Patterns of non-randomness in the composition and characteristics of the Taiwanese bird trade

The invasion pathway is composed of a sequential series of stages that need to be quantified separately in order properly to understand the invasion process. Here, we examine the composition and characteristics of bird species being sold in the pet bird market in Taiwan. The bird trade in Taiwan is of high volume and financially lucrative. The identity of species in this trade is vital for informing later stages (introduction, establishment, spread) of the invasion pathway. We conducted interviews and surveys of 72 outlets selling pet birds from seven cities across Taiwan, from which we identified 247 bird species (within 34 families) for sale. Of these, 170 bird species (from 27 families) are exotic to Taiwan. Using randomization tests, we show that nine families are significantly over-represented in the pet trade (Psittacidae, Muscicapidae, Timaliidae, Sturnidae, Turdidae, Estrildidae, Chloropseidae, Zosteropidae and Fringillidae), and three after sequential Bonferroni correction (Psittacidae, Muscicapidae and Sturnidae). Species that have been identified in Taiwanese pet shops tend to have a larger native geographic range, originate further from the equator, are smaller-bodied, and have more aesthetically-pleasing songs than expected by chance. The native ranges of pet shop species are more likely to be situated in the Indo-Malay and Palearctic biogeographic realms, while fewer species than expected derive from the Neotropic, Afrotropic and Nearctic realms. Our results show that bird species for sale in Taiwan are determined by the interaction of species availability and societal demands.     

Geographical range expansion of alien birds and environmental matching

The international wildlife trade is a significant source of introduced alien species, some of which proceed to become invasive and cause negative environmental and economic effects. However, not all introduced aliens establish viable populations, and it is important to identify the factors that determine establishment success. We explore the role of environmental suitability (including anthropogenic influences, climate and habitat types) in the establishment success of alien bird species introduced to Taiwan. Using maximum entropy modelling, we employed a recursive feature elimination and Akaike information criterion (AIC)‐based stepwise model selection approach to assess whether the environmental suitability, native range size, body size, residence time and the numbers of birds for sale in the shops affect variation in the extent of alien bird range size in Taiwan. We show that species with larger native range sizes and larger body sizes tend to have larger alien range sizes in Taiwan. There was no effect of environmental suitability on alien range size in Taiwan, but environmental suitability influenced the establishment success of bird species there.     

Interspecific abundance-range size relationships: range position and phylogeny

A number of mechanisms have been proposed to explain the widely observed positive interspecific relationship between local abundance and extent of geographic distribution in animals Here, we use data on British birds to assess two of these hypotheses that the relationship results from the relative position of a study area with respect to the geographic ranges of the species which occur there, and that the relationship results from a simple difference between taxonomic groups, rather than any general tendency for more abundant species to have larger range sizes We find support for neither hypothesis Phylogenetically controlled comparative analyses reveal that the positive abundance-range size relationship is consistently found within taxa, even when abundance and range size are calculated at a variety of spatial and temporal scales Analyses both across species and within taxa show that bird species for which Britain is near to the centre of their distribution in Europe tend to have larger British range sizes and higher abundances than do species where Britain is close to the edge of their range in Europe However, these relationships do not cause that between abundance and range size, because this latter relationship persists within different range position categories Whether a species is near the centre or edge of its geographic range in Britain may affect its position on the abundance-range size relationship, but does not produce the relationship Range position in Britain does, however, seem to be related to the magnitude of temporal changes in the range sizes of British birds There is some evidence to suggest that species for which Britain is nearer to their European range centre have shown smaller changes in distribution over the period 1970–1990 than have species for which Britain is close to their European range edge     

