Urban predator landscapes shape avian escape behaviors

Predation can act as a very strong selective force on animals, since an inappropriate or ineffective defense mechanism could easily lead to death. This means that you might expect to see rapid behavioral changes in animals that become exposed to a new predator by moving from one habitat to another. In birds, for example, country-dwelling individuals need to be on the lookout for sparrowhawks and other avian hunters, while city-dwelling individuals tend to have more to fear from cats.

Although these broad differences in the "predator landscape" have been recognized for a while, nobody really knew what effect they were having on avian behavior. Theoretically, urban birds should respond to a predation event--or a simulated predation event, such as capture by a human--differently than their rural relatives. Further, the presence of these behavioral variations should be related to the amount of time that species have been living in urban areas, as well as with the density of predators found in those habitats.

(Sparrowhawk with avian prey. Image courtesy of Wikipedia.)

These were the hypotheses of two European researchers who analyzed behaviors in over 1100 individual birds of 15 different species in Denmark and Spain. The birds had been captured in mist-nets as part of a banding study, and the researchers took advantage of this simulated predation event by observing and cataloging several antipredation behaviors: wriggling, producing alarm and fear vocalizations, biting, losing feathers (thus making themselves harder to hold on to), and demonstrating "tonic immobility," the avian equivalent of becoming a deer in the headlights in response to fear and stress. The researchers also performed raptor censuses in order to determine whether rural birds really were exposed to more aerial predators. Susceptibility to predation by cats and sparrowhawks was calculated using a formula that accounts for the density of other potential prey items (which is generally higher in urban areas). Finally, the researchers chatted with bird watchers and looked through ornithological records in order to see when each focal species first began appearing in urban areas; this allowed them to calculate the length of time the birds had had to respond to their new predators.

The four-year study revealed that escape behaviors were significantly different in rural and urban habitats. Urban birds were more likely to produce fear and alarm vocalizations, but were less likely to bite or wriggle intensely; city birds also lost feathers at a higher rate and stayed in tonic immobility for longer periods of time. The differences in vocalization probably stem from the fact that urban birds live at higher densities and therefore have more friends and family that they a) want to save from a fate similar to theirs, and/or b) want to call to their assistance. Differences in the four other behaviors suggest that overall predation rates are lower in urban environments, causing city birds to "forget" how to respond appropriately.

The raptor censuses revealed significantly higher numbers of aerial predators in rural environments than in urban ones. Susceptibilities to sparrowhawk and cat predation were negatively correlated, suggesting that birds in most habitats either have to deal with one predator or the other, but not both. The only escape behavior that was significantly related to predation even after the researchers had accounted for phylogeny (or the fact that related species tend to have similar characteristics) was feather loss; the difference in urban and rural feather loss was positively related to susceptibility to sparrowhawk predation.

Both biting frequency and wriggle intensity were related to the length of time that birds had been living in urban areas. In species that had been urbanized for a long time, and therefore had much more time over which to show habitat-related divergences, biting frequency was higher in rural areas. Likewise, recently urbanized species tended to wriggle more intensely than species that had lived in cities for a longer period of time. Both of these patterns support the idea that predation is less intense in cities, and so urban birds have begun to lose some of their anti-predator behaviors.

(Death by cat seems to be more common in urban areas, though overall predation levels are lower than in rural habitats. Image courtesy of Terrierman.)

The authors admit that other urban-rural differences could have contributed to the patterns seen here. Cats and sparrowhawks, for instance, are only two of many species that birds will encounter at different rates in different types of habitats; humans, dogs, rats, and foxes may also help shape avian behaviors. So, too, could variations in other environmental attributes such as habitat features or the density of conspecifics.

Assuming, though, that there are significant differences between urban and rural birds, and that they stem from the presence and behavior of particular predators, the next big question is, what is the chain of events that led to the new set of antipredator behaviors in urban birds? Perhaps urban settlers were bolder individuals, and these unreactive birds passed on their nonchalant behaviors to their offspring. Alternatively, maybe urban birds are simply responding to their immediate environment and would increase their antipredator behaviors if moved back to a rural environment. A third possibility is that ancestral populations of urban birds might have adapted to urban environments after arriving there and encountering a new predatorial landscape. If so, these findings suggest that other new and different characteristics in urban areas could drive the evolution of the species that dwell within them.

