Abundance Of Insectivorous Birds Research Articles

Decomposing drivers in avian insectivory: Large‐scale effects of climate, habitat and bird diversity

AbstractAimClimate is a major driver of large‐scale variability in biodiversity, as a likely result of more intense biotic interactions under warmer conditions. This idea fuelled decades of research on plant‐herbivore interactions, but much less is known about higher‐level trophic interactions. We addressed this research gap by characterizing both bird diversity and avian predation along a climatic gradient at the European scale.LocationEurope.TaxonInsectivorous birds and pedunculate oaks.MethodsWe deployed plasticine caterpillars in 138 oak trees in 47 sites along a 19° latitudinal gradient in Europe to quantify bird insectivory through predation attempts. In addition, we used passive acoustic monitoring to (i) characterize the acoustic diversity of surrounding soundscapes; (ii) approximate bird abundance and activity through passive acoustic recordings; and (iii) infer both taxonomic and functional diversity of insectivorous birds from recordings.ResultsThe functional diversity of insectivorous birds increased with warmer climates. Bird predation increased with forest cover and bird acoustic activity but decreased with mean annual temperature and functional richness of insectivorous birds. Contrary to our predictions, climatic clines in bird predation attempts were not directly mediated by changes in insectivorous bird diversity or acoustic activity, but climate and habitat still had independent effects on predation attempts.Main ConclusionsOur study supports the hypothesis of an increase in the diversity of insectivorous birds towards warmer climates but refutes the idea that an increase in diversity would lead to more predation and advocates for better accounting for activity and abundance of insectivorous birds when studying the large‐scale variation in insect‐tree interactions.

Understorey structural complexity mediated by plantation management as a driver of predation events on potential eucalypt pests

Current forest management aims to reduce the economic and environmental impact of pests on forest ecosystem productivity and to develop sustainable control approaches. The enemies hypothesis states that more diverse plant communities support a greater number and diversity of predators and parasitoids leading to a reduction in pest damage via top-down control. In forests, research on the enemies hypothesis typically focuses on tree species diversity. Here, we modify this hypothesis to determine how structural complexity of the forest understorey, as mediated by management, influences the abundance of predators and predation events on potential forest insect pests. To test this, we studied Eucalyptus sp. plantations managed under two approaches of tree establishment, hypothesising that those managed under the less disturbed system of regrowth (regeneration from clear cut stumps) will have greater vegetation structural complexity, predator abundance and predation events (as an indirect measure of predation rate) than the more disturbed seedling planting system. In six stands of each management type, we measured vegetation understorey layers (ground-, shrub- and sub-canopy cover), predator abundance (insectivorous birds, spider web counts) and predation events (artificial larvae attacks, spider web prey items).Vegetation structural complexity, abundance of insectivorous birds and spider webs, and artificial larvae attacks and web prey items were all greater in the regrowth than in the seedling stands. Path analysis evidenced direct support for our modified enemies hypothesis for birds, the regrowth management with low disturbance levels after clearcutting promotes both predator abundance and predation events via increased vegetation structural complexity. However, for spiders the increase in web abundance and predation events was directly and positively associated with regrowth management, but there was no indirect link via vegetation structural complexity, suggesting other factors driven by forest management are important.Manipulative experiments explicitly exploring the cause-and-effect relationship between predation rates and herbivory rates and consideration of the economic implications of the different approaches are required before changes to management are implemented. Our study agrees with the overarching paradigm in sustainable forest management that promotion of structural complexity will be beneficial to biodiversity, ecosystem function and resilience.

The use of cavity-nesting wild birds as agents of biological control in vineyards of Central Chile

Insectivorous birds provide key ecosystem services for agricultural production, such as biological pest control. However, habitat loss and degradation by agriculture are among the main causes of biodiversity loss globally, including the recent decline in bird populations. Habitat loss has particularly affected insectivorous birds due to the associated decrease in the availability of suitable nesting sites. Our study assessed a tool of ecological intensification to increase insectivorous bird abundance and biological control in vineyards. We evaluated the effects of nest boxes on prey removal by insectivorous birds in five vineyards in central Chile, using a two-year sentinel prey experimental trial. Our results showed significantly more sentinel larvae removal by birds in plots with nest boxes than control plots. Deploying the nest boxes resulted in a 43% higher consumption of sentinel prey. Therefore, we recommend using nest boxes as an environmentally-friendly method to increase native predators and enhance biological control in agricultural fields. This would have the potential to improve biodiversity conservation and maximize crop yields.