Quantification of climatic niches in birds: adding the temporal dimension

Quantification of the climatic niche from geographic occurrences is an increasingly important tool for studying species’ relationships to their environment, for example to predict responses to climate change. However, as the geographic distributions of birds are seasonally dynamic, they pose a challenge to carrying out comparable and appropriate quantification of climatic niches. In this review, we first assess how relevant seasonal dynamics are across birds as a whole by compiling a database of migratory behaviour for 10 443 bird species. Second, we examine how studies have quantified climatic niches of birds. Finally, using Australia as a case study, we investigate how well existing distribution datasets represent temporal dynamics by comparing seasonal patterns of species richness obtained from point‐occurrence data with those from range maps and assess the consequences for niche quantification. We provide a consistent classification of migratory behaviour across all birds, and find that a huge variety exists between and within species that should be considered when quantifying climatic niches. Despite this, our review of the literature revealed that seasonal dynamics have often not been accounted for. For future studies, we provide a framework for selecting appropriate occurrence data depending on migratory behaviour and data availability. Our comparison of seasonal species richness patterns obtained from extent‐of‐occurrence range maps and point‐occurrence data suggests that range maps are less able to detect temporal dynamics of bird distributions than point‐occurrence data. We conclude that seasonally explicit range maps combined with climatic data for the corresponding time period can be used to adequately quantify climatic niches for resident birds, but are not adequate to quantify the climatic niches of migratory and nomadic species. Therefore, consistent quantification of climatic niches across all birds requires temporally explicit occurrence points. As such, increasing the availability of occurrence data and methods correcting biases should be a priority.     

A global analysis of the determinants of alien geographical range size in birds

Aim Determining the causes of range size variation in the distributions of alien species is important for understanding the spread of invasive species. Factors influencing alien range size have been explored for some species at a regional level, but to date there has been no global analysis of an entire class. Here, we present such an analysis for birds, testing for the effects of introduction event, location and species‐level variables on alien range sizes. Location Global. Methods We used a novel dataset on the global distributions of alien bird species to test for relationships between alien range size and colonization pressure, residence time, extent of the global climatic niche, native range size, body mass and specialization, using a statistical approach based on phylogenetic generalized least squares models. We performed this analysis globally, and for separate biogeographical realms. Results Approximately half of the variation in alien bird range size is explained by colonization pressure in univariate analysis. We identified consistent effects of higher colonization pressure at global and realm levels, as well as support for effects of native range size and residence time. We found less support for effects of body mass, specialization or extent of the global climatic niche on alien range size. Main conclusions Alien bird range sizes are generally small relative to their native range sizes, and many are continuing to expand. Nevertheless, current variation is predictable, most strongly by the event‐level factor of colonization pressure. Whether a species is widespread is a better predictor of alien range size than whether a species could be widespread (estimated by global climatic niche extent), while we also find effects of residence time on alien range size. These relationships may help to identify those alien species that are more likely to spread and hence have greater environmental and economic impacts where they have been introduced.     

Bird diversity patterns in Neotropical temperate farmlands: The role of environmental factors and trophic groups in the spring and autumn

Productivity, habitat heterogeneity and environmental similarity are of the most widely accepted hypotheses to explain spatial patterns of species richness and species composition similarity. Environmental factors may exhibit seasonal changes affecting species distributions. We explored possible changes in spatial patterns of bird species richness and species composition similarity. Feeding habits are likely to have a major influence in bird–environment associations and, given that food availability shows seasonal changes in temperate climates, we expect those associations to differ by trophic group (insectivores or granivores). We surveyed birds and estimated environmental variables along line‐transects covering an E‐W gradient of annual precipitation in the Pampas of Argentina during the autumn and the spring. We examined responses of bird species richness to spatial changes in habitat productivity and heterogeneity using regression analyses, and explored potential differences between seasons of those responses. Furthermore, we used Mantel tests to examine the relationship between species composition similarity and both the environmental similarity between sites and the geographic distance between sites, also assessing differences between seasons in those relationships. Richness of insectivorous birds was directly related to primary productivity in both seasons, whereas richness of seed‐eaters showed a positive association with habitat heterogeneity during the spring. Species composition similarity between assemblages was correlated with both productivity similarity and geographic proximity during the autumn and the spring, except for insectivore assemblages. Diversity within main trophic groups seemed to reflect differences in their spatial patterns as a response to changes between seasons in the spatial patterns of food resources. Our findings suggest that considering different seasons and functional groups in the analyses of diversity spatial pattern could contribute to better understand the determinants of biological diversity in temperate climates.     

