José F. Calvo’s research while affiliated with University of Murcia and other places

There has been increasing recognition of the adverse effects of outdoor recreation on the behavioural ecology, breeding success and ultimate abandonment of territories in several raptor species, such as the Bonelli's Eagle (Aquila fasciata). We assessed the effects of human activities on the behaviour and breeding success of Bonelli's eagles breeding in south‐eastern Spain, using a 14‐year long‐term data set. Our results showed a weak behavioural response to human activities. The probability of eagle reaction varied among the human activities assessed and increased when they occurred close to a nest, being most marked for ecotourism activities. In general, the probability of a bird reacting increased sharply when an activity occurred closer than 480 m from the nest, but reactions were negligible when an activity occurred 1000 m away. Ecotourists only affected Bonelli's eagle behaviour at distances <300 m from the nest. We found a negative relationship between human activity and Bonelli's eagle behaviour: the probability of a reaction decreased with the increasing frequency of human activities, suggesting a degree of eagle habituation. Breeding success did not vary with a pair's experience of disturbance, nor between the periods before, during and after the COVID‐19 lockdown but did increase with the frequency of human activities. Our results indicated that Bonelli's eagles can develop a degree of tolerance to human activities during the nesting season. This behavioural plasticity offers the opportunity to harmonize anthropogenic activities with the application of specific conservation measures for this species in humanized landscapes. Our findings led to suggestions to minimize the detrimental effects of human activities and to optimize the conservation management of Bonelli's eagles in Southeastern Spain. More generally, our study emphasises the value of behavioural ecology studies for guiding conservation.

Anticoagulant rodenticides (ARs) are widely used for pest control, resulting in their pervasive presence in the environment and posing significant toxicological risks to a range of predatory and scavenging species. Our study mainly aimed to evaluate AR exposure and effects in nestlings of eagle owl (Bubo bubo) from the Region of Murcia (southeastern Spain). We analysed ARs in blood samples (n = 106) using high-performance liquid chromatography-triple quadrupole (HPLC-TQ), assessed the influence of potential anthropogenic (presence of livestock farms, landfills and human population density) and environmental (land uses and proximity to watercourses) variables, and measured prothrombin time (PT) and plasma biochemical parameters as biomarkers of effects. Our results showed the presence of AR residues in 91.5% of the nestlings, with 70.8% exhibiting multiple ARs (up to six compounds in a single individual). Second-generation ARs (SGARs) were the most prevalent compounds. The analysis of biochemical parameters indicated that the sampled individuals were in good physiological condition. Although PT was positively correlated with total AR concentration (ΣARs), the relationship was not significant (Rho = 0.04; p = 0.49). Regarding environmental factors, higher ΣARs were associated with the most urbanised study site and the presence of landfills, likely due to the increased availability of rodent prey. The prevalence of two SGARs (brodifacoum and difenacoum) was linked to closer proximity to riverbeds, suggesting a contamination pathway associated with inland aquatic ecosystems, where these AR compounds may concentrate due to water scarcity. This study underscores the widespread exposure of eagle owls to ARs and highlights the importance of effective monitoring and management of these pollutants to protect conservation-concern wildlife in Mediterranean semiarid regions.

Second-generation anticoagulant rodenticides (SGARs) are commonly used for rodent control, affecting various non-target wildlife species. Here, blood samples from common kestrels (Falco tinnunculus, n = 70 chicks) and barn owls (Tyto alba, n = 54 chicks and 12 adults) from Southeastern Spain were analysed using HPLC-TQ. SGAR prevalence was 68.6% in kestrel chicks, 50% in barn owl chicks and 100% in adult barn owls, with multiple SGARs in both species. Prothrombin time analysis in barn owls revealed a positive correlation with blood ΣSGARs, suggesting a potential adverse effect on coagulation. Analysis of variables potentially influencing SGAR prevalence indicated that, for kestrels, it was only related to the extent of artificial surface, showing no differences across study sites. In owlets, the highest prevalence occurred in the most urbanized study site, with human population density being a key factor. This study highlights species-specific differences in SGAR exposure, likely influenced by ecological traits. Barn owls probably encounter contaminated prey near anthropized areas, with widespread SGAR use and higher presence of target rodents. Conversely, kestrels, hunting a variety of prey often near human settlements, face consistently elevated exposure from multiple sources. Understanding these variations is crucial for effective conservation and minimizing SGAR impact on non-target wildlife.

