Determinants of tree species preference for foraging by insectivorous birds in a novel Prosopis–Leucaena woodland in Puerto Rico: the role of foliage palatability

The foliage palatability hypothesis predicts that avian insectivores will preferentially forage in tree species with the greatest abundance of their arthropod prey, which in turn are associated with the tree’s foliage nutrition and palatability. We tested this hypothesis in a novel Prosopis–Leucaena woodland in Puerto Rico by determining foraging preferences of five insectivorous bird species for six tree species (five alien, one native) and relating preferences to foliage arthropod biomass and leaf chemistry. The most frequently preferred tree species for foraging were the alien Prosopis juliflora (preferred by five bird species) and Pithecellobium dulce (preferred by four bird species). Both species had high foliage arthropod biomass, high N content, low lignin/N ratios, and low hemicellulose content. Compounds, previously known to affect herbivore responses to Albizia lebbeck and Leucaena leucocephala, may explain low arthropod biomass despite high N content in Albizia and avoidance of Leucaena by four bird species despite its high arthropod biomass. The native Bucida buceras had tough leaves with low N content, low arthropod biomass, and only one bird species showed a weak preference for foraging in it. Biomass of predaceous arthropods showed strong negative correlations with the ratios of lignin/N and hemicellulose/N. Some alien tree species had highly palatable foliage with high arthropod biomass and hence were preferred for foraging by avian insectivores as predicted by the foliage palatability hypothesis. High foliage palatability of some alien tree species may weaken the effect of enemy release in some novel plant communities.     

Bat and bird diversity along independent gradients of latitude and tree composition in European forests

Species assemblages are shaped by local and continental-scale processes that are seldom investigated together, due to the lack of surveys along independent gradients of latitude and habitat types. Our study investigated changes in the effects of forest composition and structure on bat and bird diversity across Europe. We compared the taxonomic and functional diversity of bat and bird assemblages in 209 mature forest plots spread along gradients of forest composition and vertical structure, replicated in 6 regions spanning from the Mediterranean to the boreal biomes. Species richness and functional evenness of both bat and bird communities were affected by the interactions between latitude and forest composition and structure. Bat and bird species richness increased with broadleaved tree cover in temperate and especially in boreal regions but not in the Mediterranean where they increased with conifer abundance. Bat species richness was lower in forests with smaller trees and denser understorey only in northern regions. Bird species richness was not affected by forest structure. Bird functional evenness increased in younger and denser forests. Bat functional evenness was also influenced by interactions between latitude and understorey structure, increasing in temperate forests but decreasing in the Mediterranean. Covariation between bat and bird abundances also shifted across Europe, from negative in southern forests to positive in northern forests. Our results suggest that community assembly processes in bats and birds of European forests are predominantly driven by abundance and accessibility of feeding resources, i.e., insect prey, and their changes across both forest types and latitudes.     

The role of farm structure on bird assemblages around a Kenyan tropical rainforest

Although it is clear that the farmlands neighbouring fragmented forests are utilized by some forest birds, it is not clear how birds in general respond to farmland habitat mosaic. An effort was made to determine how bird density and foraging assemblages were influenced by farm structural characteristics and distance from forest edge. Thirty farms up to a distance of 12 km around Kakamega forest in western Kenya were studied. Farm structure entailed size, hedge volume, habitat heterogeneity, woody plant density, plant diversity and crop cover. Birds were surveyed using line transects and DISTANCE analyses and classified into six feeding guilds and three habitat associations. Size of farms increased away from the forest, as woody plant density, plant diversity, indigenous trees and subsistence crop cover declined. The most important farm structure variable was hedge volume, which enhanced bird species richness, richness of shrub‐land bird species and insectivorous bird density (R = 0.58, P < 0.01). Bird density increased with tree density while indigenous trees were suitable for insectivores and nectarivores. There were very few forest bird encounters. Agricultural practices incorporating maintenance of hedges and sound selection of agroforestry trees can enhance conservation of birds on farmland, though, not significantly for forest species.     

