Effects of Human Subsistence Activities on Forest Birds in Northern Kenya

Abstract: Indigenous tribes and conservation biologists may have common goals and may be able to collaborate on the maintenance of biodiversity, but few researchers have evaluated the impacts and potential benefits of human subsistence activities. I studied the effects of subsistence activities (primarily wood collection) of nomadic pastoralists in 3 Afromontane forests of northern Kenya. In surveys of 404, 25‐m‐radius plots, I recorded vegetation structure and composition of the forest bird community. Plots with higher levels of human activity had significantly different vegetation structure, with more‐open canopies, more grass, and fewer tree stems. Nectarivores (abundance +231%) and aerial insectivores (+66%) were more abundant in plots with more‐intense wood collecting than in plots with less human activity, whereas abundance of forest specialists (?28%) decreased in plots with more‐intense human activity. Abundance of 58% of the bird species either increased or decreased significantly in plots with more‐intense human activity. Generally, the number of individuals of forest specialists decreased (6 of 7 species showed significant responses) and the number of individuals of edge and nonforest species increased with increasing human activity. Canonical correspondence analysis showed that an intensification of human activities would favor nectarivores, aerial insectivores, granivores, and omnivores and would negatively affect large‐sized, ground‐foraging species and arboreal frugivores. Subsistence human activities favored the invasion of forest by edge species at the expense of forest specialists; thus, further intensification of forest exploitation by local peoples is not recommended. At the same time, however, subsistence activities in northern Kenya forests appeared to increase the structural diversity of the vegetation and provided suitable habitat for part (but not all) of the forest avifauna, which suggests that subsistence human activities may have a role in the maintenance of bird diversity.     

Long-Term Landscape Change and Bird Abundance in Amazonian Rainforest Fragments

Abstract:  The rainforests of the Amazon basin are being cut by humans at a rate >20,000 km²/year, leading to smaller and more isolated patches of forest, with remaining fragments often in the range of 1–100 ha. We analyzed samples of understory birds collected over 20 years from a standardized mist-netting program in 1– to 100-ha rainforest fragments in a dynamic Amazonian landscape near Manaus, Brazil. Across bird guilds, the condition of second growth immediately surrounding fragments was often as important as fragment size or local forest cover in explaining variation in abundance. Some fragments surrounded by 100 m of open pasture showed reductions in insectivorous bird abundance of over 95%, even in landscapes dominated by continuous forest and old second growth. These extreme reductions may be typical throughout Amazonia in small (≤10 ha), isolated fragments of rainforest. Abundance for some guilds returned to preisolation levels in 10- and 100-ha fragments connected to continuous forest by 20-year-old second growth. Our results show that the consequences of Amazonian forest loss cannot be accurately described without explicit consideration of vegetation dynamics in matrix habitat. Any dichotomous classification of the landscape into "forest" and "nonforest" misses essential information about the matrix.     

Effects of Road Clearings on Movement Patterns of Understory Rainforest Birds in Central Amazonia

Abstract:  The impacts of potential linear barriers such as roads, highways, and power lines on rainforest fauna are poorly understood. In the central Brazilian Amazon, we compared the frequency of local movements (≤300 m long) of understory birds within intact forest and across a 30- to 40-m-wide road over a 2-year period. Rainforest had regenerated along some road verges, to the extent that a nearly complete canopy was formed in some areas, so we also assessed whether this facilitated bird movement. Movement data were determined from 1212 recaptures of 3681 netted birds at six study sites. The road significantly inhibited total bird movement across roads at five of the six sites. Bird foraging guilds varied in their responses to the road and different ages of regrowth. Movements of frugivorous and edge and gap species were not inhibited at any site, whereas most forest-dependent insectivores (mixed-species flocks, terrestrial species, and army-ant followers) had markedly inhibited road-crossing movements, except at sites with extensive regrowth. Solitary understory species were especially vulnerable, rarely crossing even roads overgrown by tall regrowth. For sensitive species, road-crossing movements were inhibited because individuals tended to avoid both edge-affected habitat near the road and the road clearing itself. Our results suggest that even narrow roads with low traffic volumes can reduce local movements of many insectivorous birds in Amazonia.     

