Avian Richness Research Articles

Assessing Avian Richness and Diversity in Different Regions of Oil Palm Plantation in Selangor, Malaysia

Malaysia is characterized by a variety of habitats such as forests, clearings, thickets, and cropland that attract various species of birds. This study examined the bird community in terms of richness and diversity at oil palm plantations habitat. The abundance of birds was determined by using distance sampling point count method. A total of 2722 birds belonging to 38 families representing 86 species of birds were detected. Diversity analysis indicates that the species of birds in the oil palm plantation at Sungai Pelek is more diverse (Shannon-Wiener Diversity Index H; 3.52) and richness (Margalef’s Richness Index R1; 10.2) than oil palm plantation in Teluk Panglima Garang-Pulau Carey and Banting-Jenjarum. However, the species of birds in the oil palm plantations at Teluk Panglima Garang-Pulau Carey and Banting-Jenjarum show higher evenness (Pielou’s Evenness Index E; 0.82) compared with oil palm plantations in Sungai Pelek. The results of this study indicate that the species composition and distribution of the avian species in the oil palm plantations are affected by habitat characterization of that particular area and its vicinity.

An empirical investigation of why species-area relationships overestimate species losses.

It is generally assumed that, when natural habitat is converted to human-dominated land cover, such habitat is lost to its native species. Most literature assumes that species richness should vary as a function of remaining natural area, following the well-known species-area relationship (i.e., classic SAR). However, classic SARs have consistently overestimated species losses resulting from conversion of natural forested land cover to human-dominated landscapes. Moreover, richness is sometimes a peaked function of remaining natural habitat. Recent studies propose modified SAR models based on species' utilization of multiple habitat types, yet none fully explain a peaked species-area relationship. Here, we evaluate the responses of total avian richness, forest bird richness, and open-habitat bird richness to remaining natural land cover within 991 quadrats, each 100 km2, across southern Ontario, Canada. Total bird species richness peaks at roughly 50% natural land cover. Richness of forest birds varies as a classic power function of forested area. In contrast, richness of birds that prefer open habitats does not increase monotonically with either natural- or human-dominated land cover. Richness of open-habitat species can be predicted when we partition human-dominated land cover into an "available human-dominated" component and "lost" habitat. Disiinguishing three land-cover types (natural, available human-dominated, and lost) can thus permit accurate predictions of species richness in landscapes with differing levels of natural habitat conversion.

Avian Richness, Status, and Conservation in the Northwestern Neotropics in Sonora, Mexico

ABSTRACT We assessed the status and richness of birds in a remote region of northwest Mexico and provided the first description of a bird community in foothills thornscrub vegetation across the full annual cycle of seasons. Our efforts were part of a broad program to describe biodiversity and conservation value of the Northern Jaguar Reserve. This large private reserve was recently proposed for federal protection, in part, because it supports the northernmost breeding population of jaguars (Panthera onca) and extensive riparian woodlands along the largest free-flowing river in western Mexico. The reserve and surrounding region are dominated by foothills thornscrub, which is a vegetation community that covers a vast transition zone between tropical forest and desert-scrub in northwest Mexico but is not represented in the federal system of Natural Protected Areas. Bird species richness was similar to that found in other protected areas in western Mexico. Over seven years, we observed 214 species of birds an...

The diversity and abundance of North American bird assemblages fail to track changing productivity.

Plant biomass or productivity and the species richness of birds are associated across a range of spatial scales. Species-energy theory is generally assumed to explain these correlations. If true, bird richness should also track productivity temporally, and there should be spatial and temporal relationships between productivity and both bird abundance and bird richness. Using the summer normalized difference vegetation index (NDVI) for 1982-2006 and the North American Breeding Bird Survey, we evaluated the response of avian richness and abundance to interannual changes in plant biomass or productivity. We found positive spatial relationships between richness and NDVI for all 25 years. Temporally, however, richness and NDVI were positively associated at 1579 survey sites and negatively associated at 1627 sites (mean r2 = 0.09). Further, total abundance and NDVI were unrelated spatially (r2 values spanning < 0.01 and 0.03) and weakly related temporally (mean r2 = 0.10). We found no evidence that productivity drives bird richness beyond the spatial correlations, and neither prediction arising from species-energy theory was confirmed. Spatial relationships between productivity and bird richness may thus be largely spurious, arising via covariance between plant biomass or productivity and vegetation structural complexity, and the latter may be driving bird communities. This is consistent with the MacArthurs' classic hypothesis that the vertical profile of foliage drives bird species diversity.