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Moller, A.P. and Ibanez-Alamo, J.D. 2012. Escape behaviour of birds provides evidence of predation being involved in urbanization. Animal Behaviour 84:341-348.

Shedding light on the effects of anthropogenic illumination

If you live in an area with lots of artificial lighting, chances are you draw your curtains at night so the brightness doesn't keep you awake. That's not an option available to wildlife, though, and researchers have long wondered whether they suffer as a consequence. Exposure to nighttime light might, for instance, disrupt internal clocks, causing animals to behave in ways that are inappropriate for particular times of day or season.

This possibility was recently examined by researchers in The Netherlands, who installed artificial lights above the nest boxes of breeding great tits (Parus major). They hypothesized that increased exposure to light would cause the birds to forage more, which, in turn, would allow them to provision their young with more food. While this might work out well for the chicks, the increased time and energy expended by the adults could be detrimental to their health over the long term.

(Image courtesy of JYI.)

The researchers performed the light treatment in two shifts. During the first half of the chick-rearing phase (which lasts just over 2 weeks), they exposed half the boxes (n = 26 total) to light and left the other half in darkness; during the second half of the phase, this was reversed, so that previously-lit boxes went dark, while previously dark boxes received illumination. At the beginning of the study, nest boxes were fitted with transponder readers that logged visits from the adults; females had been tagged with transponders at the beginning of the nesting attempt, while males were caught and tagged midway through. Transponder data were used to calculate the beginning, end, and duration of each box visit event. Effects of the feeding regime were gauged by measuring juveniles on days 9 and 16 after hatching.

The effect of artificial light turned out to be unusual, and hard to interpret. Chicks in lit boxes received significantly more parental visits, but only during the second half of the nestling stage, and only from females--though male feeding rates didn't lag far behind. The increases in feeding did not have any impacts on chick size, indicating that parental care didn't translate into faster growth--perhaps because the adults were not able to take the time to forage for the biggest, juiciest prey items before each visit.

(Great tit, Parus major. Image courtesy of Treehugger.)

Interestingly, the presence of artificial light did not cause the birds to start feeding their young earlier in the day, or stop feeding them later; in other words, the illumination wasn't mistaken for an earlier dawn or later sunset. Instead, all the extra light may have tricked the birds into thinking that it was later in the breeding season, when days are longer. This could have prompted them to invest more time and energy into chick care, since "later"-breeding birds can't be certain of having the time to try for a second nest, and therefore want to ensure that their first one turns out well. Alternatively, the researchers hypothesize that chicks in lit areas may beg more, thus prompting the adults to increase feeding rate; however, it is not clear what might prompt this alteration in nestling behavior.

Perhaps the most interesting aspect of the study was the difference between the two parents. Unlike females, males don't spend the night in the box, and so they probably weren't exposed to the artificial increases in light. This means that their extra feeding visits were probably prompted by the upswing in parental care demonstrated by the females--an intriguing insight into the dynamics of mated pairs.

(Great tit nest, with begging chick. Image courtesy of Wikipedia.)

All in all, the study raises almost as many questions as it answers. Might chicks actually benefit from light because they get extra parental care? Does this negatively impact the adults by decreasing the likelihood that they will rear 2 broods per season, or survive from one breeding season to the next? Could artificial light act as an ecological trap? Although this work indicates that light can impact wild birds, more work will be needed to fully understand how, and with what outcome.

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Titulaer, M., Spoelstra, K., Lange, C.Y.M.J.G., and Visser, M.E. 2012. Activity patterns during food provisioning are affected by artificial light in free living great tits (Parus major). PLOS ONE 7(5):e37377.

Consumer power: The case of vegetable oil

The supermarket setup makes it easy to forget that the groceries we buy were raised or grown somewhere, requiring resources such as water and fertilizer and, most importantly, space. When you multiply these requirements by every package in every store across the country, and then add together all the countries in which similar stores exist, you end up with some staggering numbers.

Take, for instance, the case of edible vegetable oil, the global consumption of which has increased sevenfold over the past three decades. Approximately one-third of this is palm and soybean oil that comes from the tropics. As the result of increasing demand for cooking oil in China, India, the EU, and the US, farms have had to expand markedly, tripling in Indonesia and Malaysia, and growing by a factor of 20 in Brazil and Argentina combined. Space for plantations is usually carved out of rain forests, leading to reductions in biodiversity and ecosystem health.