Unveiling the environmental drivers of intraspecific body size variation in terrestrial vertebrates

Aim

Whether intraspecific spatial patterns in body size are generalizable across species remains contentious, as well as the mechanisms underlying these patterns. Here we test several hypotheses explaining within-species body size variation in terrestrial vertebrates including the heat balance, seasonality, resource availability and water conservation hypotheses for ectotherms, and the heat conservation, heat dissipation, starvation resistance and resource availability hypotheses for endotherms.

Location

Global.

Time period

1970–2016.

Major taxa studied

Amphibians, reptiles, birds and mammals.

Methods

We collected 235,905 body size records for 2,229 species (amphibians = 36; reptiles = 81; birds = 1,545; mammals = 567) and performed a phylogenetic meta-analysis of intraspecific correlations between body size and environmental variables. We further tested whether correlations differ between migratory and non-migratory bird and mammal species, and between thermoregulating and thermoconforming ectotherms.

Results

For bird species, smaller intraspecific body size was associated with higher mean and maximum temperatures and lower resource seasonality. Size–environment relationships followed a similar pattern in resident and migratory birds, but the effect of resource availability on body size was slightly positive only for non-migratory birds. For mammals, we found that intraspecific body size was smaller with lower resource availability and seasonality, with this pattern being more evident in sedentary than migratory species. No clear size–environment relationships were found for reptiles and amphibians.

Main conclusions

Within-species body size variation across endotherms is explained by disparate underlying mechanisms for birds and mammals. Heat conservation (Bergmann's rule) and heat dissipation are the dominant processes explaining biogeographic intraspecific body size variation in birds, whereas in mammals, body size clines are mostly explained by the starvation resistance and resource availability hypotheses. Our findings contribute to a better understanding of the mechanisms behind species adaptations to the environment across their geographic distributions.     

Poleward shifts in breeding bird distributions in New York State

Like other regions of the northern hemisphere, the northeastern United States has experienced a general increase in regional temperatures over the past 20 years. Quantifying the ecological implications of these changing temperatures has been severely constrained by a lack of multispecies distributional data by which to compare long-term changes. We used the New York State Breeding Bird Atlas, a statewide survey of 5332 25 km² blocks surveyed in 1980–1985 and 2000–2005, to test several predictions that the birds of New York State are responding to climate change. Our objective was to use an information-theoretic approach to analyze changes in three geographic range characteristics, the center of occurrence, range boundaries, and states of occurrence to address several predictions that the birds of New York State are moving polewards and up in elevation. As expected, we found all bird species ( n =129) included in this analysis showed an average northward range shift in their mean latitude of 3.58 km [ Prob ( H _a|data)=0.87)]. Past studies have found that northern range boundaries are more likely to be influenced by climatic factors than southern range boundaries. Consequently, we predicted that northward shifts would be more evident in northern as opposed to southern range boundaries. We found, however, that the southern range boundaries of northerly birds moved northward by 11.4 km [ n =43, Prob ( H _a|data)=0.92], but this pattern was less evident in northern range boundaries of southerly birds. In addition, we found that bird species demonstrated a general shift downhill in their mean elevation, but demonstrated little change in their elevational boundaries. The repeated pattern of a predicted northward shift in bird ranges in various geographic regions of the world provides compelling evidence that climate change is driving range shifts.     

