Ibis最新文献

Tufted Titmice Baeolophus bicolor are a well-studied species known for their gregarious nature and complex communication system. Black-crested Titmice B. atricristatus are a closely related species, but much less is known about their communication system. In this study, we compared the chick-a-dee calls of Tufted Titmice and Black-crested Titmice. We examined note use, main call sequence types, note transition probabilities, and first-order and second-order uncertainty (complexity) of calls. Black-crested Titmice used more D notes and more overall notes than Tufted Titmice. Tufted Titmice used more Z notes and more hybrid D notes (D_h) notes. Tufted Titmice used more calls with the call sequence type [Z][I][D] and [Z], whereas Black-crested Titmice used more [D] call sequence types. Tufted Titmouse calls had greater first- and second-order uncertainty than Black-crested Titmouse calls. More research needs to be done on Black-crested Titmouse ecology and social behaviours, but early evidence suggests that Black-crested Titmice have fewer individuals in their flocks than Tufted Titmice. The results of our study appear to lend support to the Social Complexity Hypothesis for Communication, which argues that more complex social systems (e.g. larger groups) need to have greater communicative complexity. Future research should consider whether the differences found in this study are related to genetic differences or to other differences like habitat preferences. Work should also be done to examine whether the difference in call complexity affects each species' role within their communities.

Farmland bird diversity has declined precipitously for decades because of the incessant intensification of agricultural practices in semi-natural landscapes in Europe. Consequently, formerly common and widespread ground-nesting species, such as the Eurasian Skylark Alauda arvensis, have shown severe declines on intensive grasslands and arable areas in western mainland Europe. In the Swiss Alps, populations are more stable, suggesting that high-elevation areas could act as refugia for Skylarks. We studied the habitat preferences of Skylarks in subalpine and alpine habitats across Switzerland. Using 3 years of territory mapping across a wide range of habitat types, land-use management and topographical characteristics, we aimed to elucidate the limiting factors for these populations to better inform conservation management. Skylarks occurred more frequently at lower elevation (1400 m versus 2600 m), with gentler, south-facing slopes and areas with higher land-management diversity. Skylark occurrence was lower closer to tall structures and higher in the presence of conspecifics. Skylark densities in these alpine areas are also much lower than in remaining intact lowland populations in Switzerland and their reproductive output is lower because of a shorter breeding season, questioning the role of alpine areas as refugia. The areas with high Skylark occurrence are also those most at risk of development for agricultural intensification or infrastructure projects. At the same time, the abandonment by farmers of extensively used agricultural areas – exacerbated by a longer vegetative growing season due to climate change – results in shrub encroachment in higher-elevation areas thereby further limiting the potential of alpine areas as a refuge for Skylarks. Management should limit the intensification of agricultural areas, but also prevent further abandonment of extensively used meadows and pastures to maintain open landscapes. Our results also indicate that establishing new populations in areas unoccupied by Skylarks could be far more difficult than maintaining or expanding existing populations. We therefore stress the importance of protection of those grasslands that currently host Skylark populations.

Passive acoustic monitoring (PAM) is emerging as a powerful tool for wildlife research. In this study we evaluate the effectiveness of PAM for automatic bird detection and distance estimation, focusing on Golden-crowned Warbler Basileuterus culicivorus and Southern Antpipit Corythopis delalandi. We found how the birds' spatial position influences sound pressure levels (SPLs) by building suitable attenuation models. Models adjust well to the data, even though B. culicivorus exhibited a spherical spreading, whereas C. delalandi exhibited a somewhat more cylindrical model, probably reflecting a larger influence of ground and canopy. By automatically detecting the songs using template matching we were able to automatically measure received level (RL) from the recordings and use the values to estimate the distance of 271 songs of B. culicivorus. Our distance estimates ranged from 2 to 8 m, occasionally reaching 16 m, much smaller than the distances found in the literature for manual inspection of PAM recordings. We failed to automatically detect the songs of C. delalandi, as template matching efficiencies were quite low. Overall, our results suggest a promising automatic workflow to estimate the distance of the singer. Nevertheless, we found no significant correlation between the overall number of detections and the species abundance on point counts (2011–21), underscoring PAM's limitation to provide somewhat more traditional ecological data on species populations. Current models require refinement to improve their accuracy for a better understanding of species' spatial distribution and habitat use. Enhanced attenuation models and improved detection techniques could provide more reliable distance estimates in the future.

Invasive species like the European Starling Sturnus vulgaris, which is rapidly expanding in South America, can threaten native birds through nest usurpation, making timely threat recognition essential for nest defence. Using model presentation experiments at 20 White-fronted Woodpecker Melanerpes cactorum active cavities, we recorded 78 attacks of woodpeckers across 40 experimental sessions in Córdoba, Argentina, to test the hypothesis that their defensive behaviour towards this aggressive competitor is learned. Woodpeckers with previous exposure to European Starlings exhibited significantly higher aggression towards this species model, while naive individuals showed no differential response between European Starling and control models. These findings highlight the behavioural adaptability of native woodpeckers when facing novel aggressive invaders like the European Starling, but also underline their potential vulnerability during the initial stages of the invasion.