(Land cleared to make room for a palm oil plantation. Image courtesy of Oxfam.)


Conservationists Lian Pin Koh and Tien Ming Lee recently addressed this problem in a special issue of Biological Conservation aimed at advancing environmental conservation. Like many other conservationists, they hope that the increasing consumer interest in "green" products will provide an incentive for vegetable oil companies to reduce their ecological footprint by investing in new techniques and technologies. At the same time, the researchers also recognize a "reluctance of agribusinesses to compromise on yield and profit." In order to circumvent this problem, the researchers hope that consumers themselves might be convinced to alter their behaviors in order to ease pressure on farmers and companies, and, therefore, on the forests they threaten to convert into plantations.

To illustrate the potential power of the consumer, and to motivate buyers into action, Koh and Lee analyzed three different scenarios linking vegetable oil consumption with space use. They focused on the four main oil markets--India and China (which have expanding economies and are therefore likely to increase consumption over the next 100 years), and the EU and US (which currently demonstrate the approximate levels of consumption to which India and China might eventually rise). The first potential scenario, known as the "Aspiring East," (AE) is one in which EU and US consumption levels remain consistent at ~80 g per day, while Indian and Chinese levels increase dramatically (to ~81 g per day). The second scenario, the "Recalcitrant West," (RW) is one in which EU and US consumption again remains steady, but Indian and Chinese levels rise only moderately, to 56 g per day. The final scenario, "Converging Sensibilities" (CS) is one in which all four countries converge on the moderate, 56-gram-per-day consumption.

(Soybean oil. Image courtesy of Farming Pak.)

Each scenario incorporated data on projected population growth, which would also influence demand for oil. Projected growth in India, for instance, is likely to increase consumption by anywhere from 16 to 46 megatons per year over the next hundred years; on the other hand, China's population contraction could lead to decreases of as much as 6.8 megatons per year. Across all four focal countries, these projected changes could lead to increased requirements of 3 to ~13 megatons per year. This, in turn, would be associated with conversion of forest to cropland. Under the AE, croplands were projected to increase to 11.7 megahectares in 2040, then fall to 7.3 by 2100; under the RW and CS scenarios, land use would follow a similar peak-and-trough pattern, but at levels approximately 60% and 70% lower, respectively.

In case your mind is spinning from all that math, the bottom line is that curbed consumption of vegetable oil could dramatically reduce pressure on farmers to expand their plantations onto rain forest land. It would be a good start to discourage countries with developing economies from becoming "Western" in their consumption patterns, but it would be most beneficial to do this while also encouraging Western countries to reduce their current levels of oil use.

(Cutting this much oil out of the daily diet of every Western consumer could dramatically decrease the chances that tropical rain forests will be cut down to make room for palm or soy plantations. Image courtesy of MPR.)

Given that oil can be unhealthy in large quantities, this could also have health benefits. The 56 grams-per-day moderate consumption level from the RW and CS scenarios is one calculated based on World Health Organization recommendations for a healthy diet, meaning that, on average, consumers in the EU and US eating quite a bit more daily fat than they need. In fact, the authors calculate that the CS scenario could be achieved if "each person in the EU and US reduces his/her oil consumption by an average of 25 grams per day, roughly equivalent to forgoing one large serving of French fries." It's not often that going on a diet is associated with saving the rain forest, and it certainly provides a unique source of motivation to eat fewer fried foods. It is, as Koh and Lee state, "some serious food for thought."

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Koh, L.P., Lee, T.M. 2012. Sensible consumerism for environmental sustainability. Biological Conservation 151:3-6.

Unseen coworkers: office space bacteria

If you're a germophobe, you won't want to read a recent PLoS ONE report detailing the abundance and diversity of bacteria inhabiting urban office spaces. That's because researchers from San Diego State University and the University of Tucson found almost 4,000 "operational taxonomic units" (or, for lack of a better word, species) belonging to >500 genera across 20 bacterial divisions--all in just 54 offices distributed across 3 cities. Groups most commonly represented include Proteobacteria, Firmicutes, and Actinobacteria--all of which include pathogenic members that can cause serious infections in humans. San Francisco workers can congratulate themselves on having the lowest bacterial abundances measured in the study; likewise, female readers can feel smug about the fact that office spaces belonging to women had significantly fewer bacteria than those utilized by men. Those looking to minimize contact with microbes should take particular care near phones and chairs; researchers found that these harbored much higher bacterial abundances than the other office surfaces they sampled.