The relative role of rivers,environmental heterogeneity and species traits in driving compositional changes in southeastern Amazonian bird assemblages

Amazonian rivers have been proposed to act as geographic barriers to species dispersal, either driving allopatric speciation or defining current distribution limits. The strength of the barrier varies according to the species’ ecological characteristics and the river's physical properties. Environmental heterogeneity may also drive compositional changes but has not been well assessed in Amazonia. Aiming to understand the contributions of riverine barriers and environmental heterogeneity in shaping compositional changes in Amazonian forest bird assemblages, we focus on the Tapajós River. We investigate how spatial variation in species composition is related to physical barriers (Tapajós and Jamanxim rivers), species’ ecological characteristics (distinct guilds), and environmental heterogeneity (canopy reflectance, soils, and elevation). We sampled birds through point-counts and mist nets on both banks of the Tapajós and Jamanxim rivers. To test for relationships between bird composition and environmental data, we used Mantel and partial Mantel tests, NMDS, and ANOVA + Tukey HSD. The Mantel tests showed that the clearest compositional changes occurred across the Tapajós River, which seems to act unequally as a significant barrier to the bird guilds. The Jamanxim River was not associated with differences in bird communities. Our results reinforce that the Tapajós River is a biogeographical boundary for birds, while environmental heterogeneity influences compositional variation within interfluves. We discuss the combined influence of geographical barriers, environmental heterogeneity, and ecological characteristics of species in shaping species distributions and community composition and the complexity of extrapolating the patterns found for birds to other Amazonian organisms. Abstract in Portuguese is available with online material.     

Of mice and wrens: the relation between abundance and geographic range size in British mammals and birds

We examine the relation between population size and geographic range size for British breeding birds and mammals. As for most other assemblages studied, a strong positive interspecific correlation is found in both taxa. The relation is also recovered once the phylogenetic relatedness of species has been controlled for using an evolutionary comparative method. The slope of the relation is steeper for birds than for mammals, but this is due in large part to two species of mammals that have much higher population sizes than expected from their small geographic ranges. These outlying mammal species are the only ones in Britain to be found only on small offshore islands, and so may be exhibiting density compensation effects. With them excluded, the slope of the abundance–range size relation for mammals is not significantly different to that for birds. However, the elevation of the relation is higher for mammals than for birds, indicating that mammals are approximately 30 times more abundant than birds of equivalent geographic range size. An earlier study of these assemblages showed that, for a given body mass, bats had abundances more similar to birds than to non-volant mammals, suggesting that the difference in abundance between mammals and birds might be due to constraints of flight. Our analyses show that the abundance–range size relation for bats is not different for that from other mammals, and that the anomalously low abundance of bats for their body mass may result because they have smaller than expected geographic extents for their size. Other reasons why birds and mammals might have different elevations for the relation between population size and geographic range size are discussed, together with possible reasons for why the slopes of these relations might be similar.     

The role of body size in nest-site selection by secondary cavity-nesting birds in a subtropical Chaco forest

Most bird species that nest in tree cavities globally occur in diverse assemblages in little-studied tropical and subtropical forests which have high rates of habitat loss. Conservation of these communities will require an understanding of how species traits, such as body size, influence nest-site selection. We examined patterns of nest-site selection of secondary cavity-nesting birds at the nest patch, tree and cavity scale, and investigated how these patterns are influenced by body size. Using conditional logistic regression, we compared characteristics of 155 nest tree cavities paired with 155 unused tree cavities in quebracho Schinopsis balansae forests in Chaco National Park, Argentina (2016–2018). The odds of a cavity being used for nesting increased with its depth and height above ground, decreased with entrance size, and were greater for dead trees than live. Small-bodied (13–90 g) species used floor diameters in proportion to availability, but medium- (150–200 g) and large-bodied (400–700 g) species selected cavities with larger floors. Model selection indicated that characteristics at the nest patch scale (canopy cover, tree density) had little effect on nest-site selection when cavity-scale variables were included. Cavity floor diameter, entrance size, cavity height and tree diameter (but not cavity depth) increased with body mass, and larger bird species more often used live trees. Two tree species proved to be key for the community: large and medium-sized birds used almost exclusively large live Schinopsis balansae, whereas small birds used live and dead Prosopis spp. in a proportion greater than its availability. Small birds could be differentiated according to species-specific cavity characteristics, but medium and large species overlapped considerably with one another. Although body mass explained much of the overall variation in tree and cavity characteristics between small and medium/large species, several small-bodied species consistently used cavities outside of the expected characteristics for their body size, suggesting that other natural history traits may play important roles in nest-site selection by small-bodied birds. To retain the full suite of secondary cavity-nesters in species-rich tropical and subtropical forests, it is necessary to conserve a diversity of trees and cavities that meet the full range of nesting requirements of these trait-diverse communities.     