Trait-dependent responses of birds and bats to season and dry forest distance in tropical agroforestry

Agricultural expansion and intensification increasingly threaten birds and bats, especially insectivorous species from the tropics. Cacao agroforests in tropical rainforest areas have been shown to support higher bird and bat biodiversity than other land-use systems, but their suitability for tropical dry forest biodiversity remains unclear. We present the first assessment of bird and bat diversity patterns in cacao agroforests inside tropical dry forest landscapes. We investigated the response of bird and bat species richness and abundance to forest distance and season across 12 smallholder, organic cacao agroforests and adjacent tropical dry forests in the Peruvian lowlands of Piura. We found that insectivorous bird abundance and species richness increased with forest distance in the dry but not in the rainy season, indicating the value of cacao agroforests for these birds when resources are scarce in forests. In the case of bats, we observed more species in agroforests with increasing forest distance independent of season, and the abundance of insectivorous species increased along the gradient. Other dietary groups and forest specialists of both taxa did not vary notably across the forest distance gradient. Our findings point to the relevance of cacao agroforests as alternative habitats for insectivorous birds and bats in tropical dry forest landscapes, especially during the dry season. We suggest that the maintenance of wildlife friendly cacao agroforests, parallel to dry forest conservation and restoration, creates win-win situations for both the conservation of tropical dry forest fauna and the maintenance of related ecosystem services from which cacao smallholders may benefit.

Abundance of insects and aerial insectivorous birds in relation to pesticide and fertilizer use

BackgroundThe abundance of insects has decreased considerably during recent decades, resulting in current abundance showing 70–80% reductions in more than 15 studies across temperate climate zones. Dramatic reductions in the abundance of insects are likely to have consequences for other taxa at higher trophic levels such as predators and parasites. Pesticides, fertilizers and agricultural land use are likely candidates accounting for such reductions in the abundance of insects.MethodsHere we surveyed the abundance of flying insects, and the reduction in the abundance of insects as a consequence of intensive reduction in agricultural practice linked to fertilizer use and pesticide use. Finally we demonstrated consistency in abundance of birds among study sites.ResultsWe demonstrated that the use of fertilizers and pesticides had reduced the abundance of insects, with consequences for the abundance of insectivorous bird species such as Barn Swallows (Hirundo rustica), House Martins (Delichon urbicum) and Swifts (Apus apus). Juvenile Barn Swallows were negatively affected by the reduced abundance of insects and hence the reproductive success of insectivorous bird species. These effects imply that the abundance of insects could be reduced by the availability of insect food.ConclusionsThese effects of intensive agriculture on insect food abundance are likely to have negative impacts on populations of insects and their avian predators. This hypothesis was validated by a reduction in the abundance of insects, linked to an increase in the abundance of fertilizers and a general change in farming practice.

Pest-removal services provided by birds on subsistence farms in south-eastern Nigeria.

To what extent birds provide the ecosystem service of pest control in subsistence farms, and how this service might depend on retained natural habitats near farmlands is unexplored in West Africa. To fill this knowledge gap, we placed plasticine mimics of insect pests on experimentally grown crops on the Mambilla Plateau, South Eastern Nigeria. We recorded bird attacks on the mimics and the proportion of mimics removed by birds. We also determined the influence of distance of crops from forest fragments on both attack and removal rates. We placed 90 potted plants of groundnut (Arachis hypogea) and bambara nut (Vigna subterranea) along 15 transects running 4.5 km from forest edge into open grassland. Each plant had six of the 540 mimics in total placed on their leaves. We inspected the potted plants weekly for 12 weeks to record (i) the presence of bird beak marks on mimics, and (ii) the number of missing mimics. Once a week we collected all the mimics from the plants and counted the number of assumed beak marks. After counting we replaced the mimics on the plants, mark free. We found a strong positive correlation between the abundance of insectivorous birds and the mean number of missing mimics and/or bird attack marks on mimics. However, this positive effect of insectivorous bird abundance on prey mimic attack/removal became less strong the farther they were from a forest fragment. We found increased predation rates and abundance of insectivorous birds closer to forest fragments. Our data suggest that pest predation may be a key ecosystem service provided by insectivorous birds on Nigerian farmlands. Farmlands that are closer to forest fragments may experience a higher rate of pest control by insectivorous birds than those further away, suggesting that retaining forest fragments in the landscape may enhance pest control services in sub-Saharan subsistence farms.

