Thursday, 30 June 2011

Brazilian marmosets avoid human noise

As profiled in the last post, human noise has become a serious issue for animals that need to communicate in anthropogenic environments. However, vocalizations are not the only behavior that animals may alter in response to noise pollution. Just like people, wildlife may find loud levels of noise to be unpleasant or even physically stressful. Unlike us, they do not have the option of closing the window or wearing ear plugs, but they can relocate to a quieter spot—a behavior that has recently been observed in black-tufted marmosets (Callithrix penicillata) living in the Parque Municipal Américo Renné Giannetti in the Belo Horizonte city center of Minas Gerais, Brazil.

(Black-tufted marmoset, Callithrix penicillata)

Researchers from the Pontificia Universidade Católica de Minas Gerais, the Universidade Federal de Minas Gerais, and the Universidade Federal de São João del Rei Rod studied the marmosets in an effort to investigate, for the first time, how noise might affect use of space in a terrestrial animal species. To do so, they collected ambient noise recordings throughout the approximately 45-acre park; measurements were made at multiple times per day over both weekdays and Sundays, generating noise patterns that reflected the long-term sound environment in the park. In addition to observing which areas of the park the marmosets were using, researchers collected information on how many plant species were available for the herbivorous marmosets to include in their diet. This was an important factor to consider because, under natural conditions, marmosets select their home ranges based on food availability.

(Parque Municipal Américo Renné Giannetti)

Unsurprisingly, the park was loudest at its boundaries, where it was bordered by busy roads. However, when the number of park visitors swelled over the weekend, noise levels increased in the center of the park, and across the park in general. On both weekdays and Sundays, marmosets were found significantly more often in quieter areas, indicating that they were actively avoiding noise. They even chose quieter home ranges when this forced them to utilize habitat with lower food availability. This raises the possibility that, over time, marmosets in noisy environments might have nutritional deficits, possibly leading to poorer body condition, shorter life spans, or lower reproductive success. If they want to improve the lives of their urban marmosets, perhaps the citizens of Minas Gerais can find a way to reduce noise pollution in and around the park, or implement a food supplementation program to improve nutrition in the park's quietest, most-used areas.

Duarte, M.L., Vecci, M.A., Hirsch, A., and Young, R.J. Noisy human neighbours affect where urban monkeys live. Biology Letters. Online advance publication.

Thanks to the following websites for the photos used in this post:


Tuesday, 28 June 2011

Vocal responses of two songbirds to human-generated noise

(Rattlesnake Canyon, New Mexico)
Anyone who has spent any time in a city knows that humans, and human activities, can be loud. This isn't just the case in urban centers, but also in more remote environments--for example, northwest New Mexico's Rattlesnake Canyon Habitat Management Area, which contains natural gas wells that make noise in excess of 95 dB(A)--well past the level that is considered potentially dangerous for employees in noisy occupations.

Just as that noise can prove hazardous for humans, it may also have negative impacts on wildlife, in some surprising ways.
Researchers from the National Evolutionary Synthesis Center, the San Juan Institute of Natural and Cultural Resources, and the University of Colorado, Boulder have investigated the effects of gas well noise on two closely related species of songbird--the plumbeous vireo (Vireo plumbeus), and the grey vireo (Vireo vicinior).

(Plumbeous vireo, Vireo plumbeus)

(Grey vireo, Vireo vicinior)

Males of these species use song to attract potential mates and warn off rivals, so living in a noisy environment where their songs may be "masked" (acoustically obscured by) anthropogenic noise could challenge their ability to maintain a territory (which provides trees to roost in and food to eat) and to acquire a breeding partner. Thus, researchers predicted that habitat occupancy should decrease with increasing levels of gas well noise. However, among birds remaining in the noisier areas, the researches expected to observe some changes to standard song parameters--variations in song pitch, duration, and singing rate--indicating that the birds were attempting to improve their ability to communicate in the midst of noise pollution.

Unexpectedly, numbers of both plumbeous and grey vireos were similar across all habitats surveyed, regardless of noise level. In other words, in contrast to some of the other bird species examined in previous studies, the vireos put up with intense levels of noise in their environment. Both types of bird were found to vary their song parameters with respect to background noise levels, suggesting that perhaps they did not need to relocate because they could mitigate the amount of masking done by the noise. While plumbeous vireos increased their minimum song frequency by over 700 Hz, grey vireos increased their maximum song frequency by over 900 Hz. Plumbeous vireos also sang shorter songs in response to louder ambient noise, while grey vireos sang songs that were nearly 1.5 times longer.

