Hunting Grounds Research Articles

The prevalence of American liver fluke Fascioloides magna (Bassi 1875) in red deer from Croatian hunting grounds

From October 2002 till April 2003, 194 feces samples and 28 liver samples of red deer shot in the Republic of Croatia territory were examined to determine the prevalence of Fascioloides magna in this game population. The majority of study samples were obtained from animals originating from the east part of Croatia, and only a minor proportion from animals originating from the central and west parts and littoral of Croatia. F. magna eggs were detected in 67/194 (34.53%) feces samples and F. magna adults in 8/28 (28.57%) liver samples. The majority of invaded red deer originated from the east part of Croatia, Baranya region, where F. magna eggs were found in 64/120 (53.33%) and F. magna adults in 8/15 (53.33%) animals. F. magna eggs were detected in only 3/74 (4.05%) animals originating from the other parts of Croatia.

Evaluation of the eye lens method for age determination in roe deerCapreolus capreolus

Eye lens weight curves were obtained from a sample of 522 male and 171 female free-living roe deerCapreolus capreolus (Linnaeus, 1758), collected during the regular annual harvest 1998/99–2005/06 (May–January) in 12 different field hunting grounds in Vojvodina (North part of Serbia). We found no significant differences in eye lens weight between males and females within the same age class (except age class 1). Thus, the eye lens weight data for both sexes within the same age class were pooled for further analyses. The rate of increase in eye lens weight declined at a relatively early age, but lenses continued to increase in weight through age class 9. However, there was a considerable overlap in ranges of eye lens weights within all age classes, which restricted the usefulness of this method. The estimate precision of the eye lens method in determining age was evaluated by the comparison of “known age” (cementum layer technique) and predicted age (eye lens weight technique). We examined model validity on 78 roe deer not used previously to construct the regression line. The lack of correspondence between the two techniques was evident among individuals within older age classes. The percentage of correctly determined age rapidly declined already from age class 4 (<30%).

Increased hunting effort buffers against vole scarcity in an urban Kestrel Falco tinnunculus population

Capsule In years with low vole abundance birds visited hunting grounds more frequently and for longer. Aims To describe diet composition, hunting behaviour, habitat choice and reproductive success of urban Kestrels during changing vole abundance. Methods For five years, we studied the hunting effort of Kestrels in a medium-sized city during the breeding season. Pitfall traps were used for determining vole abundance. Kestrel diet composition was determined from pellet analyses. The number of eggs and offspring was recorded during at least two consecutive visits for each nest and each breeding stage. Results In contrast to larger European cities, the Common Vole Microtus arvalis was a key part of the Kestrels' diet and did not fluctuate significantly according to vole availability. Reproductive success was quite high and stable throughout years with different vole abundance. In years of low vole abundance, the arrival frequency at hunting grounds and time spent there increased. During years with a low vole population, Kestrels had less hunting success and the rate of successful visits decreased. Therefore, Kestrels probably had to change hunting grounds more frequently. During low vole years Kestrels used less demanding techniques, e.g. perching, despite the lower success of these hunting techniques, to avoid extremely high energetic costs. Conclusions An increase in hunting helps to maintain a proper diet and consequently reproductive success. Vole abundance did not change dramatically during the study period, as reported by studies from western and northern Europe. The proportion of ruderal habitats on the city periphery is higher than in more monotonous farmland habitats. Ruderal habitats can be important when Kestrels look for mammals other than voles, especially during vole scarcity.

