Summary 1.There is a long-term trend of depopulation of rural areas and pasture abandonment throughout the Alps. This trend peaked after the Second World War and is now omnipresent. Its ecological consequences are evident mostly below the timberline, where grassland gradually turns into shrub and, ultimately, to forest. This study addresses the consequences of land abandonment and the decline of pastoral practices on the diversity and structure of the bird communities of the Italian Alps. 2. The breeding birds of Gran Paradiso Natural Park in north-western Italy were surveyed, and bird diversity, abundance of grassland, ecotone, woodland and shrub species were analysed using regression in relation to a set of explanatory variables including elevation, local habitat variables, landscape variables and grazing intensity. 3. Avian diversity increased in abandoned pastures as higher numbers of shrub species followed tree and shrub encroachment. Conversely, open habitat species that benefited from grazing were mostly confined to pure grasslands and high altitudes. 4. The effects of grazing were more evident in the montane belt. Grazing maintained open habitats by limiting tree and scrub encroachment, thereby favouring grassland bird species. At higher altitudes, however, grazing had little effect on typical open habitat alpine species (choughs Pyrrhocorax spp., water pipit Anthus spinoletta , alpine accentor Prunella collaris , wheatear Oenanthe oenanthe , snow finch Montifringilla nivalis , rock thrush Monticola saxatilis ) and only skylark Alauda arvensis and linnet Carduelis cannabina preferred grazed meadows. 5. Synthesis and applications . This study shows that the abandonment of grazing in the Alps has significant effects on bird species diversity and abundance, especially below the timberline where pastoral decline leads to significant changes in vegetation structure. However, grazing importance differs markedly depending on whether the focus is avian α -diversity or grassland bird abundance. Pastoral abandonment leads to an overall increase in avian diversity, but most species invading abandoned pastures are already common, whereas several grassland bird species that are dependent upon grazed pastures have an unfavourable conservation status. Overall, in terms of bird conservation objectives, large-scale abandonment of long-established pastoral habitats and their complete replacement with scrub, or even forest, is likely to be detrimental.

This review reports on the effects of human activities on animal acoustic signals published in the literature from 1970 to 2009. Almost 5% of the studies on variation in animal communication tested or hypothesized on human impacts, and showed that habitat fragmentation, direct human disturbance, introduced diseases, urbanization, hunting, chemical and noise pollution may challenge animal acoustic behaviour. Although acoustic adaptations to anthropogenic habitats have been documented, human impacts have most often generated neutral variation or potential maladaptive responses. Negative impacts have been postulated in the sexual signals of fishes, amphibians, birds, and mammals; these are concerning as any maladaptive alteration of sexual behaviour may have direct bearings on breeding success and ultimately population growth rate. Acoustic communication also facilitates other vital behaviours influenced by human-driven perturbations. Bat and cetacean echolocation, for instance, is disrupted by noise pollution, whereas bird and mammal alarming is also affected by introduced diseases and hunting. Mammal social signals are sensitive to noise pollution and hunting, and birds selecting habitats by means of acoustic cues are especially vulnerable to habitat loss. Anthropogenic intervention in these cases may have a negative impact on individual survival, recruitment and group cohesion, limiting rescue effects and triggering Allee effects. Published evidence shows that acoustic variation may be used as an early-warning indicator of perturbations even when not directly affecting individual fitness. Acoustic signalling can be studied in a broad range of ecosystems, can be recorded, analyzed, synthesised and played back with relative ease and limited economic budget, and is sensitive to many types of impacts, thus can have great conservation significance.

In the global scenario of increasing habitat fragmentation, finding appropriate indicators of population viability is a priority for conservation. We explored the potential of learned behaviours, specifically acoustic signals, to predict the persistence over time of fragmented bird populations. We found an association between male song diversity and the annual rate of population change, population productivity and population size, resulting in birds singing poor repertoires in populations more prone to extinction. This is the first demonstration that population viability can be predicted by a cultural trait (acquired via social learning). Our results emphasise that cultural attributes can reflect not only individual-level characteristics, but also the emergent population-level properties. This opens the way to the study of animal cultural diversity in the increasingly common human-altered landscapes.

Landscape structure may affect individual dispersal abilities, thus influencing the genotypic and phenotypic composition of populations. We analyzed the interplay among landscape, behavior, and evolutionary processes by correlating habitat patchiness to the variability in vocalizations of Dupont's Lark Chersophilus duponti, one of the most habitat-selective and rare European songbirds. We tape-recorded males throughout the species distribution in Spain, analyzed the spatial patterns of territorial call variation at different scales (individuals, populations, and broad geographic areas), and related acoustic variability to patterns of isolation by geographic distance and by landscape unsuitability (calculated by building a predictive model of habitat suitability). The differentiation of spectro-temporal call features resulted from both isolation by distance and isolation by landscape unsuitability mechanisms. Landscape connectivity was often a better determinant of call differentiation than simple straight-line distance between individuals, providing the first evidence that call transmission can be limited by the presence and distribution of patches of adequate habitat, which likely mediates bird dispersal. Landscape patchiness resulted in a reduction of acoustic diversity (repertoire size) within populations, and a parallel increase in differentiation among populations. Landscape bioacoustics can represent a promising tool for estimating population structure, although the study of animal communication cannot be viewed as an alternative, but a source of complementary information to genetics, given that it provides evidence of male-male transmission and social and cultural phenomena that are currently undetectable from molecular data.