Patch Size and Tree Species Influence the Number and Duration of Bird Visits in Forest Restoration Plots in Southern Costa Rica

Efforts to restore tropical forest in abandoned pasture are likely to be more successful when bird visitation is promoted because birds disperse seeds and eat herbivorous arthropods that damage leaves. Thus, it is critical to understand bird behavior in relation to different restoration strategies. We measured the likelihood of visitation, number of visits, and duration of visits for all birds and for Cherrie's Tanager ( Ramphocelus costaricensis ), a common seed disperser, in five sizes of forest restoration patches planted with four tree species in southern Costa Rica. We predicted that the largest patches, and the tree species with the greatest canopy cover, would be visited most frequently and have the longest visits because we assumed that these patch types had the greatest food resources and the lowest predation risk. We found that birds were more likely to visit large patches and the tree species with the highest canopy cover ( Inga edulis ). Birds visited Inga trees more often and stayed in Inga and Erythrina poeppigiana trees for longer periods of time than in other tree species. We found similar results for Cherrie's Tanagers. Thus, we identified two factors, tree species and patch size, which may be manipulated in restoration projects to increase bird visitation.     

Avian richness and abundance in temperate Danish forests: tree variables important to birds and their conservation

Many studies on avian diversity and forest structure have focused onfiner scale forest variables such as foliage height diversity, foliagediversity, foliage density, vertical distribution of vegetation and horizontalvegetation density. From a conservation and forestry operational point of viewit would be of great interest if tree variables influenced directly by forestrymanagement decisions also had significant influence on avian richness andabundance. The species, age and size of a tree are examples of such treevariables. A great number of studies also have focused on avian diversityindices to reveal relationships with vegetation variables. However, it may bemore appropriate for foresters and conservation officers to operate withrichness and abundance measures directly, because indices complicateinterpretations on the relative importance of the two variables (richness andabundance) constituting the index. Fourteen managed temperate forests in Denmarkwere investigated for avian species richness and abundance and related tomeasures on different tree variables influenced directly by forestry managementdecisions. A rapid assessment method of avian richness and abundance wasemployed. It consisted of point-counts of bird richness and abundance within 1km² of forest. General linear models were tested byanalyses of variance statistics to reveal the tree variables most important toavian richness and abundance. It was found that more old trees, more treespecies and more tree size-classes correlated with more bird species andindividuals. However, some variation in bird richness and abundance was alsorelated to site quality and/or chance colonization. Moreover, it was shown thatthe guild of cavity-nesting birds correlated positively to age of tree stand.The potential number of bird species in Danish forest is similar to that innearly pristine forest in Poland, and much larger than that recorded in any ofthe forests investigated. Together with the results above, this indicates a highpotential for squeezing in more avian species in a higher quality forest from abiodiversity point of view. Modern Danish forestry affects tree variablesinfluenced directly by forestry management decisions. Such tree variables havegreat influence on avian richness and abundance, but simple measures in forestrypractices can be taken to enhance the conservation of bird richness andabundance.     

Foraging behavior of Cerulean Warblers during the breeding and non‐breeding seasons: evidence for the breeding currency hypothesis

Birds require additional resources for raising young, and the breeding currency hypothesis predicts that insectivorous species exploit large soft‐bodied prey during the breeding season, but shift to small, likely hard‐bodied, prey during the non‐breeding season. To test this hypothesis, we examined prey use by Cerulean Warblers (Setophaga cerulea), foliage‐gleaning Nearctic‐Neotropical migrants, during the breeding and non‐breeding seasons. We collected data on foraging behavior during the breeding season (including observations of prey items fed to young) in upland mixed‐oak forest in southeastern Ohio in 2009 and 2010 and, during the non‐breeding season, in shade coffee in the Cordillera de Merida, Venezuela, in 2008–2009. Cerulean Warblers captured 7% more large prey (visible prey extending beyond the bill) during the breeding than the non‐breeding season, but foraged at similar rates during both seasons. Large, soft‐bodied prey appeared to be especially important for feeding young. We found that adults delivered large prey on >50% of provisioning visits to nests and 69% of identifiable large prey fed to nestlings were greenish larvae (likely Lepidoptera or caterpillars) that camouflage against leaves where they would tend to be captured by foliage‐gleaning birds. Availability of specific taxa appeared to influence tree species foraging preferences. As reported by other researchers, we found that Cerulean Warblers selected trees in the genus Carya for foraging and our examination of caterpillar counts from the central Appalachian Mountains (Butler and Strazanac 2000 ) showed that caterpillars with greenish coloration, especially Baileya larvae, may be almost twice as abundant on Carya than Quercus. Our results provide evidence for the breeding currency hypothesis, and highlight the importance of caterpillars to a foliage‐gleaning migrant warbler of conservation concern.     

