Long-Term Effects of Group-Selection Timber Harvesting on Abundance of Forest Birds

Abstract:  Relatively few studies have examined the ecological effects of group-selection timber harvesting, and nearly all have been short-term and have lacked experimental manipulations that allow pre- and posttreatment comparisons. We have been documenting the effects of a group-selection timber harvest on bird abundance in a Maine forest for 24 years (preharvest, 1983–1987; postharvest, 1988–2006). Here we characterized the trends in bird abundance over the first 20 years of the study in the managed and control halves of the 40-ha study area. Species responses to the group-selection harvest were idiosyncratic, but in general the mature-forest bird community was retained and species dependent on early successional habitat temporarily (≤8 years) benefited. The Eastern Wood-Pewee ( Contopus virens ) , Winter Wren ( Troglodytes troglodytes ) , Pine Warbler ( Dendroica pinus ) , and White-throated Sparrow ( Zonotrichia albicollis ) increased in abundance in the managed half of the study area following timber harvest, whereas the Veery ( Catharus fuscescens ) decreased. The Black-and-White Warbler ( Mniotilta varia ) , Nashville Warbler ( Vermivora ruficapilla ) , and Common Yellowthroat ( Geothlypis trichas ) responded positively to harvesting, as indicated by decreases in abundance in the control area and more protracted declines or stable abundances in the managed area. This study constitutes the longest experimental investigation to date of the effects of a group-selection harvest on birds and thus provides important information on the strength, direction, and duration of temporal changes in bird populations following forest management.     

Trophic Flexibility and the Persistence of Understory Birds in Intensively Logged Rainforest

Effects of logging on species composition in tropical rainforests are well known but may fail to reveal key changes in species interactions. We used nitrogen stable‐isotope analysis of 73 species of understory birds to quantify trophic responses to repeated intensive logging of rainforest in northern Borneo and to test 4 hypotheses: logging has significant effects on trophic positions and trophic‐niche widths of species, and the persistence of species in degraded forest is related to their trophic positions and trophic‐niche widths in primary forest. Species fed from higher up the food chain and had narrower trophic‐niche widths in degraded forest. Species with narrow trophic‐niche widths in primary forest were less likely to persist after logging, a result that indicates a higher vulnerability of dietary specialists to local extinction following habitat disturbance. Persistence of species in degraded forest was not related to a species’ trophic position. These results indicate changes in trophic organization that were not apparent from changes in species composition and highlight the importance of focusing on trophic flexibility over the prevailing emphasis on membership of static feeding guilds. Our results thus support the notion that alterations to trophic organization and interactions within tropical forests may be a pervasive and functionally important hidden effect of forest degradation. Flexibilidad Trófica y la Persistencia de Aves de Sotobosque en un Bosque Lluvioso Talado Intensivamente     

Effects of Roads on Movements by Understory Birds in Mixed-Species Flocks in Central Amazonian Brazil

Abstract: Roads through tropical forest create linear disturbances that have unknown consequences for forest birds. We studied how a narrow, rarely used road through otherwise undisturbed Amazonian forest affected the movements and area requirements of understory birds that form mixed-species flocks. Differences in road maintenance led to two distinct treatments along the same road. Trees along the "closed" road formed a partial canopy connecting the two sides of the road, although the roadway itself was kept open. The "open" road was regularly maintained, making a complete opening 10–30 m wide.We followed 15 flocks, 5 each in interior forest, along the open road, and along the closed road. These flocks were led by Thamnomanes antshrikes, and each flock had a discreet, permanent territory. Flock territory size (mean = 8.5 ha) did not differ among the three locations. The open road formed the territorial boundary for all five flocks, although birds moved within a few meters of the edge of the road. The closed road was less of a barrier: 2 of 5 flocks used both sides of the closed road. Playback experiments showed that flocks readily crossed the closed road to approach agonistic vocalizations. Along the open road, even though birds responded to playback by becoming agitated and moving to the extreme edge of the roadside vegetation, they were less likely to cross the road and did so only after a longer duration of playback. Our results suggest that flocks respond to a road as they would to a long linear gap. They use the vegetation along the edges of the road, but because they are unwilling to cross the open area, it becomes a flock territory boundary. Similarly, as in forest gaps, successional change along the closed road produced suitable habitat for flocks. Although this suggests that roads are a trivial problem, we caution that this result applies only to narrow roads that are not accompanied by deforestation or other disturbance.     