Using citizen science to measure recolonisation of birds after the Australian 2019–2020 mega-fires

Large and severe fires (‘mega-fires’) are increasing in frequency across the globe, often pushing into ecosystems that have previously had very long fire return intervals. The 2019–2020 Australian bushfire season was one of the most catastrophic fire events on record. Almost 19 million hectares were burnt across the continent displacing and killing unprecedented numbers of native fauna, including bird species. Some bird species are known to thrive in post-fire environments, while others may be absent for an extended period from the firegrounds until there is sufficient ecosystem recovery. To test for systematic patterns in species use of the post-fire environment, we combined citizen science data from eBird with data on sedentism, body size, range size and the specialisation of diet and habitat. Using generalised additive models, we modelled the responses of 76 bird species to the 2019–2020 Australian mega-fires. Twenty-two species decreased in occurrence after the fire; 30 species increased; and no significant effect was found for the remaining 24 species. Furthermore, diet specialists, and birds with smaller body sizes and range sizes were less likely to be found in burnt areas after the fire event compared to before, a result which generates testable hypotheses for recovery from other mega-fires across the globe. Being displaced from the firegrounds for an event of this geographic magnitude may have severe consequences for population dynamics and thus warrant considerable conservation attention in pre-fire planning and in the post-fire aftermath.     

Going Cheap: Determinants of Bird Price in the Taiwanese Pet Market

BackgroundInternational wildlife trade is the largest emerging source of vertebrate invasive alien species. In order to prevent invasions, it is essential to understand the mechanics of trade and, in particular, which traded species are most likely to be released or escape into the wild. A species’ economic value is a key factor, because we expect cheaper species to be less assiduously secured against escaping, and more likely to be deliberately released. Here, we investigate determinants of the price of species in the Taiwanese bird trade. Taiwan is an international hub for bird trade, and several native species are threatened by alien bird species.MethodologyWe investigated the relationship between the traded species sale price in Taiwan and the species availability for trade (the number of birds for sale, geographic range size and their origin, conservation and CITES status) and traits (body size, coloration, song attractiveness). We used phylogenetic generalized least squares models, with multi-model inference, to assess the variables that are best related to the price of birds in the Taiwanese pet trade.

Principal Findings / Conclusions

We found that species available for sale in larger numbers, native to Taiwan, not globally endangered, and small-bodied are all relatively cheaper, as too are species lacking yellow coloration and without attractive songs. Our models of price revealed high levels of phylogenetic correlation, and hence that closely related species tended to be sold for similar prices. We suggest that, on the basis of price, native species are more likely to be deliberately or accidentally released than alien species. Nevertheless, our survey of bird shops recorded 160 species alien to Taiwan (7,631 individuals), several of which are for sale cheaply and in large numbers. Alien bird species in trade therefore present an ongoing, non-trivial invasion risk on the island.     

Global patterns of geographic range size in birds

Large-scale patterns of spatial variation in species geographic range size are central to many fundamental questions in macroecology and conservation biology. However, the global nature of these patterns has remained contentious, since previous studies have been geographically restricted and/or based on small taxonomic groups. Here, using a database on the breeding distributions of birds, we report the first (to our knowledge) global maps of variation in species range sizes for an entire taxonomic class. We show that range area does not follow a simple latitudinal pattern. Instead, the smallest range areas are attained on islands, in mountainous areas, and largely in the southern hemisphere. In contrast, bird species richness peaks around the equator, and towards higher latitudes. Despite these profoundly different latitudinal patterns, spatially explicit models reveal a weak tendency for areas with high species richness to house species with significantly smaller median range area. Taken together, these results show that for birds many spatial patterns in range size described in geographically restricted analyses do not reflect global rules. It remains to be discovered whether global patterns in geographic range size are best interpreted in terms of geographical variation in species assemblage packing, or in the rates of speciation, extinction, and dispersal that ultimately underlie biodiversity.     

