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To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.anbehav.2007.11.005 Byline: Alex Sansom, Will Cresswell, Jeroen Minderman, Johan Lind Abstract: Animals gain antipredation benefits from being in larger groups through increased probability of predator detection, dilution of individual risk of being attacked and confusion of predators during attack. A further benefit is that individuals in larger groups can decrease the amount of time they spend being vigilant, while maintaining a high probability of predator detection. They may then gain extra time to forage, so increasing overall intake rate. Increasing group size, however, can also increase competition so that intake rates decrease. We investigated whether there was a foraging benefit in redshanks, Tringa totanus, that show the group size decrease in individual vigilance. Intake rates did not change with group size, despite an increase in time spent foraging. Interference competition increased with group size because individuals travelled more to find prey. Redshanks used the extra time available to forage to maintain intake rates under increased competition. Although the group size effect on vigilance did not accrue direct foraging benefits, larger groups formed, conferring other antipredation benefits. Intake rates were maintained because the interference competition was compensated by the benefits of reduced individual vigilance. Author Affiliation: (a) School of Biology, University of St. Andrews, U.K. (a ) School of Biology & Psychology, Newcastle University, U.K. (a ) Department of Zoology, Stockholm University, Sweden Article History: Received 8 June 2007; Revised 6 August 2007; Accepted 13 November 2007 Article Note: (miscellaneous) MS. number: 9411R

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Light pollution is rapidly increasing and can have deleterious effects on biodiversity, yet light types differ in their effect on wildlife. Among the light types used for street lamps, light-emitting diodes (LEDs) are expected to become globally predominant within the next few years., In a large-scale field experiment, we recorded bat activity at 46 street lights for 12 nights each and investigated how the widespread replacement of conventional illuminants by LEDs affects urban bats: we compared bat activity at municipal mercury vapour (MV) street lamps that were replaced by LEDs with control sites that were not changed., Pipistrellus pipistrellus was the most frequently recorded species; it was 45% less active at LEDs than at MV street lamps, but the activity did not depend on illuminance level. Light type did not affect the activity of Pipistrellus nathusii, Pipistrellus pygmaeus or bats in the Nyctalus/Eptesicus/Vespertilio (NEV) group, yet the activity of P. nathusii increased with illuminance level. Bats of the genus Myotis increased activity 4·5-fold at LEDs compared with MV lights, but illuminance level had no effect., Decreased activity of P. pipistrellus, which are considered light tolerant, probably paralleled insect densities around lights. Further, our results suggest that LEDs may be less repelling for light-averse Myotis spp. than MV lights. Accordingly, the transition from conventional lighting techniques to LEDs may greatly alter the anthropogenic impact of artificial light on urban bats and might eventually affect the resilience of urban bat populations., Synthesis and applications. At light-emitting diodes (LEDs), the competitive advantage - the exclusive ability to forage on insect aggregations at lights - is reduced for light-tolerant bats. Thus, the global spread of LED street lamps might lead to a more natural level of competition between light-tolerant and light-averse bats. This effect could be reinforced if the potential advantages of LEDs over conventional illuminants are applied in practice: choice of spectra with relatively little energy in the short wavelength range; reduced spillover by precisely directing light; dimming during low human activity times; and control by motion sensors. Yet, the potential benefits of LEDs could be negated if low costs foster an overall increase in artificial lighting. [ABSTRACT FROM AUTHOR]

Over half of the world's forests are secondary regrowth and support considerable biodiversity. Thinning of these forests is a widespread management practice that can affect forest species, including echolocating bats and their prey., We compared total activity of 11 bat taxa, foraging activity of six bat guilds and biomass of 11 insect orders across four forest thinning categories in managed remnant eucalypt forests in south-eastern Australia: unthinned regrowth, forest thinned recently (0-4 years) and in the medium term (5-10 years) and reference (mature open forest). Thinning had been carried out at large (˜350 ha) spatial scales., Total bat activity was 60% less and foraging activity was 80% less in unthinned regrowth, compared to reference sites, but activity levels were similar among thinned and reference sites. Insect biomass was greatest in unthinned sites, and while bat activity was related to prey biomass, this relationship was weak in unthinned sites. Together, this suggests that forest structure was more important than prey availability or time since thinning in influencing bat activity patterns., Synthesizing our findings with the broader literature on bats and thinning, we found support for a clutter threshold of 1100 stems ha−1, above which bat activity was markedly lower, across two continents (the USA and Australia) and four broad vegetation types (eucalypt, conifer, deciduous and mixed forests)., While elsewhere bats with adaptive traits for open habitats generally respond positively to thinning, in our study, species with traits consistent with clutter tolerance (high call frequency and low wing aspect ratio) had lowest activity levels (up to 22 times) in unthinned regrowth compared to all other forest types., Synthesis and applications. Widespread dense regrowth forest can restrict movement and foraging of bats, even those adapted to clutter. We recommend thinning dense regrowth or plantations to below 1100 stems ha−1 when targeting bat foraging habitat, but effects of thinning on roost habitat and other forest biota require further investigation. [ABSTRACT FROM AUTHOR]