Estimating the susceptibility of tree species to attack by the gypsy moth, Lymantria dispar

ABSTRACT.

• 1 Numbers of gypsy moth larvae feeding on each of 922 randomly sampled trees in a Quercus—Acer—Fraxinus forest in southwestern Quebec, Canada were counted in 1979 and in 1980 to quantify the larval feeding preferences as observed in the field for eighteen deciduous and one coniferous tree species at the northern range limit of the gypsy moth.
• 2 Both the diameter at breast height (dbh) and the estimated foliage biomass of the sampled trees were used to calculate the relative proportions of foliage represented by each of the nineteen tree species in the forest canopy. With these data on availability and utilization of the tree species by the gypsy moth larvae an Ivlev-type electivity index was used to quantify the larval feeding preferences. These preferences observed in the field define the susceptibility of a tree species to attack by the gypsy moth.
• 3 The feeding preferences calculated using estimated foliage biomass were comparable to the simpler calculation based on dbh (Spearman's rho = 0.79; P= 0.0001). The dbh-based feeding preferences remained almost unchanged in 1979 and 1980 (Spearman's rho = 0.83; P= 0.0001).
• 4 The composite 1979—80, dbh-based feeding preferences show Quercus rubra, Populus grandidentata, Ostrya virginiana, Amelanchier spp. and Acer saccharum were preferentially attacked by gypsy moth. Prunus serotina, Betula lutea, Acer rubrum, A. pensylvanicum, Fraxinus americana, Ulmus rubra, P. pensylvanicum and B. papyrifera were avoided. All nineteen tree species were, however, utilized to at least some degree by gypsy moth larvae.
• 5 These results quantitatively affirm and clarify earlier reports of gypsy moth feeding preferences in North America and Eurasia. The advantages and limitations of using an electivity index to estimate the susceptibility of different tree species to attack by folivores like the gypsy moth are discussed.

     

Foliage-canopy structure and height distribution of woody species in climax forests

The correlation between foliage-canopy structure and vertical woody species distribution was examined in seven climax forests ranging from alpine tree limit to tropical rain forest. Foliage density was measured by two-dimensional canopy tomography using photographs. Both foliage density and the vertical species density (the number of woody species having a maximum height within a vertical 1 m) were high in the upper canopy of warm-temperate and subtropical forests, but they were high at lower stratums in the tropical rain forest. Two variables correlated significantly despite the differences in foliage-canopy structures. In contrast to evergreen broad-leaved forests, a clear correlation could not be detected in northern cool-temperate and sub-alpine forests. A possible reason for species convergence in the foliage dense stratum is that species with maximum height in that stratum may be able to survive in the stratum due to symmetrical crown-to-crown interaction. If the maximum height of dwarf species is less than the foliage dense stratum, it may be difficult to survive in the community. The lack of correlation in northern forests may be due to poor canopy tree flora and a mixture of different life forms (non-sprouting trees and sprouting shrubs).     