(This study highlights a whole new reason why hand-washing is important at work. Image courtesy of Gary Fage.)

Contrary to what you might think, the study wasn't designed to make your skin crawl, but instead to improve our understanding of the "dynamic microbial environments" found in anthropogenic areas. Although previous studies have examined bacterial diversity in popular human hangouts like schools, houses, and airplanes, very little work has focused on offices--where millions of people worldwide spend the bulk of their time each day. Developing a "baseline" of bacterial diversity in offices may be useful for understanding the dynamics behind infectious outbreaks, as well as for determining which features of office buildings--including microclimate and space usage patterns--contribute to the spread of pathogens.

To collect their samples, the researchers visited 30 offices (15 belonging to men, 15 belonging to women) in each of 3 cities (San Francisco, New York, and Tucson). In each office, they swabbed similar-sized patches of the same 5 surfaces: chairs, phones, computer mice, computer keyboards, and desktops. A cell-counting assay revealed that chair and phone surfaces contained the highest levels of bacterial DNA, and so samples from these locations (n = 54 offices) were subjected to "deep-sequencing" analyses that allowed the researchers to identify bacteria down to the genus level. The resulting genera abundance patterns were then correlated with city, surface type, and sex of (human) office inhabitant.

(E. coli, one of many types of Proteobacteria. Image courtesy of the Encyclopedia of Life.)

According to the researchers, sex-related variations in bacterial abundances likely stem from the fact that men are known to wash their hands and brush their teeth less frequently than women (a claim supported by actual scientific research). Additionally, men are generally larger than women, and therefore possess a greater surface area that can transport and shed hitchhiking bacteria.

Indeed, humans were "clearly the primary source of office bacterial contamination," as shown by the fact that the most common genera are known to inhabit human skin or cavities. However, the study also revealed a surprising prevalence of bacteria associated with the human digestive tract--potentially suggesting that post-bathroom-visit hand-washing behaviors could be improved among office workers. Environmental microbes were also common, though researchers were surprised that this category included thermophilic bacteria that are normally associated with hot springs. This result indicates that this hardy group of species is capable of dispersing--and surviving--over quite an impressive range. In fact, the researchers suggest that sampling techniques such as the ones used in this study might be helpful for performing future in-depth investigations of microbe dispersal in general.

 (Image courtesy of XMDR.)

One other useful follow-up study will be an examination of diversity at the level of species and strains. However, this will require the development of "easier and less expensive" techniques. Such studies may be useful not only for illuminating the spread of disease--as mentioned above--but also the spread of genes: Bacteria often share genetic material with their neighbors through the process of horizontal, or lateral, gene transfer. Thus, data on which species intermingle in modern human environments may allow scientists to better understand and predict the evolution of microbes in anthropogenic areas.

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Hewitt, K.M., Gerba, C.P., Maxwell, S.L., and Kelley, S.T. 2012. Office space bacterial abundance and diversity in three metropolitan areas. PLoS ONE 7(5):e37849.

How to improve environmental education efforts

According to the United States Environmental Protection Agency, environmental education (EE) "increases public awareness and knowledge about environmental issues or problems. In doing so, it provides the public with the necessary skills to make informed decisions and take responsible action." In a recent essay in the Natural Areas Journal, however, biologist and educator Courtney Hughes argues that EE is not always as perfect as it is often portrayed. After all, many of today's biggest conservation challenges were also issues decades ago, when many environmental education programs were first initiated.

The major problem, Hughes argues, is not the concept of EE in general, but the way in which education efforts are developed and implemented. She worries that many shortcomings result from the fact that EE programs tend to be initiated and run by environmentalists rather than educators--and, while she admits that anyone can help other people learn, she also points out that educational experts have many useful insights into the learning process. This expertise can be helpful when tailoring programs to achieve a particular goal or reach a particular target audience. Thus, Hughes believes that environmental education should be viewed as a field unto itself, comprising "a body of comprehensive knowledge, skills, and abilities that could be put to good use in the conservation world." Conservationists should recognize that specialists in this field can make valuable contributions to EE initiatives.

