Understorey Birds Research Articles

Replacing Grasslands with Pine Plantations on the Karkloof Plateau: The Edge Effects on Downslope Forest Understorey Birds

The aim of this study was to examine if and how the exposure of indigenous forest edges to flanking exotic pine plantations transform the avian community and forest ecosystem found in the forest periphery. I compared bird diversity indices between forest bordering grassland and forest bordering pine plantation at 10 study locations. At each location, understorey birds were sampled with mist nets at the edge (0 m) and progressively deeper into each forest interior in spring and autumn. Crown cover was measured at these sites in autumn. Crown cover decreased from the edge into the forest, more so in forest bordering plantation, and at 60 m was, on average, 18% lower than forest bordering grassland. Furthermore, in forest bordering grassland, bird species richness and total abundance (of individuals) increased with edge distance in both seasons, but in forest bordering plantation, these trends were absent. In addition, in forest bordering plantation, different dominant species were recorded in spring and spe...

Comparison of understorey bird species in relation to edge–interior gradient in an isolated tropical rainforest of Malaysia

Forest fragmentation results in a loss of forest interior and an increase in edge habitat. As a result, these changes may affect the bird species distribution and composition. We studied how understorey bird community composition and habitat variables changed along an edge-to-interior gradient in a fragmented lowland rainforest in Peninsular Malaysia. Birds and environmental variables were recorded at each of the 93 sampling points distributed along the 14 parallel transects that were systematically placed across the gradient of distance from the forest edge to the forest interior. Species composition was different along the edge–interior gradient, although only a few species were strictly confined to either edge or interior habitat. Based on bird–habitat associations along the edge–interior gradient, some of these edge-preferred species occurred in high numbers at the matrix surrounding the patch. In contrast, the interior-specialist group, mainly terrestrial insectivores, avoided the forest edge and was positively associated with humidity, canopy cover, the number of dead trees, percentage of litter cover, and depth of the litter layer. Species endemic to the Sunda subregion were more abundant in the interior of the forest. From a conservation perspective, forest remnants in the lowlands of Peninsular Malaysia that have a deep leaf litter layer, dense canopy cover, high number of dead trees, and high relative humidity are able to support understorey bird species that are sensitive to edge effects. The forest has important conservation value even though it is fragmented and isolated.

A slippery slope: logging alters mass–abundance scaling in ecological communities

Summary Natural ecosystems face ever‐increasing anthropogenic threats from activities such as logging. It is therefore important to: (i) understand anthropogenic impacts on key community characteristics with implications for community structure and function and (ii) identify metrics with mechanistic underpinnings, providing a more functional understanding of anthropogenic impacts on biodiversity. Mass–abundance scaling is the most fundamental property of ecological communities, with implications on energy and resource partitioning and on how species and population traits translate to community structure and function. In habitat patches representing a continuum of logging intensity, I examined the impact of logging on mass–abundance scaling in understorey bird species using mist netting and bird ringing. I used regression quantiles to estimate the slope and intercept of upper bound of the polygonal local‐scale mass–abundance relationship. I show that this slope becomes more negative (and the intercept higher) as logging intensity increases. Logging might therefore significantly alter resource and energy partitioning among species in natural communities. The mechanism underlying this pattern is likely to be an interaction between resource depletion, body size and density compensation. Larger species face more severe resource shortages from depleted resource availability and are expected to decline in abundance following logging, leading to more negative mass–abundance scaling. Density compensation by smaller species following large species decline can ‘push up’ the intercept of the mass–abundance relationship. This might result in both steeper slopes and higher intercepts in logged habitats. Synthesis and applications. This study shows for the first time that anthropogenic habitat change can alter fundamental community properties such as mass–abundance scaling and that this property of ecological communities was better at detecting logging impacts than other standard community measures. Identifying key metrics that provide a functional understanding of anthropogenic impacts on biodiversity is a crucial need, for both the assessment of these impacts and the continued monitoring of habitat change. This study highlights the need to supplement commonly used community descriptions with more mechanistic measures of human impacts on biodiversity.