Effects of Future Infrastructure Development on Threat Status and Occurrence of Amazonian Birds

Abstract:  Researchers predict that new infrastructure development will sharply increase the rate and extent of deforestation in the Brazilian Amazon. There are no predictions, however, of which species it will affect. We used a spatially explicit model that predicts the location of deforestation in the Brazilian Amazon by 2020 on the basis of historical patterns of deforestation following infrastructure development. We overlaid the predicted deforested areas onto maps of bird ranges to estimate the amount of habitat loss within species ranges. We also estimated the amount of habitat loss within modified ecoregions, which were used as surrogates for areas of bird endemism. We then used the extent of occurrence criterion of the World Conservation Union to predict the future conservation status of birds in the Brazilian Amazon. At current rates of development, our results show that at least 16 species will qualify as threatened or will lose more than half of their forested habitat. We also identified several subspecies and isolated populations that would also qualify as threatened. Most of the taxa we identified are not currently listed as threatened, and the majority are associated with riverine habitats, which have been largely ignored in bird conservation in Amazonia. These habitats and the species they hold will be increasingly relevant to conservation as river courses are altered and hydroelectric dams are constructed in the Brazilian Amazon.     

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.     

Interspecific Patterns of Genetic Diversity in Birds: Correlations with Extinction Risk

Abstract:  Birds are frequently used as indicators of ecosystem health and are the most comprehensively studied class in the animal kingdom. Nevertheless, a comprehensive, interspecific assessment of the correlates of avian genetic diversity is lacking, even though indices of genetic diversity are of considerable interest in the conservation of threatened species. We used published data on variation at microsatellite loci from 194 bird species to examine correlates of diversity, particularly with respect to conservation status and population size. We found a significant decline in mean heterozygosity with increasing extinction risk, and showed, by excluding species whose heterozygosity values were calculated with heterospecific primers, that this relationship was not dependent on ascertainment bias. Results of subsequent regression analyses suggested that smaller population sizes of threatened species were largely responsible for this relationship. Thus, bird species at risk of extinction are relatively depauperate in terms of neutral genetic diversity, which is expected to make population recovery more difficult if it reflects adaptive genetic variation. Conservation policy will need to minimize further loss of diversity if the chances of saving threatened species are to be maximized.     

Effects of Reduced-Impact Logging on Fish Assemblages in Central Amazonia

Abstract: In Amazonia reduced‐impact logging, which is meant to reduce environmental disturbance by controlling stem‐fall directions and minimizing construction of access roads, has been applied to large areas containing thousands of streams. We investigated the effects of reduced‐impact logging on environmental variables and the composition of fish in forest streams in a commercial logging concession in central Amazonia, Amazonas State, Brazil. To evaluate short‐term effects, we sampled 11 streams before and after logging in one harvest area. We evaluated medium‐term effects by comparing streams in 11 harvest areas logged 1–8 years before the study with control streams in adjacent areas. Each sampling unit was a 50‐m stream section. The tetras Pyrrhulina brevis and Hemigrammus cf. pretoensis had higher abundances in plots logged ≥3 years before compared with plots logged <3 years before. The South American darter (Microcharacidium eleotrioides) was less abundant in logged plots than in control plots. In the short term, the overall fish composition did not differ two months before and immediately after reduced‐impact logging. Temperature and pH varied before and after logging, but those differences were compatible with normal seasonal variation. In the medium term, temperature and cover of logs were lower in logged plots. Differences in ordination scores on the basis of relative fish abundance between streams in control and logged areas changed with time since logging, mainly because some common species increased in abundance after logging. There was no evidence of species loss from the logging concession, but differences in log cover and ordination scores derived from relative abundance of fish species persisted even after 8 years. For Amazonian streams, reduced‐impact logging appears to be a viable alternative to clear‐cut practices, which severely affect aquatic communities. Nevertheless, detailed studies are necessary to evaluated subtle long‐term effects.     

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.     

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.     

Effects of Road Networks on Bird Populations

Abstract: One potential contributor to the worldwide decline of bird populations is the increasing prevalence of roads, which have several negative effects on birds and other vertebrates. We synthesized the results of studies and reviews that explore the effects of roads on birds with an emphasis on paved roads. The well‐known direct effects of roads on birds include habitat loss and fragmentation, vehicle‐caused mortality, pollution, and poisoning. Nevertheless, indirect effects may exert a greater influence on bird populations. These effects include noise, artificial light, barriers to movement, and edges associated with roads. Moreover, indirect and direct effects may act synergistically to cause decreases in population density and species richness. Of the many effects of roads, it appears that road mortality and traffic noise may have the most substantial effects on birds relative to other effects and taxonomic groups. Potential measures for mitigating the detrimental effects of roads include noise‐reduction strategies and changes to roadway lighting and vegetation and traffic flow. Road networks and traffic volumes are projected to increase in many countries around the world. Increasing habitat loss and fragmentation and predicted species distribution shifts due to climate change are likely to compound the overall effects of roads on birds.     