Measuring prehistoric mobility strategies based on obsidian geochemical and technological signatures in the Owens Valley, California

We compare the organization of obsidian flaked stone technologies in two different time periods at CA-INY-30, a village site in southern Owens Valley, eastern California. Previous archaeological studies suggest a reorganization in settlement patterns between the Newberry (ca. 3500–1500 BP) and Marana (ca. 650-contact) periods, from a highly mobile to a more residentially sedentary one. New geochemical data, based on laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) analyses of obsidian artifacts associated with discrete house floors, support this basic settlement model, but reveal new detail in how people moved across the landscape and accessed, extracted, reduced and used obsidian resources. In the earlier Newberry period, there is no relationship between flake size and distance-to-source, and the falloff curve relating frequency of obsidian against distance is more gradual, as expected, but contrary to our expectations, source diversity is not higher. These factors suggest extremely high mobility, but also selective extraction of particular sources. Newberry obsidian may have been acquired by groups of hunters who embedded quarrying within long-distance trips to distant hunting grounds, and subsequently transported bifacial cores to base camps. By contrast, Marana patterns show strong relationships between flake size and distance from source and steeper fall-off curves, suggesting groups acquired their obsidian primarily from closer sources, likely via exchange networks. At the same time, geochemical diversity, especially among smaller resharpening flakes, is higher in the Marana period, highlighting the wide-ranging conveyance systems through which obsidian moved.

Roost and hunting site fidelity of female and juvenile Daubenton's bat Myotis daubentonii (Kuhl, 1817) (Chiroptera: Vespertilionidae)

We investigated roosting and hunting site fidelity of Daubenton's bats Myotis daubentonii (Kuhl, 1817) in the Forêt de Soignes, an old-stand forest dominated by 150–200-year-old beeches, during the summers of 2003 and 2004. Roosting behaviour and hunting activity over ponds of adult females and juveniles were monitored using radio-telemetry. Eighteen roosts were located, all in natural cavities. The bats occupied a limited number of trees located in a specific and small roosting area. This roost aggregation was not linked to the distribution of hollow trees. Furthermore, whereas all 11 ponds in the study area were exploited by Daubenton's bats, monitored individuals were limited to two ponds to which they showed high fidelity. These two ponds were not the closest to the roosting area. Overall, these results show that at least for the time we conducted our experiment, female and juvenile Daubenton's bats are highly faithful to specific roosting and hunting grounds.

How Urban KestrelsFalco tinnunculusDivide Their Hunting Grounds: Partitioning or Cohabitation?

The hunting ranges of 34 male urban Kestrels were studied in a small city (40 km2) in S Bohemia (Czech Republic). It was assumed that males from the city center and hunt for voles mainly on the city's outskirts. The males are unable to defend their hunting ranges on the because of aggression on the part of the periphery Kestrels. To counter this, they may either 1) invade the hunting ranges of males or 2) establish their own exclusive hunting ranges. Our data supported the first suggestion. Hunting range size varied greatly, from 0.8 to 25.0 km 2 (7.2 ± 6.9 km 2 ), with large overlaps of between 0.3% and 51.4% (12.5 ± 11.6%). The ranges of city-center males were several times larger than those of the males, and greatly overlapped the ranges of other city center and males. Overlapping of the hunting ranges of males was less extensive. The higher energy costs in terms of flying to distant suitable hunting areas and frequent changes of hunting grounds should decrease the preference for nesting in the city center. Therefore, we suggest that Kestrels derive other advantages from living in the city center (e.g., the high quality of nest sites). Cohabitation, whereby city center males invade the hunting grounds of males, appears to be a more effective strategy than partitioning.

Landscape heterogeneity shapes predation in a newly restored predator–prey system

Because some native ungulates have lived without top predators for generations, it has been uncertain whether runaway predation would occur when predators are newly restored to these systems. We show that landscape features and vegetation, which influence predator detection and capture of prey, shape large-scale patterns of predation in a newly restored predator-prey system. We analysed the spatial distribution of wolf (Canis lupus) predation on elk (Cervus elaphus) on the Northern Range of Yellowstone National Park over 10 consecutive winters. The influence of wolf distribution on kill sites diminished over the course of this study, a result that was likely caused by territorial constraints on wolf distribution. In contrast, landscape factors strongly influenced kill sites, creating distinct hunting grounds and prey refugia. Elk in this newly restored predator-prey system should be able to mediate their risk of predation by movement and habitat selection across a heterogeneous risk landscape.