As land-use cover types affect wintering birds’ strategies, studying their habitat suitability for species conservation is relevant. Predictive spatial models are considered excellent tools for conservation planning and improving our understanding of species distribution. Here we build models to predict the spatial distribution of raptor species that overwinter in SE Spain. We modelled the wintering raptor species distribution based on the presence-only data obtained between 2017 and 2019 and analysed their habitat preferences based on elevation and land-use cover variables. Our results show that altitude and distance to the coastline are the most important environmental factors to affect most species’ habitat suitability. Habitat type-related factors are other important predictors, and raptors subject of this study prefer lowlands and areas close to the coastline for overwintering by selecting open habitats, which include wetlands and irrigated and rainfed crops. This study highlights the importance of the habitat heterogeneity generated by wetlands and herbaceous crops within a low-altitude range as the optimal environment for wintering raptors. Such information should be considered for raptor conservation planning in human-altered landscapes.

The widespread use of anticoagulant rodenticides (ARs) poses a worldwide threat to farmland wildlife. These compounds accumulate in tissues of both target and non-target species, potentially endangering both direct consumers and their predators. However, investigations on ARs in blood of free-ranging predatory birds are rare. Here, the long-eared owl (Asio otus) has been used as a model predator to assess AR exposure in different agricultural landscapes from a Mediterranean semiarid region. A total of 69 owlets from 38 nests were blood-sampled over 2021 and 2022, aiming to detect AR residues and explore factors that determine their exposure, such as land uses. In addition, prothrombin time (PT) test was conducted to assess potential effects of AR contamination. Overall, nearly all the samples (98.6 %) tested positive for at least one compound and multiple ARs were found in most of the individuals (82.6 %). Among the ARs detected, flocoumafen was the most common compound (88.4 % of the samples). AR total concentration (ΣARs) in blood ranged from 0.06 to 34.18 ng mL−1, detecting the highest levels in the most intensively cultivated area. The analysis of owl pellets from 19 breeding territories showed relevant among-site differences in the contribution of rodents and birds into the diet of long-eared owls, supporting its high dietary plasticity and indicating AR presence at multiple trophic levels. Moreover, a positive and significant correlation was found between ΣARs and PT (Rho = 0.547, p < 0.001), which demonstrates the direct effect of ARs on free-living nestlings. Our results provide a preliminary overview of AR exposure in a little-studied owl species inhabiting agricultural and rural landscapes. Despite the low detected levels, these findings indicate widespread exposure -often to multiple compounds- from early life stages, which raises concern and draws attention to an ongoing and unresolved contamination issue.

Aim When studying the effects of global change on biodiversity, it is far more common for the effects of climate change and land‐use changes to be assessed separately rather than jointly. However, the effects of land‐use changes in recent decades on species richness in areas affected by climate change have been less studied. We assess the temporal turnover in species richness of an avian community between a historical period and a modern one as a consequence of global change. Location Semiarid Mediterranean ecosystem (southeastern Spain). Method We fitted a hierarchical multispecies occupancy model for each period (1991–1992, and 2012–2017), obtaining avian species‐specific estimates of occupancy probability in relation to environmental covariates (elevation and forest cover). We analyse the relationships between changes in the bird community and environmental variables, analysing the temporal turnover of the species richness and the richness‐based species‐exchange ratio. Results The estimated species richness accounting for detectability was higher than observed species richness, and decreased in the more recent period. Following our hypotheses, we observed a dual pattern of species richness increase associated with different elevations, showing different species turnover rates due to the joint effects of climate change and land‐use change. There is a trend towards greater species richness with higher elevations that is associated with climate change, where the species turnover rate is low. Also, species richness increased towards lower elevations, but with a high turnover rate. The latter can be due to species expansions throughout new habitat configurations in bordering forest systems associated with anthropic land‐use changes. Conclusions Our study is of great interest to understand the temporal turnover of avian species richness associated with areas experiencing both climate and land‐use change.

Agricultural intensification has caused a rapid loss of singular landscape elements worldwide, such as farmland ponds, hedgerows and field margins, leading to a steep decline in farmland bird populations. Farmland ponds and traditional small waterbodies (SWB) have been recently reported to support species-rich bird communities at landscape scale in several agroecosystems. However, a comprehensive assessment on the potential ecological functions provided by SWB to terrestrial birds has been never conducted. Here, we used data from breeding bird surveys at 39 traditional SWB to highlight the variety and magnitude of ecological functions provided to terrestrial birds. These SWB belonged to three different structural types and were spread along an environmental gradient in Mediterranean agroecosystems from southeastern Spain. We identified up to six cross-system services benefiting different functional guilds of terrestrial birds. Apart from to the well-documented supply of drinking water, traditional SWB delivered other ecologically relevant and commonly overlooked services to terrestrial birds, such as the provision of bathing sites, essential food resources (e.g., emerging insects), nest-building material and suitable adjacent perches for territorial display or thermoregulation. Structural and environmental variables at waterbody scale played an important role as determinants of the recorded ecological functions. Importantly, most of these ecological functions were evenly observed across the three types of traditional SWB, thus supporting the key role of these singular landscape elements for bird conservation regardless their structural attributes. Agri-environment schemes and farmland biodiversity conservation strategies should account for the ecological multifunctionality of traditional SWB by ensuring the protection and nature-friendly management of these valuable habitats, as well as by promoting the diversity of microhabitats at SWB scale.

