A meta‐analysis of bird and mammal response to short‐rotation woody crops

Short‐rotation woody cropping (SRWC) refers to silvicultural systems designed to produce woody biomass using short harvest cycles (1–15 years), intensive silvicultural techniques, high‐yielding varieties, and often coppice regeneration. Recent emphasis on alternatives to fossil fuels has spurred interest in producing SRWC on privately owned and intensively managed forests of North America. We examined potential bird and small mammal response at the stand level to conversion of existing, intensively managed forests to SRWCs using meta‐analysis of existing studies. We found 257 effect sizes for birds (243 effect sizes) and mammals (14 effect sizes) from 8 studies involving Populus spp. plantations. Diversity and abundance of bird guilds were lower on short‐rotation plantations compared with reference woodlands, while abundance of individual bird species was more variable and not consistently higher or lower on SRWC plantations. Shrub‐associated birds were more abundant on SRWC plantations, but forest‐associated and cavity‐nesting birds were less abundant. Effects on birds appeared to decrease with age of the SRWC plantation, but plantation age was also confounded with variation in the type of reference forest used for comparison. Both guilds and species of mammals were less abundant on SRWC plantations. These conclusions are tentative because none of these studies directly compared SRWC plantations to intensively managed forests. Plantations of SRWCs could contribute to overall landscape diversity in forest‐dominated landscapes by providing shrubby habitat structure for nonforest species. However, extensive conversion of mature or intensively managed forests to SRWC would likely decrease overall diversity, especially if they replace habitat types of high conservation value.     

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

Bell 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.     

Resources and global avian assemblage structure in forests

Explaining spatial variation in a number of bird species, particularly from temperate to tropical regions, has been a longstanding challenge. We test at a global scale whether species‐rich forest assemblages are associated with division of a larger resource pool, a finer division of that pool, or some combination of the two. Species richness increases with increasing assemblage abundance, biomass and energy use. As assemblage abundance, biomass and energy use increase with increasing energy availability, and as per species numbers of individuals, biomass and energy use do not decrease with increasing energy availability, we provide direct evidence that the avian species–energy relationship in forests is associated foremost with an increase in the size of the resource pool and not with a finer level of its subdivision.     

The relationship between multi‐scale habitat heterogeneity and farmland bird abundance

It has recently been proposed that losses in farmland habitat heterogeneity may have been a primary driver of the profound declines exhibited by many farmland bird species in recent decades. However, it has yet to be demonstrated which facets of heterogeneity and what spatial scales are most important for birds. Here we analyse the relationship between abundance and features of landscape heterogeneity at three spatial scales (1, 9 and 25 km²) for 32 bird species commonly associated with farmland. Heterogeneity was quantified using three contrasting indices reflecting 1) the spatial mixing of land uses, 2) variation in field sizes and 3) the density of field boundaries. The spatial mixing of land‐uses explained, on average, the most variation in, and was most likely to be positively associated with, abundance at all spatial scales. The majority of species (66–75%, depending on the spatial scale) were more common in heterogeneous landscapes overall; however, migrants, those under a high level of conservation concern and farmland specialist species tended to be less abundant in more heterogeneous landscapes at all scales. Ground‐nesting species were also more likely to be found in more homogeneous habitats than non‐ground‐nesters, but only at the finest spatial scale. Relationships between abundance and heterogeneity were generally consistent across spatial scales; however, species of high conservation concern had more variable associations compared with other species. These results highlight a potential role for farmland habitat heterogeneity in determining the abundance of many farmland species but suggest that population responses to an increase in heterogeneity would not be unanimously positive and would probably have negative impacts on some species, notably those that are already threatened.     

Does bird community structure vary with landscape patchiness? A Chihuahuan Desert perspective

During the springs of 1995–1997, we studied birds and landscapes at 70 sites in the Chihuahuan Desert to assess relations between bird community structure and landscape patchiness. Within each of two spatial extents (1‐km and 2‐km‐radius areas centered on each site), we measured the number of patches of individual land‐cover types and the total number of patches of all land‐cover types. Mean bird richness, and the mean abundance and probability of occurrence of most bird species were significantly correlated with one or more of these variables. Contrary to evidence from other systems, positive association with landscape patchiness did not increase with the degree to which species were habitat generalists, was not negatively related to body size, and did not differ between neotropical migrants and nonmigrants. For the communities’ primary constituent species as a group, the strength of positive and negative associations with patchiness did not differ between landscape extents. Within the 1‐km but not the 2‐km extent, habitat specialists were more positively and negatively associated with patchiness than were habitat generalists. In general, however, neither habitat breadth, body size, nor migratory status seemed to be responsible for associations with landscape patchiness. Mean richness, and the mean abundance and probability of occurrence of most species were significantly correlated with patchiness within one or both extents, and patchiness of all of the most extensive land‐cover types was influential. The simplest explanation for most of the bird‐patchiness relations we found is that the associations reflected species‐specific habitat needs. Through effects on avian richness, abundance, and occurrence, landscape patchiness affected bird community structure. A more complete understanding of the effects of landscape patchiness on bird community structure is likely to emerge when ecologists study the patchiness of major land‐cover types at various spatial extents.     

