The continuing increase in the global urban human population will exert profound pressures on biodiversity and ecosystem services. Urban planners face the challenge of accommodating such growth while minimising its impact on biodiversity. This could be achieved through urban land sparing (developing currently low density urban areas without expanding into adjacent semi-natural habitats) or land sharing (creating relatively low density areas in place of semi-natural habitats). We assessed support for these two strategies by examining how urban breeding bird diversity and associated ecosystem services (bird aesthetic attractiveness) and disservices (occurrence of species prone to generate human-wildlife conflicts) responded to a gradient of human population density measured across six Italian cities. As human population density increased, there was a decline in avian taxonomic and functional diversity and a bird-mediated ecosystem service, but an increase in bird biomass and a bird-related ecosystem disservice. Land sparing was supported in forest species and cavity nesters. Other relationships were linear, with no support for either strategy. To enhance bird diversity and related ecosystem services in our study region, we recommend increasing human population densities within already urbanised areas, while conserving existing bird diversity by preserving semi-natural habitats, particularly at the urban fringe. Among these, forest and urban green spaces significantly enhanced bird diversity, in contrast to the simplified assemblages in peri-urban farmlands. To design more bird-friendly cities, we recommend to: 1) improve the quality of existing urban forest remnants, 2) prioritise urban reforestation on farmland at the urban-rural fringe, and 3) expand urban green infrastructures to support forest-associated bird-diversity and to reduce social costs of densely populated cities.

Areas of higher socio-economic status within cities often support greater biodiversity than poorer areas, representing a form of environmental injustice. This inequality may result in lower income areas experiencing both lower cultural (e.g., bird aesthetics) and regulating (e.g., pest control) ecosystem service provision. Urban areas are also hotspots for non-native species, which can alter community functional structure and, consequently, ecosystem service provision. However, the influence of socio-economic status on services provided by both native and non-native urban biodiversity remains underexplored. We assessed how functional diversity related to avian cultural and regulating ecosystem services varied along the socio-economic gradient of functional urban areas (FUAs) in the Iberian Peninsula. Using breeding bird atlases from Spain and Portugal, we characterised bird communities in all FUAs, calculating species richness and functional dispersion based on traits linked to ecosystem services. We used generalised linear mixed models to examine relationships between diversity metrics and median household income. Additionally, we evaluated whether the presence of non-native species moderated community responses along the gradient. Both cultural and regulating ecosystem services were negatively associated with socio-economic status, while species richness increased with income. However, invaded communities supported higher species richness and cultural service provision than non-invaded ones. Our findings reveal a counterintuitive pattern in which ecosystem service provision is higher in lower-income areas, partly due to non-native species. These results underscore the need for urban management strategies that simultaneously address socio-economic and ecological inequalities, while considering the complex roles of non-native species in shaping urban biodiversity and its benefits.

Mountains are global biodiversity hotspots that are increasingly vulnerable to climate change. In the European Alps, rising temperatures and land-use changes have caused shifts in vegetation, impacting bird communities, particularly alpine specialists. Protected areas (PAs) are critical for buffering climate effects and safeguarding cold-adapted species, but their effectiveness in a warming world remains unclear. This study assessed shifts in bird assemblages across the elevational gradient in the Italian Alps over 13 years, using point counts to sample bird communities, and the Community Temperature Index (CTI) as a measure of community thermal tolerance. By comparing shifts inside and outside PAs, we identified key species and elevation bands driving CTI changes and modelled species-specific elevational shifts. Results revealed a critical divergence: CTI remained stable outside PAs, but increased sharply within PAs, reflecting a 1.19 degrees C rise in mean annual temperature in the study area. Initially, PAs harboured cold-adapted species, but over time, their bird assemblages became more similar to those outside PAs, likely driven by a decline in high-elevation species. The most marked changes occurred near the treeline, a key zone for sensitive species. CTI increases were driven by treeline and alpine grassland species which are most vulnerable to vegetation encroachment. Our findings suggest that PAs facilitate upward shifts, but are insufficient to prevent declines in populations of high-elevation species under rapid warming. Adaptive conservation strategies, such as targeted grazing, are urgently needed to counteract vegetation shifts, preserve habitat heterogeneity, and maintain elevational connectivity. Continuous monitoring is crucial to track ecological changes and refine conservation priorities, ensuring mountain biodiversity resilience under climate change.

