Tolerance of frugivorous birds to habitat disturbance in a tropical cloud forest

In view of the continued decline in tropical forest cover around the globe, forest restoration has become a key tool in tropical rainforest conservation. One of the main - and least expensive - restoration strategies is natural forest regeneration. By aiding forest seed influx both into disturbed and undisturbed habitats, frugivorous birds facilitate forest regeneration. This study focuses on the tolerance of a frugivorous bird community to anthropogenic habitat disturbance within the broader context of natural forest regeneration with conservation purposes. It was carried out in the tropical cloud forest of Costa Rica’s Talamanca Mountains. Bird community response and tolerance to habitat disturbance was assessed by comparing bird presence and densities along a disturbance gradient, ranging from open pastures to closed mature forests. Birds were censused along nine transects applying the variable width line transect procedure. Forty relevant frugivorous bird species were observed during 102 h of survey time. Densities were calculated for 33 species; nine species responded negatively to increasing level of disturbance and nine others positively. Results indicate that large frugivores are generally moderately tolerant to intermediate, but intolerant to severe habitat disturbance, and that tolerance is often higher for medium and small frugivores. It appears that moderately disturbed habitats in tropical cloud forests are highly suitable for restoration through natural regeneration aided by frugivorous birds. Due to a lack of large forest seed dispersers, severely disturbed habitats appear less suitable.     

Diversity and structure of the bird community overwintering in the Himalayan subalpine zone: is conservation compatible with tourism?

In this paper data on the bird community overwintering in the subalpine zone of Sagarmatha National Park (Khumbu Himal area, Nepal) are presented, with particular emphasis on habitat structure and bird-habitat relationships. The impact of land use and management on the conservation of diversity is analysed and discussed. Four habitat types were considered: mixed forest, pure juniper forest, dwarf rhododendron shrubbery and cultivations. Mixed forest supports the richest avifauna, but forest birds are sensitive to over-exploitation of their habitat: bird density, species richness and diversity are significantly lower in heavily utilised forest. Here, the lower density of rhododendrons, firs and birches, together with their younger age, seem to be unattractive to insectivorous gleaners and granivores, which prefer tree- and understorey-rich spots of unutilised forest. Terraced cultivations also are a rich habitat for wintering birds, and traditional cultivations with hedgerows and scattered bushes have a great potential for bird conservation. Juniper woods are important habitats mainly for frugivores, whereas dwarf rhododendron shrubberies support the poorest avifauna. This study emphasises that forest birds and habitats are severely threatened. As deforestation is the consequence of the tourist pressure for fuelwood along the trekking route to Mt. Everest Base Camp, a strict regulation of tourist-related developments is essential to preserve biodiversity and manage land uses within sustainability.     

The role of remnant trees in seed dispersal through the matrix: Being alone is not always so sad

Remnant trees within the non-forest matrix are common structures of forest landscapes which have high conservation value due to their supposed roles as biological legacies and stepping stones in fragmented forest scenarios. Fleshy-fruited remnant trees are dispersal foci for many forest plants, as seeds accumulate under their canopies after visitation by forest frugivores. Despite this recognized effect, little is known about the relative role of remnant trees in maintaining their seed dispersal function after forest fragmentation. In this work, conducted in the Cantabrian Range (Northern Spain), seed deposition by frugivorous birds and post-dispersal seed predation by rodents were compared beneath the canopies of hawthorn (Crataegus monogyna) trees scattered in the non-forested matrix, to those embedded in forest patches. We studied two years which had strong differences in community-wide fruit abundance (high in 2004, and low in 2005). Hawthorn and holly (Ilex aquifolium) seeds dominated the seed rain. The density of dispersed seeds differed between years and tree type, with higher values under patch trees relative to remnant ones. However, the effect of tree type depended on both the year and the seed species, as larger differences were found in the year of high fruit availability, and with holly seeds. Higher levels of post-dispersal seed predation on holly seeds also contributed to offset the differences between tree types. Our results suggest that remnant trees, by functioning as dispersal foci, facilitate the dispersal of the two most abundant plant species for forest succession through the matrix. More importantly, we demonstrated that in years of low fruit availability in which forest frugivores are forced to exploit scattered fruit resources, the role of remnant trees may even be equivalent to that played by forest trees.     