Are invasive species drivers of native species decline or passengers of habitat modification? A case study of the impact of the common myna (Acridotheres tristis) on Australian bird species

Habitat modification and invasive species are significant drivers of biodiversity decline. However, distinguishing between the impacts of these two drivers on native species can be difficult. For example, habitat modification may reduce native species abundance, while an invasive species may take advantage of the new environment. This scenario has been described as the driver‐passenger model, with ‘passengers’ taking advantage of habitat modification and ‘drivers’ causing native species decline. Therefore, research must incorporate both habitat modification and invasive species impact to successfully investigate native species decline. In this paper, we used the common myna (Acridotheres tristis) as a case study to investigate the driver‐passenger model. We investigated changes in bird abundance, over 2 years, in relation to different habitat types and common myna abundance. We hypothesized that the common myna is both a passenger of habitat change and a driver of some bird species decline. Our results indicated that the abundance of many native species is greater in high tree density nature reserves, while the common myna was uncommon in these areas. Common myna abundance was almost three times higher in urban areas than nature reserves and declined rapidly as tree density in nature reserves increased. Our findings indicated that the common myna is primarily a passenger of habitat change. However, we also observed negative associations between common myna abundance and some bird species. We stress the importance of simultaneously investigating both invasive species impact and habitat modification. We suggest habitat restoration could be a useful tool for both native species recovery and invasive species control. Understanding the drivers of native species decline will help inform impact mitigation and direct further research.     

Influence of crop type,heterogeneity and woody structure on avian biodiversity in agricultural landscapes

Agriculture is a primary factor underlying world-wide declines in biodiversity. However, different agricultural systems vary in their effects depending on their resemblance to the natural ecosystem, coverage across the landscape, and operational intensity. We combined data from the North American Breeding Bird Survey with remotely sensed measures of crop type and linear woody feature (LWF) density to study how agricultural type, woody structure and crop heterogeneity influenced the avian community at landscape scales across a broad agricultural region of eastern Canada. Specifically, we examined whether 1) avian diversity and abundance differed between arable crop agriculture (e.g., corn, soy) and forage (e.g., hay) and pastoral agriculture, 2) whether increasing the density of LWF enhances avian diversity and abundance, and 3) whether increasing the heterogeneity of arable crop types can reduce negative effects of arable crop amount. Avian diversity was lower in landscapes dominated by arable crop compared to forage agriculture likely due to a stronger negative correlation between arable cropping and the amount of natural land cover. In contrast, total avian abundance did not decline with either agricultural type, suggesting that species tolerant to agriculture are compensating numerically for the loss of non-tolerant species. This indicates that bird diversity may be a more sensitive response than bird abundance to crop cover type in agricultural landscapes. Higher LWF densities had positive effects on the diversity of forest and shrub bird communities as predicted. Higher crop heterogeneity did not reduce the negative effects of high crop amount as expected except for wetland bird abundance. In contrast, greater crop heterogeneity actually strengthened the negative effects of high crop amount on forest bird abundance, shrub-forest edge bird diversity and total bird diversity. We speculate that this was due to negative correlations between crop heterogeneity and the amount of shrub and forest habitat patches in crop-dominated landscapes in our study region. The variable response to crop heterogeneity across guilds suggests that policies aimed at crop diversification may not enhance avian diversity on their own and that management efforts aimed at the retention of natural forest and shrub patches, riparian corridors, and hedge-rows would be more directly beneficial.     