Lianas maintain insectivorous bird abundance and diversity in a neotropical forest.

The spatial habitat heterogeneity hypothesis posits that habitat complexity increases the abundance and diversity of species. In tropical forests, lianas add substantial habitat heterogeneity and complexity throughout the vertical forest profile, which may maintain animal abundance and diversity. The effects of lianas on tropical animal communities, however, remain poorly understood. We propose that lianas have a positive effect on animals by enhancing habitat complexity. Lianas may have a particularly strong influence on the forest bird community, providing nesting substrate, protection from predators, and nutrition (food). Understory insectivorous birds, which forage for insects that specialize on lianas, may particularly benefit. Alternatively, it is possible that lianas have a negative effect on forest birds by increasing predator abundances and providing arboreal predators with travel routes with easy access to bird nests. We tested the spatial habitat heterogeneity hypothesis on bird abundance and diversity by removing lianas, thus reducing forest complexity, using a large-scale experimental approach in a lowland tropical forest in the Republic of Panama. We found that removing lianas decreased total bird abundance by 78.4% and diversity by 77.4% after 8 months, and by 40.0% and 51.7%, respectively, after 20months. Insectivorous bird abundance and diversity 8 months after liana removal were 91.8% and 89.5% lower, respectively, indicating that lianas positively influence insectivorous birds. The effects of liana removal persisted longer for insectivorous birds than other birds, with 77.3% lower abundance and 76.2% lower diversity after 20months. Liana removal also altered bird community composition, creating two distinct communities in the control and removal plots, with disproportionate effects on insectivores. Our findings demonstrate that lianas have a strong positive influence on the bird community, particularly for insectivorous birds in the forest understory. Lianas may maintain bird abundance and diversity by increasing habitat complexity, habitat heterogeneity, and resource availability.

Landscape composition is more important than local vegetation structure for understory birds in cocoa agroforestry systems

Biodiversity-friendly agricultural systems allow the maintenance of native species even in highly fragmented landscapes by providing corridors to species dispersion and offering supplementary resources for animal populations. In the tropical region, cocoa agroforestry systems are of great importance for biodiversity conservation as they maintain part of the native vegetation, and therefore can be used by the local fauna. In this system, understory of native forests is replaced by cocoa trees, which are shaded by large old-growth trees. However, the persistence of native species in cocoa agroforests depends on local vegetation characteristics but also the landscape structure in which these systems are located. Here, we investigated the influence of landscape composition (i.e. amount of forest cover, cocoa agroforestry and cattle pasture) and local vegetation structure (i.e. number of native and cocoa trees, basal area of native trees and canopy closure) on understory birds in 18 cocoa agroforestry systems located in three regions in the Brazilian Atlantic forest, presenting distinct land use contexts. Specifically, we assessed the effects of these landscape and local features in predicting richness and abundance patterns of the entire community, and also in distinct ecological groups, such as forest-dependent and non-forest-dependent birds, and insectivores, frugivores, and omnivores. Using generalized linear models and Akaike information criterion, we observed lower species richness of complete community, non-forest and omnivorous birds in the most deforested region. Also, our findings demonstrated that cocoa agroforests integrated in more forested landscapes harbor greater richness and abundance of frugivorous birds. Conversely, the increase in cattle pasture amount at the landscape had a harsh effect on all bird groups evaluated. Regarding local vegetation, we observed that the increase of canopy closure leads to greater abundance of insectivorous birds in cocoa agroforestry systems. Similarly, abundance of non-forest species increased in agroforests with higher number of cocoa trees. Our study demonstrated that cocoa agroforestry systems can provide complementary habitats for many species, including forest birds, and therefore can mitigate the effects of habitat loss. However, this key benefit for bird conservation will be more effective when these agroforestry systems are located in more forested landscapes, with low amount of cattle pastures. Our findings therefore reinforce the alarming need to maintain and recover landscape-scale forest amount to ensure species persistence of birds in anthropogenic landscapes, even in those comprising biodiversity-friendly land uses such as cocoa agroforestry systems.

