Habitat requirements of passerines and reedbed management in southern France

Reedbeds have high conservation value in Europe. In southern France, they are the major breeding habitat of five passerine species. Yet, habitat management is done primarily by water control to serve socio-economic rather than conservation interests, because we lack information on the species' ecological requirements. Determinants of passerine abundance were assessed through a comparative analysis of water regime, plant structure, and arthropod (food) distribution at 12 sites consisting of at least 10 ha of marsh densely covered with common reed (Phragmites australis). Overall bird abundance estimated through standardised mist netting was positively correlated with food availability (sweep-netted arthropods weighted by their occurrence in birds' diet), which was in turn negatively correlated with duration of ground dryness between June and December. Abundance of four of the five bird species was associated with specific vegetation parameters (reed diameter, dry reed density, growing reed height, etc.), which could be associated with particular management practices, especially with regard to water levels and salinity. Potential impact of socio-economic activities through their water management is addressed, as well as possible ways to minimise these impacts.     

Impact of grassland farming intensification on the breeding ecology of an indicator insectivorous passerine, the Whinchat Saxicola rubetra: Lessons for overall Alpine meadowland management

The decline of insectivorous farmland passerines has been attributed mostly to global decrease in arthropod availability, as a result of intensification of agricultural practices. The diminution of the Alpine Whinchat, once a widespread insectivorous passerine, has been ascribed to nest losses due to earlier and more frequent mowings. However, potential conjugated effects of deteriorated arthropod food availability had yet to be investigated. We compared food supply and nestling diet in intensively vs. traditionally managed grassland. Abundance and diversity of arthropods were much lower in intensive areas, where small-sized invertebrates, which do not enter nestling diet, were also predominant. Parents breeding in intensive habitats fed less biomass to nestlings than adults from traditional habitats. Nestling diet was less diverse and dominated by less profitable prey items in intensive than in traditional habitats. Feeding rate did not differ between the two habitats, but foraging distances from nest tended to be greater in intensive farmland. There were no significant differences in clutch sizes and hatching success with respect to management intensity, but fledging success was higher in traditional habitats. The recent intensification of farming practices has led to a decrease in the availability of grassland invertebrates, and of important Whinchat nestling food in particular, affecting parents’ foraging efficiency and reproductive success. Conservation actions must not only reduce nest losses by postponing mowing, but should also promote grassland farming that is less detrimental to invertebrates. Dominant at the study site, organic grassland farming does seemingly not provide sufficient conditions for Alpine Whinchats.     

Conservation of reed beds and their avifauna in England and Wales

Large mono-dominant stands of Phragmites australis harbour several rare birds in Britain, and their future is threatened both by man's activities and hydroseral processes. A survey in 1979 and 1980 aimed to locate, map and catalogue details of all reed beds in excess of 2 ha in England and Wales. 109 sites were found and their major features, causes of origin and conservation status are outlined. The distribution and habitat requirements of five rare and characteristic breeding birds (bittern, marsh barrier, bearded tit, Savi's warbler and Cetti's warbler) are considered, and other ornithological features outlined. In discussion, the loss of commercial beds and the recent origin of most present day sites is emphasised. A satisfactory number receive some protection as nature reserves, but the scale and cost of the management to improve or merely to maintain them may not yet be fully appreciated. Management should, however, be able to sustain or enlarge populations of birds typically associated with this habitat and there is little reason why new reed beds should not be created.     

Reed harvest and summer drawdown enhance bittern habitat in the Camargue

The vulnerable Eurasian bittern Botaurus stellaris has recently benefited from conservation actions in several European countries. The Camargue in Mediterranean France holds 8000 ha of reed marshes and 50% of the French bittern population estimated at 300-350 booming males. Although reed cutting in Europe is a current practice, we provide the first analyses on habitat selection relative to reed exploitation. The contribution of reed harvesting and water management was assessed at a fine scale (digitized aerial photographs of 50-cm resolution) based on multi-modelling data analyses. GLMs applied to random and bittern points of 50-m radius showed that bitterns preferred areas with less than 10% open water enclosing 1-year reeds. Only in harvested reedbeds had the water management a significant impact on habitat selection, with bitterns avoiding areas dried during less than two months and flooded since less than 8 months. Water edge played a role in non-harvested reeds only, with bittern seeking for areas with the highest ratio water edge to open water. Although reed cutting is generally considered as detrimental in the short term, two 4-year experiments showed a marked increase in bitterns the first spring after cutting was interrupted. Based on these results, we propose various management scenarios that conciliate economic constraints of reed harvesters and protection of Eurasian bittern populations.     