Comparative Study of Understorey Birds Diversity Inhabiting Lowland Rainforest Virgin Jungle Reserve and Regenerated Forest

A comparative study of understorey birds inhabiting different habitats, that is, virgin jungle reserve (VJR) and regenerated forest (RF), was conducted in Ulu Gombak Forest Reserve and Selangor and Triang Forest Reserve, Negeri Sembilan, Peninsular Malaysia. The objective of this study was to assess the diversity of understorey birds in both habitats and the effects of forest regeneration on the understorey bird community. The mist-netting method was used to capture understorey birds inhabiting both habitats in both locations. Species composition and feeding guild indicated that understorey bird populations were similar in the two habitats. However, the number of secondary forest species such as Little spiderhunter (Arachnothera longirostra) in VJR is increasing due to its proximity to RF. This study discovered that RFs in both study areas are not yet fully recovered. However, based on the range of species discovered, the RFs have conservation value and should be maintained because they harbour important forest species such as babblers and flycatchers. The assessment of the community structure of understorey birds in VJR and RF is important for forest management and conservation, especially where both habitats are intact.

Evaluating the legacy of landscape history: extinction debt and species credit in bird and small mammal assemblages in the Brazilian Atlantic Forest

Summary There is now an extensive literature on extinction debt following deforestation. However, the potential for species credit in landscapes that have experienced a change from decreasing to expanding forest cover has received little attention. Both delayed responses should depend on current landscape forest cover and on species life‐history traits, such as longevity, as short‐lived species are likely to respond faster than long‐lived species. We evaluated the effects of historical and present‐day local forest cover on two vertebrate groups with different longevities – understorey birds and non‐flying small mammals − in forest patches at three Atlantic Forest landscapes. Our work investigated how the probability of extinction debt and species credit varies (i) amongst landscapes with different proportions of forest cover and distinct trajectories of forest cover change, and (ii) between taxa with different life spans. Our results suggest that the existence of extinction debt and species credit, as well as the potential for their future payment and/or receipt, is not only related to forest cover trajectory but also to the amount of remaining forest cover at the landscape scale. Moreover, differences in bird and small mammal life spans seem to be insufficient to affect differently their probability of showing time‐delayed responses to landscape change. Synthesis and applications. Our work highlights the need for considering not only the trajectory of deforestation/regeneration but also the amount of forest cover at landscape scale when investigating time‐delayed responses to landscape change. As many landscapes are experiencing a change from decreasing to expanding forest cover, understanding the association of extinction and immigration processes, as well as their interactions with the landscape dynamic, is a key factor to plan conservation and restoration actions in human‐altered landscapes.

The confounded effects of habitat disturbance at the local, patch and landscape scale on understorey birds of the Atlantic Forest: Implications for the development of landscape-based indicators

The search for surrogates of changes in species richness and community structure in fragmented landscapes involves not only the selection of predictors, such as landscape metrics or environmental variables, but also the identification of the spatial scale that is most relevant to the taxa in question. However the heavily intercorrelated nature of many structural features in fragmented landscapes complicates analyses, and the wide variation in species responses prevents the identification of a general trend. In this study, we used a two-tiered hierarchical variation partitioning to identify the unique and shared effects of: 1 – changes in vegetation structure at the plot scale, patch structure (size and shape), and forest cover at the landscape scale; and 2 – variables within these scales; as predictors of species richness and species’ abundances of birds in a fragmented landscape of Atlantic Forest; with the goal of aiding to the development of biodiversity indicators. Birds were sampled with mist-nets with a constant effort of 680 net-h at each of 23 sites, which resulted in almost 2600 captures. At the community level, regression models showed that changes in plot, patch and landscape scale variables explained a large proportion of the variation in species richness, but results from variation partitioning showed that the intercorrelation among predictors was so high that the unique contribution of each was non-significant. Our results point to a relatively large unique effect of local and landscape scale variables at the community level, but we also show that results vary greatly depending on the trophic guild being analysed. At the species level, multiple scale models also presented high explanatory power, however, species responses were so varied that we could not detect a general trend. We conclude that there is no single ‘best’ scale that could function as a proxy for changes in bird communities because each species and functional guild is uniquely affected by the environment, and suggest that efforts should be focused on finding indicators that encompasses all scales and the needs of different taxa.

