BackgroundThe White-browed Crake (Pololimnas cinereus, family: Rallidae, hereafter WbC) is a climate sensitive bird with a tropical/subtropical distribution in Southeast Asia, Australasia, and the Philippines. Range expansion into higher latitudes would be predicted for this species in a warming climate. In this study, we first photographed a WbC in a park of Motuo County on the southeast Tibetan Plateau. Then we compiled geographic data from the Global Biodiversity Information Facility (GBIF) to illustrate its distribution characteristics. We also used a MaxEnt model to simulate its global suitable range under different future climate change scenarios.ResultsThe results showed: (1) this observation constitutes a new distributional record of the WbC on the Tibetan Plateau. This expanded northern boundary (29°19′25.40″N) increased the latitudinal limit of the species by 171.58 km. (2) The coldest monthly minimum temperature, the wettest seasonal precipitation, and the human footprint index were the main environmental factors affecting the distribution of WbC, the rise in the coldest monthly minimum temperature has facilitated the expansion of the WbC's habitat. (3) Future climate warming will lead to a significant increase of suitable areas for WbC, with its distribution center shifting 196.11 km and 153.80 km towards northwest in 2041–2060 and 2081–2100, respectively. Under the scenarios for the 2041–2060 and 2081–2100, the globally suitable distribution range of the WbC might expand by 1,125,400 km² and 1,275,200 km², respectively. In China, the corresponding expansion was 27,500 km² and 29,200 km², respectively, mainly distributed in Guangdong, Yunnan, Taiwan, Guangxi, Hainan, Xizang, and Fujian provinces.ConclusionsThe WbC photographed in Motuo County is a new distribution record of this species on the Tibetan Plateau, with Motuo County in Xizang being the northernmost boundary of the current WbC range. The wettest seasonal precipitation, and the human footprint index were the main environmental factors affecting the distribution of the WbC. Under future climate change scenarios, the WbC's range is expanding rapidly, and tends to dispersal in a northwesterly direction.

Strong seasonal and elevational dynamics in community assembly mechanisms of tropical montane birds in the Eastern Himalayas

Parasitism can play a key role in shaping species' adaptability to environmental changes. Understanding how intrinsic traits of bird species influence susceptibility to haemosporidian infection is critical for understanding host-parasite dynamics, especially in biodiverse tropical regions. This study aimed to determine the host traits that influence the probability of haemosporidian infection in birds in a tropical country. We compiled published haemosporidian diagnoses of birds from Colombia and data on ecological, morphological, coloration, and sexual selection (dimorphism and dichromatism) traits. We also calculated an index for habitat specialization. Using phylogenetic generalized linear models (phylo-GLMs), we performed a phylogenetically informed comparative analysis of 115 bird species from different families with diverse characteristics. Our analysis revealed that migratory species, birds with larger body sizes, and those with more colorful plumage had a higher probability of infection. Conversely, habitat specialization was negatively associated with infection risk. Our results are explained in the framework of increased exposure to haemosporidian vectors. However, further studies are needed to better understand the relationship between the traits related to sexual selection and infection. These findings provide valuable insights into host-parasite dynamics in tropical bird communities and help to understand susceptibility factors, considering the potential negative consequences for avian communities.

Mutualistic interactions support many ecological functions including pollination. Interactions are, however, vulnerable to cheaters, species that benefit from interactions without providing anything in return. Nectar robbing, where the nectar is depleted but the flower not pollinated, is a well‐known example of cheating and often observed in pollination networks. Further, pollinating birds often switch between legitimate (i.e. mutualistic) and nectar robbing flower visits. In this study, we quantify how widespread nectar robbing is at high elevations in the northern Andes using interactions recorded with time‐lapse camera traps. Additionally, we assess the importance of two trait‐based mechanisms in explaining legitimate versus nectar robbing flower visits by birds: trait complementarity, measured as the continuous difference between bird bill and flower tube lengths, and trait barrier, which is a binary assessment of whether a species pair is physically able to interact based on the length difference between the flower tube and the bird bill. Nectar robbing occurred in 7% of the interactions we sampled, and the specialised flowerpiercers ( Diglossa ; Thraupidae) relied on this technique at higher frequencies than hummingbirds (Trochilidae). We further observed that the use of nectar robbing was strongly driven by trait barrier: nectar robbing happened mostly when the bill of the bird was shorter than the flower tube. This suggests that legitimate flower visits is the favoured foraging strategy for nectarivorous birds, and that robbing is used mostly to feed on otherwise inaccessible resources. These results suggest that nectar robbing is an important, yet overlooked, characteristic of tropical bird pollination networks.