(Classroom visits with wild animals are one technique that can be used for environmental education. Image courtesy of the Pittsburgh Zoo and PPG Aquarium.)

Hughes also worries that people tend to think of EE only as something that is useful and appropriate for schoolchildren. She emphasizes that environmental education is much more than just nature walks and environmentally-themed coloring books. Rather, it is a suite of strategies that can be used not only to spread information, but to actively encourage participants to internalize that information and use it to change their lifestyles--for instance in developing herding or farming techniques that minimize human-wildlife conflict, or turning aside from poaching in favor of ecotourism. Such goals are weightier--and will have longer-lasting conservation impacts--than the types of targets that EE usually focuses on.

In order to facilitate improvements in the way that EE is employed, Hughes offers four major suggestions. First, she encourages conservationists to define "environmental education" in the context of individual projects, and explicitly determine how EE will help achieve particular outcomes. These details should be helpful in selecting which materials and activities will be included in education programs--thereby tailoring them to specific circumstances, target audiences, and goals. Second, Hughes warns environmental educators not to think of their programs as quick solutions: "Success will not happen simply by disseminating an information pamphlet or by hosting an outreach session." Rather, she says, people will need time to ingest the things they are learning and rebuild their understanding of these topics. Once they begin to "construct new understandings based on new knowledge and experience," target audiences will be more likely to develop new outlooks and ways of doing things. Third, she strongly recommends the inclusion of educators in the program development and implementation process. These individuals, she says, have "disciplinary knowledge related to pedagogy, learning styles, learner behaviors, and resource development." In other words, they have the expertise needed to predict whether a certain program will be effective and, if not, to modify it accordingly. Finally, Hughes advocates the inclusion of planning and evaluation periods for every program. An extended planning period can ensure that programs include all the integral information and are designed to provide it in the most accessible and meaningful way possible. An evaluation period, meanwhile, is essential for reviewing the outreach efforts and deciding whether they have actually been successful. If not, educators can go back to the drawing board and develop new tactics.

(Education initiatives may also involve trips to the field. Although many education efforts involve young students, Hughes emphasizes that adult education is also important. Image courtesy of Essex Region Conservation Authority.)

Overall, Hughes feels that "inclusion of EE as a discrete process in conservation projects is a valuable and worthy pursuit." She hopes that by shedding light on some of its potential pitfalls--and recommending ways to avoid these--she can inspire environmental educators and conservationists to work more closely and effectively.

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Hughes, Courtney. 2012. Environmental education for conservation: consideration to achieve success. Natural Areas Journal: 32(2):218-219.

Keeping a Leash on It in National Parks

One of the biggest challenges in wildlife management is balancing the needs of humans and wildlife. As important as it is to protect natural and cultural resources, it is also vital to help visitors enjoy themselves, experience the wonder of nature and, hopefully, feel inspired to offer political and/or economic support for future preservation efforts. The balancing act can be particularly difficult in urban settings, where high densities of people can be found utilizing public areas for a variety of purposes--including dog-walking, a sometimes contentious activity because of potential canine aggression, habitat destruction, and, of course, the animals' propensity to leave behind waste.

(Fort Caroline National Memorial Area, Jacksonville, Florida. Image courtesy of U.E.)

Surprisingly, though, one of the main concerns about canine companions stems not from what things they might do, but, instead, the things that might be done to them--by dangerous wildlife such as snakes, alligators, and mountain lions. Because of this potential for pet injury, many parks have dog leash rules; unfortunately, however, these can be difficult to enforce. This prompted staff at the Fort Caroline National Memorial Area (Timucuan Ecological and Historical Preserve, Jacksonville, Florida) to think outside the box and develop a novel approach for encouraging park visitors to keep their dogs leashed. The method was so successful that Daniel Tardona, one of the park's officials, recently described it in the Natural Areas Journal in the hopes that other facilities might implement a similar program.

