Tuesday, 31 January 2012

Flight initiation distance and tolerance to human disturbance

The term "bioindicators" is often used to describe species that can be used to infer environmental changes. Birds are commonly used in this capacity because they demonstrate a number of variations that can be easily measured, including abundance and density patterns, physiological or morphological characteristics, and behaviors. One behavior that is frequently quantified in order to evaluate the effects of anthropogenic habitats is "flight initiation distance" (FID), or the distance at which a bird will take flight when approached by a human. If FID becomes increasingly small as human disturbances become increasingly common, then this metric may provide researchers a quick and easy way to evaluate species' tolerances to anthropogenic factors, as well as to rate how disturbed particular habitats are.

Most previous studies have typically compared FID between urban and rural sites only, rather than across an entire anthropogenic gradient. However, collaborators from the Chinese Academy of Sciences, the Xiamen Key Lab of Urban Metabolism, the Institute of Applied Ecology, Xiamen University, and the University of Rostock recently addressed this deficit by quantifying FID for 36 species living across an 8-site disturbance gradient associated with the rapidly developing Xiamen City, China. At each site, researchers approached focal birds on foot  at a steady pace; when the birds took flight, the distance between the takeoff point and the pedestrian was measured.

(A little egret, Egretta garzetta)

One species, the little egret (Egretta garzetta), was present at all sites. This allowed the scientists to perform an analysis investigating whether birds of a single species are increasingly less wary as they are surrounded by more, and more frequent, human disturbances. By pooling data for all 36 species, though, the researchers could look for broader patterns--for instance, whether variation in FID generally reflects tolerance to urban conditions. In this case, "tolerance" was measured in two ways: abundance of each species of bird at each site along the anthropogenic gradient, and total number of sites occupied by each of the species. FID is strongly related to body size (since bigger birds need more time to get airborne), so for the second set of analyses the researchers controlled for this important morphological variable.

Data from 254 trials revealed that grey herons (Ardea cinerea) have the largest FID (at 41.5 m), while Temminck's stints (Calidris temminckii) have the smallest (at 9.0 m, but with a sample size of only 1 bird). The little egret showed the greatest variation in FID, and an analysis of the bird's habits across the entire anthropogenic gradient revealed that FID was negatively related to the degree of urbanization. In other words, birds in the least disturbed sites were much warier of humans than birds in the most disturbed areas. Across all species, size-adjusted FID was shorter for birds that were found across more sites and in higher densities--or, in other words, those that were "urban tolerant."

(A grey heron, Ardea cinerea, which displays a large FID)

Of 17 particularly tolerant species (identified using a calculation that compared expected and observed FID values given the birds' body sizes), 12 were present in multiple sites along the urban-to-rural gradient. For these species, the researchers were able to investigate how FID incrementally varied along the disturbance gradient. As expected given the results of the previous analyses, the majority of species exhibited increasingly shorter FID at increasingly disturbed sites; these patterns were particularly strong among the most tolerant species.

These results indicate that FID (or size-adjusted FID) can be used in situations where researchers need to quickly evaluate species-specific tolerance to urban environments. This could be useful, for instance, in predicting how many species in a given area might be negatively impacted by a proposed construction project, or even, to some extent, in guessing how strongly birds might respond when exposed to human activities. Specifically, birds with the greatest variation in FID were most tolerant to anthropogenic activities and habitats, so species with the least variation are those that are most likely to suffer from human disturbance. Measurement of FID within different habitats may also be a "quick and dirty" way to evaluate the amount of disturbance typically present within those areas. This could be particularly useful for researchers who need to quantify this characteristic in a large number of sites, or who are visiting a particular area for the first time and want to quickly learn a bit about its disturbance regime.

 (Temminck's stint, Calidris temminckii, which has a very small FID)

Unfortunately, the data collected in this study--and in so many FID-related studies before it--are not sufficient to answer one of the biggest questions in disturbance research today: Are tolerant birds predisposed towards adapting to urban environments, or are urban exploiters evolving to become more tolerant? It is a difficult question to address, and the results may vary for different species. As the authors state, though, it is a worthy topic of future research, as the answer "could contribute to a better understanding of why some species can cope with urbanization and others cannot."