Broad-scale reciprocity in an avian seed dispersal mutualism

Aim Coevolved relationships between individual species of birds and plants rarely occur in seed dispersal mutualisms. This study evaluates whether reciprocal relationships may occur between assemblages of bird and plant species. Location Vancouver Island, British Columbia, Canada (48°50′‐N, 125°22′‐W). Methods The distribution and fruiting phenologies of seven shrub species were compared to seasonal changes in habitat selection and seed dispersal by six fruit‐eating bird species. Results Shrub species inhabiting forest understorey habitat had earlier fruiting phenologies than shrub species inhabiting forest edge habitat along lake and bog margins. Birds showed a parallel pattern in habitat selection, being more abundant in the forest understorey early in the fruiting season, and more abundant in the forest edge later in the season. Rates of seed deposition covaried with avian habitat selection, in such a way that birds directed seed dispersal into habitats preferred by shrubs. Conclusions These results depict a broad‐scale pattern in the abundance of birds and fruits indicative of reciprocal interactions. Seasonal changes in seed dispersal to each habitat appear to reinforce the relationship between shrub habitat affinities and fruiting phenologies. Phenological differences between habitats may also reinforce seasonal changes in avian habitat selection. Therefore, although reciprocal interactions between pairs of bird and plant species are rare, broad‐scale reciprocal relationships may occur between assemblages of bird and plant species.     

Perennial biomass feedstocks enhance avian diversity

Federal mandates to increase biofuel production in North America will require large new tracts of land with potential to negatively impact biodiversity, yet empirical information to guide implementation is limited. Because the temperate grassland biome will be a production hotspot for many candidate feedstocks, production is likely to impact grassland birds, a group of major conservation concern. We employed a multiscaled approach to investigate the relative importance of arthropod food availability, microhabitat structure, patch size and landscape‐scale habitat structure and composition as factors shaping avian richness and abundance in fields of one contemporary (corn) and two candidate cellulosic biomass feedstocks (switchgrass and mixed‐grass prairie) not currently managed as crops. Bird species richness and species density increased with patch size in prairie and switchgrass, but not in corn, and was lower in landscapes with higher forest cover. Perennial plantings supported greater diversity and biomass of arthropods, an important food for land birds, but neither metric was important in explaining variation in the avian community. Avian richness was higher in perennial plantings with greater forb content and a more diverse vegetation structure. Maximum bird species richness was commonly found in fields of intermediate vegetation density and grassland specialists were more likely to occur in prairies. Our results suggest that, in contrast to corn, perennial biomass feedstocks have potential to provide benefits to grassland bird populations if they are cultivated in large patches within relatively unforested landscapes. Ultimately, genetic improvement of feedstock genets and crop management techniques that attempt to maximize biomass production and simplify crop vegetation structure will be likely to reduce the value of perennial biomass plantings to grassland bird populations.     

Avian species richness and abundance at Lake Constance: diverging long-term trends in Passerines and Nonpasserines

In Central Europe, massive losses in species richness of breeding birds have been documented in the last decades, but the question arises whether species richness is currently still decreasing or again increasing due to conservation efforts. In this study, we investigated regional and local species richness as well as mean number of breeding pairs and mean biomass per tetrad over a period of some 20 years at Lake Constance. Three quantitative censuses of 303 tetrads (2 × 2 km²) repeated at 10-year intervals (1980–1981, 1990–1992, 2000–2002) revealed an increase in regional species richness (total number of breeding species). At the same time, however, a strong decline in local species richness (number of breeding species per tetrad), number of breeding pairs, and estimated biomass were observed. Changes of species richness differed markedly between Nonpasserine and Passerine birds. Whereas species richness of Nonpasserines remained constant from 1980 to 1990, and even increased between 1990 and 2000, that of Passerines decreased in both periods. This indicates that effects of conservation efforts apparently eclipse more general effects of climate and habitat change in Nonpasserines. The massive abundance and biomass losses observed in formerly common Passerine species are not compensated by gains in populations of Nonpasserine species. The results of the three bird censuses at Lake Constance imply that ongoing habitat degradation and human impacts as well as increasing effects of climate change are the main drivers of the observed population changes.     

The native versus alien dichotomy: relative impact of native noisy miners and introduced common mynas

Human activity can dramatically affect biodiversity, often by introducing non-native species, or by increasing the abundance of a small number of native species. Management strategies aimed at conserving biodiversity need to be informed by the actual impacts of highly abundant species, whether native or introduced. In this study we examined characteristics of two bird species, introduced common mynas and native noisy miners, both of which are highly abundant in urbanised areas along the East coast of Australia. Current managerial practices have a strong focus on eradication of common mynas, while noisy miners are largely ignored. However, in this study noisy miners were found in a broader range of habitats, and in greater abundance, than common mynas; displayed more aggressive behaviour; and were linked to a decline in the diversity and abundance of other species where common mynas were not. We suggest that the adaptability of a species and the variety of habitats it can colonise may be a better predictor of its potential impact, than whether it is native or introduced.     