The Solar Neighborhood. XVIII. Discovery of New Proper-Motion Stars with 0.40" yr-1&gt; μ ≥ 0.18" yr-1between Declinations -90° and -47°

We report 1606 new proper-motion systems in the southern sky (declinations -90° to -47°) with 0.40'' yr-1 > μ ≥ 0.18'' yr-1. This effort is a continuation of the SuperCOSMOS-RECONS (SCR) proper-motion search to lower proper motions than reported in Papers VIII, X, XII, and XV in this series. Distance estimates are presented for the new systems, assuming that all stars are on the main sequence. We find that 31 systems are within 25 pc, including two systems (SCR 0838-5855 and SCR 1826-6542) that we anticipate to be within 10 pc. These new discoveries constitute a more than 10-fold increase in new systems found in the same region of sky searched for systems with μ ≥ 0.40'' yr-1, suggesting a happy hunting ground for new nearby slower proper-motion systems in the region just north (declinations -47° to 0°), much of which has not been rigorously searched during previous efforts.

Bridging native and scientific observations of snowshoe hare habitat restoration after clearcutting to set wildlife habitat management guidelines on Waswanipi Cree land

Large-scale timber harvesting in the northern black spruce forest, on Quebec Cree territory, causes immediate loss of productive wildlife habitat for Cree hunters. Duration of this impact is key information to improve forest management. The objective here was to examine the postharvesting habitat restoration delay for snowshoe hare, a species valuable to Cree hunters, as well as a wildlife indicator of the sapling stage. A minimum threshold for vegetation development was established, at which the return of hare populations is considered acceptable by Cree hunters. To do so, an adaptive approach was used, combining Cree hunter knowledge and biological assessment. Hare populations were monitored in 36 cut blocks, ranging from 0 to 30 years after harvest. Cree hunters were interviewed to determine when a cut block becomes adequate for snaring. The combined analysis of the two knowledge sources indicated that stands that meet the threshold average 4 m in height, 6300 trees/ha in density, and are aged between 13 and 27 years. Current regulation sets this threshold at 3 m in height, regardless of cut block scale, and at 20 years postcut when considering family hunting ground scale, and thus, does not fully meet sustainable resource development objectives.

Motives for Voluntary Wildlife Monitoring in Finnish Hunting Teams

Information about game population states and hunting regulation are important prerequisites in ensuring the sustainability of populations. Voluntary game monitoring has a potential of being an important factor in addition to the monitoring made by professionals. The main method in the monitoring of many game species in Finland is the wildlife triangle scheme (WTS), providing abundance estimates of about 30 species. The WTS is largely carried out by voluntarily participating hunting teams. Regardless of the long traditions in the hunters' monitoring activity and hunting regulation, very little is known about the characteristics of the hunting teams that have been active in the WTS. To gain more insight into the characteristics of the hunting teams at a national and regional scale, we analysed quantitative questionnaire data on various activities of hunting teams collected by the Hunters' Central Organization. A typical team carrying out censuses has a large number of members and large hunting grounds, and its monitoring activity is also associated with the voluntary regulation of the hunting of grouse as well as other management actions. The findings indicate that especially large hunting teams are active in voluntary game monitoring in Finland, but also small groups of motivated individuals can successfully participate in the WTS.

Cover Essay—English Version: The Achuar and “Production Waters”