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

Lin, T., Coppack, T., Lin, Q-x, Kulemeyer, C., Schmidt, A., Behm, H., and Luo, T. 2012. Does avian flight initiation distance indicate tolerance towards urban disturbance? Ecological Indicators 15:30=35.

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

Sunday, 29 January 2012

Distant noise pollution can have local consequences

Underwater noise pollution does not usually receive as much attention as its terrestrial counterpart, despite the fact that many aquatic animals may be negatively impacted by loud noises. Because the speed of sound is 5 times faster in water than it is in air, acoustic pollution can maintain its intensity over much greater areas and affect a wide variety of animals located some distance from the noise source. Depending on the strength of a particular disturbance event's sound waves, exposed animals may suffer injuries (some lethal), hearing damage, and/or disruptions to their behavioral time budgets. Although a number of species are thought to face such dangers, researchers are particularly concerned about the impacts of noise on whales, many of which rely heavily on acoustic communication to facilitate social interactions.

(Humpback whale, Megaptera novaeangliae)

Previous work on endangered right whales (Eubalaena glacialis) has shown that noise-exposed individuals alter the acoustic characteristics of their calls when their habitats are polluted by ship traffic noise. A recent study conducted in the Stellwagen Bank National Marine Sanctuary (SBNMS) has revealed that humpback whales (Megaptera novaeangliae) also make adjustments in response to anthropogenic noise--a result that is, perhaps, unsurprising given the previous findings. What is sure to raise some eyebrows is the fact that the whales in the current study were responding to noise pollution generated approximately 200 km away from the study site.

The humpback study was initiated after collaborators from Integrated Statistics, the Northeast Fisheries Science Center, and Marine Acoustics, Inc. found some intriguing patterns while reviewing data collected by an underwater array of autonomous recording units in the SBNMS. By chance, the units were running during the 2006 Ocean Acoustic Waveguide Remote Sensing (OAWRS) experiment, which used low-frequency noise pulses to create images of fish shoals over a 100-km area. The recorders picked up the noise pulses despite the fact that they were generated in a study site some 200 km off; they also collected recordings of vocalizations delivered by local male humpback whales during the OAWRS study period.

(Map showing the Massachusetts coastline and the Stellwagen Bank National Marine Sanctuary)

It seemed to the researchers that there were markedly fewer recordings of whale calls during the noise pollution period, but they couldn't be certain whether this stemmed from variations in the acoustic environment or from normal seasonal differences in communication patterns. In order to explore further, the scientists collected additional acoustic data at the same portion of the year (late September-early October) in both 2008 and 2009. This window of time was broken into 3 phases: before, during, and after the calendar period when the noise pulses were delivered in 2006.

During the focal periods of 2008 and 2009, environmental noise regimes were similar to each other and also to that recorded during the non-OAWRS period of 2006; in other words, they appear to reflect a "normal" ambient noise environment for the whales. In the years with no ambient noise pollution, whale songs were increasingly common throughout the focal period--there were more in the "during" phase than "before," and more "after" than "during." In 2006, however, there were significantly fewer songs recorded in the "during" phase of the focal period than during the "after" phase--a reverse of the pattern observed in normal years.

(Sonogram showing a humpback whale song; the Y-axis shows frequency and the X-axis shows time)

Massachusetts humpbacks migrate south in the winter in order to take advantage of warmer tropical waters. Thus, over the course of the focal period examined here, the study animals were getting ever closer to their departure date. The corresponding increase in singing behavior during the "normal" years suggests that the whales' song may be used to coordinate some aspect of migration, though currently scientists have little understanding of the role of song in humpbacks' life histories. If singing does play a role during this important transition period, then anthropogenic noise pollution during this time might have a serious impact on the animals' efforts to gather into appropriate social groups for their move south.