The value of primary, secondary and plantation forests for Amazonian birds

Secondary forests and exotic tree plantations are rapidly expanding across tropical landscapes, yet we currently have a very poor understanding of the value of these human-dominated forest landscapes for biodiversity conservation. Mist netting, point counts and transect walks were used to compare the bird communities of these habitats and neighboring primary forest in north-east Brazilian Amazonia. The extensive spatial scale of plantations and second-growth in our study area enabled us to implement a robust replicated design, with survey plots approximately two to three orders of magnitude larger than most previous studies of land-use change in the tropics, thus minimising the influence of the surrounding landscape. Species richness was highest in primary forest and lowest in Eucalyptus plantations, and community turnover between habitats was very high whether based upon matrices of relative abundance or species presence-absence data, and for both point count and mist net data. Monthly line-transect censuses conducted over an annual cycle showed an increase in the detection of canopy frugivores and seed predators during the peak of flower and fruit availability in primary forest, but failed to suggest that second-growth or Eucalyptus stands provide suitable foraging habitat at any time of the year. The conservation value of both secondary forest and plantations was low compared to conclusions from previous studies. Our results indicate that while large-scale reforestation of degraded land can increase regional levels of diversity, it is unlikely to conserve most primary forest species, such as understorey insectivores and canopy frugivores.     

Protected areas do not fulfil the wintering habitat needs of the trans-Saharan migratory Montagu’s harrier

Populations of migratory birds can be affected by events happening at both breeding and wintering grounds. The Sahel is a vast region holding a large number of wintering trans-Saharan migratory European birds, and current land-use changes there may represent a threat for these species. We used satellite tracking data from the migratory Montagu’s harrier to evaluate habitat use of the species during the wintering season, and whether the current network of protected areas is effective to provide their habitat needs during that season. We also developed an ecological niche model for the species in Western-Central Sahel to check if the most suitable sites are included within current protected areas. Tracked harriers occupied a large region encompassing a total of eight countries. The most preferred habitats during winter were croplands and some natural vegetation habitats, especially grasslands. Protected areas only covered a small proportion of the overall wintering grounds of tracked harriers and the most suitable areas for the species in Western-Central Sahel. Increasing the extent of preferred natural habitats within protected areas should benefit the conservation of this and probably other insect-eating raptors. However, substantial increases in extent and number of protected areas in sub-Saharan Africa are very unlike to occur. Conservation actions in the region should therefore be mostly focused on improving land use planning and management outside protected areas, specially enhancing agricultural practices to make biodiversity conservation compatible with poverty alleviation. These can be chiefly targeted at an area of <20,000 km² of very suitable habitat for these species.     

Bird conservation in fragmented Mediterranean forests of Spain: effects of geographical location, habitat and landscape degradation

The effects of habitat fragmentation on forest bird assemblages were analysed in 214 holm oak (Quercus ilex) remnants spread across the northern and southern plateaux of central Spain. Bird richness was highly dependent on fragment area for all species regardless of isolation, and barely affected by habitat traits. Geographical location was associated with high differences in richness of bird assemblages, which included 17 species exclusive to northern remnants and one exclusive to southern remnants. This supports the hypothesis that habitat suitability deteriorates sharply from north to south for forest birds in Spain. The species-area relationships of bird assemblages sampled in fragmented forests along a broad continental gradient (from Norway to southern Spain) showed that true forest birds only nest in woodlands >100 ha in southern Spain, whereas the full complement of forest species occurs in much smaller fragments in central-western Europe. Loss of species that are particularly sensitive to habitat fragmentation accounts for these differences between dry Spanish and mesic European woodlands. These results are explained by the low habitat suitability of Spanish woodlands, associated with the restrictive conditions for plant regeneration in the Mediterranean climate and long-standing human usage. There is, therefore, a particular need to develop management strategies that conserve birds, and probably other forest organisms, in Mediterranean regions by preventing habitat deterioration and decreases in fragment size, and by conserving all woods >100 ha.     