Predator-prey relationships and responses of ungulates and their predators to the establishment of protected areas: A case study of tigers, leopards and their prey in Bardia National Park, Nepal

Interactions among sympatric large predators and their prey and how they respond to conservation measures are poorly known. This study examines predictions concerning the effects of establishing a protected area in Nepal on tigers (Panthera tigris), leopards (Panthera pardus), and their ungulate prey. Within a part of the park, after 22 years the total density of wild ungulates had increased fourfold, to ca. 200 animals/km², almost exclusively due to a remarkable increase in chital deer (Axis axis). Tiger density also increased markedly to nearly 20 animals/100 km², whereas leopard density did not and was ca. 5 animals/100 km². The prediction that grazers should increase more than browsers was only partially supported. The prediction of positive density dependence in prey selection was not supported. Instead, the most abundant species (chital and hog deer, Axis porcinus) were killed less frequently than expected, whereas the lower-density wild boar (Sus scrofa) was preferred. Predictions that (i) initially rare species suffer highest predation was partially supported, that (ii) predation is highest among the most abundant prey was not supported, and that (iii) predation is highest among the most preferred prey independently of their densities was supported. Clearly, the conservation efforts adopted in Bardia were successful, as both tigers and their natural prey base increased. However, the positive numerical response of tigers limited and depressed the abundance of some prey species. Thus, conservation activities aimed at restoring large predators are likely to change in the composition of the overall mammal community, potentially eliminating rare but preferred prey species.     

The evaluation of key sites for breeding waders in lowland Scotland

This study considers the selection of sites based on the densities of breeding waders that would be considered to be distributed widely across common habitats in Scotland: so-called ‘wider countryside’ species. Five methods to provide a hierarchical classification of sites are assessed. Fifty percent of the populations of redshank (Tringa totanus) and snipe (Gallinago gallinago) occur on just 2 and 4.5% of Scottish lowlands, respectively, yet neither are suitably protected by conservation measures and both would benefit from a carefully targeted approach to their conservation. Three species, lapwing (Vanellus vanellus), curlew (Numenius arquata) and oystercatcher (Haematopus ostralegus) are more appropriately considered to be dispersed species. We propose that, if the density of a breeding wader on a site exceeds the threshold level predicted for the top 1% of Scottish lowland for that species, and if the area of the site exceeds 1 km² then that site be considered to be a key site for farmland waders. The minimum density (in pairs km⁻²) must exceed 16.8 for lapwing, 10.1 for oystercatcher, 6.1 for snipe, 7.5 for curlew or 3.6 for redshank.     

Reconciling the dichotomy between single species and ecosystem conservation: black kites (Milvus migrans) and eutrophication in pre-Alpine lakes

In recent times there has been a growing dichotomy between preservation of single species and broader, ecosystem-based approaches to conservation. Freshwater habitats are among the most highly human-impacted ecosystems. We used a long-term data set on black kites (Milvus migrans), a threatened raptor dependent on aquatic habitats, to explore ways to reconcile single species and biodiversity-driven approaches to conservation. In the pre-Alpine lakes of northern Italy, black kite populations showed medium-low density, extremely low breeding success and widespread declines. Spatio-temporal variations showed density and breeding success to be positively related to ecosystem productivity (as estimated by phosphorus concentrations in lakes), availability of aquatic habitats and grassland, and to be negatively related to extent of farmland and fish harvest by professional fishermen. Fish species richness, used as a surrogate of biodiversity, was highest in one oligotrophic lake, but on average increased with increasing ecosystem productivity (i.e. lake eutrophication). Given expected future declines in ecosystem productivity, kite conservation will be helped by enhancing populations of alternative prey in terrestrial habitats (e.g. through incentives for grassland), and higher regulation of fish harvest. On the other hand, ecosystem management may profit from the use of black kites or other aerial piscivores as indicators of biodiversity and of diffuse ecosystem stress, such as sustainability of fishing practices.     