Bird functional diversity and wildfires in the Amazon: the role of forest structure

AbstractFire is becoming a common phenomenon in Amazonian forest, modifying the structure and composition of natural assemblages. In particular, fire is known to affect patterns of bird diversity in tropical forests, but we have little understanding of the consequences of this for the functional diversity of bird assemblages. For example, frequent fires could act as an environmental filter selecting species with similar traits and, thus, producing a functional clustering pattern. Here, we used body mass, and dietary and foraging traits to calculate the functional structure of understorey bird assemblages in Amazonian forests analysed 3 years after they had passed under three disturbance levels within the 1997–1998 El‐Niño period: unburned, burned once and burned twice. First, we tested whether observed levels of functional diversity were different among these forests and also from what one would expect by chance. Then, we investigated if habitat structure was able to predict changes in the functional structure of the studied bird assemblages. In general, there was no evidence of fire reducing functional diversity nor selecting species functionally more similar than expected by chance. Therefore, bird functional diversity was not different from random in unburned and burned forests. This provides some evidence in favour of high functional redundancy of bird species in the tropics, but also indicates that neutral theories of biodiversity, where processes such as dispersal and survival are more important than biological traits to community assembly, may apply to the assemblages studied. Also, we showed that bird assemblages from forests disturbed by wildfires have the tendency to be functionally overdispersed whereas assemblages from pristine forests tend to be functionally clustered. Thus, environmental structure, in part driven by forest responses to fire, is more important than simple categorical definitions of burn frequency for explaining trait‐based assembly rules of understorey birds in the Amazon forest.

The importance of agricultural areas for bird conservation in the Korup region, south-western Cameroon

Recent studies have shown that a relatively high number of individuals and species from the natural forest fauna can still be found in land use systems. To detect key parameters for population development and preconditions for long-term suitability of different land use systems for forest bird populations, we investigated patterns of species richness and abundance of understorey birds using mist-net data, in 24 study sites equally distributed over two types of natural and two types of agricultural habitats. We also assessed arthropod availability, nesting sites, parasite loads, and fault bars for trapped birds. We recorded high numbers of birds in all habitats but with a tendency for smaller species with increasing habitat modification. Our data support the idea that arthropod richness and density attract many understorey forest birds in agricultural areas but that environmental stress in these habitats might be high since numbers of bird species and individuals presenting fault bars were significantly higher in the agricultural matrix. In the Afrotropical context, the management of agricultural areas should consider preserving some aspects of natural habitats, and a fallow period of five to eight years, to avoid biodiversity loss.

The influence of microhabitat, moisture and diet on stable-hydrogen isotope variation in a Neotropical avian food web

Abstract:The application of stable-hydrogen isotope (δD) measurements to the study of animal movement, resource use and physiology depends on understanding factors driving variation in δD in animal tissues. The source of micro-scale variation in δD is poorly known, yet understanding micro-scale patterns of δD could shed light on important ecological processes and improve our abilities to track animal movements. Using linear and additive models, we explored the influence of micro-scale habitat use, moisture and diet on tissue δD values of Nicaraguan cloud-forest birds. Using mist nets, we captured 211 individuals of 22 resident Neotropical species at 500–1390 m asl and collected feather and claw samples. Based on three years of data from year-round sampling, our results suggest that microhabitat, seasonal shifts in moisture δD, and diet all influence bird tissue δD values. Our model results reveal a previously undescribed microgeographical effect on δD, where foraging level (understorey versus overstorey) and foraging location (forest interior versus adjacent coffee plantation) were significant predictors of δD values in bird claws and feathers. Mean claw and feather δD values among species varied from −83‰ to −19‰. Top models for claws and feathers explained 57% and 52% of variation in δD respectively. Direct comparisons of understorey (mean ± SD of −30‰ ± 15‰) versus overstorey (−50‰ ± 15‰) claw values suggest that δD may be useful in tracking vertical, micro-scale movement. Higher δD values in forest understorey birds reveal a heavy reliance upon recycled, fog moisture. Fragmentation and climate change may result in increasingly desiccated cloud forest that may exert a more negative influence on the food webs of understorey species that seem to be supported by recycled sources of moisture in the dry season.