Originally, park officials attempted to enforce their rules by posting signs describing the leash regulations and threatening fines to all who did not comply; additionally, offenders were stopped by patrolling rangers and given warnings and citations. However, previous research has shown that these sorts of techniques alienate visitors by emphasizing limits, removing a sense of freedom, and generally making parks seem less welcoming. Further, while visitors may make short-term changes, they are unlikely to feel motivated to keep up their law-abiding behaviors over the long term. Fort Caroline staff were interested in "winning over" visitors by using a friendlier approach that allowed them to indirectly provide education about the logic and utility of leash laws. This sort of technique has been shown to be particularly useful in giving people information about the environmental, ethical, and stewardship aspects of conservation. Additionally, it allows them to have "free-choice learning experiences" that are more personal and long-lasting.

(Fort Caroline's canine visitors wall of fame. Image courtesy of the U.S. National Park Service.)

The final plan of action centered on the erection of a 2-sided bulletin board labeled "Our Canine Visiting Friends." This was placed halfway between Fort Caroline's visitor center and the trailhead of a 1.6-km walking path frequently used by dog-walkers--in other words, in a place where it was unmissable. Park staff approached visitors to request permission to photograph pets and put their portraits on the board; the only catch was that all dogs had to be leashed during the photo shoot. When mentioning this requirement, staff could subtly discuss why the leash rule was in place, and emphasize the ecological and safety relevance of this requirement.

The bulletin board quickly generated interest, not just among people who had seen it first-hand, but also among those who had found out about it by word-of-mouth; visitors soon approached park staff in order to request participation in the program, and eventually the board became so full of photos that a second one had to be installed. Anecdotal evidence suggests that the technique was useful for more than just producing a collection of canine glamor shots: Complaints about unleashed animals have dropped markedly since the program was initiated and park staff now report fewer sightings. Further, creation of the board seems to have galvanized the dog-walking community into taking a more active role in creating and maintaining a canine-friendly environment at the park: In addition to more diligently cleaning up after their pets, dog owners have successfully requested an "expansion of services," including the installation of dog waste stations and the creation of a series of ranger-led interpretive hikes open to both humans and their canine companions. One frequent park visitor has even initiated a "dog patrol" during which volunteers place a lightweight pet jacket--labeled with a National Park Service VIP patch--on their dogs and patrol the walking trails, providing natural history information and dispensing advice about human and canine hazards in the park.

(Dog patrol volunteers Wayne (2 legs) and Jackson (4 legs). Image courtesy of the U.S. National Park Service.)

Perhaps most rewarding has been the creation of a dialogue about non-canine issues, such as problems with feral cats and invasive plants. According to Tardona, this increased interest in the general ecology of the park "[supports] the notion that visitors with their companion animals can be facilitators of social interactions that increase the likelihood of social networking that inspires a sense of community and neighborhood good will and trust." In other words, dog-walkers and park staff now form a single cohesive community working together to preserve Fort Caroline's natural resources and make the park a place that can be enjoyed by many types of visitor, furry or otherwise.

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Tardona, D.R. 2012. Promoting companion animal leash compliance on an urban park trail system. Natural Areas Journal 32(2):215-217.

Noise pollution may cause nestlings to go hungry

As regular Anthrophysis readers are probably well aware by now, scientists are becoming increasingly concerned about the potential negative effects of anthropogenic noise. Among other things, noise pollution can mask the vocalizations of acoustically communicating species like birds, thereby leading to alterations in abundance, community structure, predator-prey relationships, and reproductive output.

(Airplanes--one of many sources of anthropogenic noise pollution. Image courtesy of Wikipedia.)

To date, there are three (non-mutually exclusive) hypotheses about the mechanisms responsible for these patterns. First, the presence of noise may interfere with the mate choice process by obscuring male vocalizations; this could cause females to feel insecure about the quality of their mates, and therefore invest less time and energy in reproduction. Second, noisy territories may be seen as lower quality and therefore contain the less experienced, younger, and/or poorer quality individuals who were not able to claim and defend better habitats. Third, noise may impair chick development by increasing stress levels in chicks and/or obscuring their begging calls and causing them to receive less food from their parents.

Distinguishing among these hypotheses requires a study setup permitting long-term data collection and the ability to identify individuals. Happily, these are two characteristics of an ongoing study on Lundy Island, located in the Atlantic Ocean/Bristol Channel off the coast of North Devon, UK. The island's electricity is supplied by noisy generators that run for 6 hours each day; birds nesting in the immediate vicinity of the generators are exposed to noise up to 68 dB in volume, while those nesting in the woods, or on the other side of nearby barns, experience "natural" levels of noise. By reviewing 8 years of breeding data collected for house sparrows nesting across this noise gradient, an international team of collaborators has been able to explore not only how noise impacted breeding success, but why.