Mountainous regions host globally unique biodiversity, but face growing threats from climate and land-use change. The Alps stand out as a key mountain range in Europe, where the ski industry is extensive and impacts ecosystems and their associated biodiversity. However, climate change is projected to reduce natural snow precipitation, thus understanding snow dynamics and the ski industry's role is crucial for developing effective conservation strategies. Ski-piste creation generally has detrimental consequences for mountain biodiversity, yet pistes often retain substantial snow throughout spring that, when melting, may create favourable foraging conditions for mountain birds. This study investigates whether ski-pistes provide suitable foraging habitat and explores their broader importance for mountain avifauna. Field surveys in spring 2023 in the western Italian Alps recorded 17 bird species using the melting snow on ski-pistes as a foraging habitat. Snow presence was a significant factor influencing bird presence. Birds systematically selected areas with intermediate snow cover interspersed with muddy patches, a microhabitat that likely has a high availability of invertebrate prey emerging from the soil. Given that snow is retained on ski-pistes for longer than on the surrounding habitat, the pistes may represent a useful source of food for mountain birds in spring. However, this needs to be considered in relation to the negative impacts of skiing on alpine biodiversity, which may include a likely increased reliance on artificial snow in response to the projected decline in natural snow precipitation under climate change. Understanding these effects is essential to ensure that future conservation strategies support mountain bird communities without exacerbating the environmental costs associated with artificial snow production.

Urbanization is rapidly transforming natural landscapes, intensifying socio-environmental inequalities, and creating disparities in both the provision of ecosystem services (ES) and urban biodiversity. This paper suggests a multidisciplinary and multi-methodological approach to evaluate urban biodiversity, ES supply, and socioeconomic vulnerability to examine environmental justice. Based on the "Luxury Effect" hypothesis, which supposes a positive association between wealth and biodiversity in urban environments, the paper investigates the relationship between differences in urban nature and more general trends in social inequality. Biodiversity and green infrastructure may significantly improve urban quality of life, but the benefits are often unequally distributed, being wealthy communities usually favored more than others. To bridge the gap between theory and practice, the study suggests a new framework integrating quantitative and qualitative data, like biodiversity surveys with geographical and multicriteria decision analysis (MCDA). The methodology will be tested and validated in four Italian cities - Milan, Rome, Turin, and Naples - each reflecting distinct ecological, social, and economic situations. Our technique identifies regional patterns of inequality and prioritizes areas for policy intervention by overlaying biodiversity and ES data over socioeconomic characteristics. This integrated paradigm advances theoretical discussions on environmental justice and encourages the development of more inclusive, data-driven urban planning methods. The approach is still in the validation phase but shows strong potential for scalability and adaptability across diverse urban contexts. Ultimately, the study aims to inform sustainable planning practices that ensure a fairer distribution of environmental benefits, enhancing cities' ecological resilience and social well-being.

Urbanisation is a major driver of global biodiversity decline, profoundly affecting animal communities. While most studies on bird communities have primarily focused on the breeding season, we aimed to identify species responses and their associated traits by adopting a stratified design and using a multi-season approach considering a gradient from highly urbanised city centres to the urban-rural fringe across six Italian cities. We found that bird assemblages exhibited different responses to urbanisation according to season. Winners (i.e. species positively affected by urbanisation) were characterised by traits such as colonial nesting, high productivity and longevity. In winter, these species displayed generalist foraging strategies and solitary behaviour. Losers (i.e. species negatively affected by urbanisation) tended to be insectivorous, ground-nesting and short-distance migratory species. Interestingly, intra-specific variations emerged, with wintering populations of some species exploiting highly urbanised areas despite not breeding there. Urban adapters, although not strictly winners, displayed resilience by navigating a range of urban conditions, effectively exploiting intermediate levels of urbanisation. This study provides novel insights into the complex ecological dynamics occurring within the urban matrix in different seasons. Our findings emphasise the importance of adopting a multi-season approach in research and urban planning to better understand species responses and develop more effective, sustainable strategies for biodiversity conservation in urban environments.