Maximizing the wildlife conservation value of road right-of-ways in an agriculturally dominated landscape.

There has been a growing recognition that the narrow linear strips of uncultivated vegetation that lie between roads and agricultural crops, referred to as roadside right-of-ways or verges, can serve as areas for the conservation of wildlife. The features of right-of-ways that should influence the composition of wildlife communities vary considerably. Our goal was to determine what features of right-of-ways increased the conservation potential of right-of-ways for wildlife in a grassland system dominated by agricultural production. We sampled 100 right-of-ways for birds and 92 right-of-ways for small mammals in McDonough and Warren Counties in west-central Illinois. We found that the sizes of right-of-ways and the amount of traffic on the adjacent roads synergistically worked to influence wildlife communities. On roads with low traffic, avian species richness increased rapidly with increased right-of-way width, while on roads with high traffic, avian richness increased only slightly with increasing right-of-way widths. We found that wider roadside right-of-ways (preferably across the road from equally wide right-of-ways) with thicker and taller vegetation had the greatest conservation value for birds and small mammals. The features that enhanced the conservation value of right-of-ways in our study area were uncommon. Efforts to create or enhance these features for the benefit of wildlife would likely face numerous obstacles. Nonetheless, from a grassland conservation perspective, working with stakeholders to implement specific strategies to enhance these often neglected areas may be an effective complement to purchasing and restoring conservation lands away from roads.

Fine‐scale impacts on avian biodiversity due to a despotic species, the bell miner (Manorina melanophrys)

AbstractBell miners (Manorina melanophrys; Meliphagidae) are a highly social and very aggressive honeyeater. They are despotic and cooperate in the defence of their territories against other bird species, leading to the almost complete exclusion of other avifauna from miner‐occupied regions. This study aimed to resolve some of the fine‐scale effects of bell miner aggression on avian diversity both within and adjacent to colonies to determine the true impact of a colony on local avifaunal abundance. Three areas, distributed throughout the range of the bell miner, were surveyed across both non‐breeding and breeding seasons to assess the temporal and spatial impacts of bell miner aggression on other bird species. Bell miner colonies were found to occupy very clearly defined areas and had the expected negative impact on avian diversity within their colony. The effects of bell miner colony presence on abundance and richness of avian species were found to cease at the colony boundary, with both recovering to normal levels immediately outside the bell miner colony. Whether bell miners were breeding or not, and irrespective of the amount of vegetation coverage, bell miner colonies were found to have relatively marginal impacts on avian richness and abundance. No impact of colony presence/absence was found on the richness or abundance of the avian species that dwell in the undergrowth, with some evidence that these species were actually more common at the colony edge. Our results demonstrate that the influence of bell miner colony presence upon avian biodiversity is restricted to the confines of the colony and does not radiate outwards into the surrounding habitat. Colony presence influences, therefore, have implications when considering the impact of bell miner behaviour on the diversity of insectivorous birds and processes, most notably the propagation of Bell Miner Associated Dieback.

Impacts of agricultural intensification on avian richness at multiple scales in Dry Chaco forests

Agricultural expansion and intensification is driving rapid landscape modification in the South American Gran Chaco, affecting biodiversity at multiple spatial scales. Research on biodiversity change in modified landscapes has focused mainly on remnant habitat patches. However, the habitat quality of the matrix is increasingly recognized as a key element for planning conservation in agricultural landscapes. We employed a multi-model selection approach to test 13 hypotheses about the influence of spatial scales and structural attributes on the richness of bird assemblages and forest specialist species within matrix types at the Argentine Dry Chaco. We selected 27 cattle ranches where six structural attributes of vegetation operating at different spatial scales (plot, edge and landscape) varied independently across a matrix intensification gradient in the agricultural frontier. We found that structural attributes operating at the plot, edge and landscape scale have significant influence on overall richness, with plot-scale attributes being more important than edge and landscape-scale attributes in driving bird occurrence in the grazing matrix. Factors operating at the plot scale had the largest influence on the richness of forest specialist species in the matrix. These results suggest that planning for the long-term conservation of Dry Chaco forests avifauna should pay attention to the effects of local agricultural management. Where further cattle production intensification cannot be avoided, implementation of highly selective clearing methods can mitigate the degradation of habitat quality for birds. Where cattle production intensification has already occurred, native tree plantings on cleared areas can restore significant bird diversity.