(Lundy Island, UK. Image courtesy of English Heritage.)

The scientists used 2 techniques that add an extra layer of uniqueness to their study. First, they randomly selected a subset of chicks to "cross-foster" each year. In other words, chicks that were born in noisy habitats would be swapped with chicks born in quiet habitats (and vice versa), then raised by their foster parents in their new acoustic environment. This helps eliminate the possibility that results are driven by genetic differences between noisy-habitat and quiet-habitat birds, as opposed to the environments themselves. Second, the researchers have been giving the birds unique combinations of number and color bands. This allows them to follow individuals re-nesting within a single season and from one season to the next. Since birds often moved from one type of habitat to another, and since birds in the noisy habitats experienced periodic increases in environmental noise when generator fans kicked on, this means that the scientists could look for both among- and within-individual variations in breeding behavior and reproductive success.

The major finding of the study was that survivorship was significantly lower for chicks raised in noisy environments. Specifically, these juveniles were less likely to survive between hatching and fledging, as well as between fledging and the next breeding season. This is probably at least partly caused by the fact that chicks that were reared in noisy areas had significantly lower body mass at 12 days (just before fledging). This, in turn, was likely driven by lower brood-provisioning rates among noisy-habitat females--something that was seen over both the long term (between breeding attempts at boxes in different types of habitat) and over the short term (between quieter and louder periods within the noisy habitat).

(House sparrow male. Image courtesy of A.W. Birder.)

Other reproductive parameters--including number of eggs, number of chicks, lay date, and number and length of incubation visits--were similar between the two types of site. Likewise, house sparrows settled in both noisy and quiet sites at the same rate, indicating that the former are probably not perceived as being "sub-par." In fact, males in noisy areas were significantly older--a characteristic that is usually associated with dominance and, therefore, occupancy of preferable, higher-quality territories.

Cumulatively, these results provide strong support for the "impaired chick development" hypothesis. At this point, the authors are not able to determine exactly what is impairing chick development, but a likely candidate is the inadequate provisioning rate of sparrow mothers living in noisy habitats. This bad parenting probably doesn't stem from willful neglect, but rather the mothers' inability to hear the begging calls of their offspring. Fathers--in both this and other house sparrow populations--tend to feed their chicks at a constant rate regardless of environmental conditions; thus, it is up to mothers to pick up the slack. Noise seems to interfere with this process, leaving the chicks to go hungry.

 (Female house sparrow feeding nestlings. Image courtesy of Dr. Adam Porter.)

In addition to providing interesting and useful information for avian conservation efforts in general, this study may also have produced some clues vital to solving the mystery of why house sparrows have been declining over much of their native range. Although they are "thought to be well adapted to living in close association with humans, where chronic background noise is pervasive," the current results suggest that even the most human-tolerant of species may have a threshold beyond which it cannot cope with anthropogenic disturbance. Managers may be able to use this information to create sparrow-friendly habitats where the birds can breed in peace--and quiet.

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Schroeder, J., Nakagawa, S., Cleasby, I.R., and Burke, T. 2012. Passerine birds breeding under chronic noise experience reduced fitness. PLoS ONE 7(7):e39200.

Who feeds wild birds?

The rapid disappearance of "large terrestrial land parcels" available for conservation work has led to an increased interest in non-traditional conservation environments--including your own backyard. Cumulatively, household gardens cover an impressive amount of space, so home-based green initiatives can quickly have noticeable impacts on wildlife. In addition to helping individual species, these efforts can also have positive side effects including supporting ecosystem functioning and improving the physical and mental health of human residents.

(Image courtesy of Appletree Garden Designs)

There are many potentially beneficial garden activities, but one of the most popular--and highly advocated by conservation organizations--is bird feeding. Although scientists have been studying the biological impacts of bird feeding for several years, there has been very little work concentrating on the human dimension--until recently, that is. An international group of researchers from Europe and Australia has just published a study investigating which characteristics are most likely to predict bird-feeding behavior. Their main goal in identifying these traits was improving the ability of conservationists to develop effective outreach programs. However, their findings might also be useful for predicting where backyard human-bird interactions are most common--a piece of information that could also be useful for future biological research.