Modelling the responses of Australian subtropical rainforest birds to changes in environmental conditions along elevational gradients

Montane birds face significant threats from a warming climate, so determining the environmental factors that most strongly influence the composition of such assemblages is of critical conservation importance. Changes in temperature and other environmental conditions along elevational gradients are known to influence the species richness and abundance of bird assemblages occupying mountains. However, the role of species‐specific traits in mediating the responses of bird species to changing conditions remains poorly understood. We aimed to determine whether different bird species responded differently to changing environmental conditions in a relatively understudied biodiversity hotspot in subtropical rainforest on the east coast of Australia. We examined patterns in avian species richness and abundance along two rainforest elevational gradients using monthly point counts between September 2015 and October 2016. Environmental data on temperature, wetness, canopy cover and canopy height were collected simultaneously, and trait information on body size and feeding guild membership for each bird species was obtained from the Handbook of Australian, New Zealand and Antarctic Birds. We used a generalized linear mixed modelling (GLMM) framework to determine the drivers of species richness and abundance and to quantify species’ trait–environment interactions. GLMMs indicated that temperature alone was significantly positively correlated with species richness and abundance. Species richness declined with increasing elevation. When modelling abundance, we found that feeding guild membership did not significantly affect species’ responses to environmental conditions. In contrast, the predicted abundance of a species was found to depend on its body size, due to significant positive interactions between this trait, temperature and canopy cover. Our findings indicate that large‐bodied birds are likely to increase in abundance more rapidly than small‐bodied birds with continued climatic warming. These results underline the importance of temperature as a driving factor of avian community assembly along environmental gradients.     

Land‐use change promotes avian diversity at the expense of species with unique traits

Land‐use change may alter both species diversity and species functional diversity patterns. To test the idea that species diversity and functional diversity changes respond in differing ways to land‐use changes, we characterize the form of the change in bird assemblages and species functional traits along an intensifying gradient of land use in the savanna biome in a historically homogeneous vegetation type in Phalaborwa, South Africa. A section of this vegetation type has been untransformed, and the remainder is now mainly characterized by urban and subsistence agricultural areas. Using morphometric, foraging and breeding functional traits of birds, we estimate functional diversity changes. Bird species richness and abundance are generally higher in urban and subsistence agricultural land uses, as well as in the habitat matrix connecting these regions, than in the untransformed area, a pattern mainly driven through species replacement. Functionally unique species, particularly ground nesters of large body size, were, however, less abundant in more utilized land uses. For a previously homogenous vegetation type, declines in the seasonality of energy availability under land‐use change have led to an increase in local avian diversity, promoting the turnover of species, but reduced the abundance of functionally unique species. Although there is no simple relationship between land‐use and diversity change, land‐use change may suit some species, but such change may also involve functional homogenization.     

The efficacy of common species as indicators: avian responses to disturbance in British Columbia,Canada

Common species can be major drivers of species richness patterns and make major contributions to biomass and ecosystem function, and thus should be important targets for conservation efforts. However, it is unclear how common species respond to disturbance, because the underlying reasons for their commonness may buffer or amplify their responses to disturbance. To assess how well common species reflect changes in their community (and thus function as indicator species), we studied 58 bird species in 19 mixed conifer patches in northern British Columbia, Canada, between 1998 and 2010. During this time period two disturbance events occurred, stand level timber harvest and a regional-scale bark beetle outbreak. We examined relationships among densities of individual species, total bird density and overall species richness, correlations in abundance among species, and responses to disturbance events. We found three broad patterns. First, densities of common species corresponded more strongly with changes in total bird density and overall species richness than rare species. These patterns were non-linear and species with intermediate-high commonness showed similar or better correspondence than the most common species. Second, common species tended to be more strongly correlated with abundances of all other species in the community than less-common species, although on average correlations among species were weak. Third, ecological traits (foraging guild, migratory status) were better predictors of responses to disturbance than species commonness. These results suggest that common species can collectively be used to reflect changes in the overall community, but that whenever possible monitoring programs should be extended to include species of intermediate-high commonness and representatives from different ecological guilds.     