The Northwest Forest Plan: Origins, Components, Implementation Experience, and Suggestions for Change

Abstract:  In the 1990s the federal forests in the Pacific Northwest underwent the largest shift in management focus since their creation, from providing a sustained yield of timber to conserving biodiversity, with an emphasis on endangered species. Triggered by a legal challenge to the federal protection strategy for the Northern Spotted Owl ( Strix occidentalis caurina ), this shift was facilitated by a sequence of science assessments that culminated in the development of the Northwest Forest Plan. The plan, adopted in 1994, called for an extensive system of late-successional and riparian reserves along with some timber harvest on the intervening lands under a set of controls and safeguards. It has proven more successful in stopping actions harmful to conservation of old-growth forests and aquatic systems than in achieving restoration goals and economic and social goals. We make three suggestions that will allow the plan to achieve its goals: (1) recognize that the Northwest Forest Plan has evolved into an integrative conservation strategy, (2) conserve old-growth trees and forests wherever they occur, and (3) manage federal forests as dynamic ecosystems.     

Effects of Timber Harvesting on Southern Appalachian Salamanders

We compared the species richness and abundance of salamanders on six recent clearcuts (< 10 years old) with that of salamanders on 34 mature forest stands (>50 years old) in southern Appalachian forests in western North Carolina, U.S.A. Catches of salamanders from plots in mature forest stands were about five times higher than those on recent clearcuts. Almost all species and major taxonomic groups of salamanders were adversely affected by timber removal. Mean number of species collected per plot was about twice as great in mature forest stands as in clearcuts. Analyses of stand age versus salamander catch for 47 plots indicate that 50–70 years are required for populations to return to predisturbance levels following cutting. We conservatively estimate that clearcutting in U.S. national forests in western North Carolina results in a loss of nearly 14 millton salamanders annually. It also is chronically reducing regional populations by more than a quarter of a billion salamanders (9%) below that which could be sustained if mature forests were not cut.     

Demographic Responses by Birds to Forest Fragmentation

Abstract:  Despite intensive recent research on the effects of habitat loss and fragmentation on bird populations, our understanding of underlying demographic causes of population declines is limited. We reviewed avian demography in relation to habitat fragmentation. Then, through a meta-analysis, we compared specific demographic responses by forest birds to habitat fragmentation, providing a general perspective of factors that make some species and populations more vulnerable to fragmentation than others. We obtained data from the scientific literature on dispersal, survival, fecundity, and nesting success of birds. Birds were divided into subgroups on the basis of region, nest site, biogeographical history, and migration strategy. Species most sensitive to fragmentation were ground- or open-nesters nesting in shrubs or trees. Residents were equally sensitive to fragmentation in the Nearctic and Palearctic regions, but Nearctic migrants were more sensitive than Palearctic migrants. Old World species were less sensitive than New World species, which was predicted based on the history of forest fragmentation on these two continents. Pairing success was the variable most associated with fragmentation, suggesting an important role of dispersal. Fledgling number or condition, timing of nesting, and clutch size were not associated with sensitivity to fragmentation, suggesting that negative fragmentation effects on birds do not generally result from diminished food resources with increasing level of fragmentation. Future studies on demographic responses of birds to habitat fragmentation would be more effective if based on a combination of measures that can distinguish among the demographic mechanisms underlying population changes related to habitat fragmentation.     

Response of a Reptile Guild to Forest Harvesting

Abstract:  Despite the growing concern over reptile population declines, the effects of modern industrial silviculture on reptiles have been understudied, particularly for diminutive and often overlooked species such as small-bodied snakes. We created 4 replicated forest-management landscapes to determine the response of small snakes to forest harvesting in the Coastal Plain of the southeastern United States. We divided the replicated landscapes into 4 treatments that represented a range of disturbed habitats: clearcut with coarse woody debris removed; clearcut with coarse woody debris retained; thinned pine stand; and control (unharvested second-growth planted pines). Canopy cover and ground litter were significantly reduced in clearcuts, intermediate in thinned forests, and highest in unharvested controls. Bare soil, maximum air temperatures, and understory vegetation all increased with increasing habitat disturbance. Concomitantly, we observed significantly reduced relative abundance of all 6 study species (scarletsnake [Cemophora coccinea] , ring-neck snake [Diadophis punctatus] , scarlet kingsnake [Lampropeltis triangulum] , red-bellied snake [Storeria occipitomaculata] , southeastern crowned snake [Tantilla coronata] , and smooth earthsnake [Virginia valeriae] ) in clearcuts compared with unharvested or thinned pine stands. In contrast, the greatest relative snake abundance occurred in thinned forest stands. Our results demonstrate that at least one form of forest harvesting is compatible with maintaining snake populations. Our results also highlight the importance of open-canopy structure and ground litter to small snakes in southeastern forests and the negative consequences of forest clearcutting for small snakes.     