Restricted elevational ranges are common across tropical montane species, but the mechanisms generating and maintaining these patterns remain poorly resolved. A long-standing hypothesis is that specialized thermal physiology explains these distributions. However, biotic factors such as habitat and interspecific competition have also been proposed to limit tropical species’ elevational ranges. We combined point-level abundances, respirometry-based measurements of metabolic rate, habitat surveys and playback experiments to simultaneously test these three hypotheses for four species of Central American cloud forest songbirds. Contrary to the physiological hypothesis, we found no evidence that thermoregulatory costs constrain species distributions. Instead, thermal conditions across each species’ elevational range remained well within sustainable limits, staying ≤65% of hypothesized thresholds for tropical birds, even at the highest elevations. By contrast, we found some support for a combined role of habitat and competition in shaping elevational ranges. In one related species pair, the dominant lower-elevation species appears restricted by microhabitat, while the higher-elevation species is likely prevented from expanding downslope by the presence of this congener. Taken together, we conclude that thermoregulatory costs are an inadequate explanation for elevational range limits of tropical birds at our site and suggest that biotic factors can be key in shaping these distributions. We provide a Spanish translation of the in the supplementary materials.

Biodiversity conservation requires effective monitoring of ecological communities in remote locations, where limited accessibility often restricts survey efforts. Passive acoustic monitoring (PAM) is becoming an established method for measuring biodiversity, facilitated by the increased accessibility of autonomous recording units. Comparing the performance of PAM and traditional survey methods can provide insights into how species characteristics such as foraging strata, vocal behaviour and taxonomy influence the detection ability of each method. Here, avian species occurrences were collected using PAM and point count surveys (PCS) across three forest fragments in the Taita Hills, an Afromontane sky‐island in southeastern Kenya. These montane forests contain high species‐richness and endemism, but they have been severely fragmented and degraded as a result of deforestation, making comprehensive monitoring critical for conservation. We grouped detected species into clusters based on their foraging strata, using partitioning around medoid cluster analysis. From 25 survey sites, PAM and PCS detected 60 and 57 species, respectively, indicating that PAM is as effective as PCS for surveying montane tropical birds. However, species that primarily foraged on the ground and secondarily used the understorey, and species that primarily used the understorey and secondarily used the canopy, were more likely to be recorded by PAM than by PCS. Species that only used the understorey were more likely to be recorded by PCS. Investigation of broad taxonomic groupings showed that PAM was 20% more likely to record non‐passerines than PCS, while passerines were equally likely to be recorded by either method. This study highlights how species characteristics, such as foraging strata and taxonomic group, influence the performance of surveying methods. By identifying which species are best monitored by each method, this study can inform more targeted monitoring strategies, improving accuracy and supporting biodiversity management efforts to mitigate ongoing species loss.

Agricultural land-use change is a key driver of biodiversity loss. Two alternative strategies have been discussed to align biodiversity conservation with agricultural production in landscapes containing agriculture: (i) land sparing, with intensive agriculture strictly separated from natural land, and (ii) land sharing, a mosaic of low-intensity agriculture and natural elements. Sparing builds on high-yielding intensive production to provide more area for natural habitats; sharing aims to support biodiversity within agricultural landscapes by employing wildlife-friendly farming practices. A considerable body of literature addresses conceptual aspects of these strategies, but empirical evidence on how they support biodiversity is scarce. We assessed the empirical evidence by analyzing 57 peer-reviewed articles identified in a systematic literature review, of which only 17 allowed a comparison of the strategies. These 17 articles contained 27 cases of comparisons, of which 52% reported that context-specific solutions combining sharing and sparing performed best, and exclusively focusing on one strategy cannot balance the competing demands of food production and biodiversity. In 41% cases, land sparing performed best and in 7% land sharing. However, these 17 studies almost exclusively focus on specific contexts and metrics (e.g. species population density of tropical forest birds) and the other 40 studies lack important elements for a comparison, such as the assessment of agricultural production performance. The empirical basis is thus sparse and does not support statements claiming that, in general, either land sharing or land sparing strategies are unequivocally better. It rather highlights the importance of context-specific solutions for aligning agricultural production and biodiversity conservation.