Remarkably, the whales appeared capable of hearing sonic pulses over 200 km from the noise source. The researchers calculated that the sounds were only 5-22 dB above local ambient noise levels by the time they reached the whales. Although these are not uncomfortably loud amplitudes, they appear to have been sufficient to disrupt the whales' normal behavior patterns. Unfortunately, the dataset collected here is not sufficient to indicate why less whale song was recorded during the noise pollution period: Did the animals respond to the noise by singing less, or by leaving the area altogether? Visual data collected at the same time for another study suggests that the whales were present, but chose not to vocalize; however, further studies would be needed to definitively characterize typical humpback responses to noise. Additional research might also investigate whether the songs that were produced during the noisy period differed from those delivered in normal conditions--for instance, by being louder or at a different frequency.

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

Risch, D., Corkeron, P.J., Ellison, W.T., and Van Parijs, S.M. 2012. Changes in humpback whale song occurrence in response to an acoustic source 200 km away. PLoS ONE 7(1):e29741.

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

Friday, 27 January 2012

How do noisy miners cope with noise?

Vocal differences between urban and rural birds have frequently been documented, as have variations in the vocalizations of birds living in different types of "natural" habitat. Based on these findings, it seems logical to assume that birds in different types of urban habitat should have measurably different vocal characteristics from each other, but this possibility has only rarely been studied. In fact, no research at all has addressed whether birds in quieter and louder territories within an urban setting respond to local noise regimes by delivering quieter and louder vocalizations, respectively. This particular vocal manipulation is known as the "Lombard effect," and is thought to be one of the most effective ways to prevent being masked by ambient noise.

(A noisy miner, Manorina melanocephala. Alternative and more poetic names include "garrulous honey-eater," "black-headed miner," "snakebird," "cherry-eater," "mickey," and "squeaker.")

Researchers from Australia's Monash University recently investigated use of the Lombard effect among noisy miners (Manorina melanocephala) living in two types of urban habitat in Melbourne: in vegetation along either major roadways or residential streets. Miners, native Australian honeyeaters, can easily be recognized by the loud alarm calls they use to warn each other of potential danger. Miners live in large aggregations, or colonies--80 of which were examined in the current study. Each was visited on a weekday morning when traffic was heaviest and birds were most vocally active. One researcher, in the company of a potential "predator" (her dog Persephone), approached a focal bird until it began to produce alarm calls. These, along with the local ambient noise regime, were then recorded. Analysis of the recordings revealed the minimum, maximum, and mean amplitude of each; by measuring the distance between the microphone and the vocal bird, the researchers were able to standardize their amplitude measurements so they reflected volumes at 1 m from each bird. While visiting each site, the scientists also observed other behaviors related to miner communication, including how high the birds perched and whether they delivered calls while in flight.

(The Melbourne skyline, with arterial roads in the foreground)

Comparisons of the ambient noise data showed that environmental noise levels differed significantly between arterial and residential sites; specifically, arterial roads were an average of 15 dB louder than those in residential neighborhoods (66 vs. 51 dB). Correspondingly, noisy miners in colonies along arterial roads delivered alarm calls that were an average of 9 dB louder than those of their residential road counterparts (89 dB vs. 80 dB). Analyses of all calls across all noise regimes revealed that alarm call volume was significantly correlated with background noise level; in other words, no matter where the miners lived, they tailored their calls to suit their habitat.

The birds did not alter call-related behaviors such as choice of perch height and use of in-flight calling. However, there were some interesting relationships between habitat type and choice of alarm call. In arterial road colonies, miners were more likely to use "alarm call 2", while birds in residential areas were more likely to use "alarm call 3." Both calls signal the approach of a terrestrial predator and consist of loud, repeated single notes; the main difference is that the latter sounds more "husky." It is not yet clear why miners in different areas should prefer to use different calls, since acoustic analyses suggest that they are equally likely to be masked by ambient noise.