Canopy arthropod communities on Mexican oaks at sites with different disturbance regimes

We examined the effects of forest disturbance and fragmentation on diversity and composition of canopy arthropod fauna in six oak species in central Mexico. Canopy fogging of 54 trees during rainy and dry seasons was conducted on three temperate forests with different levels of disturbance and habitat fragmentation. In total, we found 831 morphospecies belonging to 20 arthropod orders. Diversity of arthropods was higher in the rainy season. Acari, Hymenoptera and Diptera orders dominated during the dry season, and Acari and Collembola during the rainy season. Oak species distributed in sites with lower disturbance had significantly higher arthropod diversity than those distributed in disturbed and fragmented sites. Mean density of arthropod fauna ranged from 47.0 individuals m⁻² in the dry season to 375.5 m⁻² in the rainy season. Forest disturbance and fragmentation reduced the number of arthropod morphospecies and modified the relative abundance of arthropods at order level.     

An unseen foe in arthropod conservation efforts: The case of Wolbachia infections in the Karner blue butterfly

Infection by endosymbiotic bacteria is an underappreciated threat to endangered arthropods with serious implications for captive management programs. We examined the nature of Wolbachia infection in the North American endangered Karner blue butterfly, Lycaeides melissa samuelis, as a case study. Screening for Wolbachia across the range of the species confirmed widespread infection in the western half of the Karner blue’s range. Multilocus sequence typing using six genes confirmed that the infection in the western populations is attributable to a single strain of Wolbachia. This strain was also detected in the closely related Melissa blue butterfly, L. m. melissa, the presumed source of the infection. The infection in the Karner blue butterfly was perfectly correlated with the presence of a foreign mitochondrial DNA variant present in the Melissa blue butterfly, consistent with the hypothesis that the mitochondrial introgression was driven by the spread of Wolbachia. A single individual out of 71 screened from the eastern portion of the range of the Karner blue butterfly was also infected, however this infection was attributable to a different strain. Simulation models of the demographic effects of the spread of Wolbachia infection to uninfected populations and metapopulations suggest that such an infection might further reduce already small population sizes and substantially increase the probability of population extirpation. We discuss threats to other endangered arthropods in the light of this case study and make recommendations for minimizing the impact of endosymbiont infections in conservation plans, especially those including captive propagation and augmentation of endangered arthropod populations.     

Species-specific barrier effects of a motorway on the habitat use of two threatened forest-living bat species

It is generally recognized that roads can adversely affect local animal populations but little is known how roads affect bats. In particular, no study compared the response of bats that differ in foraging ecology to motorways that cut through the breeding habitat. As bats are key species in conservation, such data are urgently needed for designing management plans. Using radio-telemetry, mist netting, and mark-recapture data we investigated the effects of a motorway with heavy traffic on the habitat use of two threatened forest-living bats. We compared barbastelle bats (Barbastella barbastellus), which forage in open space, to Bechstein’s bats (Myotis bechsteinii), which glean prey from the vegetation. Five of six radio-tracked barbastelle bats crossed the motorway during foraging and roost switching, flying through underpasses and directly over the motorway. In contrast, only three of 34 radio-tracked Bechstein’s bats crossed the motorway during foraging, all three using an underpass. Bechstein’s bats, unlike barbastelle bats, never crossed the motorway during roost switching. Moreover, only in Bechstein’s bats individuals foraging close to the motorway had smaller foraging areas than individuals foraging further away, whereas other forest edges had no such effect. Our data show that motorways can restrict habitat accessibility for bats but the effect seems to depend on the species’ foraging ecology and wing morphology. We suggest that motorways have stronger barrier effects on bats that forage close to surfaces than on bats that forage in open space, and discuss the implications of our findings for bat conservation during road construction.     