The climate is often evoked to explain broad-scale clines of body size, yet its involvement in the processes that generate size inequality in the two sexes (sexual size dimorphism) remains elusive. Here, we analyse climatic clines of sexual size dimorphism along a wide elevation gradient (i) among grasshopper species in a phylogenetically controlled scenario and (ii) within species differing in distribution and cold tolerance, to highlight patterns generated at different time scales, mainly evolutionary (among species or higher taxa) and ontogenetic or microevolutionary (within species). At the interspecific level, grasshoppers were slightly smaller and less dimorphic at high elevations. These clines were associated with gradients of precipitation and sun exposure, which are likely indicators of other factors that directly exert selective pressures, such as resource availability and conditions for effective thermoregulation. Within species, we found a positive effect of temperature and a negative effect of elevation on body size, especially on condition-dependent measures of body size (total body length rather than hind femur length) and in species inhabiting the highest elevations. In spite of a certain degree of species-specific variation, females tended to adjust their body size more often than males, suggesting that body size in females can evolve faster among species and can be more plastic or dependent on nutritional conditions within species living in adverse climates. Natural selection on female body size may therefore prevail over sexual selection on male body size in alpine environments, and abiotic factors may trigger consistent phenotypic patterns across taxonomic scales.

Summary 1.Males of many bird species match song with neighbours during territorial interactions. Although bird vocal mimicry has received much attention, the relationships between song variation and ecological factors such as landscape geometry and habitat fragmentation are still poorly known, and most previous research has been limited to one or a few populations of a species. In this study we analysed the spatial patterns and ecological determinants of song matching in Dupont's lark Chersophilus duponti , a rare and specialized steppe passerine. 2. By recording bird songs from 21 Spanish and Moroccan localities, we analysed the effect of habitat fragmentation and the availability of suitable steppe habitat on the patterns of song matching in Dupont's lark, controlling for other potential determinants such as period in the breeding season, intensity of competition, geographical location and spatial distribution of individuals. 3. Both song-type sharing (match of song types in the repertoire) and spectrotemporal matching (convergence in the acoustic features of the same song type) were greater between counter-singing neighbours than between non-neighbours, and spatial autocorrelation (similarities between singing individuals) only occurred at short distances. The study localities differed in the amount of overall acoustic matching between individuals, seemingly as a consequence of local differences in the intensity of male competition and in the availability of suitable habitat. 4. The levels of song-type sharing between non-neighbours tended to increase and those among neighbours to decrease with the increase of steppeland availability. Moreover, the existing differences in sharing between neighbours and non-neighbours were significantly affected by the presence of elements of fragmentation in the steppe. In fragmented habitats, song sharing among neighbours was enhanced, possibly because of harsher competition for limited resources; conversely, sharing among non-neighbours dropped, probably because of the lack of interactions among individuals isolated by habitat barriers. 5. Synthesis and applications . Anthropogenic habitat barriers could alter bird perception of the spatial distribution of rivals over distance, leading to a contraction of the spatial range of the individual acoustic niche. We suggest that communication systems of habitat-sensitive species might be used as a behavioural indicator of anthropogenic environmental deterioration. Because of their rapidly evolving cultural nature, bird vocalizations might become an early warning system detecting the effects of fragmentation over relatively short times and before other indicators (such as genetic markers) show any change.

Individuals of some species differentiate each other on the basis of the acoustic features of their vocalizations, and this can be used in individual-based population monitoring studies. No research has tested for the effectiveness of individual marking through voice recognition as compared to traditional monitoring methods relying on physical marks. We compared voice recognition and physical marking using the Dupont's lark Chersophilus duponti as a study species. This bird needs to be attracted with playback in order to be seen (or captured). We first demonstrated that the territorial calls from a sample of banded males were individually distinctive and constant over time by means of discriminant function analysis, which correctly classified 100% of marked males. Then, we applied similarity techniques on call spectrotemporal features to define a threshold value of similarity within banded individuals, to be combined with qualitative spectrogram inspection for the classification of all recorded birds. Eventually, we compared the voice and the capture samples, to test for differences in relation to re-location rate, territory fidelity and dispersal movements both within and between years. Voice recognition was less time-consuming than capture-recapture method in the field, but it was useless for monitoring yearlings in call development stage. The two methods provided the same results in terms of territory fidelity and dispersal movements, but differed in re-location rates, which were significantly greater in the case of voice recognition method. By means of physical captures we possibly trapped a large sample of young and silent floaters, with low probability of recapture or recording. This mismatch between methods could bias the estimates of annual survival, which strongly depend on re-location rates. We suggest considering the two methods as complementary rather than alternatives for monitoring populations. Each technique offers unique information, and the two sources should be combined to provide correction factors that would eventually sharpen our knowledge on bird population ecology.

In the study of fragmented populations, genetic diversity has received a good deal of attention, whereas traits that are not genetically inherited have been generally overlooked. We analyzed variation in cultural traditions (song and call repertoire) of a small songbird, Dupont's lark (Chersophilus duponti), with respect to landscape and demographic parameters associated with anthropogenic habitat fragmentation. As patch size, male population, and mean dispersal distance decrease, individual and population song repertoires pass through a cultural bottleneck and significantly decline in variety. Similarly, isolation is associated with impoverishment of population call pools. That declining populations face problems of cultural erosion, possibly anticipating extinction, suggests cultural diversity should be taken into account when dealing with the conservation of species in which social learning is important. Cultural elements could be viewed as a novel, fourth level of biodiversity that may complement the traditional dimensions of ecosystem, species, and genetic diversity.