The Role of Isolated Trees in Facilitating Tree Seedling Recruitment at a Degraded Sub-Tropical Rainforest Site

Successional development at abandoned farmlands in southern Queensland, formerly occupied by sub-tropical rain forest is centred around scattered, isolated trees. Soil seed banks contain few woody plants and most tree species appear to be recruited from seed dispersed into the site by birds or bats. Scattered, low-growing trees <3 m in height act as the initial focus for the activities of seed-dispersing birds, but this process is accelerated by the development of taller trees> 6 m in height that act as bird perches. The identity of these trees and whether or not they offer a fruit reward appears to matter less than their structure and suitability as a bird perch. The process of seedling recruitment may be accelerated when two or more trees form a cluster. The proportion of seedlings that survive and grow beyond 150 cm in height appears to be very small. Most of those that do can be classed as secondary rather than primary forest species, even though many primary forest species initially colonize the site. These observations were used to develop guidelines to accelerate the recovery of rainforest at degraded sites. The guidelines promote the early establishment of species that are usually poorly dispersed (e.g., large-fruited species), planted in scattered clumps. The guidelines should be suitable for situations where relatively large areas are in need of rehabilitation.     

Bird Assemblage and Visitation Pattern at Fruiting Elmerrillia tsiampaca (Magnoliaceae) Trees in Papua New Guinea

Most tropical trees produce fleshy fruits that attract frugivores that disperse their seeds. Early demography and distribution for these tree species depend on the effects of frugivores and their behavior. Anthropogenic changes that affect frugivore communities could ultimately result in changes in tree distribution and population demography. We studied the frugivore assemblage at 38 fruiting Elmerrillia tsiampaca, a rain forest canopy tree species in Papua New Guinea. Elmerrillia tsiampaca is an important resource for frugivorous birds at our study site because it produces abundant lipid-rich fruits at a time of low fruit availability. We classified avian frugivores into functional disperser groups and quantified visitation rates and behavior at trees during 56 canopy and 35 ground observation periods. We tested predictions derived from other studies of plant–frugivore interactions with this little-studied frugivore assemblage in an undisturbed rain forest. Elmerrillia tsiampaca fruits were consumed by 26 bird species, but most seeds were removed by eight species. The most important visitors (Columbidae, Paradisaeidae and Rhyticeros plicatus) were of a larger size than predicted based on diaspore size. Columbidae efficiently exploited the structurally protected fruit, which was inconsistent with other studies in New Guinea where structurally protected fruits were predominantly consumed by Paradisaeidae. Birds vulnerable to predation foraged for short time periods, consistent with the hypothesis that predator avoidance enhances seed dispersal. We identified seven functional disperser groups, indicating there is little redundancy in disperser groups among the regular and frequent visitors to this tropical rain forest tree species.     

The direct and indirect effects of insectivory by birds in two contrasting Neotropical forests

A goal among community ecologists is to predict when and where trophic cascades occur. For example, several studies have shown that forest birds can limit arthropod abundances on trees, but indirect effects of bird predation (i.e. decreased arthropod damage to trees) are not always observed and their context is not well understood. Because productivity is one factor that is expected to influence trophic cascades, we compared the extent to which birds indirectly limit herbivore damage to trees in two lowland Neotropical forests that differed in seasonality of leaf production and rainfall. We compared the effects of bird predation on local arthropod densities and on damage to foliage through a controlled experiment using bird exclosures in the canopy and understory of two forests. We found that birds decreased local arthropod densities and leaf damage in the canopy of the drier site during periods of high leaf production, but not in the wetter forest where leaf production was low and sporadic throughout the year. Birds had no effect on arthropod abundances and leaf damage in the understory where leaf production and turnover rates were low. In support of these experimental interpretations, although we observed that arthropod densities were similar at the two sites, bird densities and the rate at which birds captured arthropods were greater at the drier, seasonally productive site. The influence of top-down predation by birds in limiting herbivorous insects appears to be conditional and most important when the production and turnover of leaves are comparatively high.Electronic Supplementary Material Supplementary material is available for this article at     

Use of Tropical Dry Forests and Agricultural Areas by Neotropical Bird Communities