Enhanced niche opportunities: can they explain the success of New Zealand's introduced bird species?

Aim  The niche hypothesis could explain why some species introduced to new locations reach higher densities than in their native range: it posits that the new environment provides more abundant or higher quality resources or habitat, a more suitable physical environment or both. We investigate whether 11 bird species occur at higher densities in their introduced range than in their native range and whether the differences can be explained by the availability of preferred habitat or the suitability of climatic conditions in their introduced range relative to their native range.
Location  South Island, New Zealand (the introduced range); UK (the native range).
Methods  We first develop a series of models that accurately predict the density of 11 bird species at 54 UK farmland sites, which are closely matched to our New Zealand sites, from habitat and climatic variables. We then use these models to predict the density of the 11 species at 54 New Zealand farmland sites and compare the predicted and observed values.
Results  Actual densities at New Zealand sites were on average (median) 22 times (range: 1–6361) higher than predicted from the UK models and similarly higher than actually observed at comparable UK sites. Habitat and climatic variables can accurately predict bird densities in the UK but grossly underestimate densities for all species except Turdus merula in New Zealand.
Main conclusions  These findings indicate that factors other than the measured habitat and climatic variables must differ between the two regions and explain the much higher densities of New Zealand birds. We suggest that introduced birds, other than T. merula , in New Zealand may still experience enhanced niche opportunities due to greater availability of higher quality resources within habitats, release from natural enemy regulation, less exposure to extreme weather events, particularly during winter, or some combination of these processes.     

Patterns of contact call differentiation in the panmictic East African Abyssinian White‐eye Zosterops abyssinicus (Aves: Passeriformes)

Species distribution patterns range from highly disjunct to continuous, depending on their ecological demands and the availability of respective habitats. East African savannahs are mostly interconnected and ecologically comparatively homogenous and thus provide a prerequisite for a rather panmictic distribution pattern for species occurring in this habitat. The Abyssinian white‐eye Zosterops abyssinicus is a savannah inhabiting bird species, representing such a continuous distribution. This species occurs in high abundances and is very mobile, and past population genetic studies have suggested that gene flow is high and genetic differentiation is low even across relatively large geographic distances. Further, only little morphological differences were found. In order to test for potential divergence in acoustic traits despite its interconnected geographic distribution, we analyzed 2795 contact calls of Z. abyssinicus, which were recorded at 19 sites across Kenya. Our data indicate weak, but significant differentiation in call characteristics across latitudinal gradients. We found strong changes in call characteristics in populations where Z. abyssinicus occurs in sympatry with its highland congener, Zosterops poliogaster. However, the changes in call characteristics in sympatry were in different directions and lead to strong differentiation of the sympatric populations to other conspecific populations potentially representing a case of cascade reinforcement. The detected spatial gradients likely result from ecological differences and balancing effects of natural and sexual selection.     

Interspecific geographic range size–body size relationship and the diversification dynamics of Neotropical furnariid birds

Among the earliest macroecological patterns documented, is the range and body size relationship, characterized by a minimum geographic range size imposed by the species’ body size. This boundary for the geographic range size increases linearly with body size and has been proposed to have implications in lineages evolution and conservation. Nevertheless, the macroevolutionary processes involved in the origin of this boundary and its consequences on lineage diversification have been poorly explored. We evaluate the macroevolutionary consequences of the difference (hereafter the distance) between the observed and the minimum range sizes required by the species’ body size, to untangle its role on the diversification of a Neotropical species‐rich bird clade using trait‐dependent diversification models. We show that speciation rate is a positive hump‐shaped function of the distance to the lower boundary. The species with highest and lowest distances to minimum range size had lower speciation rates, while species close to medium distances values had the highest speciation rates. Further, our results suggest that the distance to the minimum range size is a macroevolutionary constraint that affects the diversification process responsible for the origin of this macroecological pattern in a more complex way than previously envisioned.     