Land is life for the Achuar people: it is a supermarket, a university, a sacred place, a hospital. Therefore without land there would be no human life, nor any of the other beings who live around us. —Lucas Irar, Achuar leader, Pastaza River, Northern Peru At dawn on October 10, 2006, more than 800 Achuar men, women, and children from 31 communities along the Corrientes River occupied all of Pluspetrol’s installations in Blocks 1AB and 8 in the Northern Peruvian Amazon. Their goal was to put a stop to the dumping of ‘‘production waters’’ into their rivers and streams. More than 180 working oil wells went quiet that morning: more than half of Peru’s oil production stopped. ‘‘Production waters’’ is the term given to the ‘‘water’’ that is pumped up with subsoil fossil fuels. It is the remains of the ancient seas in which the animals lived, whose bodies turned into oil and gas. Production waters have salt concentrations six times greater than our oceans and contain oil, heavy metals, radioactive elements, and treating chemicals (pumped into the well as part of the extraction process). Along the Corrientes, they reach the surface at extremely high temperatures (90 C/194 F). More than a million barrels of production waters are dumped, untreated, into the waterways of Achuar territory each day, as they have been for 35 years. In 2006, a government health study reported that 99% of the population has cadmium blood levels over acceptable limits and 66% has excessive blood lead levels. The Achuar have said for years that their people are sickening and dying of ‘‘new’’ illnesses; they talk of stomach pains, nausea, vomiting, and skin diseases, symptoms surprisingly like the effects of petrol contamination. For years, they have lobbied the government to improve controls on company activities in their territory and to enforce existing legislation. Recent government water quality studies have not found cadmium and lead in the water. In the case of cadmium, the test used is unable to discern the low ‘‘maximum permissible levels’’ recommended by WHO guidelines so it cannot detect if these have been exceeded. This has enabled Pluspetrol and government representatives to continue to wriggle out of their responsibilities. The Achuar number some 15,000 people living in communities on both sides of the Peru–Ecuador border. They live by hunting, fishing, and keeping small cultivated gardens. Human, animal, and vegetable spirits share their land with the ancestral spirits of the Achuar and the guardians of the forest. Water is a defining element of Achuar territory. All their territory is low-lying forest, and has been recognized as a Ramsar Wetland, the Abanico del rio Pastaza. Much of it is flooded for most of the year, particularly the low-lying, palm-filled swamps called achu in Achuar. In their language, their name means ‘‘the people of the swamps.’’ These achu are a crucial part of Achuar hunting grounds; during the fruit season, the palms attract Published online: February 22, 2007 Correspondence to: Lily la Torre Lopez, e-mail: lilylatorre@ungurahui.com EcoHealth 4, 110–114, 2007 DOI: 10.1007/s10393-007-0083-7

Selection of resting sites by the European hare as related to habitat characteristics during agricultural changes

The decline of the European hare Lepus europaeus populations has been shown to be correlated with agricultural intensification, which has caused loss of habitat heterogeneity. We aimed to investigate the diurnal spring habitat selection using Jacobs’ second selection index in an intensively cultivated farmland to reveal how the habitat choice by resting hares was affected by changes in the habitat availability. Clearance counts of hares driven out of known areas were made during an 11-year field investigation within two sectors of a private hunting ground located in the Paris basin (France). The loss of habitat heterogeneity included the disappearance of pastures dedicated to a last remaining sheep farm in the area, the removal of non-cropped areas and field boundaries and the increase of mean field size. Breeding stocks of hare declined during the study. Harrowed fields were always avoided. Pastures, alfalfa fields, thickets and fallow land were selected at the start of our study, whereas the remaining part was avoided at the end. The preference for ploughed fields decreased with the growth of vegetation in the winter-wheat fields. To benefit hares, land management should provide year-round vegetative cover and food from non-cropped areas in intensive arable farms.

QUALITY OF THE RED DEER (CERVUS ELAPHUS) HARVESTED IN HUNTING GROUNDS OF THE BIAŁOWIEŻA PRIMEVAL FOREST

The aim of the present study was to compare the red deer (Cervus elaphus) from the hunting grounds of the Bialowieza Primeval Forest and those from other regions of Poland, as well as to extend our knowledge of the Masurian red deer population. In the hunting grounds of the Bialowieza Primeval Forest, analysed in this study, the mean carcass weight of stags was 121.4 kg and varied within a relatively wide range. Stags with ten- and eight point- antlers were the most common (30% and 26%, respectively). The largest stag harvested had an 18-point antlers. The average carcass weight of hinds and calves harvested over the experimental period amounted to about 71 kg and 39.5 kg, respectively. The carcass weight of calves increased in successive months, from 37.5 kg in October to 41 kg in February.