Agricultural activities represent a global threat to biodiversity, yet little is known about the relative importance of different agricultural land uses in relation to their wildlife communities. We explored bird community structure, diversity, and composition in a landscape dominated by primary tropical dry forest, and in three agricultural systems (i.e., tree orchards, herbaceous cropfields, cattle pastures) to evaluate the way in which birds use different habitats within the landscape. Tropical dry forests had the highest species richness and community evenness, although the bird community in tree orchards was also relatively species rich and even. Cattle pastures had more bird species than cropfields but both habitats were comparatively species poor with low evenness. Our results are related to habitat structure and the spatial location of sites within the landscape matrix. Based on our observations, we recommend including native tree species within agricultural systems and surrounding areas to provide additional resources for birds. Finally, we suggest promoting natural recruitment of native trees and shrubs within cattle pastures to provide suitable habitat for species that use tropical dry forest plants. Abstract in Spanish is available at http://www.blackwell‐synergy.com/loi/btp .     

Nesting habitat of Warbling Vireos across an elevational gradient in the southern Sierra Nevada

ABSTRACT.   Populations of Warbling Vireos ( Vireo gilvus ) are declining in California, apparently due to low reproductive success. From 1989–2002, I studied the nest-site selection and reproductive success of Warbling Vireos across an elevational gradient in the southern Sierra Nevada. Warbling Vireos regularly nested in upland coniferous forests with few or no deciduous trees, and tree species used by nesting vireos included five species of conifers and four species of deciduous trees. Overall, hardwoods were used more than expected based on their availability, but 69% of all nests were in conifers. Hardwood trees were found only in low and mid-elevation ponderosa pine ( Pinus ponderosa ) and mixed-conifer sites. In low-elevation ponderosa pine habitat, 87% of nests were in hardwoods, with 67% in California black oaks ( Quercus kelloggii ), a species that typically occupies upland sites. In mixed-conifer sites where reproductive success was high, 65% of nests were in incense cedar ( Calocedrus decurrens ) and California black oak was the next most commonly used species. Because fire suppression has likely increased numbers of shade-tolerant tree species like incense cedar, shade-intolerant species like black oaks may have been more important as a nest substrate for vireos in the past. Only conifers were used as nesting substrates at higher elevations. Nest success was greater for Warbling Vireos that nested in tall trees in areas with high basal area. My results suggest that Warbling Vireos in the Sierra Nevada would benefit from management activities that encourage retention and recruitment of California black oaks at lower elevations, and development of stands with large trees, dense foliage, and semi-open canopy throughout their elevation range.     

Patterns of resource use in an assemblage of birds in the canopy of a temperate alluvial forest

In our study, we assessed patterns of resource use in an assemblage of birds by observing their foraging behaviour from a crane in the canopy of a temperate alluvial forest. We selected 12 bird species and addressed seasonal changes in feeding activity during a 2-month period in spring focussing on average staying time and utilisation of crown strata in two tree species, the common oak (Quercus robur) and the sycamore maple (Acer pseudoplatanus). We further examined ecological characteristics of the trees (i. e., crown density) that are likely to influence resource use in birds. The selected birds differed in their preference for the tree species. Most birds preferred common oaks. This preference was probably associated with higher food abundance related to substrate characteristics (i.e., roughness of bark) which offer more microhabitats for arthropods and thus permit higher densities of potential prey. Some bird species switched feeding preferences within the study period from sycamore maples to common oaks in association with tree phenology. We found two main foraging techniques. All birds searched for prey at short distance (≤50 cm) and gleaned food from substrate except the Pied Flycatcher that foraged by hovering and searched over longer distances (>50 cm). Overall, we demonstrate in our study that canopy access with mobile crane systems provides excellent opportunities to observe canopy birds and enables detailed analysis of their foraging behaviour. The main result of our study reveals fine-grained resource partitioning of birds within the canopy as an important factor structuring assemblages, with species-specific and in part also seasonal differences in stratification and substrate use.     