 (A small flock of noisy miners)

In Melbourne and elsewhere in Australia, miners are a very successful colonizer of anthropogenic habitats. The results of the current research demonstrate that this may, in part, result from the birds' adaptability to human noise regimes. By altering their call amplitudes when necessary, the birds can prevent their warning signals from being masked by the sounds of nearby traffic. Interestingly, a follow-up analysis revealed that signal-to-noise ratios (SNR) in arterial roadway sites were lower than those in residential areas, indicating that the arterial birds may merely be lessening the negative impacts of noise rather than completely preventing them. Perhaps the reduction in SNR is not harmful given the distances over which these birds are communicating, or maybe the miners have simply reached the limits of what amplitudes they can achieve. Further work will be needed to investigate these, and other, possibilities, as well as the consequences of the reduced SNR.

Previous studies on other species have documented a close link between body size and the energetic cost of vocalizing at high amplitudes. While many small birds can produce calls and songs at even louder amplitudes than those recorded here for miners, it is more metabolically demanding for little species than for the relatively sizable miner. As a result, the authors of the current study suggest that smaller birds may be particularly susceptible to anthropogenic noise regimes--another possibility that will need to be examined in future research.

For supplemental images related to this post, please visit the Anthrophysis pin board at Pinterest

Lowry, H., Lill, A., and Wong, B.B.M. 2012. How noisy does a noisy miner have to be? Amplitude adjustments of alarm calls in an avian urban "adapter." PLoS ONE: 7(1):e29960.

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

Thursday, 26 January 2012

Simple exclusion methods keep badgers out of farm buildings

European badgers (Meles meles) are in the news again this week, this time as the focus of a study seeking to determine the efficacy of badger exclusion methods installed on cattle farms.

As recently discussed in another Anthrophysis post, badgers are an important reservoir of Mycobacterium bovis, the pathogen that causes tuberculosis in cattle. Previous research indicates that badgers and cattle appear to come in direct contact only infrequently; thus, scientists are still unclear on how M. bovis infections are transmitted between the two species. However, it is known that badgers can excrete the bacteria in feces, urine, sputum, and other exudates, and also that the animals frequently visit pastures and farm buildings. Therefore, it seems reasonable to suppose that badgers might contaminate cattle feed while defecating, urinating, and grooming in areas utilized by cows. The current study was designed to examine rates of badger visitation at cattle farms and investigate whether these might be diminished via the installation of exclusion structures.

(European badgers, Meles meles)

The work, conducted by researchers from the Food and Environment Research Agency and the University of Exeter, was performed on 32 farms in Gloucestershire--an area with a high incidence of bovine tuberculosis. During the first part of the study, the scientists used infrared, motion-triggered digital cameras to record badger visits to farmyards, in general, and to specific buildings in particular (e.g., those housing cows vs. those housing feed). During the second half of the study, farm buildings were subjected to one of four treatments: no exclusion measures, measures to reduce visits to cattle housing/feeding areas only, measures to reduce visits to feed stores, or measures to reduce visits to both cattle housing/feeding areas and feed stores. Exclusion measures were tailored to each farm, but primarily consisted of galvanized aluminum sheets installed as gates, panels on gates, or fencing; aluminum feed bins; or electric fencing. After these devices were installed, cameras were used to monitor changes in badger activity.

Over the course of the initial surveillance period, badger visits occurred on 59% of all farms, during as many as 71% of nights investigated. Activity was not uniform across all farms, however; some particularly popular areas (or, those with particularly active badger neighbors) received visits on more than 60% of nights. Intensity of badger visits was influenced by time of year, with activity peaking in the late spring and early summer.

(Images from Figure 1 of Judge et al. 2011: Various exclusion methods used to prevent badger entry into farmyard buildings.)