Alpine grasslands are increasingly facing pressures of climate and land-use changes. Higher temperatures and pastoral abandonment lead to treeline shift and to bush encroachment, while agricultural intensification causes soil eutrophication and landscape homogenization. Alpine grasslands in Europe host important populations of mountain specialists that are subject to range contraction, such as Water Pipits Anthus spinoletta. Moreover, insectivorous, ground-breeding migratory species, such as Northern Wheatears Oenanthe oenanthe and Whinchats Saxicola rubetra, still have stronghold populations in high-elevation habitats. These species are undergoing Europe-wide declines, and the Alps are a key region for their conservation. While lowland farmland has suffered acute biodiversity loss and received substantial research attention, fewer studies have characterized community composition and species-specific habitat preferences in changing Alpine grasslands. We conducted repeated bird surveys during the breeding season in a high-elevation valley. We analysed landscape-scale habitat use and fine-scale niche partitioning in the four most common insectivorous species, relating them to topography, vegetation productivity and habitat composition. Water Pipits, Northern Wheatears and Whinchats were most abundant in gently sloping, productive areas that are the prime target of pastoralism in mountain regions but are often subject to intensification. Shrub cover had positive effects on the abundance of Whinchats but was avoided by Water Pipits. Black Redstarts Phoenicurus ochruros had higher densities on steeper slopes. At a finer scale, species' niches partially overlapped, with clearer differentiation between Northern Wheatears, Whinchats and Black Redstarts. These divergent species-specific preferences call for maintaining landscape heterogeneity and low-intensity management, to preserve the crucial role of Alpine grasslands for declining species like Whinchats.

Songbirds are a well-established model group for the study of cultural evolution as their songs are learned (i.e. culturally transmitted), which may lead to divergence in song characteristics between populations. Song variation across populations may be affected by geographical isolation, timing and duration of the learning period, and life strategies such as migratory behaviour. In this study, we explored geographical song variation in two congeneric sister species of songbirds with a simple song: the Palaearctic migrant Tawny Pipit Anthus campestris, and the sedentary Berthelot's Pipit Anthus berthelotii, endemic to Macaronesian archipelagos. We recorded songs of territorial males from six Tawny Pipit populations on the European mainland, and of Berthelot's Pipits on three Canary and two Madeiran islands. We confirmed that both species have individually unique repertoires, usually consisting of a single song type per male. The structural characteristics of song types within each species were compared by dynamic time warping analysis. In addition, we quantified several temporal and frequency measures to characterize geographical patterns of song dissimilarity. These were remarkably similar between species, despite differences in their natural history. In both species, we observed very high within-population variation of song types, possibly reflecting rapid cultural evolution of song driven by the constant introduction of novel, although minor, individual-specific differences. Mean song dissimilarity was higher when song types were compared between different regions (mainland localities or islands) than within them. However, only Berthelot's Pipits showed significant differences in geographical song variation at the smallest and largest spatial scales, which might reflect the sedentary behaviour of this species and the isolation of Macaronesian archipelagos, respectively. Nevertheless, and contrary to our expectations, the divergence in song observed at even the largest spatial scales was not sufficient in either species to infer the country or archipelago of origin of individual birds. The congruent patterns between the two species indicate that, in songbirds with individually unique song types, cultural evolution may promote high local diversity, largely obscuring geographical differentiation at broader spatial scales.

Artificial light is increasing worldwide, and has biological effects from molecular to ecosystem levels, which may be particularly severe for crepuscular and nocturnal animals. We investigated how artificial light affected spatial and temporal patterns of habitat use by Common Nighthawks Chordeiles minor in the southern Grassland and northern Boreal regions of Alberta, Canada. We measured two types of artificial light: upward radiance (light emitted directly from ground sources towards space) and skyglow (light scattered back towards Earth). Nighthawks potentially benefit from hunting aerial insects that aggregate near light sources and using skyglow to see their prey, but they may suffer increased predation risk at their cryptic ground nests if artificial light increases their visibility. We predicted a negative association with artificial light for territorial habitat use (where nighthawks are probably nesting) and a positive association for extra-territorial habitat use (where they are probably foraging). We recorded the different sounds made by nighthawks that reveal when they are defending a breeding territory and then measured the intensity of territorial and extra-territorial habitat use at 514 acoustic recording stations. Where nighthawks were present in more than 5% of recordings, we also determined associations between diel patterns of vocal activity and artificial light, measured via sun angle. We found a negative association with artificial light for both territorial and extra-territorial spatial patterns of habitat use in the Grassland, but not in the Boreal. Similarly, we found no effect of artificial light on temporal patterns of habitat use in the Boreal, whereas the morning activity peak in the Grassland occurred earlier at sites with skyglow when cloud cover was high. Our other measurement of artificial light – upward radiance – had no effect on temporal patterns of habitat use in either region, indicating that artificial light did not extend the foraging activity period of nighthawks. Our results may generalize to other crepuscular species, suggesting that artificial light is more likely to affect habitat use during the breeding season at lower latitudes where natural illumination is lower during twilight.