Eucalypt plantings on farms benefit woodland birds in south‐eastern Australia

Abstract Most of the original forest and woodland cover on the western slopes of New South Wales and the northern plains of Victoria has been cleared for agriculture (wheat, sheep and cattle) and what remains is highly fragmented and modified by a long history of disturbance. Over the past three decades, native eucalypt trees and shrubs have been planted extensively in a part of this region to provide a range of environmental benefits. Our aim was to determine the extent to which these plantings could improve biological diversity in agricultural landscapes in south‐eastern Australia and to identify the variables influencing their effectiveness. We sampled birds at 120 sites encompassing the range of available patch sizes, stand ages, floristic and structural conditions, and habitat attributes for revegetated areas and remnants of native vegetation, and we compared these to nearby paddocks. Eucalypt plantings were found to provide significant improvements in bird population density compared with cleared or sparsely treed paddocks, and mixed eucalypt and shrub plantings had similar bird communities to remnant native forest and woodland in the region. Birds displayed a strong response to patch size, with both larger (≥5–20 ha) eucalypt plantings and larger (≥5–20 ha) remnants having more species and more individuals per unit area than smaller (<5 ha) patches of these vegetation types. Older (10–25 years) plantings had more bird species and individuals than young (<10 years) plantings. The distance from remnant forest and woodland (habitat connectivity) appeared to be an important variable influencing bird species richness in eucalypt plantings. The main differences were due to the greater numbers of species classified as woodland‐dependent in the larger‐sized patches of plantings and remnants. Eucalypt plantings provided useful habitat for at least 10 declining woodland‐dependent species, notably for the Speckled Warbler, Red‐capped Robin and Rufous Whistler. The Brown Treecreeper and Dusky Woodswallow appeared to be the species most limited by the extent of remnant forest and woodland in the region. Plantings of all shapes and sizes, especially those larger than 5 ha, have an important role to play in providing habitat for many bird species. Restoration efforts are more likely to be successful if eucalypt plantings are established near existing remnant vegetation.     

Are Replanted Floodplain Forests in Southeastern Australia Providing Bird Biodiversity Benefits?

Revegetation of massively altered landscapes for multiple benefits (including biodiversity and ecological function) has accelerated over the past two decades in southern Australia. However, much of the action has been conducted piecemeal, with little apparent strategy. We consider here replanted woodlands on the floodplain of the Murray River, northern Victoria, Australia. All are small in area (<18 ha) and recent (<30 years) and have been planted with appropriate trees and shrubs. We employed a scoring system devised to rapidly measure bird breeding success and linked these results to in-site and landscape variables. Most bird species using the replantings were those that are tolerant of much disturbed landscapes and of open country. Factors related to breeding success were different for each of the six species for which inferences could be made, indicating that it would be difficult to simultaneously plan for all species. Birds characteristic of the major forest floodplain remnants were poorly represented and there was little evidence of their breeding in the replantings. The value of the replanted sites for birds is marginal at present, although it may be that the sites are still too young to have realized their usefulness for species of conservation concern. We believe that most production landscapes in this region have far too little native vegetation to support the many species that are declining, and more strategic planning is necessary to overcome these deficiencies.     

Ecomorphological relationships in a group of insectivorous birds of temperate forests in winter

We examined the relationships between morphology and foraging behaviour in a group of insectivorous birds wintering in temperate mixed forests in northern Iberia. Using principal components analysis we reduced 11 biometric variables to three major morphological components and 20 foraging categories to four major ecological factors. The relative length of the tarsometatarsus and bill morphology were the most important morphological variables predicting foraging ecology. Birds exploiting distal parts of trees and foliage were generally smaller and had relatively longer tarsometatarsi than those foraging on trunks. Foraging on the ground and branches of medium diameter was associated with bill thickness. Ecomorphological patterns were discernible at the level of substrate use and foraging methods, but bear no relation to selection of tree species or foraging height. Morphology correctly predicted niche breadth and interspecific overlap. In Parus spp. interspecific differences in bill shape could explain 63% of the interspecific segregation according to substrate use (R²= 0.63, p <0.01).     