Species–area relationships in the Andaman and Nicobar Islands emerge because rarer species are disproportionately favored on larger islands

The island species–area relationship (ISAR) describes how the number of species increases with increasing size of an island (or island‐like habitat), and is of fundamental importance in island biogeography and conservation. Here, we use a framework based on individual‐based rarefaction to infer whether ISARs result from passive sampling, or whether some processes are acting beyond sampling (e.g., disproportionate effects and/or habitat heterogeneity). Using data on total and relative abundances of four taxa (birds, butterflies, amphibians, and reptiles) from multiple islands in the Andaman and Nicobar archipelago, we examine how different metrics of biodiversity (total species richness, rarefied species richness, and abundance‐weighted effective numbers of species emphasizing common species) vary with island area. Total species richness increased for all taxa, as did rarefied species richness controlling for a given sampling effort. This indicates that the ISAR did not result because of passive sampling, but that instead, some species were disproportionately favored on larger islands. For birds, frogs, and lizards, this disproportionate effect was only associated with species that were rarer in the samples, but for butterflies, both more common and rarer species were affected. Furthermore, for the two taxa for which we had plot‐level data (reptiles and amphibians), within‐island β‐diversity did not increase with island size, suggesting that within‐island compositional effects were unlikely to be driving these ISARs. Overall, our results indicate that the ISARs of these taxa are most likely driven by disproportionate effects, that is, where larger islands are important sources of biodiversity beyond a simple sampling expectation, especially through their influence on rarer species, thus emphasizing their role in the preservation and conservation of species.     

A review of the impacts of corvids on bird productivity and abundance

Corvids are often viewed as efficient predators capable of limiting prey species populations. Despite this widely held belief, a comprehensive review quantifying the effect of corvids on the demography of prey species is lacking. We examine the impacts of crows, ravens Corvus spp. and Eurasian Magpies Pica pica on the population parameters of other bird species. We summarize results from 42 studies, which included 326 explicit evaluations of relationships between a corvid and a potential prey species. Population parameters of studied prey species were categorized as abundance‐related (numbers, nest density) or productivity‐related (nest success, brood size). Information from both experimental removal studies and correlative studies was examined. Combining all studies, no negative influence of corvids on either abundance or productivity of prey species was found in 81% of cases. Negative impacts were significantly more likely in cases examining productivity rather than abundance (46 vs. 10%). Experimental studies that removed only corvid species were significantly less likely to show a positive impact on productivity than those removing corvids alongside other predators (16 vs. 60%). This suggests that the impact of corvids is smaller than that of other predators, or that compensatory predation occurs. The impact of corvids was similar between diverse avian groups (such as gamebirds, passerines and waders; or ground‐nesting and other species). Crows were found to be significantly more likely to have a negative impact on prey species productivity than were Magpies (62 vs. 12%), but no differences were found in relation to prey abundance. We conclude that while corvids can have a negative impact on bird species, their impact is small overall, and nearly five times more frequent for productivity than for abundance. These results suggest that in most cases bird populations are unlikely to be limited by corvid predation and that conservation measures may generally be better targeted at other limiting factors. However, negative impacts were found in a minority of cases, and those may require further investigation to develop management tools to mitigate such impacts where they are of economic or conservation concern.     

Seed Dispersal by Birds and Bats in Lowland Philippine Forest Successional Area

In the tropical forests of SE Asia, only a few studies have dealt with the role animal dispersal plays in early forest succession and rehabilitation, and a comparison of bird and bat dispersal is even rarer. We investigated seed dispersal by birds and bats in a successional area in the lowland dipterocarp forest of the Subic Watershed Forest Reserve (SWFR) in Luzon Island, Philippines. Using pairs of day and night traps, we collected seeds during 3 mo of wet season and 3 mo of dry season in a 1.2-ha study site. Bird-dispersed seeds predominated over those dispersed by bats in terms of both seed abundance and number of seed species. The most abundant endozoochorous seed species were significantly biased toward either bird or bat dispersal. Birds and bats appeared to compete more strongly for fruit resources during the dry season than during the wet season, and bats responded more to changes in the seasons than birds did. GLM analyses showed that the factor that had the strongest influence on overall seed distribution was the number of fleshy-fruited trees surrounding the traps, and that the distribution pattern of day-dispersed seeds was affected by more physical factors (number of trees, size of trees, presence of fleshy-fruited and conspecific trees) in the study site than the pattern of night-dispersed seeds were. Given that birds are the more important dispersers in the study site, restoration efforts in SWFR might benefit by focusing on attracting these dispersers into its degraded habitats.     