Species of the same guild often show ecological, biological or genetic similarities, yet they should also show different micro-habitat requirements or local spatial distributions to coexist in the same area. These patterns may be fundamental in reducing interspecific competition and maintaining biodiversity across ecological and evolutionary timescales. We examined habitat differences and spatial segregation in a guild of five sympatric woodland songbirds (family Paridae) inhabiting mixed forests of south-central Europe. Specifically, we performed interspecific comparisons of habitat and space use across two phenological periods (breeding and non-breeding) and two spatial scales (home-range and foraging habitat). At the home-range scale, habitat preferences revealed two distinct and seasonally consistent subgroups within the guild, namely ‘broadleaf’ and ‘conifer’ species. During breeding, we showed that all species largely overlapped in their use of different foraging micro-habitats within the tree canopy, even within each subgroup. Yet, we detected significant spatial segregation of breeding territories among species. Conversely, during the non-breeding period, individuals of different species within mixed flocks foraged on different and complementary sectors of the canopy, potentially partitioning foraging habitats. This study suggests that the coexistence of species within the south-central European tit guild across different phenological periods is facilitated by differentiation of habitat use at the home-range and foraging habitat scales, as well as by spatial segregation of breeding territories. These findings highlight how long-term coexistence among sympatrically and ecologically similar species can be shaped by temporal shifts in space and habitat use, which differ across the annual cycle.

The migration of birds through a stopover site may be understood as a physical process of hydrological flow through a reservoir whose water levels rise and fall over a migration period. Hydrological flow models show promise as a way of integrating information on storage (daily counts of birds), inflow/outflow (number of birds arriving/departing each day) and transit time (length of stay (LOS)) over a migration period. We used a hydrological flow model to evaluate the relationship between stopover duration and passage population sizes of migrant birds under variable wetland conditions in two case studies. First, we considered the northward migration of Common Cranes Grus grus at Gallocanta Nature Reserve in Spain. We calibrated the model with daily counts recorded in 1984 and 1985, and then used it to predict transit time distributions based on counts of cranes 30 years later (2015–17). The model was calibrated with a mean transit time of 6.5 days observed in 1984/85, consistent with observed values of LOS, and predicted a mean transit time of 5.2 days for the 2015–17 period. The model also predicted an ~6.2× increase of the total migratory passage population of cranes at Gallocanta, which qualitatively agreed with the large increase in the overall population from the 1980s to 2010s. Second, migration dynamics of Eurasian Spoonbills Platalea leucorodia were considered during southward migration at two intertidal coastal wetlands in northern Spain from 2002 to 2005. The model well captured the observed differences in transit time between Urdaibai Biosphere Reserve (median transit time of 1.1 days) and Santoña Marshes Natural Park (median transit time of 2.1 days). Transit times of both species were negatively correlated with estimates of annual population sizes. These results indicate that hydrological flow models can provide insights into the migration ecology of waterbirds (or species where regular counts during migration are available), and that LOS is a dynamic decision that can depend on the population sizes of migratory birds.

Monogamy in birds was long considered a general mating system until molecular studies provided evidence of alternative reproductive strategies (ARS), which are now assumed to be present in ~90% of bird species. These ARS or tactics (ART), as we consider them in this study, include extra-pair copulation, which can lead to extra-pair paternity or extra-pair maternity, also referred to as quasi-parasitism, and conspecific brood parasitism. Within the family Rallidae, where several species exhibit high rates of ART, the social system of Water Rails Rallus aquaticus has been poorly studied because of their secretive behaviour and occurrence in difficult-to-access habitats. In this study, we analysed microsatellites of embryos from 52 eggs collected across six Water Rail nests to infer their parents' reproductive strategies. Our study showed that the species is not genetically monogamous, revealing a complex network of ART. Even quasi-parasitism, which has been detected in only a few avian species and is poorly understood, was observed in one nest, where the resident male sired one egg each with two other females. Additionally, given recent findings that some female birds lay eggs with a relatively consistent and distinct appearance, we tested the use of photographic data as a potential non-invasive method for identifying maternity and exploring ART. Although our investigations into the shape, colour and pattern of eggs showed individuality in the morphology of eggs laid by different females, the level of discrimination was not high enough to allow non-invasive identification of ART in the field using egg morphology alone. Nevertheless, our study confirmed an unexpected high rate of ART in Water Rails.