The impact of reed management on wildlife: A meta-analytical review of European studies

We reviewed European studies on the effect of reed management (harvesting, burning, mowing and grazing) on reedbed wildlife, and in addition, on the performance of re-growing reed (Phragmites australis). Our database consisted of 21 studies conducted on 10 plant species, 17 taxonomic groups of invertebrates and 11 bird species, and published between 1982 and 2006.We found that reed management modifies the structure of re-growing reed stands: reed stems were shorter and denser in managed sites than in unmanaged sites. However, harvesting does not have an impact on aboveground biomass. Plant species richness increased by 90% in managed stands in fresh water marshes, but not in saline water marshes.Overall, reed management had a significant negative impact on invertebrate community, but the duration of management was an important factor determining the magnitude of the effect. Short-term management (1-2 years) had no effect on invertebrates, whereas management for longer period significantly reduced invertebrate abundance. Reed harvesting and burning reduced abundance of passerine birds by about 60%. This was probably associated with food limitation as the numbers of butterflies, beetles and some spiders were reduced. Therefore, the optimal reed management regime to preserve number of birds and invertebrates in reedbeds could be a rotation of short-term management (1-2 years). However, the optimal interval between management applications should be established in future studies.     

The role of introduced mammals and inverse density-dependent predation in the conservation of Hutton's shearwater

This study investigated the impact of stoat Mustela erminea predation on the endangered Hutton's shearwater Puffinus huttoni. Breeding success of Hutton' shearwaters was significantly lower in two seasons of stoat control than in eight seasons with no control: suggesting that natural environmental variation has a greater influence on breeding success than stoat predation. Monitoring Hutton's shearwaters and mainland colonies of sooty shearwaters Puffinus griseus indicated that small colonies suffered higher predation and lower breeding success than large colonies, demonstrating that predation in these two species is inversely density dependent and explaining the low predation rates observed in the very large Hutton's shearwater colonies. The presence of another introduced predator, feral pigs Sus scrofa, within six extinct colonies of Hutton's shearwaters and at the boundaries of the two extant colonies, strongly suggests that this species was responsible for the historic contraction in breeding range. Controlling stoats within the two remaining colonies is unlikely to assist in the conservation of Hutton's shearwater. Conservation efforts would be better spent protecting the two remaining colonies from pigs and in trying to establish new breeding sites.     

Soil microarthropod response to the application of entomopathogenic nematode-killed insects in maize and flower strip habitats

Insects killed by entomopathogenic nematodes (EPN) represent a resource with which soil arthropods can interact. These interactions can be positive for EPN (e.g., arthropods serve as parasitic or phoretic hosts) or negative (e.g., EPN serve as prey). Plant diversity and soil disturbance may influence these interactions. We investigated the effects of maize and flower strip habitats on microarthropod abundance and community composition in soil surrounding greater wax moth larvae, Galleria mellonella, infected with the EPN Steinernema carpocapsae (Sc). In the first year of the experiment (2005), we compared microarthropod communities responding to burial of Sc-killed insects with a control (no soil disturbance). In 2006, we added two control treatments: burial of freezer-killed insects and sham burial. Soil samples (including G. mellonella) were collected 2 and 20 days (2005) or 2 and 12 days (2006) after application. In 2005, arthropod abundance and community composition were similar between maize and flower strip habitats. In 2006, we detected more arthropods in the maize than the flower strips. In both years, community composition differed between treatments providing resources (Sc-killed and freezer-killed insects) and those without (sham burial and no disturbance), with the greatest difference on the final sampling date. Soil surrounding Sc-killed and freezer-killed insects contained more dipterans, acarid mites, staphylinid beetles, onychiurid and entomobryid collembolans, and immature and male mesostigmatid mites than soil at sham burial and no disturbance sites. Most of these taxa are capable of nematophagy; however, EPN relative abundance was not associated with arthropod community composition.     

Integrating environmental conditions and functional life-history traits for riparian arthropod conservation planning