The restoration of El Partido stream watershed (Doñana Natural Park): A multiscale, interdisciplinary approach

1800 ha of El Partido stream watershed, SW Spain, have been purchased by the Spanish Ministry of Environment to enlarge Doñana National Park. Prior to incorporation, a functional restoration will be carried out. El Partido stream is building a depositional sandy delta on Doñana Marsh (now ca. 400 ha) with little or no vegetation. Restoration Project envisages: - Building a hydraulic scheme favoring sand deposition upriver avoiding its transfer to the Marsh. - Restoring natural ecosystems previously existing in the area. The restoration project was divided into phases. First phase (342 ha) was based on self-organization of plant communities (self-design) during succession. Existing remnants of woody vegetation covering about 7.66 ha (2.2%) will be restored, adding about a three-fold surface (26.8 ha, 7.8%) of new plantations. Also, 545 new vegetation patches, initially covering 20.53 ha (about 6% of the area) will be planted, following composition and structure of the natural shrubbery. Each patch combines 5–10 perennial species: a core of a few trees, an inner area with some fruit–bearing scrub and the outer fringe with flower–bearing scrub. River banks will also be vegetated. Patch vegetation will attract insects and vertebrates (mostly birds), the latter eventually performing as dispersers of seeds, thus expanding the shrubbery. Finally, the restored area will provide the menaced Imperial eagle and Iberian lynx an appropriate hunting ground.

Foraging in the fallows: Hunting patterns across a successional continuum in the Peruvian Amazon

Studies comparing hunting between secondary and mature forests are critical to understanding secondary forests’ potential as sustainable hunting grounds. I examined hunting across a successional continuum by surveying 67 households in three communities near the Cordillera Azul National Park, Peru, and analyzing the potential for sustainable hunting. Ninety-nine percent of households surveyed went hunting during the six-month study. Ninety-one species were recorded from seven vertebrate and invertebrate classes, with mammals the most hunted. Five percent of extraction events were species of concern on IUCN’s Red List. Households extracted significantly more, in terms of number of species, number of collection events, and biomass, from older forests (>20 y) than from young secondary (1–5 y) or old secondary forests (5–20 y). However, when extraction is measured per unit area (kg/km 2 or collection events/km 2), households extracted more wildlife from old secondary forest. Households consumed meat at rates below Amazon regional averages. However, because human population densities are well above carrying capacity, current low harvest rates are likely a relic of past overharvests and do not reflect sustainability. Even if management focuses on source-sink dynamics with buffer zone hunting resupplied by protected area populations, long-term sustainability seems doubtful. As more agricultural clearing converts older forests to fields and fallows, the role of secondary forests in resource management plans will increase. The impact of high human population densities in the region means conservation and development programs should focus more on supplying alternative sources of protein and income and limiting immigration into the area.

Yali's Question: Sugar, Culture, and History (review)