CapsuleIn many bird species, differences in breeding parameters are often reported between (inexperienced) yearlings and adults (with previous breeding experience), likely due to increased foraging and chick rearing abilities in older, more experienced, individuals.AimsWe aimed to assess the effect of male age on breeding parameters in an Alpine population of Northern Wheatears.MethodsWe compared several performance parameters (nesting habitat, lay date, daily failure rates, nest survival and nestling mass) between yearling (inexperienced) and adult (experienced) Northern Wheatears in a population in the western Italian Alps.ResultsThere was no statistically significant effect of male age (i.e. yearlings vs older birds) on breeding success, territory quality or breeding phenology, but there was a weak trend of a higher nest survival among adults.ConclusionUnpredictable weather and overall high food abundance at higher elevations during the breeding period may reduce any difference in nest survival or nestling mass between age classes, even if older birds have better foraging capabilities. Compared to lowland studies, the results suggest that our Alpine population of Northern Wheatears differed in the constraints acting on breeding success and phenology: harsh and unpredictable environmental conditions on arrival and superabundant food availability for nestlings likely reduce age differences in breeding success, territory quality and phenology. Biases due to potential unrepresentative sampling of age groups must be more fully assessed to further explore these hypotheses.

The effectiveness of agri-environment schemes (AESs), the largest conservation-related expenditure for farmland biodiversity conservation within the European Union, is often compromised by a limited spatial scale of implementation. We focused on multiannual forage crops, a surrogate habitat for grassland birds, to assess the scale-dependent effects of mowing timing and frequency on the local population size of an iconic species, the skylark (Alauda arvensis). While there is much evidence for a negative impact of in-field mowing activities on grassland birds, whether such effects occur also at broader spatial scales is largely unknown. We surveyed breeding skylarks in the Po Plain (northern Italy) to determine (1) the association between landscape composition/configuration and abundance and (2) how abundance is affected by forage crop mowing timing and frequency. We addressed both questions through scale optimisation, identifying the most influential spatial scales for each covariate. Forage crop mowing timing was assessed through a novel remote sensing algorithm based on high-resolution Sentinel-2 satellite images. We observed a strong scale dependence on the importance of different habitats in determining skylark abundance. Abundance increased with an increasing cover of forage crops locally (200 m) and of winter crops at a landscape scale (2600 m), suggesting that the species is favoured by heterogeneous agroecosystems. Locally (150-350 m), skylarks were more abundant when crops were aggregated, being negatively impacted by crop fragmentation caused by urbanization and by seminatural habitats. At the landscape scale (1150 m), the timing of mowing was consistent across years, with early-mown areas supporting fewer skylarks. This is probably because, over longer temporal scales, early-mown forage patches have limited or null productivity, eventually limiting local population size. Synthesis and applications. We provide a new perspective on the overarching influence of spatial scale in driving the abundance