River banks are naturally disturbed habitats, in which local flood events and the landscape structure are expected to govern riparian species assemblages. Not solely effects of flooding per se, but also related changes in vegetation structure will affect species distribution. By elucidating the relationships between species occurrences and multivariate habitat conditions on a restricted spatial scale, insight into conservation strategies to preserve riparian species is gained. Ordination and grouping methods revealed important environmental and functional trait constraints on the composition of predatory riparian arthropods. Mainly flooding disturbance appeared to affect spider and carabid beetle assemblages. Habitat affinity and dispersal ability were retained as important traits explaining similarity between arthropod assemblages. River banks similar in species composition differed in absolute and functional group species richness. Furthermore, Poisson regressions demonstrated the importance of variation in discharge regime, sediment composition and vegetation structure for the preservation of rare riparian arthropods. Xerothermophilic specialists were disfavoured by increased flooding disturbance, whereas hygrophilic species benefited from increased vegetation cover. In contrast to flight-active riparian carabids, occurring throughout the river system, especially cursorial spiders are expected to go extinct under increased anthropogenic alterations of discharge regimes. In general, river restoration should generate the required heterogeneity in environmental conditions (e.g. dynamic processes) at the river bank level, thereby increasing the sustainability of dynamic riverine landscapes and the conservation of vulnerable riparian arthropods. Moreover, we argue that the understanding of functional responses towards environmental factors on a local scale results in general and widely applicable guiding concepts for species conservation and ecosystem management.     

Efficiency of conservation shortcuts: an investigation with otters as umbrella species

The use of shortcuts is widespread in conservation practices to help ensure biodiversity conservation with minimal expenditures. An umbrella species is a species whose conservation confers protection to a large number of naturally co-occurring species. The aim of this study is to test the usefulness of the umbrella species concept for conservation management. As our umbrella, we chose a wide-ranging and flagship species, the European otter (Lutra lutra). Otters are widely distributed predators with numerous genera and species, so otter occurrence could virtually be used as “umbrella” in every freshwater habitat. To test the usefulness of the concept, we investigated whether an umbrella species might protect other species in the long term. We compared (1) bird and amphibian species richness in 1993 and in 2003 on nine sites where otters were monitored for 20 years, and (2) bird, amphibian and mollusc species richness between the previous sites and nine bio-equivalent sites where no otter occurrence has been detected for 20 years. The study was carried out for two spatial scales: total otter home range and core areas (most intensely exploited areas). Our results show that species richness was significantly different between years on sites inhabited by otters. However, we showed that biodiversity did not differ between pairs of bio-equivalent sites inhabited or deserted by otters, whatever the estimation method. Our results cast doubt on the validity of umbrella species use as an objective tool for conservation. However, the keystone functional role that otters could play in ecosystems might be an interesting way to reconsider the purpose of the umbrella species concept.     

The influence of food availability on breeding success of African penguins Spheniscus demersus at Robben Island, South Africa

From 1989 to 2004, the breeding success of African penguins Spheniscus demersus at Robben Island, South Africa was significantly related to estimates of the abundance of both their main prey species, anchovy Engraulis encrasicolus and sardine Sardinops sagax, and to the combined biomass of these species. When the combined spawner biomass of fish prey was less than 2 million ton, pairs fledged an average of 0.46 chicks annually. When it was above 2 million ton, annual breeding success had a mean value of 0.73 chicks per pair. Given previously estimated values of survival and age at first breeding, these levels of breeding success are inadequate to sustain the African penguin population. With the higher level of breeding success, an equilibrium situation might be attained if adult survival could be increased by 6-7% per annum. Attempts to reduce mortality of penguins have included the collection, cleaning and return to the wild of oiled birds, culling of Cape fur seals Arctocephalus pusillus pusillus seen preying on penguins around breeding localities and control of the spread of disease. Management of the purse-seine fishery should ensure adequate escapement of fish to maintain the combined biomass of anchovy and sardine above 2 million ton. The maintenance of suitable breeding habitat and removal of feral predators from breeding localities will also be important in improving breeding success.     

Impact of invasive earthworms on Ixodes scapularis and other litter-dwelling arthropods in hardwood forests,central New York state,USA

Invasive earthworms alter the structure of soils in northern hardwood forests, but the quantitative impacts on litter-dwelling invertebrates are unclear. Litter loss should reduce the habitat space, but nutrient-rich earthworm burrows might provide food resources. We investigated the impact of invasive earthworms on populations of Ixodes scapularis (black-legged ticks) and other litter-dwelling arthropods to determine the impact of a reduced litter environment. We used five pairs of one-hectare sites (earthworm invaded versus reference) within four separate contiguous forests in New York state. The presence of earthworms decreased the density of nymphal I. scapularis by 46.1% and larval I. scapularis by 29.3%. We also observed a dramatic decline in the total abundance of litter-dwelling arthropods with 69.9% of the arthropod population disappearing in the presence of earthworms. Additionally, litter arthropod populations declined disproportionately to leaf litter mass reduction indicating that the quality of the remaining litter material in the earthworm sites was poor. The impact of earthworm invasion on the litter environment and implications for the position of an important disease vector (I. scapularis) within the litter ecosystem are explored.     