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 Road Fencing on Population Persistence

Abstract:  Roads affect animal populations in three adverse ways. They act as barriers to movement, enhance mortality due to collisions with vehicles, and reduce the amount and quality of habitat. Putting fences along roads removes the problem of road mortality but increases the barrier effect. We studied this trade-off through a stochastic, spatially explicit, individual-based model of population dynamics. We investigated the conditions under which fences reduce the impact of roads on population persistence. Our results showed that a fence may or may not reduce the effect of the road on population persistence, depending on the degree of road avoidance by the animal and the probability that an animal that enters the road is killed by a vehicle. Our model predicted a lower value of traffic mortality below which a fence was always harmful and an upper value of traffic mortality above which a fence was always beneficial. Between these two values the suitability of fences depended on the degree of road avoidance. Fences were more likely to be beneficial the lower the degree of road avoidance and the higher the probability of an animal being killed on the road. We recommend the use of fences when traffic is so high that animals almost never succeed in their attempts to cross the road or the population of the species of concern is declining and high traffic mortality is known to contribute to the decline. We discourage the use of fences when population size is stable or increasing or if the animals need access to resources on both sides of the road, unless fences are used in combination with wildlife crossing structures. In many cases, the use of fences may be beneficial as an interim measure until more permanent measures are implemented.     

Patterns of Nest Predation on Artificial and Natural Nests in Forests

Abstract:  Artificial nest experiments have been used in an attempt to understand patterns of predation affecting natural nests. A growing body of literature suggests that neither relative rates nor patterns of predation are the same for artificial and natural nests. We studied nest predation and daily mortality rates and patterns at real and artificial ground and shrub nests to test the validity of artificial nest experiments. We monitored 1667 artificial and 344 natural nests, over seven trials, in three regions, across 58 sites in Ontario. We controlled for many of the factors thought to be responsible for previously reported differences between predation rates on natural and artificial nests. Although artificial nests in our study resembled natural nests, contained eggs of appropriate size, shape, and color of target bird species, and were placed in similar microhabitats as natural nests, the rates of predation on these nests did not parallel rates on natural nests for any region in terms of absolute rate or pattern. Predation rates on artificial nests did not vary between years, as they tended to for natural nests, and the magnitude of predation pressure on artificial ground nests compared with shrub nests did not show the same pattern as that on natural nests. In general, rates of predation on artificial nests were significantly higher than on natural nests. Our results suggest that conclusions derived from artificial nest studies may be unfounded. Given that many influential ideas in predation theory are based on results of artificial nest experiments, it may be time to redo these experiments with natural nests.     

Direct Effects of Cattle on Grassland Birds in Canada

Effects of grazing on grassland birds are generally thought to be indirect, through alteration of vegetation structure; however, livestock can also affect nest survival directly through trampling and other disturbances (e.g., livestock‐induced abandonment). We extracted data on nest fates from 18 grazing studies conducted in Canada. We used these data to assess rates of nest destruction by cattle among 9 ecoregions and between seasonal and rotational grazing systems. Overall, few nests were destroyed by cattle (average 1.5% of 9132 nests). Nest destruction was positively correlated with grazing pressure (i.e., stocking rate or grazing intensity), but nest survival was higher in more heavily grazed areas for some species. Because rates of destruction of grassland bird nests by cattle are low in Canada, management efforts to reduce such destruction may not be of ecological or economic value in Canada. Efectos Directos del Ganado sobre las Aves de Pastizales en Canadá     

二嗪磷对鸟类脑组织乙酰胆碱酯酶活性的影响

为了初步研究有机磷农药二嗪磷对鸟类的毒性作用,采用室内饲喂染毒的方法,分析了二嗪磷对鹌鹑、鹧鸪及斑鸠3种鸟脑组织乙酰胆碱酯酶(AChE)活性的影响。鹌鹑、鹧鸪采用经食饲喂,染毒剂量分别为0、40、80、160、320、600mg·kg-1饲料和0、400、800、1600、3200、6000mg·kg-1饲料,试验周期8d;斑鸠采用拌种饲喂(1mL50%二嗪磷乳油拌500g麦种),染毒剂量为0、1.2、2.0、4.0、8.0mg·kg-1体重,一次性染毒后进行常规饲养,试验周期15d。结果表明,二嗪磷对3种鸟脑组织AChE活性均有一定程度的抑制作用:各染毒组死亡鸟AChE活性较对照降低显著(p<0.05,p<0.01),活性抑制率均超过40%;各染毒组存活鸟AChE活性较对照也有所降低,但活性抑制率均未超过20%.以上结果提示,抑制脑组织AChE活性可能是二嗪磷致鸟类死亡的重要原因。     

Effects of an Exotic Plant Invasion on Native Understory Plants in a Tropical Dry Forest