of a declining farmland bird species, supporting the urgency of designing landscape scale-effective AESs. This should be framed within the new EU Common Agricultural Policy reform and operated by farmer collectives, whereby management interventions should be monitored by state-of-the-art remote sensing techniques. These results suggest that implementing scale-optimized AESs could be crucial for effective farmland biodiversity conservation. L'efficacia delle misure agro-ambientali - la principale spesa dell'Unione Europea per la conservazione della biodiversit & agrave; nelle aree agricole - risulta spesso compromessa da un'applicazione a scala spaziale ridotta. Questo lavoro si incentra sulle colture foraggere poliennali, considerate un habitat surrogato per gli uccelli di ambienti aperti, al fine di valutare gli effetti scala-dipendenti delle tempistiche e della frequenza dello sfalcio sulla dimensione delle popolazioni locali di una specie iconica, l'Allodola (Alauda arvensis). Sebbene siano disponibili numerose evidenze di impatti negativi dello sfalcio per gli uccelli a scala locale, rimane in gran parte ignoto se tali effetti si manifestino anche a scale spaziali pi & ugrave; ampie. Le Allodole nidificanti sono state censite in un'area di studio della Pianura Padana (Italia settentrionale) per determinare l'associazione tra l'abbondanza della specie e: 1) composizione/configurazione del paesaggio; 2) fenologia e frequenza dello sfalcio delle colture foraggere. & Egrave; stato adottato un processo di ottimizzazione, identificando le scale spaziali pi & ugrave; influenti sull'abbondanza di allodole nidificanti per ciascuna covariata. Le variabili relative agli sfalci sono state ottenute attraverso un algoritmo di telerilevamento innovativo basato su immagini satellitari Sentinel-2 ad alta risoluzione. I risultati evidenziano una forte dipendenza dalla scala spaziale sull'associazione fra diversi habitat e abbondanza dell'Allodola. L'abbondanza aumenta con una maggiore copertura di colture foraggere a scala locale (200 m) e con una maggiore presenza di colture autunno-vernine a scala di paesaggio (2600 m), indicando che la specie & egrave; favorita da agroecosistemi eterogenei. A scala locale (150-350 m), le allodole risultano pi & ugrave; abbondanti in paesaggi agricoli aggregati, risultando invece negativamente influenzate dalla frammentazione delle colture determinata dall'urbanizzazione e dalla presenza di habitat seminaturali. A scala di paesaggio (1150 m), la fenologia dello sfalcio & egrave; risultata coerente in anni diversi e le aree sfalciate precocemente ospitavano un numero inferiore di allodole. Probabilmente ci & ograve; dipende dal fatto che, nel lungo periodo, le aree coltivate a foraggio sfalciate precocemente hanno una produttivit & agrave; limitata o nulla, influenzando negativamente la dimensione della popolazione locale a quella scala. Sintesi e applicazioni - Questo lavoro fornisce una nuova prospettiva sulla rilevanza della scala spaziale nel determinare l'abbondanza di una specie di uccello di ambienti agricoli in declino, sottolineando l'urgenza di definire misure agro-ambientali efficaci a scala di paesaggio. Si ritiene che tali interventi debbano essere inquadrati nel contesto della nuova riforma della Politica Agricola Comune dell'UE e attuati da aggregazioni di agricoltori, con interventi gestionali monitorati mediante tecniche di telerilevamento. I risultati suggeriscono che l'implementazione di misure agro-ambientali ottimizzate spazialmente potrebbe risultare cruciale per la conservazione della biodiversit & agrave; nelle aree agricole.