Yellow‐throated miners Manorina flavigula homogenize bird communities across intact and fragmented landscapes

In Australia, the role of noisy miners Manorina melanocephala in biotic homogenization of the avifauna has been well established in modified landscapes, and is listed as a threatening process under national conservation legislation. However, less is known about the effect of the congeneric and more widely distributed yellow‐throated miner, M. flavigula. In this paper we investigate the relative roles of habitat loss and increased dominance by the yellow‐throated miner in avian homogenization and species functional group decline. We examined bird community data collected from 368 woodland sites across three bioregions. For each site there was a local and a landscape scale measure of remnant vegetation cover. We used both multivariate and regression analysis to test the relative influence of yellow‐throated miner abundance and vegetation on bird community composition. There was clear compositional change and homogenization of the avifauna where yellow‐throated miners were present and vegetation cover was low. The abundance of 40 bird species was predicted by combinations of vegetation cover or yellow‐throated miner abundance, and 31 of these regressions included the term yellow‐throated miner. Of these, there was a negative relationship with 23 species, and 19 of these were insectivores or nectarivores. We postulate that the combination of clearing and yellow‐throated miner abundance can interact to disrupt the ecological function of woodlands, by the depletion of insect‐ and nectar‐feeding species and the disturbance to mixed feeding flocks. We propose future research objectives that include a continental‐scale analysis of the determinants of yellow‐throated miner overabundance, the numerical and geographical thresholds of their potential impacts, and the ecological consequences on both avifauna and the woodlands they inhabit.     

The impact of cattle grazing regimes on tropical savanna bird assemblages

Globally, agricultural land use is implicated in the decline of avifauna. In rangelands (areas used for livestock grazing), bird community responses to grazing can be complex, species‐specific and scale dependent. A greater understanding of bird responses to grazing will lead to more meaningful management recommendations. We tested the hypothesis that foraging height predicts bird species’ responses to grazing, such that species using lower vegetation strata are most likely to respond to the impacts of livestock grazing. We examined the response of a tropical savanna bird community to four grazing strategies at a long‐term grazing trial in northern Australia. We predicted that ground‐foraging guilds would be more responsive to grazing treatment than foliage‐ or aerial‐foraging guilds. We analysed the bird community assemblage using generalised linear mixed models and examined individual species’ abundance in relation to microhabitat variables. We found that while ground‐foraging guilds were more responsive to grazing treatment, individual species dynamics within a foraging guild could be contradictory. For example, the red‐backed fairy‐wren decreased in abundance with increased grazing and was positively associated with grass and shrub (Carissa ovata) cover, whereas Australian magpies increased in abundance in the most heavily grazed paddocks. In general, the responses of bird species to grazing were more pronounced in guilds that forage closer to the ground, but whether the responses were positive or negative was driven by bird species ecology. Measures examining the responses of individual species are more useful than assemblage measures (such as richness) to describe the impacts of anthropogenic disturbance such as grazing.     

Restoring Savanna Using Fire: Impact on the Breeding Bird Community

Restoration of many terrestrial plant communities involves the reintroduction of fire. However, there have been few studies of the effects of fire on the avifauna during the restoration process. To study the effects of oak savanna restoration on avian communities, breeding birds were censused and the vegetation structure documented in seven experimental burn units (8–18 ha) that had experienced different frequencies of controlled burns during the past 31 years (0–26 burns). Data were analyzed with both direct and indirect gradient analyses using multivariate techniques. The results showed that, as savanna restoration proceeded, there was a general decline in predominantly insectivorous species, particularly those that feed in the upper canopy region (leaves and air space), and a general increase in omnivorous species, particularly those that feed on the ground and in the lower canopy. Insectivorous bark gleaners (woodpeckers) also increased during restoration and were correlated with the increase in standing dead trees resulting from the fires. Overall, savanna restoration resulted in increases in the abundance of many open country bird species, including many species that have been declining in central and eastern North America, including red‐headed woodpecker, Baltimore oriole, eastern kingbird, vesper sparrow, field sparrow, lark sparrow, brown thrasher, American goldfinch, and brown‐headed cowbird. The shifts in species and guilds were correlated with changes in burn frequency and the macro vegetation structure—tree and shrub density, leaf area index, and relative proportion of standing dead trees. The findings show that savanna restoration can increase bird diversity and provide important habitat for uncommon or declining bird species. These birds are most likely attracted to one or more of the distinctive habitat features of the restored savanna environments, including scattered mature trees, standing dead trees and snags, and presence of both shrubby and grassland vegetation. The findings also suggest that restoration ecologists and wildlife biologists will need to work together to achieve desired goals, since different types of savanna restoration efforts may produce different effects on the breeding bird community.