Local and landscape factors determine functional bird diversity in Indonesian cacao agroforestry

Large-scale intensification of smallholder cacao management is currently affecting the agroforestry landscapes of Sulawesi (Indonesia), the world’s third largest cacao producer. Little is known about how this shift from diverse plantations to full-sun cacao will affect functionally important biodiversity within the agroecosystem, and how this is related to landscape-wide patterns in land-use and natural ecosystems. We recorded birds in 43 cacao plots differing in woody and herbaceous vegetation as well as distance to forest in two valleys around the Lore Lindu National Park in Central Sulawesi. Species richness of frugivores and nectarivores decreased with increasing distance to forest, whereas granivorous birds increased in richness. Forest specialists, but not habitat generalists, responded positively to forest edge proximity. Species richness of all functional groups except seed eaters increased at higher density of tall shade trees. Greater species richness of shade trees was associated with higher species richness of frugivores and nectarivores, while herbaceous vegetation did not have a strong impact on the avifauna. The positive effect of shade trees was independent of distance to forest. In conclusion, our study shows the relative importance of local and landscape effects on bird diversity with shade trees being critical for bird conservation in cacao agroforestry landscapes.     

Effects of forest fragmentation, anthropogenic edges and fruit colour on the consumption of ornithocoric fruits

We investigated effects of fruit colour (red, black or white), habitat (anthropogenic edges and forest interior) and fragment size on the removal of artificial fruits in semideciduous forests in south-east Brazil. Eight forest fragments ranging from 251 to 36,000 ha were used. We used artificial fruits, which were placed on shrubs between 1 and 2 m in height and checked after 48 and 96 h for peck marks in the fruits. All three variables affected the probability of consumption of our fruit models. Red and black fruits were statistically more pecked than the white fruits. The probability of fruit consumption was lower in the interior than at the edge and less in small than in large fragments. However, the decrease fruit consumption in small compared with large fragments was more accentuated for red and black fruits than for white fruits. Our results show that habitat reduction and edges affect the chances of a fruit being eaten by birds, which may ultimately affect plant fitness in forest fragments.     

The influence of fruit abundance on the use of forest and cultivated field habitats by the endemic Madeira laurel pigeon Columba trocaz: Implications for conservation

This study was conducted over a two year period in the north west of Madeira Island (Macaronesian Atlantic Islands, Portugal). It investigates the relationship between fruiting patterns in the indigenous forest and the use by the Madeira laurel pigeon of forest habitats and cultivated areas. Habitat use observations were carried out using line-transects in forest sites where the availability of fruit (the most important element of the diet) was assessed. The use of agricultural fields was measured indirectly by the assessment of the damage caused to crops. The findings provided strong evidence that bird movements and shifts in abundance are related to fruit usage and availability. The use of fruits is mostly opportunistic but when many species are available, selection was observed. From an ecological perspective, our findings indirectly confirm a high concordance between pigeon diet, studied by microhistological techniques, and habitat use. The use of crops also seems to be mostly opportunistic and is governed by the birds’ movements within the adjacent forest. It is hypothesised that fruit phenology will influence the use of agricultural areas only to the extent that it governs such movements; there is no strong evidence that crops are attacked only when the availability of natural foods is low. Our results suggest that the current management strategy for the forest is adequate for the conservation of this pigeon but that the conservation value of forest edges should be redefined. It is also proposed that crop damage may be reduced by identifying the proximate factors, which lead to the use of specific fields.     

Traditional salt-pans hold major concentrations of overwintering shorebirds in Southeast Asia

Shorebirds are declining worldwide due to loss and degradation of critical breeding and wintering habitats. Some human-modified habitats, particularly salt-pans which are used by shorebirds in many regions of the world, may help substitute for natural habitats lost for a wide range of species during migration. We studied the influence of landscape characteristics on species richness, abundance, and diversity of shorebirds at 20 sites covering most of the Inner Gulf of Thailand, a landscape with a long history of salt farming. Sites with salt-pans present held significantly higher species richness, abundance and diversity of shorebirds. Areas with larger proportions given over to aquaculture tended to have lower species richness, abundance and diversity. Generalized additive models indicated that landscapes with a larger proportion of tidal flats in conjunction with salt-pans were the best predictors of sites with higher species richness, abundance and diversity. Landscape configurations with higher richness, abundance and diversity of shorebirds also tended to be less fragmented and contained slightly larger patches. Shorebirds appeared to use ponds with exposed mud in salt-pans as both roosting sites and supplementary feeding grounds during high tide. Traditional salt-pans therefore proved to contribute significantly to maintenance of overwintering shorebird populations in this landscape and should be investigated elsewhere in Asian coastal zones. Collaboration between researchers, salt farmers and planning authorities as to how best to maintain salt-pans as potential shorebird roost sites such as in the Inner Gulf of Thailand is urgently needed in order to maintain habitat for shorebird populations in critical wintering and staging areas of this flyway.     