Direct and indirect effects of agricultural practices, landscape complexity and climate on insectivorous birds, pest abundance and damage in olive groves

Pesticides used in agriculture to prevent yield and economic loss are a threat for the natural heritage worldwide. Finding win-win solutions for pest control management in sustainable and profitable agriculture is a current yet elusive challenge for human societies. The main alternative to reduce pest damage in a sustainable manner consists in fostering natural enemies through the extensification of agricultural practices or the promotion of heterogeneous landscapes. However, very few studies have analyzed the combined effects of these components on natural enemies and pests simultaneously.In this work, we fit meta-models (using Piecewise Structural Equation Models) aiming to understand the direct and indirect effects of agricultural management, landscape heterogeneity and climatic variables on insectivorous birds, pest abundance and crop damage. For this, we focus on olive groves, one of the most important woody agroecosystems worldwide, and its two main pest species.We found that management extensification and landscape heterogeneity benefited pest control and supported more insectivorous birds. Also, high temperatures diminished pest damage. Compared to landscape and temperature effects, abundance/richness of insectivorous birds were poor predictors of pest abundance and damage, suggesting that other natural enemies might be currently more important for pest control in olive groves. Lastly, we found a decoupled response of pest abundance and pest damage that may be attributed to insecticide use. This suggests that predation pressure by birds might predict better pest abundance than pest damage in our system.Current predation pressure by birds against pests in olive groves seems very low. Fostering extensive management and landscape heterogeneity increases the abundance of insectivorous birds in this system, potentially enhancing the pest control service.

Landscape heterogeneity and management practices drive habitat preferences of wintering and breeding birds in intensively-managed fruit-tree plantations

Intensively-managed fruit-tree plantations consisting of low-stem trees have progressively replaced traditional high- and mid-stem orchards in Europe during the intensification of agriculture in the second part of the 20th century. Such perennial agricultural systems often form dense, homogeneous landscapes interspersed with open fields, urban areas and semi-natural structures. This observational study investigated the patterns driving landscape- and field-scale habitat preferences of bird communities in landscape units with varying fractions of intensively-managed fruit-tree plantations. At landscape scale, habitat homogeneity, notably a large proportion of fruit-tree plantations, had negative effects on both overall bird species richness and on the abundance of insectivorous birds. A higher proportion of semi-natural features, such as natural woody structures (hedgerows, isolated trees and forest patches) and marshes, positively affected overall bird species richness and abundance as well as insectivorous bird abundance. At field scale, we detected general, trait- and species-specific preferences for older trees during both winter and spring. In winter, leftover fruit is a crucial resource driving field selection by the avifauna. In spring, bird preferences for low and sparse ground vegetation were best explained by increased food accessibility for terrestrially foraging birds. Overall landscape heterogeneity as well as in situ management practices both matter to enhance bird habitat in fruit-tree plantations. Increasing the proportion of diverse semi-natural structures would promote wintering and breeding bird diversity and abundance. At field scale, conditions for birds can be improved by preserving older fruit-tree plantations and by maintaining patches of bare ground and short vegetation in the plantation inter-tree rows. However, given the current high-intensity management in most fruit-tree plantations in our study area, promoting natural features within the wider landscape matrix might represent a more cost-effective solution to enhance bird biodiversity in this agro-ecosystem.