Increased urbanisation influences the morphometric traits of various species, often resulting in urban individuals being smaller than their non-urban counterparts. Urbanisation can affect fundamental eco-evolutionary patterns and impact species’ ability to adapt to and occupy rapidly changing environments through morphological changes. We investigated the morphometric responses of two passerine species, the non-native house sparrow (Passer domesticus) and its native congener, the Cape sparrow (Passer melanurus), along gradients of spatial and temporal urbanisation in South Africa over a 52-year period. The house sparrow was significantly heavier, larger and in better condition with increasing urban infrastructure and lower urban vegetation cover, while the Cape sparrow showed opposing trends along these gradients. Temporally, the house sparrow’s body mass increased consistently over the 52-year study period, suggesting changes in morphology were concomitant with increasing urbanisation over time. This study demonstrates distinct differences in the morphological responses of the non-native house sparrow and the native Cape sparrow to increasing urban development. These morphological responses may also underpin community-level changes caused by urbanisation, enhancing the capabilities of non-native species to thrive over their native counterparts in these environments.

Introduced alien species are associated with lower taxonomic, functional and phylogenetic diversity of native communities and negative impacts on ecosystem functioning. This is particularly evident in habitats where human disturbance may favour alien species, posing an additional stressor on native communities. Following the community resistance hypothesis (higher diversity promotes higher resistance to invasion), we predicted: 1) higher taxonomic, functional and phylogenetic diversity (TD, FD and PD respectively) in non‐invaded bird communities (i.e. no alien bird species); and 2) higher diversity and resistance to invasion in less human‐disturbed areas. We surveyed bird communities in a modified Mediterranean landscape subject to varying levels of human disturbance. We tested whether TD, FD and PD were significantly different between non‐invaded and invaded bird communities, and assessed the effect of land classes (forest, agriculture, urban), landscape composition and heterogeneity on these metrics. We found that non‐invaded communities retained higher TD and FD, but not PD, than invaded communities. Alien birds occupied marginal niches in invaded communities, and did not fully compensate for the taxonomic and functional diversity loss caused by the absence of native species. These results were consistent across different land classes, suggesting weak environmental filtering of communities. Generally, less human‐modified and more heterogeneous areas supported higher TD regardless of the presence of alien species. FD and PD of invaded communities decreased with increases in human‐modified areas, whereas non‐invaded communities were not affected. Our results suggest that even within a human‐modified landscape, invaded community diversity is more affected by, and thus has a lower resilience to, disturbance. Restoring and protecting natural habitats within human‐modified landscapes is likely to increase the resilience of native species.

Birds of open alpine grasslands are threatened by the degradation and contraction of their breeding habitat. To assess potential impacts of environmental change in alpine environments, basic ecological knowledge, such as habitat requirements during pre-breeding and breeding periods, is needed. We conducted territory and habitat mapping of a population of the northern Wheatear Oenanthe oenanthe breeding in alpine grasslands and lower elevation open habitats in the Western Italian Alps during two consecutive breeding seasons (2019-2020). For territory mapping, a study area of over 160ha was visited five times, covering an elevation gradient from 1,600 to 2,700m.a.s.l. Low elevation grasslands in the valley were exploited by birds as arrival habitat after spring migration, but were not selected as breeding territories. On territories, birds avoided areas with numerous small trees, selecting patchy habitats with high rock cover. Early arriving males first occupied the territories at lower elevations, and those with taller ground vegetation, but avoided overall higher vegetation cover. Birds were able to initiate the breeding season when snow cover was still high, as long as forbs and grass were present. The expected decrease in the area of open alpine grassland due to shrub encroachment will probably reduce the availability of suitable territory habitat and thus threatens the alpine population. Extensive seasonal grazing could help to maintain alpine grasslands above the treeline, and may provide suitable, but lower quality, habitat even at lower elevations by keeping the area open.-Alba, r., Chamberlain, D., rosselli, D. & Sander, M.M. (2024). Habitat quality drives the spatio-temporal occupation of a migratory songbird, the northern Wheatear Oenanthe oenanthe, in alpine grasslands.

Climate change is predicted to result in elevational and latitudinal shifts in species distributions. Among different taxa, high-elevation specialist species are likely to suffer the greatest impact from climate change due to the limited ability to track their niches. Although much work has been undertaken on predicting the effects of climate change on the range contraction/expansion of mountain species, one important but fairly neglected issue is to consider the impacts of non-climate data in the projections of Species Distribution Models (SDMs). We evaluated the degree to which incorporating non-climatic data into climate-based SDMs would change the predicted vulnerability of the Caspian Snowcock (Tetraogallus caspius), a poorly known high-elevation specialist species, to climate change. We first optimized the MaxEnt model for the current species distribution using: (1) only climatic variables; and, (2) both climatic and non-climatic data. We then projected the optimized model for two future time periods under different climate scenarios. Finally, we calculated differences in the mean elevation and lower and upper range limits for the species. We predicted that with changing climatic conditions, Caspian Snowcock will undergo significant elevational and some latitudinal shifts in its distribution and will face a drastic decrease in suitable habitat in the next 50 years. Including non-climatic data in the models increased model performance and resulted in reduced predictions of habitat loss under future climate scenarios. Terrain roughness was the most important predictor in this model, suggesting that more complex topography will retain favourable microclimates for the species in the future. The results thus highlight the importance of including topographic variables in climate-based SDMs. Our findings can guide biodiversity managers in prioritizing protected areas and adopting proactive measures to mitigate the negative impacts of climate change.