The importance of gallery forests in the tropical lowlands of Costa Rica for understorey forest birds

Rivers and streams lined by narrow forest strips are common in the lowland countryside of south-western Costa Rica. We studied the importance of these gallery forests for understorey birds, especially forest species. Using mist-nets, we captured 1110 birds belonging to 90 species between June and September 2007 at 16 sites spread equally over four habitat types: forest interior, forest margin, gallery forest connected to closed forest, and isolated gallery forest. Though isolated gallery forests had the greatest number of expected species in total, they supported the lowest number of forest-specialist species, lower even than connected gallery forests. Granivorous birds showed an increase from forest to isolated gallery forest, all other feeding guilds however showed no change. The studied habitats differed from each other in their faunal composition. Assemblages of three species groups categorised by their habitat preferences (forest specialists, forest generalists, non-forest species) showed nested distribution patterns across the four habitats. There was no significant difference in the proportion of birds with brood patches or of recaptures across the studied habitat types, leading to the assumption that birds not only use gallery forests for movement and foraging but also for reproduction. Though of limited conservation value for most forest understorey birds, at least for a small fraction of forest species gallery forests constitute an important secondary habitat. More significantly, they can form corridors or stepping stones that allow movements within the matrix of human-dominated habitats, and represent an important landscape component benefiting total bird species richness in the Costa Rican countryside.     

Do frugivorous birds assist rainforest succession in weed dominated oldfield regrowth of subtropical Australia?

Exotic plants often form the first woody vegetation that grows on abandoned farmland. If this vegetation attracts vertebrate frugivores which disperse the seeds of native plants, then native plants may recruit to such oldfield sites. However, there is debate about the extent to which exotic vegetation assists or suppresses the regeneration of native plants, and about its effects on faunal biodiversity. These issues were investigated in subtropical eastern Australia, where rainforests were cleared for agriculture in the 19th century, and where regrowth dominated by camphor laurel (Cinnamomum camphora, an exotic, fleshy-fruited tree) has become common on former agricultural land. The study assessed the assemblages of frugivorous birds, and the recruitment of rainforest plants, at 24 patches of camphor laurel regrowth. The patches were used by nearly all frugivorous birds associated with subtropical rainforest. Many of these birds (16 of 34 species) are considered to have a medium to high potential to disperse the seeds of rainforest plants, and eight of these were abundant and widespread in regrowth patches. Of 208 recorded plant species, 181 were native to local rainforest. The ratio of native to exotic species was higher amongst tree recruits than adult trees, both for numbers of species and individuals. Among native tree recruits, 79% of 75 species, and 93% of 1928 individuals, were potentially dispersed by birds. These recruits included many late-successional species, and there were relatively more individuals of late-successional, bird-dispersed native species amongst recruits than adult trees. The species richness, but not the abundance, of both frugivorous birds and of bird-dispersed rainforest trees decreased with distance from major rainforest remnants. Camphor laurel regrowth provides habitat for rainforest birds and creates conditions suitable for the regeneration of native rainforest plants on abandoned farmland. Careful management of regrowth dominated by fleshy-fruited exotic invasive trees can provide an opportunity for broadscale reforestation in extensively-cleared landscapes.     