Bird community composition in an actively managed savanna reserve, importance of vegetation structure and vegetation composition

The mosaic of trees, shrubs and open grassland in mesic African savannas is highly dynamic and strongly influenced by mammal herbivory and fire. We investigated the bird fauna in four different savanna habitats to help assess the impacts of vegetation change on this component of faunal diversity. Birds were censused, plant species were identified and vegetation structure was measured in four different vegetation types (Acacia nilotica woodland, Acacia nigrescens woodland, broadleaf thicket and open grassland) in the Hluhluwe-Umfolozi Park in northern KwaZulu Natal, South Africa. Multivariate ordination analyses were used to determine the relative importance of vegetation structure and floristic composition in defining bird assemblages. The bird communities of the grasslands, the acacia woodlands, and the broadleaf woodlands were clearly separated on the first axis of the detrended canonical correspondence analysis (DCCA). Canopy cover and foliage height diversity (FHD) were strongly correlated with the first axis of DCCA, possibly reflecting a secondary successional series from grassland to woodland, known as bush encroachment. Floristic composition (based on presence–absence data only) seemed to be less important for bird community composition than vegetation structure. The results indicate that changes in vegetation structure, caused by bush encroachment, could cause concomitant changes in bird community composition.     

Foraging habitat shift in the narcissus flycatcher, Ficedula narcissina, due to the response of herbivorous insects to the strengthening defenses of canopy trees

The indirect effect of tree defense on bird foraging habitat via lepidopterous larvae was studied by focusing on phenological changes in each component. The seasonal changes in foraging habitat of the narcissus flycatcher (Ficedula narcissina), the distribution pattern of arthropod populations, and the leaf characteristics related to the defense system against insect herbivores were studied in a cool-temperate deciduous forest in northern Japan. Narcissus flycatchers foraged in the canopy from late May to mid June, on the ground from late June, with lepidopterous larvae being the most preferred prey (about 80% of total prey items), and again in the canopy in July. The biomass of lepidopterous larvae was much more abundant within 3 weeks after budbreak in the canopy in late May, and thereafter decreased rapidly in mid June. By contrast, the larvae were abundant on the forest floor from early to late June. These were mainly caused by their downward migration in early to mid June. After budbreak, the leaf toughness and tannin content of two deciduous tree species (maple and oak) increased, while nitrogen and water content decreased. The strengthening of defense traits of canopy leaves caused changes in the abundance and distribution of the lepidopterous larvae. The foraging habitat of the flycatcher subsequently shifted in response to the changes in abundance and distribution of the lepidopterous larvae. In this study, the evidence of the indirect effects of trees on bird foraging habitat was presented by focusing on the phenological changes in relationships among each component in this three-trophic system.     

Winter bird communities in the northern Negev: species dispersal patterns, habitat use and implications for habitat conservation

Bird habitat conservation may require different management strategies for different seasonal bird assemblages. We studied habitat use by winter birds in forest and scrubland habitat patches in the northern Negev, Israel. Our goal was to assess whether differences in responses to landscape and habitat structure between breeding and non-breeding seasons require changes in future conservation plans that have been suggested for the Negev breeding bird community. We evaluated habitat and area effects on bird abundance and distribution and tested whether species habitat use during winter involves niche shifts. Compared with breeding birds, a larger proportion of winter bird species occupied both scrubland and forest. As in summer, forest bird species responded to habitat structure, whereas scrubland species were associated with both habitat structure and area. Resident birds disperse into habitats in which they were not present during summer. Consequently, for several species, the correlation between bird densities and environmental factors showed a better fit at the landscape rather than at the habitat scale. In addition, rather than niche shift, birds actually extended their niche breadth. Nest site selection may constrain bird distribution into a realized niche, smaller than their fundamental niche. Despite the scale differences in habitat use, the similar species diversity patterns between seasons suggest that both winter and summer birds would benefit from conservation of scrub patches larger than 50 ha, and enrichment of foliage layers within the planted forests.