Long-Term Population Changes of Native and Introduced Birds in the Alaka'i Swamp, Kaua'i

Abstract:  Within the last 30 years, five endemic bird species of the Alaka'i Swamp, Kaua'i, Hawai'i, have likely gone extinct. We documented population trends of the remaining avifauna in this time period to identify a common pattern in the Hawaiian Islands: decline of native species and expansion of introduced species. We conducted bird surveys over 100 km² of the Alaka'i and Kōke'e regions of Kaua'i in March–April 2000 to estimate population size, distribution, and range limits of seven native and six introduced forest birds. We compared the results with four previous surveys conducted over the last 30 years. Five of the seven native species we studied have fared well, maintaining sizeable populations (>20,000 individuals) and unchanged or increasing numbers. The endemic 'Akikiki ( Oreomystis bairdi ), however, declined from 6296 (SE ± 1374) to 1472 (SE ± 680) individuals and exhibited range contraction from 88 to 36 km². The 'I'iwi ( Vestiaria coccinea ) also experienced a decline and contraction, though not as severe. Populations of several introduced forest birds are increasing, but all species, excluding the Japanese White-eye ( Zosterops japonicus ), were at low numbers (<5,500 individuals in survey area). One introduced species, the Japanese Bush-Warbler ( Cettia diphone ) recently invaded, whereas another, the Red-billed Leiothrix ( Leiothrix lutea ), has been extirpated. Two hurricanes in the past 20 years appear to have most strongly affected nectarivores and may have contributed to the decline or extinction of several other species. Overall, native bird populations on Kaua'i have exhibited species-specific responses to limiting factors. Although most native populations appear stable, the extant native avifauna is vulnerable as a result of limited distributions and the potential for widespread habitat degradation.     

群落中物种多度格局的研究综述

物种多度格局是群落结构的重要内容，但在目前的生态学研究中对其重视不够；多度格局研究早在３０年代就开始，在过去的数十年中得到了重要发展；现已建立了多种多度格局模型，它们各有所长；多度格局与物种多样性指数结合，对群落结构研究更具意义；在多度格局研究中也有一些问题值得讨论。     

The Early Development of Forest Fragmentation Effects on Birds

The early development of forest fragmentation effects on forest organisms is poorly understood partly because most fragmentation studies have been done in agricultural or suburban landscapes, long after the onset of fragmentation. We develop a temporal model of forest fragmentation effects on densities of forest-breeding birds and provide data from an active industrial forest landscape to test the model. The model and our empirical data indicate that densities of several forest-dwelling bird species can increase within a forest stand soon after the onset of fragmentation as a result of displaced individuals packing into remaining habitat. Along with higher densities in the newly formed fragments, pairing success in one species, the Ovenbird ( Seiurus aurocapillus ), was lower in fragments than nonfragments, possibly due to behavioral dysfunction resulting from high densities. Thus, density was inversely related to productivity. The duration and extent of increased densities following onset of fragmentation depends on many factors, including the sensitivity of a species to edge and area effects, the duration and rate of habitat loss and fragmentation, and the proximity of a forest stand to the disturbance. Incipient forest fragmentation may affect populations differently from later stages of fragmentation when the geometry of the landscape has reached a more stable configuration. Our model and data indicate, for reasons unrelated to traditional edge effects, that large tracts of forest can be important because they are relatively free from the variety of plant and animal population dynamics that might take place near new edges, including the encroachment of individuals displaced by habitat loss.     