Perhaps the most encouraging interpretation of these results is that at least some species are capable of altering their behaviors in response to potentially damaging human activity. However, it remains to be seen whether these alterations are actually useful--it is possible that the adjustments do not improve the singers' detectability enough to allow them to maintain "normal" relationships with other birds. It is intriguing that two species that are so closely related display such different responses to environmental noise. Unfortunately, that means it may be difficult to extrapolate these results to other species living in other types of noisy environment.

Luckily, this sort of study is currently underway on a variety of species in several countries, meaning that researchers may soon have enough data to identify general patterns that apply to all birds--and perhaps even to other acoustically-communicating animals, as well, including (but not limited to!) insects, mammals, and amphibians.

Francis, Clinton D., Ortega, Catherine P., and Cruz, Alexander. Different behavioural responses to anthropogenic noise by two closely related passerine birds. Biology Letters. Online advance publication.

Thanks to the following websites for the images used in this post: http://www.birdseyeviewgis.com/blog/2011/5/15/a-day-of-hiking-and-birding-after-a-long-week-of-gis.html

Avoidance of anthropogenic habitat by migratory cranes

(Common cranes, Grus grus, in flight.)

People and wildlife often don't mix very well, with the result that shyer animals often actively avoid both humans and human habitats, leaving anthropogenic areas to the bolder, more adaptable species (such as raccoons, crows, or gulls). Researchers from the University of Debrecen, the Hortobagy National Park Directorate, the Finnish Crane Working Group, and the University of Bath recently collaborated on a project to determine whether similar patterns existed among individual common cranes utilizing stopover habitat in Hungary's Hortobagy National Park.

This area is the largest alkaline steppe in Europe and is not only a UNESCO World Heritage Site, but is also protected by the Ramsar Convention. The soil is highly basic and the region is characterized by grassland plains and a lack of trees, with the exception of those found near rivers and lakes; the semi-arid habitat is too dry to support a forest but not quite dry enough to be a desert. While this may not sound too hospitable to humans, it is very inviting to cranes who need a rest while flying from their Finnish breeding territories to their Algerian overwintering grounds.

Hortobagy is surrounded by 18 settlements that are home to anywhere from 1950 to 50,000 inhabitants. In order to measure cranes' tolerance of human presence, the scientists measured proximity of crane roosts to both tarmac roads and human settlements, as well as to human "perturbance," which they defined as the density of roads, settlements, and human population. Between 1985 and 2007, 273 crane chicks had been marked with unique combinations of colored leg rings, allowing researchers to follow the movements of individual birds both within a single migration event and between separate migration events over multiple years (1995-2007).

(A storm gathers over Hortobagy National Park.)

Within a single migration event, individual birds showed distinct preferences for particular types of habitat. The birds appeared to consider both proximity and perturbation when choosing where to go during their visit to Hortobagy; some individuals were consistently willing to settle nearer to people and roads, while others consistently avoided both. These preferences persisted across multiple years of migration, and there is even some evidence that they were influenced by the type of habitat that the cranes experienced in Finland during their "formative" nestling and fledgling stages.

Further work will need to be done to clarify why the cranes act as they do. Are they imprinted to certain levels of human disturbance as juveniles, and then deliberately seek these out later once they are adults? Given that they are in the company of their parents during their first migration, are the cranes simply following in the "footsteps" of Mom and Dad? Or might habitat preference have a genetic component?

It is interesting that the title of this report emphasizes "consistent avoidance" of human disturbance by the cranes, because the statistical analysis is actually geared towards measuring repeatability of any behavior. Thus, while some birds do consistently avoid anthropogenic structures and activities, others are also consistently willing to put up with it--which is an encouraging sign given the amount of habitat change projected for the future. Regardless, these findings clearly indicate that the "personalities" (e.g., bold or shy) of individuals and species are important to keep in mind when making management decisions; further, managers will need to consider conditions over a large geographical scale when developing conservation plans for migratory species.

Vegvari, Z., Zoltan, B., Mustakallio, P., and Szekely, T. Consistent avoidance of human disturbance over large geographical distances by a migratory bird. Biology Letters. Online advance publication.

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