. These were weighed and then dissected; each nest’s cellulose content was measured, and all ectoparasites were counted and identified. Assuming that cigarette butts act as a repellent, the scientists expected to find fewer parasites in nests with more butts. The majority of nests of both house sparrows and house finches contained bits of discarded cigarettes. Interestingly, while butts were more likely to be found in nests of the former (89% vs. 86%), they were found in higher quantities in nests of the latter (an average of 10 vs. 8 per nest). Both species suffered from similar rates of parasite infestation, and, as predicted, parasite abundance was negatively related to the presence of cigarette fibers.

The results indicate that the nicotine-laced cellulose deters parasites—and, further, suggest that the birds may be selecting these building materials on purpose. You might think that would require a bit more thoughtfulness than is possessed by the average songbird, but this is not the first time they have shown such an ability. Several other species, including both European starlings (Sturnus vulgaris) and tree swallows (Tachycineta bicolor), are known to deliberately incorporate green plant materials into their nests; like cigarettes, these botanical building blocks contain compounds that repel parasites.

(A bird nest incorporating cigarette butts. Image courtesy of Ignorance is Bliss.)

Thus, the use of the cigarette butts appears to be “an urban manifestation of a pre-existing behavior”—or, to quote the title of the paper in which these results were presented, the use of “new ingredients for an old recipe.” The sparrows and finches appear to be using the recipe to “self-medicate,” though for this to be proven definitively, further work will be required. Specifically, while it is clear that the cigarette butts reduce the likelihood of parasite infestation, it is still necessary to show that the birds are purposely selecting these items for inclusion in their nests, and that use of the butts improves the birds’ reproductive success.

The research team has suggested several additional studies that could help them identify whether the cellulose might serve another purpose (such as providing insulation) and also whether the toxic residues in the fibers might have negative effects on nestlings. These data will reveal whether—in the case of birds, at least—cigarettes can sometimes do more good than harm.

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 Suarez-Rodriguez, M., Lopez-Rull, I., and Garcia, M.C. 2013. Incorporation of cigarette butts into nests reduces nest ectoparasite load in urban birds: new ingredients for an old recipe? Biology Letters 9(1): online advance publication.

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Traffic noise causes communication breakdowns

In a perfect world, communicating animals would always be capable of hearing each other's signals and responding appropriately. In the real world, however, the environment is filled with interfering sounds such wind, rainfall, other species' vocalizations, and, increasingly, anthropogenic noise. Under these conditions, lucky animals may be able to respond to a signal when they should, and avoid responding when they shouldn't. However, some individuals might accidentally miss out on hearing an important signal, or react to one that hasn't even been given. While these mistakes might not always have repercussions, there might be times--especially when a predator is involved--when they could mean the difference between life and death.

(A Stephens' kangaroo rat, Dipodomys stephensi. Image courtesy of activerain.)

This is a possibility that has only rarely been studied experimentally and (as far as this author knows) has never been investigated in mammals--until now. A team of American researchers has just reported findings from a field study of endangered Stephens' kangaroo rats (Dipodomys stephensi) living near noisy roadsides in California's Southwestern Riverside County Multispecies Reserve. Their results indicate that human noise pollution can cause the rats to make both of the communication errors mentioned above. As a result, the researchers worry that these nocturnal animals, which rely on acoustic signals to "coordinate social interactions...in a variety of contexts," may suffer from the introduction of human noise pollution into their habitats.

The researchers explored the effects of acoustic pollution by recording both signals and noise at roadside rat burrows. In this case, the signals were footdrums, or thumps made by the rats as they rapidly stamp one foot against the ground; a series of these is known as a "footroll." These low-pitched sounds travel well through both air and soil, and are therefore audible to rats that are outdoors and to those that are holed up in their subterranean burrows. In order to compare the acoustic properties of footdrums to those of traffic noise, the researchers also recorded car traffic at distances of both 10 and 25m from the edge of the road. They then used acoustic analysis software to quantify a variety of characteristics in both sets of recordings (minimum, maximum, and fundamental frequency, plus total bandwidth), and investigate similarities in the two types of sound. In other words, they examined the likelihood that noise pollution might "mask" kangaroo rat communication.

(A view of the Southwestern Riverside County Multispecies Reserve. Image courtesy of Gossamer Tapestry.)

The scientists also conducted a series of playback experiments during which wild rats were exposed to recordings of footrolls. These signals were played during three different types of ambient noise conditions: a no-noise control, traffic noise, and cricket chirps (high-pitched noise that should not mask rat footdrums, but should still elicit any interesting responses to noise in general). Rat behavior was observed throughout each trial so that the researchers could determine whether the animals were impacted by any type of environmental noise (i.e., traffic and crickets vs. control), and also whether one type of noise was particularly disruptive to communication (i.e., traffic vs. crickets).

Across the 39 footdrum recordings collected, all four frequency characteristics were similar to those measured for the traffic recordings. For example, the minimum and maximum frequencies of footdrums were found to be 126 and 352 Hz (respectively); for traffic noise, these values were 118 and 371 Hz. In other words, both signal and noise have quite similar acoustic properties, increasing the likelihood that kangaroo rats will make mistakes while communicating.

Indeed, rats exposed to traffic sounds during the playback experiments seemed aware of the fact that the noise pollution could impair their ability to hear. Even before any footdrumming recordings were broadcast into the experimental chamber, the noise-exposed individuals spent more time alert; they also delivered more signals, themselves. While rats in the control and cricket treatments immediately responded to footdrums when they were broadcast, animals in the traffic treatment tended not to alter their behavior; they also continued to footdrum for no apparent reason. Thus, they not only failed to detect actual signals amidst the din of noise pollution, but they also sometimes interpreted the footdrum-like traffic noise as a signal from another rat that wasn't even there.

(A Stephens' kangaroo rat in the entrance to its burrow. Image courtesy of the L.A. Times--which also featured an article about whether the rats act as a "barrier to development.")

Cumulatively, these results suggest that kangaroo rats should--and do--have difficulty discriminating between signals and traffic noise. This could have several negative impacts on both individual animals and the entire population. Rats that accidentally interpret traffic as signal might waste energy producing a footdrum; further, this highly audible response might make them more obvious to predators such as owls or cats. Additionally, animals whose signals are not heard may fail to defend their territories or attract mates, and may therefore have lower reproductive success.

This is bad news given that the rats have already suffered significant habitat losses. Until these recent findings were reported, researchers had thought that roadsides were actually beneficial to this species since they offered individuals the perfect substrate for digging burrows. Noise pollution, however, may cause this anthropogenic habitat to serve as a trap rather than a refuge. One glimmer of hope is offered by previous studies of avian species living in similarly noisy habitats: In order to escape acoustic masking, some birds can improve communication by altering their signal properties (e.g., pitch, volume, timing). Though it may not be easy or likely, it is possible that the Stephens' kangaroo rats might eventually learn to drum more rapidly or more intensely; given enough time, the species might even evolve better hearing so that noise-exposed individuals are more capable of discriminating between traffic and footdrum.

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Shier, D.M., Lea, A.J., and Owen, M.A. 2012. Beyond masking: endangered Stephens' kangaroo rats respond to traffic noise with footdrumming. Biological Conservation 150:53-58.

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