In the pursuit of maximizing agricultural yields and profits, crop management under intensive agriculture has reduced the heterogeneity of crop sward structure within fields. Several farmland bird specialists that nest within arable crops have undergone marked population declines during recent periods of agricultural intensification. Understanding the mechanisms that link crop sward structure to demographic fitness and population change may be important for developing effective conservation solutions., We studied whole-season breeding performance of a declining cereal crop specialist, the corn bunting Emberiza calandra, to test the relationships between crop sward structure and both nest site selection and reproductive output within intensively farmed landscapes. Experimental double-drilling of cereal seed was used to manipulate crop sward structure and explain the observed within-field nest distribution., The density of crop tillers (reproductive cereal stems) was a strong predictor of nest site selection and a disproportionate number of nests occurred close to (15-30 m) crop edges where regular seed sowing overlaps (operational double-drilling) occurred during crop establishment. Nest survival was subject to a strong crop edge effect and re-nesting rate increased with mean tiller density in the surrounding crop., Experimental double-drilling that simulated seed sowing overlaps increased crop tiller density (by 25%) and corn bunting nest density (by 406%) compared to adjacent areas of operational double-drilling. Corn buntings breeding in intensively managed cereal crops therefore place their nests in areas of high tiller density which under normal sowing practice tend to occur close to crop edges where nest survival is low. A simple population model indicated that productivity under conventional, intensive cereal management may be too low to sustain local populations in the absence of immigration. Modern cereal husbandry therefore creates an ecological trap for nesting corn buntings., Synthesis and applications. This study highlights a novel mechanism by which modern cereal crop management lowers the potential reproductive success of a conservation priority species nesting in intensively managed cereal crops. Unavoidable overlapping of cereal seed along crop headlands, close to crop edges, systematically produces patches of dense sward that attract nesting corn buntings. This creates an ecological trap because nests close to crop edges are subject to high predation rates, and this may be linked to the loss of arable weeds elsewhere within crops. When double-drilled strips are intentionally provided adjacent to these areas, nesting preference switches to these strips, suggesting a potential conservation solution. Provision of mid-field double-drilled strips at least 100 m from crop edges, if similarly selected by nesting females, should raise nest survival rates and improve population trends. Such interventions are simple and cheap to implement, unlike most conservation measures in high-value cropping systems. [ABSTRACT FROM AUTHOR]

Maintenance of early successional and open habitats often requires active removal of encroaching vegetation. In many cases, fire or other historically applied methods can no longer maintain or create open or early-successional habitat. In these situations, managers must employ mechanical or chemical treatments to control vegetation and improve habitat quality for wildlife that depend on open habitats., We conducted a large-scale study of tree removal from 2005 to 2011 on 14 grassland sites in central North America. Beginning in the autumn of 2005, shrubs, scattered trees, shelterbelts and woodlots were removed from six of fourteen study sites with cutting and burning treatments. Trees and shrubs accounted for 7-21% of pre-treatment ground cover. We conducted vegetation and bird surveys on each site for one year before and six years after initiating tree removal treatments., Treatments effectively removed larger woody vegetation (>6 m in height), but effects of shrub removal were less consistent due to rapid regrowth. Tree removal sites also experienced reductions in grassy litter as a result of prescribed fires that were used to discourage shrub and tree regrowth., On untreated sites, abundance of all grassland birds declined throughout the study, on average declining by 62%. On tree removal sites, we estimated that grassland bird abundance dropped from 2·04 (birds per count) before treatment to a low of 0·90 in the second year after initiating treatments, but recovered in the final three years of study with a weak, but significant positive response six years after initiating treatment, with an estimated 1·42 birds per count. Waterfowl and wetland birds increased following tree removal, whereas woodland birds, particularly those that nest in cavities, declined on treated sites., Synthesis and applications. Tree removal did appear to improve habitat suitability for grassland birds, but a positive response was weak and delayed, and treatments caused short-term habitat disturbances that significantly reduced abundance of target species. When planning large-scale tree removal, it may be beneficial to allow undisturbed habitat in the surrounding landscape to ameliorate potential short-term displacement of wildlife in early phases of treatment. In addition, managers should expect site recovery to require repeated treatments over multiple years. [ABSTRACT FROM AUTHOR]