ASSESSING THE EFFECTS OF LOGGING ACTIVITIES ON AVIAN RICHNESS AND DIVERSITY IN DIFFERENT AGED POST-HARVESTED HILL DIPTEROCARP TROPICAL RAINFOREST OF MALAYSIA

Logging activities have encroached into the hill dipterocarp tropical rainforest area since the lowland dipterocarp forests have decreased in size. Hill dipterocarp tropical rainforest is rich in habitat diversity and provide a variety of resources for avian species such as food, habitat and shelter. Therefore it is important to examine the logging effects of hill dipterocarp rainforest on avian species. We compared the avian richness and diversity in different aged post-harvested hill dipterocarp tropical rainforest at the Berkelah Hill Dipterocarp Rainforest Reserve in Maran, Pahang, West Malaysia using mist-netting method. We captured a total of 1908 individuals representing 86 species and 29 families (i.e., 18.55% from two years post-harvested forest, 25.10% from ten years post-harvested, 23.90% from twenty years post-harvested and 32.44% from thirty five years post-harvested forests). Forty nine species were caught in two years and ten years, 55 species in twenty years and 59 species in thirty five years’ post-harvested forest. Seventeen species were common in all four types of forest. Pycnonotidae, Timaliidae and Nectariniidae were the most dominant families in all types of post-harvested hill dipterocarp tropical rainforest. Diversity analysis indicated that the bird species in twenty years post-harvested hill dipterocarp rainforest was most diverse (i.e., Fisher’s Alpha Diversity Index; 16.34) and evenly distributed (i.e., McIntosh Evenness index E; 0.933) as compared to two years, ten years and thirty five years post-harvested forest. However, thirty five years post-harvested forest was richest in avian species (i.e., Margalef’s Richness index R1; 9.02) as compared to other post-harvested forest. The findings of this study revealed that logging and recovery process may affects on avian distribution and diversity. However, these effects may vary from species to species.

The influence of vegetation height heterogeneity on forest and woodland bird species richness across the United States.

Avian diversity is under increasing pressures. It is thus critical to understand the ecological variables that contribute to large scale spatial distribution of avian species diversity. Traditionally, studies have relied primarily on two-dimensional habitat structure to model broad scale species richness. Vegetation vertical structure is increasingly used at local scales. However, the spatial arrangement of vegetation height has never been taken into consideration. Our goal was to examine the efficacies of three-dimensional forest structure, particularly the spatial heterogeneity of vegetation height in improving avian richness models across forested ecoregions in the U.S. We developed novel habitat metrics to characterize the spatial arrangement of vegetation height using the National Biomass and Carbon Dataset for the year 2000 (NBCD). The height-structured metrics were compared with other habitat metrics for statistical association with richness of three forest breeding bird guilds across Breeding Bird Survey (BBS) routes: a broadly grouped woodland guild, and two forest breeding guilds with preferences for forest edge and for interior forest. Parametric and non-parametric models were built to examine the improvement of predictability. Height-structured metrics had the strongest associations with species richness, yielding improved predictive ability for the woodland guild richness models (r2 = ∼0.53 for the parametric models, 0.63 the non-parametric models) and the forest edge guild models (r2 = ∼0.34 for the parametric models, 0.47 the non-parametric models). All but one of the linear models incorporating height-structured metrics showed significantly higher adjusted-r2 values than their counterparts without additional metrics. The interior forest guild richness showed a consistent low association with height-structured metrics. Our results suggest that height heterogeneity, beyond canopy height alone, supplements habitat characterization and richness models of forest bird species. The metrics and models derived in this study demonstrate practical examples of utilizing three-dimensional vegetation data for improved characterization of spatial patterns in species richness.