Sensitivity of understorey bird species in two different successional stages of the lowland Atlantic Forest, Brazil

The Atlantic Forest has a high destruction rate and there is little information available on some aspects of the neotropical bird biology. Changes in environment are important factors that affect the resources available to birds. We compared the species sensitivity level of understorey birds in two areas in distinct successional stages (primary and secondary sections). Two 100 ha plots of lowland Atlantic Forest were analysed between August and December 2006. Among 25 bird species recorded, thirteen had lower abundance in secondary forest, two in primary forest, and ten had not clear tendency. According to the criteria used, the percentages for species with low, and medium and high sensitivity to habitat change were 44% and 56%, respectively. The number of species was not associated with the endemism level or foraging strata. Results show the importance of knowing bird species' sensitivity level with regard to habitat modification, and not only forest fragmentation.

An annotated list of the avifauna of Palenque, Chiapas

The primary lowland rainforest around the Mayan ruins of Palenque, in the state of Chiapas, Mexico, has been the focus of much study. The second growth and the mosaic of pasture and farmland surrounding the protected area of Palenque National Park also have received some attention by researchers and visitors. Until now though, a complete avifaunal list for this area had not been compiled. In our judgment, 353 species have been recorded reliably, a hundred more than previously reported. An additional 27 species have been reported at the site on multiple occasions but for which we feel there is no definitive evidence. There are 202 regular breeders, most of them resident, and 87 migrants that winter or pass through regularly. Relative capture rates for understorey birds indicate that Phaethornis longirostris and Henicorhina leucosticta are most often caught, and some rarely seen birds, such a Geotrygon montana, are less rare than previously thought. In a state in which habitat destruction is routine, in which national parks are increasingly becoming forested islands, we need baseline data such as these to get a clearer idea of what occurs there if we are to understand anthropogenic effects on forests.

Population densities of understorey birds across a habitat gradient in Palawan, Philippines: implications for conservation

AbstractThere is widespread concern for many understorey and ground-dwelling bird species in the Philippines that appear intolerant of forest alteration. We present density estimates for 18 key bird species in old growth forest, advanced and early secondary growth and active cultivation within the Puerto Princesa Subterranean River National Park in Palawan. Six species were not recorded in cultivation and the abundance of these and several others increased along the successional gradient from cultivation to old growth forest. Eleven species, including five endemics and three of four threatened species, had highest density estimates in old growth forest. However, several species had high density estimates in the heavily disturbed habitats and every habitat type held highest densities of at least one of the bird species. The commonest habitat association across the bird community was a preference for areas containing large trees, indicating the importance of retention of such trees in allowing suitable ground and understorey microhabitats to persist. Old growth forests have the highest conservation value for Palawan’s endemic birds and, while some species thrive in the anthropogenic habitats that occur within the Park, the present extent of cultivation and associated successional stages within its boundaries should not be increased. We caution against extrapolation of the abundance figures from the Park to the whole island but we suggest that population sizes for the threatened species are likely to be much greater than previously thought. We urge authorities to strengthen management within the protected area network in Palawan to ensure survival of key species.