Climate change affects populations of northern birds in boreal protected areas

Human land-use effects on species populations are minimized in protected areas and population changes can thus be more directly linked with changes in climate. In this study, bird population changes in 96 protected areas in Finland were compared using quantitative bird census data, between two time slices, 1981-1999 and 2000-2009, with the mean time span being 14 years. Bird species were categorized by distribution pattern and migratory strategy. Our results showed that northern bird species had declined by 21 per cent and southern species increased by 29 per cent in boreal protected areas during the study period, alongside a clear rise (0.7-0.8 °C) in mean temperatures. Distribution pattern was the main factor, with migratory strategy interacting in explaining population changes in boreal birds. Migration strategy interacted with distribution pattern so that, among northern birds, densities of both migratory and resident species declined, whereas among southern birds they both increased. The observed decline of northern species and increase in southern species are in line with the predictions of range shifts of these species groups under a warming climate, and suggest that the population dynamics of birds are already changing in natural boreal habitats in association with changing climate.     

Common montane birds are declining in northern Europe

Large‐scale multi‐species data on population changes of alpine or arctic species are largely lacking. At the same time, climate change has been argued to cause poleward and uphill range shifts and the concomitant predicted loss of habitat may have drastic effects on alpine and arctic species. Here we present a multi‐national bird indicator for the Fennoscandian mountain range in northern Europe (Finland, Sweden and Norway), based on 14 common species of montane tundra and subalpine birch forest. The data were collected at 262 alpine survey plots, mainly as a part of geographically representative national breeding bird monitoring schemes. The area sampled covers around 1/4 million km², spanning 10 degrees of latitude and 1600 km in a northeast–southwest direction. During 2002–2012, nine of the 14 bird species declined significantly in numbers, in parallel to higher summer temperatures and precipitation during this period compared to the preceding 40 yr. The population trends were largely parallel in the three countries and similar among montane tundra and subalpine birch forest species. Long‐distance migrants declined less on average than residents and short‐distance migrants. Some potential causes of the current decline of alpine birds are discussed, but since montane bird population sizes may show strong natural annual variation due to several factors, longer time series are needed to verify the observed population trends. The present Fennoscandian monitoring systems, which from 2010 onwards include more than 400 montane survey plots, have the capacity to deliver a robust bird indicator in the climate‐sensitive mountainous regions of northernmost Europe for conservation purposes.     

Modeling the flocking propensity of passerine birds in two Neotropical habitats

We examined the importance of mixed-species flock abundance, individual bird home range size, foraging height, and foraging patch characteristics in predicting the propensity for five Neotropical passerine bird species (Slaty Antwren, Myrmotherula schisticolor; Golden-crowned Warbler, Basileuterus culicivorus; Slate-throated Redstart, Myioborus miniatus; Wilson’s Warbler, Wilsonia pusilla; and Black-and-white Warbler, Mniotilta varia) to forage within flocks, rather than solitarily. We used study plots in primary mid-elevation forest and in shade coffee fields in western Panama. We expected that all species would spend as much time as possible flocking, but that the social and environmental factors listed above would limit compatibility between flock movements and individual bird movements, explaining variability in flocking propensity both within and among species. Flocking propensity was well predicted by home range size and flock abundance together, for four of the five species. While flock abundance was uniform across plots, home range sizes varied among species and plots, so that home range size appeared to be the principle factor limiting flocking propensity. Estimates of flock abundance were still required, however, for calculating flocking propensity values. Foraging height and patch characteristics slightly improved predictive ability for the remaining species, M. miniatus. In general, individual birds tended to join flocks whenever one was available inside their home range, regardless of a flock’s specific location within the home range. Flocking propensities of individual species were lower in shade coffee fields than in forests, and probably vary across landscapes with variations in habitat. This variability affects the stability and species composition of flocks, and may affect survival rates of individual species. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.