Frederick Errington and Deborah Gewertz, Yali's Question: Sugar, Culture, and History. Chicago: University of Chicago Press, 2004. 319 pp. Why do some peoples have great wealth and power while others have precious little? This, in general terms, is the question Yali, a famous leader in Papua New Guinea, asked biologist Jared Diamond, whose answer became the thesis of his popularly celebrated but anthropologically criticized book, Guns, Germs, and Steel (Diamond 1997). Those who dominate the world, Diamond argued, have had relatively greater access to resources, technologies, and disease resistance through accidents of geography and history. This allowed them advantages over others that eventuated in the patterns of inequality that we see today. In Papua New Guinea, white Europeans arrived with the aid of the material leg-up that was their chance inheritance and, rather than just sharing their wealth and status equally with the black people they met there, they established hierarchical relationships characteristic of the empire-building and capitalism that they espoused. They built local economies based on wage labor, markets, and competition, through which they hoped not only to enrich themselves, but also to develop the country and better the lot of the Melanesians. The behavior produced by the colonists' ideals proved shocking to many native Melanesian peoples, guided by their egalitarian and spiritual worldviews, which naturalized their status and inherent rights to the wealth appearing in their territories. They found the actions of the whites selfish and insulting, and this incongruous and insufferable situation inspired not only Yali's question, but also numerous cargoistic movements, cults, and mindsets that in their turn shocked the white invaders and immigrants-and fascinated ethnographers of Melanesia. Frederick Errington and Deborah Gewertz's book Yali's Question rebuts Diamond's grand theory of how inequalities have been generated-not only between what are more accurately described as pink and brown peoples meeting in 20th century Papua New Guinea, but worldwide over the past 13,000 years. They offer an alternative answer that takes as its beginning point precisely these different cultural assumptions that led Europeans and Melanesians to come into contact and sometimes conflict. The authors do so in the manner of ethnographers, by describing in great detail a group of people converging at a particular place and time, who they have gotten to know well through extended fieldwork. The setting is a sparsely-populated region in the interior of Madang Province, once contested tribal hunting grounds, that within a few decades of first contact became the site of a smoke-belching sugar factory and vast, geometrical cane fields. This book, then, takes on Diamond's scientific theory of world history by way of a rich and particular ethnographic history of the company occupying this site, Ramu Sugar Limited. The book is really about the marvelously different people who, enacting their ideals and ideas, which Errington and Gewertz term narratives, brought this monumental, historical achievement to pass. The company and its surrounding community of Papua New Guinean nationals and expatriates serves as a basis for a case study of how inequalities and unfairness, perceived and actual, can come into being. Pointing to the cultural and ideational complexity and contingency of Ramu Sugar's rise, Errington and Gewertz argue that the material foundations that Diamond identifies as causal of the European colonization and domination of the world are necessary but not sufficient conditions. Their point is this: having the ability and resources needed to dominate others does not automatically compel one to do so. Cultural and historical contingencies influence the desires and motives of individuals in a dizzying array of ways, and it is people's narratives (3) of how life should be lived that set history-making actions into play. …

Southern IRDCs seen with Spitzer/MIPS

AbstractInfrared dark clouds (IRDCs) are generally assumed to be a promising hunting ground for tracing very early stages of massive star formation. Observations with Spitzer are a viable tool to probe their interiors that are still dominated by strong dust extinction even at 8 μm. With Spitzer/MIPS, we have observed several IRDCs at 24 and 70 micron. We generally find weak 24 micron sources within the IRDCs. However, at 70 micron these sources remain weak and thus indicate lower luminosities at the current state of evolution. Indications for internal substructures exist, separating regions with compact IR sources from even more dark regions.

Twisted tori and fluxes: A no go theorem for Lie groups of weak [formula omitted] holonomy

In this paper we prove the theorem that there exists no 7-dimensional Lie group manifold G of weak G 2 holonomy. We actually prove a stronger statement, namely that there exists no 7-dimensional Lie group with positive definite Ricci tensor Ric I J . This result rules out (supersymmetric and non-supersymmetric) Freund–Rubin solutions of M-theory of the form AdS 4 × G and compactifications with non-trivial 4-form fluxes of Englert type on an internal group manifold G . A particular class of such backgrounds which, by our arguments are excluded as bulk supergravity compactifications corresponds to the so-called compactifications on twisted tori, for which G has structure constants τ K I J with vanishing trace τ J I J = 0 . On the other hand our result does not have bearing on warped compactifications of M-theory to four dimensions and/or to compactifications in the presence of localized sources (D-branes, orientifold planes and so forth). Henceforth our result singles out the latter compactifications as the preferred hunting grounds that need to be more systematically explored in relation with all compactification features involving twisted tori.