Composition of mixed‐species flocks and shifts in foraging location of flocking species on Hainan Island, China

A total of 134 bird species were recorded at Jianfengling, Hainan Island, in China from May 2000 to September 2004, of which 44 participated in one or more of 134 mixed‐species flocks. These flocks averaged 3.8 ± 0.2 species and 20.3 ± 1.2 individuals. Flocking propensity in a given species ranged from 1.5 to 100%. For flocking species, frequency of flocking and number of individuals in flocks was positively correlated with frequency and number in point counts. Among all species pairs with flocking frequency above 5%, cluster and correlation analysis indicated there were two principal groups of flocking birds – canopy species and understorey species: associations were positive within a group, but negative between groups. Canopy birds had a higher flocking propensity than understorey birds. They also made significantly less use of inner branches and trunks and greater use of middle branches, and foraged at a significantly greater height when in mixed‐species flocks than when solitary. For understorey bird species, there were no significant differences in foraging locations between solitary and mixed‐species flocks. Higher flocking frequency occurred in the wet season for canopy birds, but in the dry season for understorey birds. Overall patterns were consistent with the explanation that flocking enables an expansion of foraging niche by reducing the risk of predation.

Bimodal breeding seasonality of an understorey bird, Premnoplex brunnescens, in an Ecuadorian cloud forest

Despite the aseasonality of temperature and day length of many tropical regions, especially when compared with temperate latitudes, most tropical animals show fairly pronounced seasonal shifts in foraging, movement patterns and reproduction (Flecker & Feifarek 1994, Saul 1975, Wolda & Fisk 1981). Understanding reproductive seasonality in tropical avian communities involves distinguishing among complex interactions between weather, resource abundance, hormones, behaviour and other life-history traits (Wikelski et al. 2003). While there is a great deal of evidence that many tropical bird species breed seasonally (Hau 2001, Marchant 1959, Miller 1963, Snow & Snow 1964), we still understand little of the causes which drive observed patterns (Wikelski et al. 2003). Most studies which address the seasonality of reproduction in tropical birds have focused on locations with fairly extreme temporal changes in rainfall (Cruz & Andrews 1989, Lack 1950, Marchant 1959, Poulin et al. 1992, Voous 1950), and comparatively few have looked at relatively aseasonal low-latitude locations (Miller 1963, Moreau 1950). Similarly, though a few studies have pointed out slight variation in the within-species initiation of breeding based on microhabitat (Wikelski et al. 2003), we know very little about how micro-habitat choice for nesting may affect (or be affected by) breeding seasonality. In this study I describe the nesting cycle of the spotted barbtail (Premnoplex brunnescens), from the Ecuadorian Andes to better understand how reproduction may be seasonal when climatic cues are subtle or absent.

Diet of understorey birds in two Atlantic Forest areas of southeast Brazil

The feeding habits of understorey birds of two fragments of Atlantic Forest in southeast Brazil were studied, based on faecal content. The 434 samples examined contained 2535 items, principally consisting of invertebrates and fruit, of which 2286 (90.2%) could be identified in detail. Although there was no significant difference between the areas with respect to the occurrence of these two food categories in the diet, there were differences in the relative proportions of some of the invertebrate and plant taxa represented. Some birds that had been considered generalists appeared to have dietary specializations, indicating that existing knowledge of the trophic ecology of neotropical birds is inadequate. To eliminate this critical knowledge gap, it is recommended that studies be undertaken at community level together with examination of faecal samples, the latter being a low-cost, non-invasive, non-lethal technique.

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.

Terrestrial and understorey insectivorous birds of a Peruvian cloud forest: species richness, abundance, density, territory size and biomass

Abstract:Terrestrial insectivorous birds in a cloud-forest on the north-western slope of the Peruvian Andes were described in terms of species richness, abundance, density, territory size and biomass. Abundance, density and territory size were also characterized for several understorey insectivores. The three terrestrial insectivore species, all in the genusGrallaria, had 35.25 territories on a 26.2-ha plot, defended territories of (mean ± SD) 1.65 ± 1.34 ha, dwelled at an average density of 4.4 ± 2.7 pairs per 10 ha per species and constituted a biomass of 2470 g per 10 ha. Eight understorey insectivore species had 122.75 territories on the plot, held territories 0.86 ± 0.62 ha in size, and lived at an average density of 5.0 ± 2.7 pairs per 10 ha per species. Six of the 11 species studied each occupied over 50% of the plot. Data on terrestrial insectivores from this study were compared with data from other Neotropical plots to examine how properties of guild structure relate to one another. Increasing densities, smaller territory sizes and higher biomasses appeared to be linked with decreasing species richness and increasing elevation, suggesting consistent patterns of covariance.