Implications of seed dispersal by animals for tropical reserve management

Many tropical trees bear fruits adapted for consumption by animals, and many tropical animals depend on fruits for food for at least part of the year. The purpose of this paper is to discuss the potential importance of: (1) uneven species abundance distributions; (2) the imperative of local seed dispersal for plant recruitment; and (3) seasonality of fruit production for managing small tropical reserves. Some mutualistic seed-dispersal systems are ‘pivotal’ for forest communities. Although most species of trees produce when other fruits are readily available in the forest, others (e.g. Casearia corymbosa in Costa Rican rainforest and Virola sebifera in Panamanian rainforest) bear fruits during annual periods of fruit scarcity, and consequently maintain species of fruit-eating birds and mammals which are critical for the dispersal and ultimate recruitment of many tree species at other times of the year. The question of relative abundance presents particular problems when ‘pivotal’ plant species are rare or confined to special habitats. This paper considers ecological relationships which accelerate species loss from habitat islands over and above ‘random’ loss of ecologically independent species predicted from biogeographic theory, and suggests management methods that can reduce such excessive loss.     

Indicator species among resident forest birds - A cross-regional evaluation in northern Europe

In European forests, plants, fungi and invertebrates have been proposed as indicator species for assessing conservation value at the stand scale. To cover larger spatial scales, wide-ranging vertebrates could be added to that set of species. For resident forest birds, we (1) explored whether the occurrence of some species could be used to indicate high species richness and abundances, and (2) compared the results among four regions in the Baltic Sea drainage basin with a common species pool but different forest management intensities and varying proportions of deciduous and coniferous trees (south-central and southern Sweden, south-central Lithuania and northeastern Poland). Assemblages of deciduous forest birds in 100-ha landscape units were generally nested, suggesting that species richness within that group may be predicted based on the presence of a few species. Birds of coniferous forests, however, showed poorer conformity to nestedness in Sweden. Specialised species such as the middle spotted (Dendrocopos medius) and lesser spotted woodpeckers (D. minor) in deciduous forest and the three-toed woodpecker (Picoides tridactylus) in coniferous forest generally figured among the best indicators. In deciduous forest, there was high cross-regional consistency in the identity of the best indicators. Moreover, the sites where the best indicator was present also harboured higher relative abundances of most background species. For coniferous forest, however, such a relationship was not found. We conclude that an indicator species approach may be useful for resident birds of deciduous forests in hemiboreal Europe, emphasising that it should constitute one of many complementary tools for conservation management.     

Avian assemblages along a gradient of urbanization in a highly fragmented landscape

Our goal was to evaluate how avian assemblages varied along a gradient of urbanization in the highly fragmented landscape of coastal southern California. We measured species richness and abundance of birds within continuous blocks of habitat, within urban habitat fragments that varied in landscape and local habitat variables, and within the urban matrix at different distances from the wildland interface. These comparisons allowed us to characterize patterns of avifaunal response to a gradient of urban fragmentation. At the fragment scale, we found that fragment area was a strong, positive predictor of the total number of breeding species detected per fragment; total bird abundance per point count also increased with fragment size. Tree cover was higher in small fragments, as was the abundance of birds that typically occupy wooded habitats. Comparisons between core, fragment, and urban transects revealed differing patterns of response of individual bird species to urbanization. In unfragmented habitat, we recorded a relatively high diversity of urbanization-sensitive birds. In urban transects, these species were rare, and a relatively few species of non-native and anthropophilic birds were common. These urbanization-enhanced birds were also recorded in previous urban gradient studies in northern California and Ohio. Bird communities along the urban gradient reached their highest richness and abundance in fragments. The marked difference in vegetation structure between urban and natural landscapes in this arid shrubland system likely contributed to this pattern; the presence of native shrubs and exotic trees in fragments enabled both shrub and arboreal nesters to co-occur. As is characteristic of biotic homogenization, urban fragmentation in coastal southern California may increase local diversity but decrease overall regional avifaunal diversity.     