Badger exclusion measures significantly reduced badger visits to farm buildings. In fact, the anti-badger devices were 100% effective, but only when maintained and used properly: Once the exclusion measures were in place, badgers were only able to obtain entry into buildings when farmers had failed to employ the devices or keep them in working order. Overall numbers of badger visits were impacted by the presence of an exclusion measure anywhere on a farm, but deterrence was most notable on farms where devices were installed on both feed stores and cattle housing buildings. Where only one building was targeted, badgers were most discouraged (predictably) by exclusion measures targeting feed stores.

Previous work has indicated that excluded badgers, when denied access to anthropogenic sources of food, simply use other resources on their pre-existing territories. Indeed, the quick abandonment of farm foraging areas by the badgers in this study suggests that the animals are not reliant on human sources of food (over the short-term, at least), but merely take advantage of them when they can. On the whole, the success of the exclusion measures is quite promising and suggests that badger-cattle contact on farms can be drastically minimized.

(A badger brigade foraging in an anthropogenic habitat)

Although the prices of the exclusion treatments ranged widely (from 600 to 12,500 pounds sterling) and could be rather expensive, they were always more affordable than the average costs associated with tuberculosis-related herd breakdown (~30,000 pounds). Thus, the measures seem to be a good investment--but only if they actually impact the transmission of bacteria. Unfortunately, the current study was unable to measure this critical factor, which means that future research will be needed to investigate whether, and how, exclusion devices affect the spread of M. bovis. Additional work might also seek to understand what prompts badgers to visit farms in the first place, and why there is such variation in badger visitations among farms--or among individual badgers.

Judge, J., McDonald, R.A., Walker, N., and Delahay, R.J. 2011. Effectiveness of biosecurity measures in preventing badger visits to farm buildings. PLoS ONE: 6(12):e28941.

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

Wednesday, 25 January 2012

Urban goose reproductive decisions are not impacted by their population densities

One of the most maligned urban birds in the U.S. is the Canada goose (Branta canadensis), which can be found at unnaturally high densities in the grassy fields of parks, golf courses, office complexes, and even the medians of highways. Among other species, such tight aggregations can have a significant impact on reproductive activities--for instance, by increasing rates of nest parasitism and cuckoldry.  However, despite the fact that urban geese often nest much closer together than their rural counterparts, and are noticeably more tolerant of the proximity of conspecifics, their breeding efforts do not appear to be significantly impacted by the high densities in which the birds occur in anthropogenic areas.

(Canada goose, Branta canadensis, with chicks)

This was the surprise finding of collaborators from Michigan State University, the Harvard Graduate School of Education, and Ducks Unlimited. Their analyses focused on data collected from 253 individuals in 42 clutches over a total of 3 breeding seasons. The researchers targeted Canada geese breeding across a density gradient in an urban region of southern Michigan, USA. At the low end of the gradient, geese nested in marshy areas surrounded by forest; at the high end of the gradient, the birds were found in urban and suburban parks. Nearest neighbor distances varied by as much as 97 m between the two types of site, with more urban birds found much closer together.

Genetic analysis indicated that over half of all clutches (~60%) were free of either parasitism or cuckoldry; 26% showed evidence of the latter, while 14% showed evidence of the former. When the high-density and low-density samples were analyzed separately, there were marked differences in the frequencies of these alternative reproductive strategies: In high-density areas, 22% clutches had been parasitized, and another 22% showed signs of cuckoldry; in low-density areas, though, these values were 32% and 5%, respectively. Despite these superficial patterns, though, statistical models indicated that the occurrence of these reproductive strategies was not significantly impacted by breeding density.

(Flock of Canada geese in an urban park)

Another surprise finding of the study was that parasitic eggs appeared to have been deposited into the nests of breeding females by closely related birds--the incubating animals' mothers and sisters, for instance. The researchers are not sure whether this reflects a deliberate collaboration between geese, or simply the fact that some females have learned to take advantage of birds who are tolerant of having neighbors in close proximity. Further research will be needed to investigate this issue in greater detail. The collaborators also feel that future studies that achieve higher sample sizes might uncover significant relationships not found here. After all, despite the lack of significant relationship between cuckoldry and breeding density, there was a very strong trend (a fourfold increase in cuckoldry between low- and high-density sites) indicating that density may be biologically relevant, if not statistically so.