Although species exhibit widespread sensitivity to environmental conditions, the extent to which human-driven climate change may have already altered their abundance remains unclear. Here we quantify the impact of climate change on bird populations from across the world by combining models of their response to environmental conditions with a climate attribution framework. We identify a dominant role of intensified heat extremes compared to changes in average temperature and precipitation. Increased interannual exposure to hot extremes reduces annual abundance growth rates most strongly in lower-latitude tropical regions, with effects robust when controlling for changing human industrial pressure and other long-term drivers. Compared to a counterfactual without human-driven climate change, the historical intensification of heat extremes has caused a 25-38% reduction in the level of abundance of tropical birds, which has accumulated from 1950 to 2020. Across observed tropical bird populations, impacts of climate change have typically been larger than direct human pressure, the opposite across sub-tropical regions. Overall, these results showcase how human-driven climate change is already reshaping biodiversity globally and may explain reported declines of birds in undisturbed tropical habitats.

Extreme heat is driving decline in tropical birds

Abstract Fires pose an increasing threat to tropical forests worldwide. However, few studies have attempted to evaluate their impacts on bird communities. Consequently, the responses of tropical birds to this disturbance remain unclear. We assessed bird community composition, species richness and functional diversity between unburned and burned forests across 15 landscapes in the Brazilian Atlantic Forest. Additionally, we analysed how these indices were influenced by native forest cover, vegetation productivity, fire severity and fire size. To address these questions, we applied generalised linear mixed models. While unburned and burned forests exhibited similar species richness and functional diversity, they differed significantly in bird species composition. Species richness was positively associated with vegetation productivity. Functional diversity was primarily explained by fire size, with the magnitude and direction of the effects varying according to the functional index used and the forest type. Functional divergence showed a positive correlation with fire size in unburned forests and a negative correlation in burned forests. Functional dispersion, when considering communities across both forest types, was negatively correlated with fire size. Synthesis and applications. This study highlights how bird communities in the Atlantic Forest respond to fires. Our findings show that fire can significantly alter species composition, even when species richness remains unchanged. Bird community responses are further shaped by vegetation productivity and fire size, emphasizing the need to consider multiple ecological factors in post‐fire conservation strategies. We emphasize the need for tailored fire management strategies aimed at reducing forest degradation and fire occurrence. Effective measures, such as forest restoration and the implementation of ‘fire‐smart management’ practices, are essential to safeguard bird diversity. These results underscore the need for proactive governmental policies to prevent and manage fires in the Atlantic Forest, particularly in highly degraded landscapes.

Forest gap dynamics are a key driver of bird community structure. Understanding the effect of forest gaps on abundance and communities is critical in an era of increasing anthropogenic disturbance in tropical forests. In this study, we investigated the impact of natural rainforest gaps on bird communities and abundance in a highly diverse lower montane rainforest in Thailand. We employed mist-netting in a 5-year study (2015-2019) to assess bird assemblages and abundance across paired sites in forest gaps and under closed canopy, resulting in 1,148 captures of 81 species. Total abundance did not differ between forest gaps and under the closed canopy. The long-term study design captured seasonality in bird composition, highlighting dynamic assemblages driven by seasonal migration. We observed a strong effect of forest gaps on bird assemblages. Interestingly, we found Hill Blue Flycatcher (Cyornis whitei) species with a strong preference for forest gaps increased in abundance with total gap size. Most species showed no relationship with forest gap sizes in this area. Our findings support previous research showing that gap sizes of 130–1,020 m² in the lower montane forest are not highly detrimental, yet still reduce bird abundance. This highlights that even moderate habitat disturbances can negatively affect sensitive bird species. Nonetheless, forest gaps may also play a key role in promoting tropical biodiversity by facilitating niche differentiation and specialization among understory birds.

Selective logging is a major driver of tropical land-use change, causing reductions in forest specialist species with concurrent increases in edge-tolerant species. A key question is understanding how selective logging impacts co-occurrence and assembly mechanisms in vertebrate communities as forests recover post-logging. Using a 10-year, repeat-sample study of understorey bird species in Borneo, we compare the structure of species co-occurrences over time between old-growth unlogged and logged forests, investigating the roles of functional traits and local abundance in driving co-occurrence patterns. Co-occurrence patterns were resilient to selective logging over time, although patterns were not consistent across all species in both forest types. Species with more specialised diets showed a significant tendency towards low fidelity, while species that engage in aerial foraging, soaring and gliding exhibited a significant tendency to have low values of fidelity in both types of forest. Changes in co-occurrence patterns were also significantly influenced by changes in local abundance. Our results indicate that niche segregation and environmental filtering operate to shape the assemblage of the avian community in both forest types, but co-occurrence was resilient to selective logging over time. Our results also underscore the role of some species in regulating avian assemblages and the long-term conservation value of logged tropical forests.