The impact of the Jacques Cartier bridge illumination on the food chain: from insects to predators

Artificial light at night can impact numerous diurnal species by influencing their distribution and habits. In this study, artificial lights placed on the Jacques Cartier bridge in Montreal, Canada were evaluated to determine their impact on insects, insectivorous birds and peregrine falcons. The impact was measured the year the illumination begun and the year following (two years in total). Insect distribution and abundance at three different sites around the bridge was measured. Insectivorous bird abundance and activity were evaluated by observing the cliff swallow as a proxy. Peregrine falcon presence and nesting behavior at the bridge was measured. Insects (aerial and aquatic) were found to be more abundant closer to the illuminated part of the bridge and particularly in the year following the illumination's beginning. Similarly, cliff swallows were more abundant at the bridge the year following the start of the illumination and their activity was more important closer to the illuminated section. Peregrine falcons were only present at the bridge in the year following the beginning of the illumination and specifically at the illuminated part of the bridge. No nesting was detected. These three groups are connected to each other through a food chain in which insect abundance impacts insectivorous bird abundance, which in turn impacts peregrine falcon presence. The illumination therefore positively impacts these three groups separately and together through their food chain. This research highlights the importance of monitoring bird and insect population close to the bridge and further continuation of these observations are necessary to determine if the observed tendency will continue to develop throughout the years.

Bird services and disservices to strawberry farming in Californian agricultural landscapes

Abstract Bird conservation in agricultural settings can be controversial. While some bird species damage some crops, others suppress insect pests. Few studies have simultaneously compared bird services and disservices to assess their net impact. Using an exclusion experiment in six California strawberry farms, we show that bird suppression of berry damage by insect pests (about 3.8% of berries) is similar in magnitude to the damage birds inflict on strawberries (about 3.2% of berries). Across 27 farms, we found that bird species richness and the relative abundance of insectivorous birds increased, while the relative abundance of strawberry‐eating birds and bird damage decreased on farms with more semi‐natural land cover in the surrounding landscapes (1000 m radius). Relative to homogeneous farms, those that implemented diversification practices, such as hedgerows, flower strips or increased crop diversity, had greater bird species richness, total relative abundance, insectivore abundance and strawberry‐eating bird abundance. Synthesis and applications. Conserving semi‐natural land cover in the surrounding landscape benefits bird species richness locally and aids farmers through reduced abundance of strawberry‐eating birds and bird damage. These results highlight the need to consider both the services and disservices of birds when making management decisions.

Insect herbivory and avian insectivory in novel native oak forests: Divergent effects of stand size and connectivity

The value of novel native broadleaf woodlands for biodiversity conservation is important to consider for adequate forest management in rural landscapes. Passive reforestation has been proposed as a cost-efficient tool for creating networks of novel native forest stands that would help restoring biodiversity and associated ecosystem services. Yet to date the ecological functioning of such stands remains strongly understudied compared to forest remnants resulting from longer-term fragmentation. We assessed how the size and connectivity of newly established Pedunculate oak (Quercus robur L.) stands in rural landscapes of SW France affect rates of herbivory by different insect guilds as well as rates of avian insectivory and the abundance and richness of insectivorous birds. Comparing 18 novel forest stands along a gradient of size (0.04–1.15 ha) and cover of broadleaf forests in the surroundings (0–30% within a 500 m radius), we found that even the smallest stands are colonised by leaf miners and chewers/skeletonizers, and that rates of herbivory are globally comparable to those reported from older and larger oak forests. The size of stands had a relatively minor effect on herbivory, whereas it increased the abundance of insectivorous bird. It also determined rates of avian insectivory as estimated by an experiment with plasticine caterpillars. These rates were however rather low and unrelated with the extent of herbivory in the stand. Overall, our study indicates that insect herbivores tend to react more rapidly to the establishment of novel native forests than their avian predators as the latter may depend on the development of larger patches of suitable habitat in the surrounding landscape. To favour a rapid build-up of diverse, and hence stable, trophic networks involving insect herbivores and their predators, woodland creation schemes should therefore primarily focus on habitat size and quality.

Forest loss increases insect herbivory levels in human-altered landscapes

Insect herbivory has been observed to be affected by habitat loss and fragmentation, although the mechanisms by which these anthropogenic disturbances affect this process are not well understood. To aid in clarifying this issue, we assessed the relation between forest cover and leaf damage caused by herbivorous insects on a representative tropical forest understory plant family, the Rubiaceae. We measured leaf area loss of Rubiaceae plants in 20 forest sites located in the Brazilian Atlantic forest, and also tested whether variation in forest cover, abundance of insectivorous birds (predators) and of Rubiaceae plants (resources) could explain the observed variation in leaf damage. Herbivory levels varied between 2.6 and 12.5 percent leaf area lost and increased with decreasing forest cover, whereas the other explanatory variables did not provide additional explanatory power. Therefore, forest loss appears to be the main driver of changes in local herbivory, and ecological processes such as top-down and bottom-up control may not account for the deforestation-related increase in herbivory levels. Other mechanisms, for example leaf quality and/or the influence of the adjoining land uses, have to be explored in future studies.