The breeding patterns described in the study suggest a couple reasons why urban geese occur in such high numbers. For one thing, resources like food and nesting habitat do not appear to be limiting factors, allowing many urban birds to successfully produce large clutches without paying too many costs. For another, the birds don't seem very concerned about personal space, which indicates that group expansion will not be limited by social preferences for solitude. In other words, it looks like groundskeepers in urban areas will not have a respite from cleaning up goose messes any time soon.

For supplemental photos associated with this post, please visit the Anthrophysis pin board.

Moore, J.A., Kamarainen, A.M., Scribner, K.T., Mykut, C., and Prince, H.H. 2012. The effects of anthropogenic alteration of nesting habitat on rates of extra-pair fertilization and intraspecific brood parasitism in Canada Geese Branta canadensis. Ibis online advance publication.

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

Tuesday, 24 January 2012

Swiss vineyards provide habitat for threatened woodlarks

Vineyards seem to be a hot topic in the field of ecology right now. Several recent reports indicate that they can provide good homes for several species of bird, some of whom earn their keep by eating pest species that damage grape crops. Now, collaborators from the University of Bern, the Swiss Ornithological Institute, the University of Lausanne, and the University of Cape Town have produced results indicating that vineyards in the Valais region of Switzerland may be able to provide both feeding and breeding habitat for the woodlark (Lullula arborea)--a vulnerable species of songbird whose numbers have been on the decline since the 1950's.

(Woodlark, Lullula arborea)

Not all vineyards are up to the task, however. This was revealed by a study of the microhabitats utilized by woodlarks within the larger vineyard landscape. To collect data for the analysis, researchers attached radiotracking devices to 7 woodlarks (5 males and 2 females) in order to see where they spent the bulk of their time. Ecological characteristics of woodlark haunts were then compared to those of nearby areas that the birds avoided.

Focal birds were tracked over a period of 88 days, during which time the animals were recorded using a total of 684 patches of vineyard. Homerange size per woodlark varied dramatically. While some birds covered only about 1 hectare, others used areas more than 10 times this size; the average territory was 5.2 hectares. The habitat characteristics that appeared to have the greatest influence on woodlark presence were vineyard type and age, herbicide application regime, ground vegetation cover, vegetation height, and the presence of anthropogenic structures such as walls and roads.

(Vineyards in Valais, Switzerland)

Specifically, woodlarks were less likely to utilize older vineyards--probably because these had more densely planted vines and were treated with higher levels of herbicide. However, the birds seemed to prefer areas planted in a more traditional style, where plants branched low above the ground and rows were planted slightly closer together. Areas with high levels of herbicide application were avoided; woodlarks were fond of areas where short vegetation was allowed to cover 45-60% of the ground. On the other hand, the birds appeared to avoid human-installed infrastructure.

Overall, the woodlarks' occurrence patterns indicate that the birds prefer a mosaic style habitat--one that offers grassy patches where they can breed, but areas of bare ground where they can forage for invertebrate prey. Older techniques of vineyard management tend to emphasize use of herbicides in order to keep a highly mineralized--or bare--ground beneath the vines. Newer, more environmentally-friendly methods (sometimes referred to as "integrated production policies") avoid adding as many chemicals--good news to the 125-150 pairs of woodlarks (half of Switzerland's total population) that live in Valais.

(Woodlark-friendly vineyard habitat, where the ground is covered by a mix of short grass and bare patches)

Unfortunately, only about 5% of Valais' vineyards currently use these new cultivation techniques. The researchers strongly suggest that more Swiss wine growers should strive to make their product in a bird-friendly way--something that can easily be achieved by treating only every second row of vines with herbicides. This simple tactic could help bring an at-risk species back from the brink--and probably win over the hearts and minds of more than a few potential wine buyers.