Debates about 'land-sparing' and 'land-sharing' strategies for conserving biodiversity in cities provide an overly simplistic characterization of alternate planning options. Increased urbanization manifests in a number of ways and sophisticated analyses of how species respond to urban environments are required before generalizations about the relative merits of either planning strategy should be made., We investigated how insectivorous bats respond to housing density (a measure of urbanization intensity) and a range of habitat variables by modelling the occupancy and activity of 12 species in Melbourne, Australia. In addition to species-level analyses, species were grouped into guilds ('matrix', 'patch' or 'edge' species) depending on their ecomorphology and level of patch-dependency., Housing density (dwellings per hectare: dph) was the dominant explanatory variable of occupancy and activity of most species studied. Site occupancy probabilities of patch and edge species were reduced by half at housing densities of just 1·1-4·5 dph depending on species, while their activity was halved at housing densities of 2·6-10·3 dph. The activity of two matrix species also declined, but at higher housing densities (reducing by half at 4·5-7·9 dph). Patch and edge species responded nonlinearly to tree cover at low housing densities, with peaks in occupancy and activity at 20-60%. This response broke down at medium housing densities, however, as most species were no longer present., Synthesis and applications. Occupancy probability and activity of almost all bat species studied were substantially reduced even at very low housing densities. Increasing tree cover had no positive effect on the occupancy and activity of patch and edge species once medium housing densities were reached. In order for land-sharing strategies to provide good habitat for patch and edge bat species housing densities would need to be so low as to be impractical in most urban planning contexts. By contrast, land-sparing with forested habitat remaining in 20% or more of the landscape could provide positive conservation outcomes for the species modelled here. We discuss the relevance of our findings in planning for conservation of bats and their habitats in other recently established and expanding cities. [ABSTRACT FROM AUTHOR]

1. Mortality caused by power lines is a conservation problem for many vulnerable bird species. Many large species are especially threatened by electrocution as they frequently perch on pylons leading to electrocution that typically causes death. Electrocution mitigation measures have been implemented to protect several species; however, a resulting decrease in mortality due to these measures has not previously been demonstrated at the population scale. 2. In this study, we used data from a long-term capture-recapture programme (combining resightings of live birds and recovery of dead birds) carried out on the French population of the Bonelli's eagle Aquila fasciata from 1990 to 2009 to estimate the impact of the insulation of power lines on key demographic rates. 3. We found that the survival probability of all age classes increased after the insulation of dangerous power lines, due to a decrease in mortality caused by electrocution. This decrease was partially compensated for by an increase in other causes of death. 4. Our findings show that insulation of power lines has a strong positive impact on juveniles and immature birds and a lesser impact on adults. The overall increase in survival due to power line insulation led to a sharp increase in predicted population growth rates (from 0.82 to 0.98), although our findings still suggest that the population is not self-sustaining. Elasticity values indicate that adult survival is the key parameter in the population dynamics of this species, and since adult mortality caused by electrocution seemed close to zero, our ability to act on this parameter is limited. 5. This study demonstrates that insulation of power lines is relevant for the conservation of large bird species at a population scale as it allows the survival rate of all age classes to increase and thus in turn has a strong positive impact on population growth rates. 6. Synthesis and applications. We demonstrated that mortality rates induced by electrocution are considerable and have major consequences for the population viability of birds. We also demonstrated that electrocution mitigation measures can lead to a sharp increase in survival through reducing mortality from electrocution leading to improved population viability. In the light of these results, there is an urgent need that conservationists contact power line stakeholders not only to urge them to generalize retrofitting actions but also, in planning new infrastructure development, to plan for less harmful power lines, since this will be far less costly than developing a posteriori mitigation actions. [ABSTRACT FROM AUTHOR]

A substantial part of the world's land base is dominated by agriculture, and forest habitat often consists of discrete patches of forest and linear woody corridors. These natural components provide habitat for some forest birds, but make conservation of these species difficult. In-field practices applied outside forest patches, such as specific juxtapositions of herbaceous field buffers adjacent to forest habitat, could increase avian diversity contributions of existing forest without creation of additional forest habitat. Our prediction was that herbaceous field buffers would increase bird richness in adjacent forest, and we evaluated four potential mechanisms., We used bird count data from a conservation buffer monitoring programme and hierarchical community models to estimate species richness of forest generalist, forest interior and shrubland (edge) species near forest edges with and without adjacent herbaceous field buffers. We accounted for heterogeneity in detection probabilities and forest cover in surrounding landscapes when estimating species- and guild-level responses., Consistent with the drift fence hypothesis, adjacent herbaceous buffers were associated with a modest increase in richness of forest interior birds in woody corridors, but not in forest blocks. Consistent with resource complementation, adjacent herbaceous buffers were associated with modest increases in richness of shrubland (edge) birds in both woody corridors and forest blocks., Across all species and guilds, adjacent buffers were generally associated with greater abundance (e.g. 28 of 39 species), but these increases were also relatively small and highly variable (i.e. overlapping 95% credible intervals). Corroborating existing research, effects of adjacent herbaceous buffers are likely real, but neither pervasive nor strong., Synthesis and applications. Conservation practices targeted to grassland species often produce measurable conservation benefits for target species. However, biodiversity return for investment would be further increased if targeted practices could be deployed in ways that also produce benefits for non-target species in adjacent habitats. Our results suggest that additional benefits for non-target species using adjacent forest habitat are likely to be modest, so conservation planning should focus on species targeted by the conservation practices and avoidance of potential negative impacts on those species when positive benefits to adjacent habitat are weak or lacking. [ABSTRACT FROM AUTHOR]