The impacts of forest clearance on lizard, small mammal and bird communities in the arid spiny forest, southern Madagascar

Madagascar is a global biodiversity hotspot threatened by forest loss, degradation and fragmentation, all of which are detrimental to the future survival of forest-dwelling organisms. For conservation purposes it is essential to determine how species respond to habitat disturbance, specifically deforestation. In this study we investigated the impacts of deforestation on three vertebrate communities, lizards, small mammals and birds, in an area of spiny forest subjected to anthropogenic forest clearance. Spiny forest has high levels of endemism, but conservation in this unique ecosystem is hindered by the lack of research. We undertook standardised trapping, time-constrained and timed species searches to assess species richness, species abundance and community composition of lizards, small mammals and birds in six areas of ‘forest’ and six ‘cleared’ areas. From surveys and opportunistic sightings we recorded a total of 70 species of birds, 14 species of mammals and 38 species of reptiles and amphibians. We found forest clearing to have a negative effect on species richness and community structure of all groups and identified loss of canopy cover as a driving factor behind this. However, the response and sensitivity to clearing varied between groups and species. Lizards (50%) and small mammals (40%) had the greatest decline in species richness in response to clearing as compared to birds (26%), although birds showed the greatest shift in community structure. The community in cleared areas contained more generalist and introduced species that have wider geographic ranges and habitat preferences, than those unique to the spiny forest. We found the first suite of species to suffer from forest clearance were those of high conservation priority due to their restricted geographic range. Our findings are discussed in relation to future spiny forest conservation and management.     

Land use and conservation value for forest birds in Central Sulawesi (Indonesia)

Unprecedented deforestation is currently underway in Southeast Asia. Since this trend is likely to continue, it is critical to determine the value of human-modified habitats (e.g., mixed-rural habitat) for conserving the regional native forest avifauna. The impacts of ongoing deforestation on the highly endemic avifauna (33%) of Sulawesi (Indonesia) are poorly understood. We sampled birds in primary and secondary forests in the Lore Lindu National Park in central Sulawesi, as well as the surrounding plantation and mixed-rural habitats. Species richness, species density and population density of forest birds showed a consistent decreasing trend in the following order: primary forests > secondary forests > mixed-rural habitat > plantations. Although primary forests contained the highest proportion (85%) of a total of 34 forest species recorded from our point count surveys, 40-yr old secondary forests and the mixed-rural habitat showed high conservation potential, containing 82% and 76% of the forest species, respectively. Plantations recorded only 32% of the forest bird species. Fifteen forest species had the highest abundance in primary forests, while two species had higher abundance outside primary forests. Our simulations revealed that all forest birds that were sensitive to native tree cover could be found in areas with at least 20% continuous native tree cover. Our study shows that although primary forests have the highest conservation value for forest avifauna, the potential of degraded habitats, such as secondary forests and the mixed-rural habitat, for conserving forest species can be enhanced with appropriate land use and management decisions.     

广西沿海红树林区的水鸟

广西沿海地区位于一条重要的候鸟迁徙通道上，那里的红树林区给为数众多的水鸟提供了繁殖、越冬和迁徙中途歇息的场所。在红树林区记录到115种水鸟。这些鸟类中，102种是候鸟，包括13种夏候鸟、64种冬候鸟、25种旅鸟，因此红树林区水鸟类的多样性表现出明显的季节性。迁徙季节水鸟的种类和数量都最多，繁殖季节则最少。黑脸瑟鹭（Platalea minor)是世界上最濒危的鸟类之一，一个越冬种群在该地区红树林中被发现。     

Long-term population declines in Afro-Palearctic migrant birds

We present the first continent-wide analysis of the population trends of European breeding birds to show that populations of Afro-Palearctic migrant birds have shown a pattern of sustained, often severe, decline. The mean trend of inter-continental migrants was significantly negative between 1970 and 1990 and non-significantly so between 1990 and 2000. Mean population trends were positively correlated between periods, suggesting little change in the trajectory of most migrant species’ populations over this 30-year period. In both periods, trends of inter-continental migrants were significantly more negative than those of short-distance migrants or residents. This negative trend appeared to be largely, although not entirely, due to declines in species wintering in dry, open habitats in Africa. Analyses of trends of 30 closely related pairs of species, one a long-distance migrant and the other not, indicated significantly more negative trends in the former, irrespective of breeding habitat. Conservation action to address these declines is required under the Convention on Migratory Species and the Pan-European Biological and Landscape Diversity Strategy, to which most European countries are signatories and which aim, respectively, to conserve migratory species and to halt the loss of biodiversity by 2010. Our results indicate that more conservation action may be required outside Europe to achieve these targets. Further research is needed to assess whether the declines are caused by factors operating on the birds’ wintering grounds, breeding grounds or on migration routes, and to identify ways to reverse them.