Arlettaz, R., Maurer, M.L., Mosimann-Kampe, Nusslé, S., Abadi, F., Braunisch, V., and Schaub, M. 2012. New vineyard cultivationpractices create patchy ground vegetation, favouring woodlarks. Journal of Ornithology 153:229-238.

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

Monday, 23 January 2012

Risk of bovine tuberculosis is increased by reactive badger culling efforts

British cattle farmers have struggled over the last several decades to find a solution to the problem of bovine tuberculosis (bTB), a disease caused by Mycobacterium bovis. Wild European badgers (Meles meles) act as a reservoir for these bacteria, inspiring culling efforts to try to stem the flow of M. bovis from badgers to nearby herds. Over 20,000 badgers were culled between 1975 and 1997, but the incidence of bTB remains high: In 2009 alone, some 35,000 cattle were slaughtered after testing positive for the disease. The Randomized Badger Culling Trial (RBCT), a 10-year study begun in 1997, was conducted to investigate the effect of badger management efforts on bTB. To the surprise of many, it revealed that badger removal did not dampen the spread of bTB; in fact, RBCT data suggested that culling may actually increase the risk of bTB among nearby cattle.

(European badger, Meles meles)

Indeed, this is the conclusion of analyses performed by researchers from the Imperial College London, who, writing in the journal Biology Letters, recently described the drawbacks of a particular type of management known as "localized reactive badger culling." This practice was suspended in 2003 after it was associated with a 27% increase in bTB "breakdowns," or restriction of the movements of affected herds. Reactive culling focuses on removing badgers whose home ranges overlap with land used by herds in which bTB has recently appeared. The authors hypothesized that reactive culling efforts fail to reduce overall levels of tuberculosis because they inadvertently increase the risk of bTB in herds located near--but not on--lands where culling operations are conducted.
The researchers investigated this possibility using a database called VETNET, with which they could access information on cattle bTB tests and herd breakdowns. They investigated a total of 1208 cattle herds--604 impacted by tuberculosis and another 604 that remained disease-free. Likelihood of bTB infection in each herd was explored with respect to the presence/absence of culling (within 1, 3, and 5 km of each herd's location), distance to any culling efforts and number of badgers killed, and a number of other potential mitigating characteristics (including herd type and size, farm area, and historic incidence of bTB in the region).

Reactive culling within 1, 3, and 5 km of a herd was found to more than double its risk of bTB. In fact, the likelihood that cows would experience an outbreak was positively related to the number of nearby culled badgers. This was true even when models simultaneously took into consideration both badger culling efforts and prevalence of bTB breakdowns in the vicinity. Indeed, the more complex multivariable analyses, which controlled for the risks posed by nearby tuberculosis outbreaks, still indicated that herds within 3 and 5 km of culling efforts were particularly likely to succumb to bTB infections following high levels of badger removal.

 (Domestic cow)

These results likely reflect the fact that some badgers may utilize vast areas of habitat; thus, culling efforts may not actually target the individuals responsible for encountering, and passing M. bovis to, cows. In other words, by removing the "wrong" individuals, culling efforts may reduce overall badger density without actually reducing the density of infected animals. Thus, while badger numbers fall, the incidence of M. bovis does not. In fact, culling efforts may cause more harm than good by acting as "perturbations" that disrupt badger social organization and spatial distribution. This, in turn, can affect badger-cow interactions and associated disease control efforts. The authors point out that such perturbations are not just an issue in this system, but in any disease control situation in which wildlife species act as reservoirs.

Vial, F. and Donnelly, C.A. 2012. Localized reactive badger culling increases risk of bovine tuberculosis in nearby cattle herds. Biology Letters 8:50-53.

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

Sunday, 22 January 2012

The benefits of biodiversity

If you've recently spent some time in a "greenspace"--an area of undeveloped landscape--you may have found that it improved your mood, reduced feelings of stress, and left you feeling more relaxed. These are only a few of the benefits of natural areas, which have also been shown to increase lifespan, reduce the length of time needed to recover from surgery, and improve cognitive abilities. Despite the growing amount of attention paid to these physical and mental effects of greenspaces, there has been little to no work investigating why natural areas have this positive impact on human visitors--until now.