Avian response to conservation buffers in agricultural landscapes during winter

ABSTRACTNative herbaceous vegetation cover along row‐crop field edges (i.e., field buffers) increases breeding densities of many bird species. However, the effect of field buffers on bird species during the non‐breeding season is less understood. We compared density, avian richness, and avian conservation value on row‐crop fields containing buffers strategically designed for wildlife versus fields without buffers in 3 southeastern U.S. states during winter 2007 and 2008. Fields with buffers were enrolled in U.S. Department of Agriculture, Conservation Reserve Program practice Habitat Buffers for Upland Birds (CP33), which targets restoration of northern bobwhite (Colinus virginianus) and other upland bird species. Overall species richness did not differ on fields with buffers versus fields without buffers in 2007, but was 29% greater on fields with buffers in 2008. Swamp sparrows (Melospiza georgiana), song sparrows (M. melodia), field sparrows (Spizella pusilla), and red‐bellied woodpeckers (Melanerpes carolinus) had greater densities on fields with buffers compared with fields without buffers. Increasing field‐buffer width did not result in greater bird densities. Our results suggest a small change in primary land use (≈7%) produced a disproportionate population response by some grassland‐dependent and woodland bird species during winter. Because field buffers provide a direct source of winter food and cover resources, they may be a pragmatic means to provide critical non‐breeding habitat with little alteration of existing agricultural systems. © 2014 The Wildlife Society.

The effect of white-tailed deer density on breeding songbirds in Delaware

Most population goals for white-tailed deer (Odocoileus virginianus) are based solely on deer data, with little consideration for other parts of the ecosystem. A wider ecological approach is needed for more justifiable target deer densities. We investigated the use of birds as coarse-scale indicators to determine an ecological carrying capacity for deer management by studying the relationship between the forest bird community and deer density in Delaware, USA. Using Breeding Bird Survey data from 2005 to 2009, targeted point-count data from 2008 to 2009 and Division of Fish and Wildlife deer-density data from the same time periods, we compared avian species richness and relative abundance with deer density. We divided deer densities into low (≤10 deer/km2), moderate (11–19 deer/km2), and high (≥20 deer/km2) categories. We placed birds into 6 deer-sensitive guilds: interior forest obligates, ground nesters, shrub nesters, ground gleaners, low-canopy foragers, and Neotropical migrants, as well as 1 “guild” that consisted of species found to be sensitive to deer density in past literature. The abundance or richness of most guilds and species did not differ by deer density. However, there were 1.08 more shrub nesters and 0.55 more species of shrub nesting birds in low-deer-density areas than in high-deer-density areas. Areas of moderate and low deer densities had ≥0.35 more species of low-canopy foragers than did areas of high deer densities. Low-deer-density areas had ≥0.59 more individual Neotropical migrants compared with moderate- or high-deer-density areas. Similarly, areas of low deer densities had ≥0.49 more migrant species than did areas of higher densities. Low-deer-density areas had ≥0.17 more ovenbirds compared with high- and moderate-deer-density areas. Great crested flycatchers (Myiarchus crinitus) had 3 times greater odds of being found in low-deer-density areas than in high-deer-density areas. Chipping sparrows (Spizella passerina), Acadian flycatchers (Empidonax virescens), and red-eyed vireos (Vireo olivaceus) all had 2 times greater odds of being found in low-deer-density areas than high-deer-density areas. Our results suggest that areas in Delaware with densities of <20 deer/km2 have the greatest avian richness and abundance. These findings are the first step toward determining an ecological carrying capacity for white-tailed deer. © 2013 The Wildlife Society.

Use of stormwater impoundments near airports by birds recognized as hazardous to aviation safety