Combining Taxonomic and Functional Approaches to Unravel the Spatial Distribution of an Amazonian Butterfly Community.

This study investigated the spatial distribution of an Amazonian fruit-feeding butterfly assemblage by linking species taxonomic and functional approaches. We hypothesized that: 1) vegetation richness (i.e., resources) and abundance of insectivorous birds (i.e., predators) should drive changes in butterfly taxonomic composition, 2) larval diet breadth should decrease with increase of plant species richness, 3) small-sized adults should be favored by higher abundance of birds, and 4) communities with eyespot markings should be able to exploit areas with higher predation pressure. Fruit-feeding butterflies were sampled with bait traps and insect nets across 25 km(2) of an Amazonian ombrophilous forest in Brazil. We measured larval diet breadth, adult body size, and wing marking of all butterflies. Our results showed that plant species richness explained most of the variation in butterfly taxonomic turnover. Also, community average diet breadth decreased with increase of plant species richness, which supports our expectations. In contrast, community average body size increased with the abundance of birds, refuting our hypothesis. We detected no influence of environmental gradients on the occurrence of species with eyespot markings. The association between butterfly taxonomic and functional composition points to a mediator role of the functional traits in the environmental filtering of butterflies. The incorporation of the functional approach into the analyses allowed for the detection of relationships that were not observed using a strictly taxonomic perspective and provided an extra insight into comprehending the potential adaptive strategies of butterflies.

Do Collared Peccaries Negatively Impact Understory Insectivorous Rain Forest Birds Indirectly Via Lianas and Vines?

AbstractTropical rain forest understory insectivorous birds are declining, even in large forest reserves, yet the mechanisms remain unclear. Abundant large mammals can reshape forest structure, which degrades foraging microhabitat. We used six sites in Nicaragua, Costa Rica, and Panama with varying collared peccary (Pecari tajacu) density to test three linked hypotheses: (1) locally declining understory insectivores forage preferentially in liana tangles; (2) vine and liana density, cover, and frequency of dense tangles are lower in the presence of abundant collared peccaries; and consequently (3) abundant collared peccaries are associated with reduced understory insectivorous bird abundance. Three insectivores that declined at La Selva preferentially foraged in liana tangles: Checker‐throated Antwren (Epinecrophylla fulviventris), Dot‐winged Antwren (Microrhopias quixensis), and Ruddy‐tailed Flycatcher (Terenotriccus erythrurus). Vine density, liana cover, liana tangle frequency, and forest cover were lower in the presence of collared peccaries relative to experimental mammal exclosures, with the greatest differences at La Selva Biological Station, Costa Rica. Across sites, five of seven vine and liana measures showed negative, curvilinear relationships with peccary densities. Vine and liana measures peaked at sites with intermediate peccary density, and were low at La Selva. Structural equation models suggest negative indirect effects of the collared peccaries on focal bird densities, mediated by vine and liana density, cover, or tangle frequency. Forest area and rainfall affected both lianas and birds, but collared peccaries also contributed to the reduced abundance of understory insectivores. Indirect effects such as that suggested here may occur even in large, protected forest reserves where large mammal communities are changing.

Effects of forest management on bird assemblages in the Bialowieza Forest, Poland

Abstract: We examined the effects of different intensities of forest management on bird communities in the Bialowieza Forest, eastern Poland. Stands that had been managed for more than 100 years (cutting, planting, removal of dead wood) and stands that were partially protected in nature reserves (sporadic sanitary cutting, removal of dead wood until 2008) were compared with unmanaged stands in the Bialowieza National Park by surveying the bird community during three breeding seasons (2010-2012). Surveys were conducted within three forest habitats: spruce-pine (Pino-Quercetum), lime-hornbeam (Tilio-Carpinetum) and ash-alder (Fraxino-Alnetum). Results showed that habitat structure significantly affected the avian community. The basal area of live trees had a positive effect on abundance of birds, while the density of live trees had negative significant effect on bird abundance and species diversity. We also found significantly lower abundance of insectivorous birds and cavity-nesters in managed compared to unmanaged stands. Birds’ assembly in the spruce-pine and ash-alder stands were most sensitive to management. These results show both that management can be used to sustain bird communities, including species of conservation concern, and that inappropriate management may harm them.