(A city park--one example of an urban greenspace)

In the latest issue of the journal BioScience, an international research team (including collaborators from the University of Sheffield, the University of Copenhagen, De Montfort University, the University of Kent, the University of Tennessee--Knoxville, and the University of Exeter) describes a recent project undertaken to test the hypothesis that people respond favorably to greenspaces because of the biodiversity contained within them. The researchers focused their efforts on 34 study sites located along the 5 rivers that run through Sheffield, UK. In each location, they surveyed local bird, butterfly, and plant populations in order to measure species richness. They also interviewed visitors to the natural areas in order to gauge which site characteristics might be responsible for "psychological well-being," as reported by the visitors themselves.

 (Location of Sheffield, which, with a population of 520,700, is the UK's 5th largest city)

Questionnaires explored two major sources of the potentially beneficial impact of greenspaces: their "restorative" nature, which helps visitors bounce back from mental fatigue, and their contribution to a "sense of place," deriving from individuals' emotional attachments with particular locations and the resulting importance of those places in forming a sense of identity.

As hypothesized, the well-being of greenspace visitors was positively related to the biodiversity of all three taxonomic groups. However, in an unforeseen twist, the relevant value was not actual biodiversity, as assessed by the researchers themselves, but the perceived biodiversity reported by survey respondents. Surprisingly, the relationships between well-being and actual species richness were inconsistent: While people responded positively to higher levels of avian biodiversity, they responded negatively to plant diversity and neutrally to fluctuations in butterfly numbers.

In reality, numbers of bird, butterfly, and plant species varied independently of each other across the sites. Values estimated by visitors were highly correlated, though, suggesting that greenspace users may use one set of cues to estimate the diversity of all classes of local species. The authors of the study suggest that visitors' estimates may reflect awareness of certain key environmental features--the presence of a particular charismatic species, for instance, or abundance of wildlife rather than diversity; the exact mechanism still requires clarification. Regardless, one pattern is clear: Sheffield's citizens are not very well informed about their local flora and fauna. Of all people surveyed, only 2 could correctly identify all species shown to them in a series of 12 photographs (4 each of birds, butterflies, and plants); approximately a quarter of those questioned were unable to name even one.

(A wren, Troglodytes troglodytes--one of the most common and widespread species of birds found across the 34 study sites. Blackbirds, Turdus merula, and wood-pigeons, Columba palumbus, were also frequently observed. Common plant species included bramble, Rubus fruticosus, dandelion, Taraxacum agg., and sycamore, Acer pseudoplatanus, while whites, Pieris spp., and the speckled wood, Pararge aegeria, were the most encountered butterfly species.)

Importantly (though not surprisingly), the researchers found a clear correlation between an individual's identification skills and his/her ability to accurately estimate biodiversity in the study site. This suggests that there could be a tangible benefit to preserving or improving biodiversity in public greenspaces--but only if such efforts are coupled with education programs equipping people with basic species recognition skills. Under such scenarios, visitors would be better able to assess the richness of local wildlife species such that, in areas with higher levels of biodiversity, they would experience greater improvements to well-being. As the authors put it, this would "[unlock] win-win scenarios in which the design and management of greenspaces [could] maximize both biodiversity conservation and human well-being."

With a larger proportion of the population able to perform basic species identification, a beneficial side effect of natural history education might be a more widespread recognition of the often depauperate nature of urbanized habitats. This awareness could fuel, and/or add momentum to, further conservation efforts.

Dallimer, M., Irvine, K.N., Skinner, a.M.J., Davies, Z.G., Rouquette, J.R., Maltby, L.L., Warren, P.H., Armsworth, P.R., and Gaston, K.J. 2012. Biodiversity and the feel-good factor: understanding associations between self-reported human well-being and species richness. BioScience 62(1): 47-55.

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