Design of privately-owned stormwater impoundments within or near airport siting criteria has received little attention with regard to potential hazards posed to aviation safety. In particular, minimizing use of these impoundments by bird species recognized as hazardous to aviation poses an important challenge. Emergent vegetation, shoreline irregularity, and proximity of other water resources are linked to avian richness and diversity within wetlands, as well as bird use of stormwater impoundments on airports. We predicted also that impoundments with bank slope >20% and those functioning as detention facilities, where water is periodically drawn down, would negatively influence use by birds; and that shoreline-vegetation diversity and local land-use diversity would be positively correlated with use. Over 104 weeks (March 2008 to March 2010), we surveyed bird use of 40 stormwater impoundments in the Auburn-Opelika Metropolitan area, Lee County, AL, USA, typical of privately-owned facilities located within or near airport siting criteria. We quantified local-scale and site-specific parameters possibly affecting bird use and evaluated fit for 17 a priori models relative to detection of 10 individual avian foraging guilds recognized as hazardous to aviation safety. Relative likelihoods of best-approximating models (Akaike weights) ranged from approximately 0.42 to 0.92. Based on best-approximating models for at least five of the 10 guilds, we suggest that broad reduction in use of stormwater impoundments, located within or near airport siting criteria, by bird species hazardous to aviation can be achieved via designs which minimize perimeter, surface area, and the ratio of open water to emergent vegetation.

Trade-offs between land use intensity and avian biodiversity in the dry Chaco of Argentina: A tale of two gradients

Studies to assess the relationship between agriculture production and biodiversity conservation usually focus on one gradient ranging from a natural reference land cover type (typically forest) to an intensive productive land use. However, many semi-arid ecoregions such as the dry Chaco are characterized by a mosaic of different land covers, including natural grasslands and woody vegetation with different degrees of transformation, frequently aimed at meat production. We analyzed the associations between avian biodiversity and meat productivity of forest, natural grasslands, three types of livestock production systems, and soybean crops in northern Argentina dry Chaco; an area of c. 19 millionha characterized by high conservation value and rapid land use change. A Generalized Lineal Model analysis of reports and publications quantified a meat productivity range in which soybean (the less diverse land cover type) doubles the most efficient livestock systems, and is eight times more productive than the widespread puestos system. A multidimensional scaling ordination identified two independent gradients of bird's response to increasing land use intensity, respectively from protected forests and from natural grasslands, to highly transformed systems. Along both gradients avian richness and density sharply declined in the transition from semi-natural land covers to planted pastures and similarity to native grasslands and protected forests decreased exponentially. Along the “grasslands gradient”, bird richness and density presented a unimodal response. Maximum likelihood-fitted curves of bird's guilds response to the productivity gradients showed that in the “forest gradient” most guilds decreased exponentially or linearly, whereas in the “grasslands gradient” most guilds peaked at intermediate levels of meat yield. Our results suggest that land sparing strategies can be more efficient to balance agriculture production with the conservation of forest avian diversity, but also that the prevailing “forest oriented” conservation schemes (e.g. Argentine Forest Law) do not capture the complexity of the system and both forests and grassland gradients should be considered in land use planning, possibly including a combination of conservation strategies.

Cryptic loss of montane avian richness and high community turnover over 100 years

Although there are numerous examples of individual species moving up in elevation and poleward in latitude in response to 20th century climate change, how communities have responded is less well understood and requires fully accounting for changes in species-specific detectability over time, which has been neglected in past studies. We use a hierarchical Bayesian occupancy model to examine bird species richness change and turnover along three elevation gradients surveyed 80-100 years apart in the Sierra Nevada of California, USA. Richness declined over the 20th century across all elevations. Turnover was greatest at the highest and the lowest elevations. These findings were only apparent, however, after species' detectability was incorporated into measures of species richness. Further partitioning of species richness changes by elevational life zone showed that numbers of low- and high-elevation species declined, without a concurrent expansion by mid-elevation species. Our results provide empirical evidence for biodiversity loss in protected montane areas during the 20th century and highlight the importance of accounting for detectability in comparisons of species richness over time.

Effects of Logged and Unlogged Forest Patches on Avifaunal Diversity

In the Hyrcanian forests of northern Iran, reduced-impact silviculture systems, (single-tree and group-tree selection) were applied over a large area, which generated different local habitat structures. The aim of this study was to assess the differences between treated and untreated areas of forest and their effect on avian richness, abundance and diversity (R.A.D). Birds were surveyed during the breeding season in 2009 by 100-point counts, equally distributed in the treated and untreated area. Avian R.A.D was significantly different and higher in the untreated area. Generally, forestry practices cause noticeable changes in canopy percentage, tree composition, snags and shrub number. Treated forest habitats in the area of study had a much more developed understory, fewer snags and fewer large diameter trees. The results highlighted the importance of forest maturity and showed that preventing silvicultural disturbances may not be the best solution for conserving and enhancing biodiversity. Rather, methods such as selective cutting seem an appropriate and sustainable way of forest management. It is suggested that forests should be managed to conserve structural elements which create favorable habitat for bird species, preventing future species losses due to logging practices.