ABSTRACTQuantifying restoration success is a key objective for the UN Decade on Ecosystem Restoration. We evaluated the potential of acoustic indices to predict the recovery success of bird communities within abandoned agricultural areas in a biodiversity hotspot in Ecuador. Using audio recordings from a lowland tropical forest region, we identified 334 bird species and calculated established acoustic indices. Community composition was analyzed using Hill numbers, accounting for incomplete sampling. Acoustic indices effectively predicted verified species data (R2 = 0.59–0.76), capturing not only taxonomic but also functional and phylogenetic composition. Taxonomic composition was best predicted for common and dominant species, while functional and phylogenetic composition was more accurately predicted for rare and common species. Our findings demonstrate that a small set of acoustic indices, once validated by stratified ground truth data, provides a powerful tool for assessing restoration success over large tropical areas, including functional composition of rare tropical birds.

Machine learning has the potential to revolutionize passive acoustic monitoring (PAM) for ecological assessments. However, high annotation and computing costs limit the field’s adoption. Generalizable pretrained networks can overcome these costs, but high-quality pretraining requires vast annotated libraries, limiting their current development to data-rich bird taxa. Here, we identify the optimum pretraining strategy for data-deficient domains, using tropical reefs as a representative case study. We assembled ReefSet, an annotated library of 57 000 reef sounds taken across 16 datasets, though still modest in scale compared to annotated bird libraries. We performed multiple pretraining experiments and found that pretraining on a library of bird audio 50 times the size of ReefSet provides notably superior generalizability on held-out reef datasets, with a mean area under the receiver operating characteristic curve (AUC-ROC) of 0.881 (±0.11), compared to pretraining on ReefSet itself or unrelated audio, with a mean AUC-ROC of 0.724 (±0.05) and 0.834 (±0.05), respectively. However, our key findings show that cross-domain mixing, where bird, reef and unrelated audio are combined during pretraining, provides superior transfer learning performance, with an AUC-ROC of 0.933 (±0.02). SurfPerch, our optimum pretrained network, provides a strong foundation for automated analysis of tropical reef and related PAM data with minimal annotation and computing costs.This article is part of the theme issue ‘Acoustic monitoring for tropical ecology and conservation’.

Bird species vary widely in their diurnal vocalization patterns, and the drivers of this variation are not well understood. Using passive acoustic monitoring, we examined species-specific vocal activity patterns at dawn and dusk for a tropical bird community in the Western Ghats biodiversity hotspot in India. We tested whether environmental factors (e.g. signal transmission conditions, ambient light, and resource availability) and social factors (e.g. territoriality) best-explained patterns of diurnal variation in vocal activity. Overall, we found that species-specific vocal activity was significantly higher at dawn (p < 0.05). Phylogenetic generalized least squares regressions revealed that territoriality and diet both predicted stronger dawn-biased activity. Specifically, highly territorial birds (standardized effect size (SES) = 1.20, lower donfidence interval (LCI)= 0.24, upper confidence interval (UCI) = 2.16, p = 0.01) and omnivores (SES = 0.82, LCI = -0.04, UCI = 1.68, p = 0.06) had higher levels of vocal activity at dawn. Surprisingly, we failed to find any evidence in support of environmental factors in explaining dawn-biased vocal activity. Our multi-taxon approach allowed us to assess the vocal activity patterns for an entire tropical bird community. Future research must incorporate additional geographic locations and combine visual and aural observations to better understand the drivers of diurnal variation in vocal activity.This article is part of the theme issue 'Acoustic monitoring for tropical ecology and conservation'.

ABSTRACT Understanding when tropical birds breed is key to life-history theory and to predicting how species will respond to environmental change. While early views emphasized the potential for year-round breeding in the tropics, accumulating evidence suggests that reproductive activity in most tropical birds follows some degree of seasonality, often linked to rainfall and associated food pulses. However, large-scale evaluations across ecological gradients remain scarce. Here, we investigated the breeding seasonality of Colombian resident birds using over 80,000 records compiled from bird banding programs and the Global Biodiversity Information Facility (GBIF). These data included birds in breeding conditions, active nests, nestlings, and adults displaying reproductive behavior. We asked four main questions: (1) Do Colombian birds exhibit seasonal breeding activity? (2) Does the degree of seasonality vary with latitude and elevation? (3) Are there geographic differences in breeding patterns across Colombia’s biogeographic regions? (4) How does breeding activity vary among feeding guilds? We used time-series, circular statistics, and generalized additive models (GAMs) to evaluate breeding patterns at national and regional levels, incorporating geographic variables and trophic guild. We found a clear seasonal pattern in breeding activity, with a main peak in April and low but consistent activity throughout the year, especially in the Andes. Breeding was more synchronized at higher latitudes and more extended near the Equator. Elevation also shaped seasonality: lowland bird assemblages showed broader breeding seasons, while mid- and high-elevation assemblages had narrower seasonal windows, driven by a shift in the breeding peak toward mid-year in highland birds. Regional and trophic guild variation was also marked. Caribbean birds bred sharply in April, Andean birds had prolonged reproductive activity peaking in March and June, and Chocoan birds peaked in March, followed by a decline. Breeding generally coincided with the start of rains and avoided extreme dry or wet months, in line with hygric niche theory. Feeding guilds differed as well: frugivores-nectarivores, omnivores, and invertivores bred mainly early in the year, while granivores peaked mid-year. Together, our findings offer new insights into tropical bird reproduction by showing that breeding activity in Colombia follows clear seasonal patterns shaped by rainfall regimes, elevation, and trophic ecology, contributing to the growing evidence of the complexity of breeding seasonality at tropical and near-equatorial latitudes.