The Combined Effects of Remnant Vegetation and Tree Planting on Farmland Birds

Abstract:  Biodiversity conservation on agricultural land is a major issue worldwide. We estimated separate and joint effects of remnant native woodland vegetation and recent tree plantings on birds on farms (approximately 500–1000 ha) in the heavily cleared wheat and sheep belt of southern Australia. Much of the variation (>70%) in bird responses was explained by 3 factors: remnant native-vegetation attributes (native grassland, scattered paddock trees, patches of remnant native woodland); presence or absence of planted native trees; and the size and shape of tree plantings. In terms of the number of species, remnant native vegetation was more important than tree planting, in a 3:1 ratio, approximately. Farms with high values for remnant native vegetation were those most likely to support declining or vulnerable species, although some individual species of conservation concern occurred on farms with large plantings. Farm management for improved bird conservation should account for the cumulative and complementary contributions of many components of remnant native-vegetation cover (e.g., scattered paddock trees and fallen timber) as well as areas of restored native vegetation.     

Effects of Traffic Noise on Occupancy Patterns of Forest Birds

Abstract: Noise may drive changes in the composition and abundance of animals that communicate vocally. Traffic produces low‐frequency noise (<3 kHz) that can mask acoustic signals broadcast within the same frequency range. We evaluated whether birds that sing within the frequency range of traffic noise are affected by acoustic masking (i.e., increased background noise levels at the same frequency of vocalizations reduce detection of vocalization) and are less abundant in areas where traffic noise is loud (44–57 dB). We estimated occupancy, the expected probability that a given site is occupied by a species, and detection probabilities of eight forest‐breeding birds in areas with and without traffic noise as a function of noise and three measures of habitat quality: percent forest cover, distance from plot center to the edge of forest, and the number of standing dead trees or snags. For the two species that vocalize at the lowest peak frequency (the frequency with the most energy) and the lowest overall frequency (Yellow‐billed Cuckoo [Coccyzus americanus] and White‐breasted Nuthatch [Sitta carolinensis]), the presence of traffic noise explained the greatest proportion of variance in occupancy, and these species were 10 times less likely to be found in noisy than in quiet plots. For species that had only portions of their vocalizations overlapped by traffic noise, either forest cover or distance to forest edge explained more variation in occupancy than noise or no single variable explained occupancy. Our results suggest that the effects of traffic noise may be especially pronounced for species that vocalize at low frequencies.     

A Multidisciplinary Approach to Assessing the Sustainability of Freshwater Crayfish Harvesting in Madagascar

Abstract:  There is growing interest among conservation decision makers in promoting harvesting of forest products as an incentive for communities to retain forest cover. Assessments of the sustainability of existing harvests are essential for implementing such policies. Madagascar's endemic freshwater crayfish, Astacoides spp., are harvested throughout their range. Despite their importance to human communities, Madagascar's crayfish, like much of the island's freshwater biodiversity, are poorly known, and there is concern that the harvest may be unsustainable. We investigated sustainability of the crayfish harvest in and around Ranomafana National Park in eastern Madagascar, focusing on the heavily harvested A. granulimanus. Several villages around the park have traditional taboos against selling crayfish, resulting in widely varying levels of crayfish exploitation. We used two approaches to assess sustainability of the harvest. First we used participatory mapping combined with a geographic information system analysis to produce a spatially accurate map of harvesting intensity. We then carried out mark-and-recapture sampling at 74 sites across a range of harvest intensities to test whether the level of harvesting was a significant predictor of crayfish density and structure. Second, we used size-structured matrix population models to estimate the forest area necessary to provide the observed annual harvest from one harvesting village and compared this estimate with the area available to the harvesters. Our findings show that the crayfish harvest in Ranomafana may be sustainable under current socioeconomic conditions, suggesting that A. granulimanus is less vulnerable to overexploitation than previously thought. We emphasize the importance of a multidisciplinary approach to assessing sustainability involving both ecological information about the harvested species and socioeconomic data about the level and spatial pattern of the harvest.     