Mountain habitats harbour significant breeding populations of alpine bird species, yet they can also be important from a biodiversity conservation point of view outside the breeding season. High-elevations are likely important fuelling habitats for birds during the post-breeding period due to seasonal peaks in arthropod abundance being later relative to lowlands. There is no detailed study of bird communities using high-elevations in the post-breeding migration period in Europe. In this study, we recorded birds on line transects from August to October in 2021 and 2022 across an elevational gradient in the Western Italian Alps to assess how the abundance and diversity of birds varied in time and space during the autumn migration period. We detected 104 species in total, representing 22

As a consequence of both climate and land-use change, open alpine habitats are shrinking. Snow avalanches are a natural disturbance that create habitat mosaics which host unique bird communities, but their frequency and severity will probably be influenced by climate change. Ski-pistes can be considered the artificial counterpart of avalanches, and have been shown to have generally negative effects on alpine fauna. In this study, we compared the bird assemblages of these two open, linear habitats in the Italian Alps, to determine if ski-pistes could compensate for the potential loss of avalanche tracks and open habitats in the future. In the forest and treeline ecotone zones, there was little difference in abundance and diversity between avalanche tracks, ski-pistes and reference points. However, above the treeline, avalanche tracks supported greater bird diversity and were characterized by high vegetation diversity, whereas ski-pistes harboured less-abundant and less-diverse bird assemblages in a homogeneous habitat with high grass cover. Shrub-related species were negatively affected by the vegetation removal involved in the creation of ski-pistes, but occurred in suitable habitats in the avalanche tracks at lower elevations. Although ski-pistes had the most negative impacts in high-elevation assemblages, they were used by some species of alpine and low-elevation grasslands, showing that pistes could provide suitable habitats below the natural treeline, which may be of benefit to threatened grassland birds. New high-elevation ski facilities should be discouraged and the conservation potential of ski-pistes could be improved with sustainable management practices by including some important habitat elements from avalanche tracks such as small trees and shrubs.

Knowledge of biodiversity is unevenly distributed across the Tree of Life. In the long run, such disparity in awareness unbalances our understanding of life on Earth, influencing policy decisions and the allocation of research and conservation funding. We investigated how humans accumulate knowledge of biodiversity by searching for consistent relationships between scientific (number of publications) and societal (number of views in Wikipedia) interest, and species-level morphological, ecological, and sociocultural factors. Across a random selection of 3019 species spanning 29 Phyla/Divisions, we show that sociocultural factors are the most important correlates of scientific and societal interest in biodiversity, including the fact that a species is useful or harmful to humans, has a common name, and is listed in the International Union for Conservation of Nature Red List. Furthermore, large-bodied, broadly distributed, and taxonomically unique species receive more scientific and societal attention, whereas colorfulness and phylogenetic proximity to humans correlate exclusively with societal attention. These results highlight a favoritism toward limited branches of the Tree of Life, and that scientific and societal priorities in biodiversity research broadly align. This suggests that we may be missing out on key species in our research and conservation agenda simply because they are not on our cultural radar.

The mountain treeline forms the ecotone between the forest and the grass/shrub-heath dominated alpine zone and is often a zone of relatively high diversity. We first assess the universality of a peak in bird diversity at the treeline across studies and regions. Defining a ‘treeline’ bird is challenging, as this zone is often a mix of habitats, thus we determine whether any species can be classified as ‘treeline specialists’. We then compare bird communities of different mountain ranges and types of treeline: climate-limited, and those limited by disturbance, including of both natural (e.g. avalanches, grazing by wild herbivores) and anthropogenic (livestock grazing) origin. Furthermore, we assess the extent to which there are commonalities in broad traits (e.g. migratory strategy, foraging strategy, nesting substrate), primary origin (e.g. montane or alpine) and taxonomy (e.g. proportion of passerines vs non-passerines) across different treeline communities. We then review the determinants of reproductive success of treeline birds, the importance of vegetation structure, and the impact of grazing of both domestic and wild animals in maintaining the habitat mosaic. Finally, we consider how key threats to treeline bird communities might be confronted through conservation strategies.