Conserving avian richness through structure retention in managed forests of the Pacific Northwest, USA

Structure retention is a practice used in managed forests to assist the conservation of biological diversity, whereby green trees, dead trees (i.e. snags), and downed wood are retained during timber harvest. This activity is recognized as beneficial. However, there is little scientific support to guide the management prescriptions (e.g. patch sizes, distribution pattern). We quantified the short-term response of birds to structure retention in timber harvest areas located in the Pacific Northwest. We used a hierarchical community model to examine how attributes of retention sites (number of trees and snags, distance to forest edge) were associated with the species richness of birds using the sites. The modeling framework integrated multiple species-specific occupancy models that accounted for imperfect detection to produce estimates of species richness. We sampled a biogeoclimatic gradient by selecting harvest units within four separate regions (two in Washington, one each in Oregon and California) that support different forest types. Observations were conducted at a random selection of retention sites (e.g. patches, individual trees) within harvest units to record bird use during the breeding seasons of 2008 and 2009. Estimated occupancy and detection probabilities differed by species and region. Retained tree count was associated with an increased occupancy probability for all observed species. The community response to tree count was consistent across all study regions and years – species richness estimates increased with tree count and approximated a species–area curve. Snag count and edge distance did not significantly affect occupancy probability for any observed species, and therefore, had no relationship with species richness. These results suggest that the diversity of birds using structure retention in harvest units can be maximized at patches of >10–15 rotation-age trees. Forest managers are encouraged to group green-trees around high-quality snags and other unique wildlife trees where possible, and to vary prescriptions across stands to provide habitat heterogeneity at the landscape scale.

Influence of Local and Landscape Characteristics on Avian Richness and Density in Wet Playas of the Southern Great Plains, USA

Playa wetlands (shallow, circular, depressional wetlands) in the Southern Great Plains are essential to the maintenance of regional biodiversity. However, the relative importance of habitat characteristics for maintaining avian species richness and density in playas is unknown. We examined influences of local- and landscape-scale characteristics on avian communities in wet playas. We conducted biweekly avian surveys on 80 playas (40 playas/year) from summer 2003 through spring 2005. Avian species richness was positively related to playa area and hydroperiod. More avian species and greater densities of birds were found at wetlands when water depths were intermediate (30–80 cm) during fall, winter and spring. Increased cultivation in playa watersheds increased total-, native-, and exotic-avian species richness. However, unsustainable sediment accumulation caused by cultivation can fill the playa basin and result in the loss of playa function, which will not benefit future bird populations. Landscape variables generally were less consistent with avian communities among seasons compared to local variables. Playas with greater numbers of other playas within 1 and 10 km had lower bird densities than those with fewer surrounding playas, likely due to the increase of habitat availability. Larger playas within predominantly uncultivated watersheds, that have an intermediate water depth, longer hydroperiod (within a season), and 26–50% vegetation cover are likely to maximize seasonal native avian richness. However, manipulating static water depths and maintaining long hydroperiods over extended periods will not meet avian objectives over the long term because playas must go through natural wet/dry fluctuations between years to maintain the desired plant community and productivity that supports diverse avian populations.

Bird and Plant Diversity in Tropical Landscape Mosaics in East Usambaras, Tanzania

The role of land uses outside protected areas in conserving tropical biodiversity remains poorly understood and contested. This paper summarizes the results of plant and bird surveys conducted in three rural landscapes in the East Usambara Mountains of Tanzania, covering a gradient from Village forest reserves to tree-based and other agricultural land uses. The species richness and occurrence of conservationally important species across the land uses were analyzed. Twelve plots of 0.2 ha, stratified among land use types, were established to survey the large trees, with sub-plots of 1 × 40 m for tree saplings, shrubs and non-woody plants, and 5 × 40 m plots for small trees. Avian richness was measured in the same sites as the plants through mist netting and timed species counts. The village forests had higher plant species richness and more conservationally important plant species compared to other land uses. Agroforest and fallows supported a relatively high number of plant species, but the species composition was largely different to the adjacent village forests. Bird species of conservation importance were recorded across all land uses. Village forest reserves and some of the tree-based agricultural land uses were found to contribute to biodiversity conservation goals in tropical landscape mosaics. There is a need to better integrate them, and address their multiple functions, in village land-use planning and conservation efforts at the landscape level.