A nine-year study of successful breeding in a Bonelli’s eagle population in southeast Spain: a basis for conservation

We analyse the factors influencing breeding success in a healthy population of Bonelli’s eagle (Hieraaetus fasciatus) from south-east Spain, a raptor that has suffered a serious decline in Europe. Between 18 and 33 pairs were annually monitored during the period 1994-2002. Several factors that may affect four breeding parameters were studied, namely human presence, vegetation, relief, climatic factors, intra- and inter-specific relationships, diet, prey abundance, nest building, adult mortality and age of reproduction. A consistently high breeding success was registered during the study period (productivity=1.43, SD=0.11), which was probably the result of high adult survival, adequate prey availability and mild weather conditions. However, a certain vulnerability to the presence of golden eagles (Aquila chrysaetos) and to human disturbance was observed. One interesting result was the reduced survival of young chicks on north-facing cliffs owing to colder conditions, which may partially explain the decline of the Bonelli’s eagle populations along its European distribution limits. We discuss the role of this healthy subpopulation in an Iberian metapopulation context, and propose that the potential interference of golden eagles should be taken into account when designing management strategies for Bonelli’s eagles. Finally, we pinpoint some conservation priorities and the importance of reducing the main causes of adult mortality (i.e. shooting and electrocution) to assure successful reproduction and survival of this species.     

Openness in management: Hands-off vs partial cutting in conservation forests, and the response of beetles

The appropriate management of forest reserves is debated; two major alternatives are succession to ‘wild’ state, or management to produce semi-open stands. For temperate conservation stands, there are no strong experiments replicated at landscape level. In each of 22 forests rich in oaks (Quercus spp.) in Sweden, we set up a closed-canopy wild plot (1 ha), and a cutting plot (1 ha) to produce semi-open conditions, studying them before and after cutting. About 25% of the tree basal area was cut (large trees and dead wood retained) and harvested as bio-fuel, a CO₂ - neutral energy source. We examined the response of beetles and trapped 59,000 individuals (1174 species; 100 red-listed species). For both the guild of herbivorous beetles (222 species) and of saproxylic beetles connected to oak wood (267 species), species richness increased by about 35% in the harvested plots, relative to the wild reference plots. Species composition within the groups changed, though not strongly. Thirteen saproxylic species of 50 analysed, and three herbivores of 12 increased in cutting plots. For red-listed saproxylic beetles, species richness did not change significantly. Regression analyses suggest that more open cutting plots disfavour the red-listed beetles of this forest type. Thus, partial cutting increased species diversity of two beetle groups, probably due to changed microclimate and increase in herbaceous plants, but some red-listed saproxylic beetles may be disfavoured. A hands-off alternative may through storms and other disturbances produce open patches, more dead wood, and favour some species. Combinations of these alternatives, carefully planned at the landscape level, need to be considered.     

Swarming of bats at underground sites in Britain—implications for conservation

We investigated the extent of visitation of underground sites during late summer and autumn (‘swarming’) by bats. Bats were captured at eight cave, mine and tunnel sites in southern England over 6 years (1995-2000). A total of 3077 bats representing 11 of Britain's 16 species was caught. Myotis bats predominated in autumn. At some sites these are rarely seen during winter hibernation counts. Myotis nattereri and M. daubentonii were most common. However, species composition changed seasonally. At one site, M. brandtii dominated early in the season and at all sites peak activity of M. daubentonii was earlier than in M. nattereri. Relatively high numbers of internationally vulnerable species such as M. bechsteinii and Barbastella barbastellus were recorded. There was a strong male bias in captures of swarming species. Swarming probably has an important reproductive function, most males are reproductively active at this time and such sites may be important for outbreeding. Due to this and the large number of individuals and species concerned, the conservation of ‘swarming sites’ is vitally important. Clearly swarming sites merit special consideration in conservation management strategies for cave-dwelling bats.