Mountain regions harbour dynamic ecosystems that have been historically shaped by interactions between natural abiotic processes and human activities, but nowadays they are threatened by climate change. Avalanches are one of the main sources of natural disturbance in mountain areas, creating habitat mosaics with a high vegetation heterogeneity that can be exploited by a suite of animal species. Since snow precipitation regimes in mountain regions will be altered by climate change, it is fundamental to study the interactions between avalanches and biodiversity. We carried out surveys on 240 points across horizontal and vertical transects in the Western Italian Alps to assess the differences in habitat, bird assemblage composition and ecological traits between avalanche tracks and control points. Differences in both habitat and bird assemblages were more pronounced at lower elevations and became less obvious towards alpine grasslands. Avalanche tracks were characterised by a higher structural vegetation diversity with a greater cover of rocks, shrubs and a higher number of small trees. Bird assemblages differed between avalanche tracks and adjacent control points, with the former being more diverse and characterised by a higher proportion of species typical of open habitats and migrants. Importantly, the avalanche track bird assemblage differed from both forest and treeline ecotone assemblages, showing that these heterogeneous areas are unique, harbouring a mixture of bird species from different habitats. Avalanche frequency may be affected by climate change in the future, with consequences for mountain biodiversity at a broader scale, and hence should be a priority for alpine ecological research.

Mountain areas have faced a rapid increase in human activities over recent decades, often leading to habitat loss or degradation. The impacts of these activities can affect bird species both directly (e.g., by altering habitat characteristics, impacting migration or disturbing breeding or wintering grounds), and indirectly by inducing physiological responses. We summarize the human activities that take place at high elevation and provide examples of species that are known to be impacted. Hiking and winter sports in particular are common in many mountain regions and there is growing evidence of a range of impacts on year-round resident mountain birds and their food resources. Increasing evidence also suggests that use of, and dependence on, human-derived foods around human settlements affects the trophic ecology of high-altitude birds. Hunting mountain birds is common place in many areas, and we review the evidence that hunting activity, including illegal persecution, has had impacts at the population level. Finally, we assess how direct disturbance and habitat alteration due to renewable energy developments (i.e. wind turbines and hydropower) are affecting mountain bird communities. There are many unknown impacts of human disturbance and we highlight missing information on specific topics that should be investigated in future research.

Mate choice is a key process in animals to optimize the fitness benefits of reproduction, and it is generally guided by phenotypic features of potential partners that mirror reproductive abilities. Assortative mating occurs when there is within-pair selection for specific functional traits that can confer fitness benefits. Assortative mating can be positive if mates are more similar, and negative if they are more dissimilar than expected by chance. Mate choice is particularly important in long-lived species with biparental care, such as procellariforms that form long term monogamous bonds. We assessed the mating strategy of a sexually dimorphic Mediterranean procellariform, the Scopoli’s Shearwater ( Calonectris diomedea ), by testing for assortative mating according to bill (in accordance with previous studies on a sister species) and tarsus size (proxy of body size). We found that shearwaters adopted a positive size-assortative mating by tarsus length, while mating for bill size was random. Moreover, tarsus length was positively correlated with the duration of incubation shifts, when individuals are fasting on eggs. The observed assortative mating could be the results of choice by similarity between individuals, likely because partners with similar relative size have similar tolerance to fasting. Alternatively, the observed pattern could be the product of mutual mate choice, with a selection for large size that could confer competitive abilities in nest selection, defense, foraging aggregations and fasting ability. While our data suggest strong assortative mating in the Scopoli’s Shearwater ( R = 0.4), we cannot fully disentangle the multiple processes at play acting on mate choice.

There are many definitions of what is a ‘mountain’ and what is a ‘mountain bird’. In this chapter, we first assess these different definitions, and then clearly outline our rationale for choosing to define a mountain bird as bird species where at least some populations of the species somewhere in their distribution spend at least one critical stage of their life cycle above treeline. We then provide an overview of the importance of mountains to biodiversity, and compare knowledge on mountain birds to lowland ecosystems. Zonation is an important aspect of mountain ecology – we review the evidence for consistent patterns in bird richness and diversity across elevation gradients, and consider the different hypotheses that might explain these patterns. Additionally, we consider variation along the elevation gradient in some general species characteristics and the extent to which these trends vary geographically. Furthermore, we give an overview of how mountain bird communities vary seasonally, in particular considering different dispersal and migration strategies, and the extent to which the prevalence of these strategies varies according to different regions. Finally, we summarise the history of human interventions in mountains and their impacts on bird communities from pre-history until the start of the mechanized age.