Effects of forest edge on pest control service provided by birds in fragmented temperate forests

Controlling herbivorous insects by insectivorous birds is one of the most important regulating services in forest ecosystems. The fragmentation of forests and the associated increase of edge effect, however, influences forest bird communities and thereby may have an impact on biological control via the modification of prey-predator interactions. In the present study we aimed to examine how insectivorous bird abundance and their predation on artificial caterpillars were affected by forest edges and vegetation structure in fragmented temperate forests of southwest Hungary. We found an unexpected negative humpedshaped pattern for predation rate as well as for bird abundance, having peaks both at the edge and in the interior (50 m from the edge). We found a positive correlation between bird abundance and predation rate, therefore the important role of birds in insect pest control was supported. Interestingly, the abundance of insectivorous birds had negative relationships to forest structure variables, such as tree basal area and tree species richness. This unexpected pattern may be a result of the context-dependency of edge effects that cannot be fully explained by our study. It highlights the need for more studies to explore the general pattern of edge effect on insect pest control.

Effects of forest heterogeneity on the efficiency of caterpillar control service provided by birds in temperate oak forests

Controlling herbivore insects by insectivorous birds is a major ecosystem service, nevertheless little is known about how local habitat features and forest management influence the efficiency of this service and about how the pest control service birds provide can be maintained and improved. We conducted an experiment in temperate oak forests in the Mátra Mountains, northern Hungary to measure bird predation rate of artificial caterpillars resembling winter moth (Operophtera brumata L.) larvae, to evaluate the relationships among insectivorous bird communities, caterpillar populations and leaf damage caused by caterpillars and to assess the effect of forest heterogeneity on these processes. We found, that structurally heterogeneous forests maintained a significantly higher abundance of insectivorous birds. Especially the tree size heterogeneity increased bird abundance. The rate of bird predation was positively related to the abundance of insectivorous birds as well as to caterpillar abundance, which indicates that birds were able to respond to caterpillar density. We were not able to demonstrate a direct negative effect of bird predation on caterpillar abundance and a positive effect of caterpillar abundance on leaf damage. Structurally heterogeneous forests, however, suffered from less leaf damage than did homogeneous forests, which result may indicates that the higher activity of insectivorous birds in heterogeneous stands resulted in lower activity of insect herbivores. Thus, we concluded that forest management can contribute to the mitigation of insect damages by maintaining the suitability of forest stands to the insectivorous bird communities through the maintenance of high stand heterogeneity and the presence of some key elements (e.g. retention tree groups, tree diversity, shrub layer).

Effects of Drainage‐Basin Geomorphology on Insectivorous Bird Abundance in Temperate Forests

Interfaces between terrestrial and stream ecosystems often enhance species diversity and population abundance of ecological communities beyond levels that would be expected separately from both the ecosystems. Nevertheless, no study has examined how stream configuration within a watershed influences the population of terrestrial predators at the drainage-basin scale. We examined the habitat and abundance relationships of forest insectivorous birds in eight drainage basins in a cool temperate forest of Japan during spring and summer. Each basin has different drainage-basin geomorphology, such as the density and frequency of stream channels. In spring, when terrestrial arthropod prey biomass is limited, insectivorous birds aggregated in habitats closer to streams, where emerging aquatic prey was abundant. Nevertheless, birds ceased to aggregate around streams in summer because terrestrial prey became plentiful. Watershed-scale analyses showed that drainage basins with longer stream channels per unit area sustained higher densities of insectivorous birds. Moreover, such effects of streams on birds continued from spring through summer, even though birds dispersed out of riparian areas in the summer. Although our data are from only a single year, our findings imply that physical modifications of stream channels may reduce populations of forest birds; thus, they emphasize the importance of landscape-based management approaches that consider both stream and forest ecosystems for watershed biodiversity conservation.