The colorfulness of bird plumage plays a crucial role in intraspecific (e.g., sexual display) and interspecific ecological interactions (e.g., camouflage and predation). Functional traits like diet, body size, and sexual dichromatism are among the primary predictors of plumage colorfulness in passerine (Passeriformes) birds. Consequently, passerine plumage colorfulness and functional traits associated with it (i.e., diet, body size, and sexual dichromatism) can affect the success of individuals in novel environments, such as urban settings. However, our understanding of the impact of urbanization on the functional traits of birds, especially in tropical regions, is limited. To address this gap, we analyzed whether urban environments serve as environmental filters for plumage colorfulness, diet, body size, and sexual dichromatism in passerine bird assemblages across the biomes of Brazil, the world's largest tropical country. Using generalized linear and generalized linear mixed models that incorporate bird checklists, functional traits, urbanization, biomes, and sampling effort, we show that urbanization increases the proportion of omnivores, the proportion of larger species, and average sexual dichromatism in bird assemblages. While the average colorfulness of bird assemblages did not change with increasing urbanization, a negative correlation between the presence of megacolorful birds (i.e., the 5% most colorful species) and urbanization was detected, particularly in biomes with high urban concentrations, such as the Atlantic Forest and the Caatinga. This suggests that urban environments can be unsuitable for the most colorful tropical bird species. Our study additionally shows that factors like body size, diet, and sexual dichromatism play a mediating role in the urban filtering process. Our analyses provide insights into how urban environments act as environmental filters and can help to better understand the consequences of urbanization for tropical biodiversity.

You are what you tweet: vocal traits communicate threat in a duetting tropical bird

Several bird species associated with agricultural landscapes in the Palearctic and in the Nearctic (i.e. farmland birds) have been experiencing severe population declines since the 1970s, mainly due to habitat loss driven by agricultural intensification. Contrastingly, many farmland birds in the Neotropics are expanding their ranges in recent years. Reconstructing the history of range change of these birds can provide insights into the ecological dynamics of expansion/retraction of bird populations in agricultural lands. In this study we investigated the temporal dynamics of the geographical distribution of a tropical farmland bird, the lined seedeater Sporophila lineola. We used data from the literature, zoological collections, and community science platforms to access the species' range in South America at different timeframes. Additionally, we used historical maps to investigate the relationship between the occurrence of the species and the type of land cover at different timeframes. Our findings suggest that lined seedeaters, which were originally restricted to part of the Brazilian state of São Paulo, expanded their range to southeastern and southern Brazil during the last century. We propose that the lined seedeater was originally associated with naturally disturbed habitats, having expanded its range over human disturbed habitats, benefiting from recent changes in land cover. Documenting range expansion in lined seedeaters allowed us to better understand how changes in land cover can favour opportunistic species into their successful occupation of man‐made habitats.

The urban communities of birds in tropical regions are generally understudied, despite these areas hosting most of the bird diversity worldwide. Therefore, understanding the factors that influence tropical urban bird communities is crucial. This study explores ecological patterns of avian communities in the India’s district of Karnataka. A variety of urban settings with different human populations were surveyed to account for the geographical variability of the bird assemblages in the region. Additionally, this study concentrated on the common but often overlooked urban environments– building structures and street vegetation. Using generalized linear mixed models, this study revealed that the most important environmental factor impacting the species richness and diversity of bird communities was the number of motor vehicles, likely inducing various kinds of disturbance to birds, and local cover of greenery, which offers foraging and breeding opportunities for birds. This underscores the importance of including quiet, traffic-free green spaces in urban areas. The most significant trait characterizing the species in the surveyed cities was diet: birds with broader dietary preferences were more abundant in urban settings. This result is consistent with knowledge on predictors of urban bird abundance shaping bird communities in Global North cities, implying common drivers acting in urban areas across the globe.