Local biodiversity monitoring is important to assess the effects of global change, but also to evaluate the performance of landscape and wildlife protection, since large-scale assessments may buffer local fluctuations, rare species tend to be underrepresented, and management actions are usually implemented on local scales. We estimated population trends of 58 bird species using open-population N-mixture models based on count data in two localities in southeastern Spain, which have been collected according to a citizen science monitoring program (SACRE, Monitoring Common Breeding Birds in Spain) over 21 and 15 years, respectively. We performed different abundance models for each species and study area, accounting for imperfect detection of individuals in replicated counts. After selecting the best models for each species and study area, empirical Bayes methods were used for estimating abundances, which allowed us to calculate population growth rates ( λ ) and finally population trends. We also compared the two local population trends and related them with national and European trends, and species functional traits (phenological status, dietary, and habitat specialization characteristics). Our results showed increasing trends for most species, but a weak correlation between populations of the same species from both study areas. In general, local population trends were consistent with the trends observed at national and continental scales, although contrasting patterns exist for several species, mainly with increasing local trends and decreasing Spanish and European trends. Moreover, we found no evidence of a relationship between population trends and species traits. We conclude that using open-population N-mixture models is an appropriate method to estimate population trends, and that citizen science-based monitoring schemes can be a source of data for such analyses. This modeling approach can help managers to assess the effectiveness of their actions at the local level in the context of global change.

Farmland bird populations are declining worldwide as a consequence of agricultural intensifi-cation, and the loss of singular landscape elements has been suggested as one of the main drivers. This scenario of agroecosystem simplification is even more exacerbated in arid and semiarid regions, where traditional small waterbodies (SWB) are rapidly vanishing due to groundwater overexploitation and the declining extensive pastoralism. Here, we used data from breeding bird surveys at SWB and adjacent control sites to assess for the first time the landscape-scale contribution of three types of traditional SWB for supporting farmland bird communities in the most arid region of continental Europe. Four community metrics were calculated for each SWB: species richness, abundance, diversity and proportion of conservation-concern species. In general, a high proportion (71% on average) of the local breeding bird communities used SWB, irrespective of the SWB type. Cattle ponds supported a greater abundance and proportion of threatened species, whereas drinking troughs were used by more diversified bird communities. Traditional artificial pools showed intermediate values for all community metrics. Our results support that in semiarid regions any type of traditional man-made SWB, if properly designed and managed, can play a pivotal role in supporting farmland bird communities at landscape scale. Despite their ecological importance, traditional SWB are often overlooked from agri-environment schemes, and their role for supporting farmland biodiversity is rarely considered. Therefore, effective SWB management and conservation measures should be implemented in the framework of the new reform of the European Common Agricultural Policy and other similar eco-schemes in order to halt the decline of farmland biodiversity.

In bi-parentally built nests, there is evidence to suggest that nests are extended phenotypic signals that accurately indicate the quality of the building parent/s. Raptors often use a variety of materials to build their nests (natural, such as branches, but also non-natural objects), presumably due to their insulating properties, their suitability to advertise occupancy of the nest, and to decrease pathogen and parasite loads. However, in raptors where both sexes collaborate in nest construction, it is unclear whether nest building (taking the amount of material carried to the nest as the potential predictor) is an indicator of parental quality, and whether the effort expended by both sexes could constitute an honest signal of parental quality to their partners. Between 2011 and 2016, we monitored 16 nests of Bonelli’s Eagles ( Aquila fasciata ), and we examined data on sex, type of material brought to the nest, breeding experience, nest quality, timing, and nest-building investment prior to egg-laying from 32 identifiable Bonelli’s Eagles during the pre-laying period to investigate the relative contribution of the sexes to the amount of nest material gathered. Our results indicate that sex is not a determining factor in nest-building effort, and that females did not increase their parental effort in response to the male’s contribution, and supply of materials did not increase during the pre-laying period. In contrast, our models showed that: (1) the type of material supplied to the nest by both sexes varied significantly throughout the pre-laying period and (2) nest-building effort was determined by individual experience and nest quality. Therefore, our study suggests that male nest-building behaviour and investment by Bonelli’s Eagles cannot be considered as an extended phenotypic signal. The differential use of hard and green material by both sexes in the early and late stages of nest-building period, and the fact that the more experienced individuals contributed a larger amount of material on low quality nests, are discussed in the contexts of signaling nest occupancy to conspecifics and competitors and the decrease of ectoparasite loads during the pre-laying period.