Factors influencing the sustainability of customary dugong hunting by a remote indigenous community

The sustainability of indigenous customary hunting and fishing in remote areas can be influenced by human factors operating at global as well as regional and local scales because of the hybrid nature and sectoral interactions of the local economic environment. The internationally significant population of dugongs (Dugong dugon or seacow) in Torres Strait between Australia and Papua New Guinea supports an important indigenous fishery. The economic, socio-cultural and environmental factors that influenced hunting activity in 1998 and 1999 by the members of the community of Mabuiag Island were investigated to inform the sustainable management of the fishery. The landed catch during the eight months March to October of 145 dugongs in 1998 and 170 dugongs in 1999 potentially provided the community with an average of 290 g of dugong meat per person per day. Fifty-seven per cent of adult males on the island participated in dugong hunting, but more than half the catch in each year was caught by only two hunters. The probability of at least one person from the community going dugong hunting in 1998 and 1999 was 0.59 ± 0.02 per day. This probability was influenced by local environmental factors, including the abundance of dugongs in the traditional hunting grounds (affected by wind speed, year, season and lunar day) and the size of the commercial crayfish catch (which is influenced by the global market price, as well as local conditions). Although dugong hunting remains a very important part of the islanders’ contemporary culture and customary economy, the capacity to hunt dugongs is facilitated by the ease with which some hunters move between the state, commercial and customary sectors of their local economy. The complexities of the economic, social and cultural environments need to be considered in planning for the sustainable harvesting of threatened species by remote indigenous communities.

BATS MODULATE CALLS FOR INCREASED ACCURACY

Embarking on twilight foraging excursions, bats have only their ears to guide them through cluttered environments. Uttering high-pitched cries and listening for their reflections, bats construct a sonic view of their world. But no two echolocation calls are the same. Marc Holderied, from the University of Erlangen, Germany, explains that each call is optimised for a different circumstance. Cries ranging over a narrow frequency-range are better suited for long-range echolocation, while cries swooping over a wide frequency-range function best for short-range detection. But no one knew whether bats tailored their calls to improve their navigational precision. Holderied and his colleague Otto von Helversen decided to record the positions and signal structures of echolocating bats to see if the bats fine-tuned their calls in response to the obstacles they encounter(p. 1816).Carefully rigging up eight microphones close to the bat's path, Holderied recorded 22 individuals' echolocating cries as the tiny aviators departed their farmhouse colony and followed a hedge to their nearby hunting grounds. But Holderied also wanted to relate the bats' calls to their surroundings, so he surveyed the bats' guiding hedge with a theodolite and laser to reconstruct the hedge's structure.Teaming up with Gareth Jones at the University of Bristol, UK, Holderied calculated the position of each bat relative to the hedge when it squeaked,and the cry's duration to see whether the animal's call length changed as they tracked the hedge. But when he analysed each call's duration, the animal's proximity to the hedge seemed to have no effect. The bats weren't moderating their call length to prevent the outgoing call interfering with the incoming reflection, as he had thought.However, when Holderied analysed each call's bandwidth as the bats progressed along the hedge, there was a strong correlation; when the bats neared the hedge, they increased the bandwidth of their cries. Holderied explains that increasing the bandwidth allows the bats to estimate the distance to near-by objects more accurately.Curious to know if the bats modulated their cries in a systematic way as they followed the hedge's contours, the team decided to calculate each cry's`distance of focus'. Holderied explains that the distance of focus is the distance where the squeaking bat can accurately estimate the position of obstacles; there are always errors in the flying bat's distance measurements if the obstacle is nearer to, or further away, than the distance of focus. Calculating each cry's distance of focus from the squeak's bandwidth and duration, and plotting it as a hemisphere centred on and in front of the bat,Holderied realised that the bats continually adjusted their calls so that the distance of focus skirted the hedge's foliage as they progressed along its length. The bats were continually adapting their calls to follow the hedge with maximum precision.Holderied suspects that echolocating bats are able to select calls with distances of focus that roughly match the location of an object as it looms,freeing the bats from complex echolocation calculations and improving their in-flight precision.