The researchers collected data from two previously conducted government surveys: the Survey of English (SEH) housing, which was distributed across all of the UK; and the CityForm questionnaire, which was distributed in 5 British cities (Edinburgh, Glasgow, Leicester, Oxford, and Sheffield). Respondents provided information not only on their bird feeding activities, but also their sociodemographic characteristics--6 of which the scientists deemed particularly likely to influence bird-feeding behavior: household ownership status, house type, age of resident, number of residents, gross annual household income, and occupation/employment status of the head of house.

(Peach-faced lovebirds eating from a feeder in Arizona, USA. Image courtesy of Wikipedia.)

Across both surveys, the bulk of respondents (>87%) lived in households that had access to outdoor spaces such as gardens, balconies, or rooftop terraces. Only data collected from these individuals formed the basis of further analyses, since residents without outdoor space would obviously be constrained in their ability to feed birds. Within the final sample size, the majority of people reported bird feeding activities, though the exact proportion varied according to survey (64% vs. 53% for SEH vs. CityForm, respectively).

Both surveys highlighted the importance of 3 major socioeconomic factors in participation in bird-feeding activities: type of house, age of householder, and household size. Specifically, feeding was increasingly common as houses were increasingly "detached"--in other words, in stand-alone homes rather than apartments or townhouses. As has previously been found in other studies, bird feeding was also more common among older residents; according to the SEH, the age effect leveled off at 55 years, but according to the CityForm questionnaire this plateau did not occur until 65 years. Finally, bird feeding was also more common in larger households--probably because they are more likely to contain at least one person interested in engaging with wildlife.

(Image courtesy of inhabitat.)

The CityForm dataset also provided insights into the regularity of bird feeding. The researchers were surprised to find that only 64% of bird feeders (or 29% of all households with outdoor space) provided bird food on a regular basis. Even more surprising was that this behavior was more common in poorer households than wealthier ones, despite the costs associated with purchasing bird food. The results of this analysis also revealed that older residents (>65 years) were more likely to engage in regular bird-feeding.

Judging from data collected in previous studies, Brits are more likely than either Americans or Australians to feed birds. However, the current study also highlighted the fact that "bird feeding, though prevalent, is...an infrequent activity." This was an unexpected finding given the number of environmental and conservation organizations advocating this type of "wildlife gardening" behavior. The researchers point out that their results may help conservationists improve these statistics. Specifically, environmental groups might focus on outreach efforts aimed at low-activity groups (e.g., younger residents or those with higher income levels) in order to raise everyone's participation to similar levels, or they might focus on high-activity groups (e.g., older residents and those in detached homes) in order to achieve the greatest participation gains with the least amount of effort.

(In the US, high densities of avian visitors to bird feeders may have helped encourage the spread of conjunctivitis. Researchers recommend regular cleaning of feeders to reduce the risk of disease transmission. Image courtesy of the Cornell Lab of Ornithology.)

The authors are quick to point out, however, that we might want to hold off on widespread increases in bird feeding until we improve our understanding of its ecological impacts: Although many studies have found that feeding efforts increase the abundance, condition, and productivity of wild birds, there are also reports that artificial food sources encourage the spread of disease, reduce diet quality, and facilitate predation (by house cats and opportunistic urban hawks, for instance). Further studies are needed to see whether the potential benefits of this "green" behavior outweigh the possible drawbacks.

For now, though, the current study reveals that it is relatively easy to use survey or census data to perform a quick-and-dirty assessment of human engagement with the natural environment. Use of this technique may help conservation organizations "successfully...promote public participation in wildlife gardening specifically and environmentally beneficial behaviour in society more generally."

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Davies, Z.G., Fuller, R.A., Dallimer, M., Loram, A., and Gaston, K.J. 2012. Household factors influencing participation in bird feeding activity: a national scale analysis. PLoS ONE 7(6):e39692.

Note: Apologies for my very long absence from Anthrophysis. I have been traveling and book-writing this summer, and it has not left much extra time for blogging. Hopefully things will pick up more from now on. Thanks for sticking with me!