Abstract: The dry forests of southern India, which are endangered tropical ecosystems and among the world's most important tiger (Panthera tigris) habitats, are extensively invaded by exotic plants. Yet, experimental studies exploring the impacts of these invasions on native plants in these forests are scarce. Consequently, little is known about associated implications for the long‐term conservation of tigers and other biodiversity in these habitats. I studied the impacts of the exotic plant Lantana camara on understory vegetation in a dry‐forest tiger habitat in southern India. I compared the richness, composition, and abundance of tree seedlings, herbs, and shrubs and the abundance of grass among plots in which Lantana was cleared or left standing. These plots were distributed across two blocks—livestock free and livestock grazed. Removal of Lantana had an immediate positive effect on herb–shrub richness in the livestock‐free block, but had no effect on that of tree seedlings in either livestock block. Tree‐seedling and herb–shrub composition differed significantly between Lantana treatment and livestock block, and Lantana removal significantly decreased survival of tree seedlings. Nevertheless, the absence of trees, in any stage between seedling and adult, indicates that Lantana may stall tree regeneration. Lantana removal decreased the abundance of all understory strata, probably because forage plants beneath Lantana are less accessible to herbivores, and plants in Lantana‐free open plots experienced greater herbivory. Reduced access to forage in invaded habitats could negatively affect ungulate populations and ultimately compromise the ability of these forests to sustain prey‐dependent large carnivores. Additional research focused on understanding and mitigating threats posed by exotic plants may be crucial to the long‐term protection of these forests as viable tiger habitats.     

Linking Management Effectiveness Indicators to Observed Effects of Protected Areas on Fire Occurrence in the Amazon Rainforest

Management‐effectiveness scores are used widely by donors and implementers of conservation projects to prioritize, track, and evaluate investments in protected areas. However, there is little evidence that these scores actually reflect the capacity of protected areas to deliver conservation outcomes. We examined the relation between indicators of management effectiveness in protected areas and the effectiveness of protected areas in reducing fire occurrence in the Amazon rainforest. We used data collected with the Management Effectiveness Tracking Tool (METT) scorecard, adopted by some of the world's largest conservation organizations to track management characteristics believed to be crucial for protected‐area effectiveness. We used the occurrence of forest fires from 2000 through 2010 as a measure of the effect of protected areas on undesired land‐cover change in the Amazon basin. We used matching to compare the estimated effect of protected areas with low versus high METT scores on fire occurrence. We also estimated effects of individual protected areas on fire occurrence and explored the relation between these effects and METT scores. The relations between METT scores and effects of protected areas on fire occurrence were weak. Protected areas with higher METT scores in 2005 did not seem to have performed better than protected areas with lower METT scores at reducing fire occurrence over the last 10 years. Further research into the relations between management‐effectiveness indicators and conservation outcomes in protected areas seems necessary, and our results show that the careful application of matching methods can be a suitable method for that purpose. Vinculación de Indicadores de Efectividad de Manejo con los Efectos Observados de la Ocurrencia de Fuego en Áreas Protegidas en la Amazonia     

Effects of Growth Form and Functional Traits on Response of Woody Plants to Clearing and Fragmentation of Subtropical Rainforest

The conservation implications of large‐scale rainforest clearing and fragmentation on the persistence of functional and taxonomic diversity remain poorly understood. If traits represent adaptive strategies of plant species to particular circumstances, the expectation is that the effect of forest clearing and fragmentation will be affected by species functional traits, particularly those related to dispersal. We used species occurrence data for woody plants in 46 rainforest patches across 75,000 ha largely cleared of forest by the early 1900s to determine the combined effects of area reduction, fragmentation, and patch size on the taxonomic structure and functional diversity of subtropical rainforest. We compiled species trait values for leaf area, seed dry mass, wood density, and maximum height and calculated species niche breadths. Taxonomic structure, trait values (means, ranges), and the functional diversity of assemblages of climbing and free‐standing plants in remnant patches were quantified. Larger rainforest patches had higher species richness. Species in smaller patches were taxonomically less related than species in larger patches. Free‐standing plants had a high percentage of frugivore dispersed seeds; climbers had a high proportion of small wind‐dispersed seeds. Connections between the patchy spatial distribution of free‐standing species, larger seed sizes, and dispersal syndrome were weak. Assemblages of free‐standing plants in patches showed more taxonomic and spatial structuring than climbing plants. Smaller isolated patches retained relatively high functional diversity and similar taxonomic structure to larger tracts of forest despite lower species richness. The response of woody plants to clearing and fragmentation of subtropical rainforest differed between climbers and slow‐growing mature‐phase forest trees but not between climbers and pioneer trees. Quantifying taxonomic structure and functional diversity provides an improved basis for conservation planning and management by elucidating the effects of forest‐area reduction and fragmentation. Efectos de la Forma de Crecimiento y Atributos Funcionales en la Respuesta de Plantas Leñosas al Desmonte y Fragmentación de Bosque Lluvioso Subtropical