Effects of landscape context on bird species abundance of tree fall gaps in a temperate deciduous forest of Northern Iran

Tree fall gaps caused by natural disturbances are a major source of heterogeneity in intact forests. Bird species are known as ecological indicators, reflecting landscape level changes. Yet, the role of landscape context in bird species abundance within small gaps is not fully addressed. We examined the difference between avian richness and abundance within tree fall gaps and closed canopy forest areas in Kheyrud forest, located on the east of Noshahr Township, Mazandaran province in Iran as a representation of Hyrcanian forest. Breeding bird census was taken in 20 selected gaps (0.1–0.4ha) and 250m from the center of each gap known as controls. Birds were surveyed during breeding season in spring 2010. We also determined whether landscape context affected the abundance, richness and particular species abundance within the gaps. For this, we assessed landscape metrics by the Landscape Context Tool for every gap. Abundance (P=0.003) and richness (P=0.014) of birds were significantly higher in the gaps than in closed canopy controls. Gaps were higher in herb cover, coarse woody debris density and volume as well as pit and mound micro topography than controls. Great Tit (Parus major), Coal Tit (Parus ater), Eurasian Nuthatch (Sitta europaea), Common Chaffinch (Fringilla coelebs) and European Goldfinch (Carduelis carduelis) were more abundant in gaps than in controls. Among which, European Goldfinch was the only gap specialist species. Song Thrush (Turdus philomelos) was the only species more abundant in controls than gaps. Mean tree diameter had a significant positive relation with avian richness and abundance in gaps, rather than landscape context rate but forest specialist richness was negatively related to gap size. Abundance of Great Tit was related to landscape context rate. Our study highlights the role of gap quality for breeding birds; therefore improving the quality of gap habitats especially maintaining dead wood should be considered as an important conservation factor. Management practices for providing habitat of gap specialists by taking out the remaining trees and making the gaps larger would increase bird species richness in a landscape scale but the shape and size of the openings should be according to the species requirements. We suggest that maintenance of tree fall gaps as a heterogeneous habitat and dead wood resource is crucial for promoting species richness.

Bird community composition across an Andean tree‐line ecotone

AbstractFew studies have found strong evidence to suggest that ecotones promote species richness and diversity. In this study we examine the responses of a high‐Andean bird community to changes in vegetation and topographical characteristics across an Andean tree‐line ecotone and adjacent cloud forest and puna grassland vegetation in southern Peru. Over a 6‐month period, birds and vegetation were surveyed using a 100 m fixed‐width Distance Sampling point count method. Vegetation analyses revealed that the tree‐line ecotone represented a distinctive high‐Andean vegetation community that was easily differentiated from the adjacent cloud forest and puna grassland based on changes in tree‐size characteristics and vegetation cover. Bird community composition was strongly seasonal and influenced by a pool of bird species from a wider elevational gradient. There were also clear differences in bird community measures between tree‐line vegetation, cloud forest and puna grassland with species turnover (β‐diversity) most pronounced at the tree‐line. Canonical Correspondence Analysis revealed that the majority of the 81 bird species were associated with tree‐line vegetation. Categorizing patterns of relative abundance of the 42 most common species revealed that the tree‐line ecotone was composed primarily of cloud forest specialists and habitat generalists, with very few species from the puna grassland. Only two species, Thlypopsis ruficeps and Anairetes parulus, both widespread Andean species more typical of montane woodland vegetation edges, were categorized as ecotone specialists. However, our findings were influenced by significant differences in species detectability between all three vegetation communities. Our study highlights the importance of examining ecotones at an appropriate spatial and temporal scale. Selecting a suitable distance between sampling points based on the detection probabilities of the target bird species is essential to obtain an unbiased picture of how ecotones influence avian richness and diversity.