Range Size and Extinction Risk in Forest Birds

Abstract:  Small geographical range size is the single best predictor of threat of extinction in terrestrial species. Knowing how small a species' range has to be before authorities consider it threatened with extinction would allow prediction of a species' risk from continued deforestation and warming climates and provide a baseline for conservation and management strategies aspiring to mitigate these threats. To determine the threshold at which forest-dependent bird species become threatened with extinction, we compared the range sizes of threatened and nonthreatened species. In doing so, we present a simple, repeatable, and practical protocol to quantify range size. We started with species' ranges published in field guides or comparable sources. We then trimmed these ranges, that is, we included only those parts of the ranges that met the species' requirements of elevation and types of forest preferred. Finally, we further trimmed the ranges to the amount of forest cover that remains. This protocol generated an estimate of the remaining suitable range for each species. We compared these range estimates with those from the World Conservation Union Red List. We used the smaller of the two estimates to determine the threshold, 11,000 km², below which birds should be considered threatened. Species considered threatened that have larger ranges than this qualified under other (nonspatial) red list criteria. We identified a suite of species (18) that have not yet qualified as threatened but that have perilously small ranges—about 11% of the nonthreatened birds we analyzed. These birds are likely at risk of extinction and reevaluation of their status is urgently needed.     

Conservation of the Northern Spotted Owl under the Northwest Forest Plan

Abstract:  Development of the Northwest Forest Plan (NWFP) was motivated by concerns about the overharvest of late-seral forests and the effects of intensive forest management on the long-term viability of the Northern Spotted Owl ( Strix occidentalis caurina ). Following several years of intense political and legal debates, the final NWFP was approved in 1994. Even though the plan evolved with a broad ecosystem perspective, it remained anchored in the Spotted Owl reserve design proposed in 1990. Based on a criterion of stable or increasing populations, a decade later it remains unclear whether the enactment of the NWFP has improved the conservation status of Spotted Owls. The results of intensive monitoring of several Spotted Owl populations for over a decade suggest a continuing range-wide decline even though rates of timber harvest have declined dramatically on federal lands. The cause of the decline is difficult to determine because the research needed to establish cause and effect relations has not been done. One plausible hypothesis is that the owl's life history greatly constrains its rate of population growth even when habitat is no longer limiting. Since enactment of the NWFP, new threats have arisen, including the movement of Barred Owls ( S. varia ) into the range of the Spotted Owl, political pressure to increase levels of timber harvest, and recent changes to forest laws that eliminate the requirement to assess the viability of wildlife populations on U.S. Department of Agriculture Forest Service lands. At this time is appears that Spotted Owl conservation rests critically on continued implementation of the protections afforded by the NWFP and the U.S. Endangered Species Act.     

湖南隆回打鸟坳迁徙鸟类资源的调查研究

采用路线调查、样方调查法、鸟类鸣叫声音统计法和走访调查等调查研究方法,对湖南隆回打鸟坳迁徙鸟类资源进行了调查研究,发现该地计有迁徙鸟类10目21科56种,其中留鸟有22种,占39%,夏候鸟有7种,占13%,旅鸟有27,占48%.同时分析了打鸟坳鸟类扑火的原因,并对打鸟坳鸟类资源保护提出了一些建议.     

Bird Extinctions in Atlantic Forest Fragments of the Viçosa Region, Southeastern Brazil

Abstract:   We studied the conservation status of Atlantic forest birds in 43 forest fragments ranging in size from 1 to 384 ha in the Viçosa region of southeastern Brazil. We compared data from 15 years of field work with historical records from the region, mainly originating from specimens collected by João Moojen during the 1930s. We used published studies associated with museum data and current field work to assess the decline of forest birds during the last 70 years and to relate their disappearance to forest fragmentation and destruction. At least 28 bird species have become locally extinct, 43 are critically endangered, and 25 are vulnerable, representing 60.7% of the original forest bird community known to exist in the region. Vulnerability to fragmentation differed among guilds, forest strata, and endemicity status. Birds that feed on fruit and seeds, and those that feed on insects, were more threatened than omnivores and carnivores. Nectarivorous species were less threatened than other guilds. Moreover, terrestrial and understory birds or birds using only one forest stratum also were more likely to have been threatened. Finally, Atlantic forest endemics were more likely to have become extinct than nonendemic species. In general, sensitivity to environmental disturbance at the local level was similar to the predicted vulnerability to regional disturbance derived from the literature. Our results indicate that a serious decline of Atlantic forest birds is underway and that many other species of birds, not previously recognized as threatened, are of conservation concern .