Twenty years of understorey bird extinctions from Amazonian rain forest fragments: consistent trends and landscape‐mediated dynamics

ABSTRACTAim We analysed presence/absence data for understorey bird species in rain forest fragments sampled from 1979 through 2001. Here we consider extinctions between 1992, when most fragments had been isolated for at least 8 years, and 2001. Our objectives were to determine whether high extinction rates documented soon after isolation continued through up to 20 years after isolation, and to examine fragment size and landscape effects on extinction.Location Biological Dynamics of Forest Fragments Project, near Manaus, Brazil.Methods Through 1992, birds were surveyed with standardized mist net sampling in ten 1‐ to 100‐ha fragments. We repeated the mist net protocol in 2000–01. We also added remote taping of the dawn chorus and tape playback surveys for species captured in 1991–92 but not in 2000–01.Results Between 1992 and 2001, 37 species went extinct in at least one fragment. As expected, extinction rate decreased with increasing fragment size. Over 30% of species went extinct in 1‐ha fragments, compared to about 5% in 100‐ha fragments. Extinction followed a predictable pattern: most species lost from 100‐ha fragments between 1992 and 2001 had already gone extinct in smaller fragments before 1992. Despite extinctions, fragments gained species between 1992 and 2001, apparently due to species moving through the developing second growth matrix. Fragments surrounded by old second growth had lower extinction rates than predicted based on fragment size alone.Main conclusions Sequential extinctions occurred for at least 20 years. Some additional species previously lost from smaller fragments may continue to go extinct in 100‐ha fragments. At the same time, species assemblages in 1‐ and 10‐ha fragments mostly reflect second‐growth dynamics by 20 years after isolation. High species loss predicted from the first few years after isolation has not occurred, almost certainly because of recolonization.

The value of forest strips for understorey birds in an Amazonian plantation landscape

Remnant forest strips are frequently proposed as valuable conservation tools in fragmented tropical landscapes, yet we currently lack evidence to evaluate their potential conservation value for native biota. We examined the potential value for understorey forest birds of 30-year-old riparian and terra firme (unflooded) primary forest strips within a large silvicultural landscape in the north-east Brazilian Amazon, where the matrix is dominated by Eucalyptus plantations. We conducted mist-netting in eight forest strips connected to continuous forest (four of each forest type), with a total of 24 replicate sampling sites located near to (<1 km), far from (2.5–9 km), and within undisturbed forest controls (i.e. 16 samples within the strips, and 8 in controls). Bird communities in both strip types changed with increasing distance along forest remnants into the plantation matrix. Matrix-embedded samples were characterised by a higher representation of birds typical of secondary growth forest but not those typical of the Eucalyptus-dominated matrix. While the long-term viability of the bird populations in these remnants remains unclear, our data demonstrate that forest strips can provide important habitat for many bird species that are otherwise rarely found outside primary forest. Forest strips therefore provide an important tool to enhance biodiversity conservation in plantation landscapes. The relative practical ease with which these areas can be selected and maintained means that the protection of forest strips as part of a wider conservation strategy is likely to have particular appeal to policy makers and landscape managers working in the human-dominated tropics.

Patch-size and isolation effects in the Fisher–Kolmogorov equation

We examine the classical problem of the existence of a threshold size for a patch to allow for survival of a given population in the case where the patch is not completely isolated. The surrounding habitat matrix is characterized by a non-zero carrying capacity. We show that a critical patch size cannot be strictly defined in this case. We also obtain the saturation density in such a patch as a function of the size of the patch and the relative carrying capacity of the outer region. We argue that this relative carrying capacity is a measure of the isolation of the patch. Our results are then compared with conclusions drawn from observations of the population dynamics of understorey birds in fragments of the Amazonian forest and shown to qualitatively agree with them, offering an explanation for the importance of dispersal and isolation in these observations. Finally, we show that a generalized critical patch size can be introduced resorting to threshold densities for the observation of a given species.