Évaluation du comptage des détections pour estimer la densité d'oiseaux à l'aide d'un suivi sonore passif : recommandations pour estimer un taux de détections fiable

Cue counting is a method developed for estimating vocally active wildlife density by dividing the density of cues (number of cues per unit area surveyed per unit time) by the average cue rate (ACR) at which individuals vocalize. It has been used successfully to estimate whale density using passive acoustic monitoring, but its efficacy has had limited testing in birds. We tested whether cue counting can be used to infer bird abundance using autonomous recording units and estimated the minimum effort required to obtain a reliable cue rate at individual and population levels. We recorded Dupont's Lark (Chersophilus duponti) vocalizations at 31 sites where traditional field censuses were also performed. We estimated the ACR using three methodologies: directional recordings, recordings from an online database of bird sounds (xeno-canto), and behavioral field studies. The ACRs estimated using directional recordings and behavioral field studies were similar, and bird numbers were over and underestimated by 0.8 and 10%, respectively (74–77% of the sampling sites were well estimated). However, the ACR estimated using xeno-canto recordings was much higher than those estimated using the other two methods, and bird numbers were underestimated by 41%. We also performed a cost-effectiveness assessment of the number of individuals and recording durations needed to optimize the estimation of a reliable ACR. We found that ACR estimates were more efficient if long (25 min) recordings were used when < 4 males were recorded, whereas 5-min recordings were more efficient for ≥ 20 males. We conclude that cue counting can be useful to infer bird density around recorders but requires an accurate measure of the ACR. Further research should evaluate the effectiveness of passive cue counting on a large number of species and under different circumstances.Le comptage des détections est une méthode qui a été élaborée pour estimer la densité de la faune active vocalement en divisant la densité de détections (nombre de détections par unité de surface étudiée par unité de temps) par le taux moyen de détections (TMD) auquel les individus chantent ou crient. Cette méthode a été utilisée avec succès pour calculer la densité des baleines à l'aide d'un suivi sonore passif, mais son efficacité a peu été testée chez les oiseaux. Nous avons testé si le comptage des détections pouvait être utilisé pour déduire l'abondance des oiseaux en utilisant des enregistreurs automatisés et avons calculé l'effort minimum requis pour obtenir un taux de détections fiable au niveau des individus et des populations. Nous avons enregistré les manifestations sonores du Sirli de Dupont (Chersophilus duponti) sur 31 sites où des recensements traditionnels ont également été effectués. Nous avons calculé le TMD de trois façons : à partir d'enregistrements directionnels, d'enregistrements provenant d'une base de données de cris et de chants d'oiseaux accessible en ligne (xeno-canto) et d'études comportementales sur le terrain. Les TMD calculés à l'aide d'enregistrements directionnels et d'études comportementales étaient similaires, et le nombre d'oiseaux était surestimé et sous-estimé de 0,8 et 10 %, respectivement (la mesure de 74-77 % des sites d'échantillonnage était juste). Cependant, le TMD calculé à l'aide d'enregistrements de xeno-canto était beaucoup plus élevé que ceux obtenus au moyen des deux autres méthodes, et le nombre d'oiseaux était sous-estimé de 41 %. Nous avons également réalisé une évaluation coût-efficacité du nombre d'individus et des durées d'enregistrement nécessaires pour optimiser le calcul d'un TMD fiable. Nous avons constaté que la mesure du TMD était meilleure si des enregistrements longs (25 min) étaient utilisés lorsque < 4 mâles étaient enregistrés, tandis que des enregistrements de 5 min étaient plus efficaces pour ≥ 20 mâles. Nous concluons que le comptage des détections peut être utile pour calculer la densité d'oiseaux autour des enregistreurs, mais une mesure précise du TMD doit d'abord être effectuée. D'autres recherches devraient se pencher sur l'évaluation de l'efficacité du comptage passif des détections dans le cas d'un grand nombre d'espèces et dans différentes circonstances.This study was supported by the Programa de Investigación y Conservación del Zoo de Barcelona within the project “Nuevas tecnologías para viejos trabajos: Uso de grabadores automáticos para la detección y censo de especies raras y amenazadas: El caso de la alondra ricotí en Lleida y otras poblaciones pequeñas”; the Education, Youth and Sport Bureau (Madrid Regional Government); and the European Social Fund for the Youth Employment Initiative (PEJ15/AMB/AI-0059 and PEJ1D-2018-PRE/AMB-8063). This work is a contribution to the Excellence Network Remedinal 3CM (S2013/MAE2719), supported by Comunidad de Madrid; and to the projects “Census of Dupont’s Lark in Guadalajara 2017 (SSCC/046/2017)”, supported by Junta de Comunidades de Castilla-La Mancha; LIFE Ricotí (LIFE15-NAT-ES-000802), supported by the European Commission, and “BBVA-Dron Ricotí”, funded by the BBVA Foundation

Effort needed to accurately estimate Vocal Activity Rate index using acoustic monitoring: A case study with a dawn-time singing passerine

Los autores del Departamento de Ecología de la UAM pertenecen al Terrestrial Ecology Group (TEG-UAM)Indices based on singing activity have often been used in wildlife surveys conducted with passive acoustic monitoring. For instance, the Vocal Activity Rate index (VAR) has been employed to estimate animal populations and detect changes in abundance between years or sites. VAR may differ greatly between days due to environmental and biological factors, therefore leading to inadequate population size estimations and recommendations. However, there is still little information about the minimum number of monitoring days required for estimating a reliable VAR to assess changes over time or sites. We describe, for first time for a terrestrial bird species, the pattern of variation of VAR as a function of the number of monitoring days. Coefficient of variation sharply decreased with the number of monitoring days, and this pattern was similar during the breeding and post-breeding period. Coefficient of variation was close to 100% when a single monitoring day was surveyed, but decreased up to 30% and 20% after six or seven and nine monitoring days, depending on the monitoring period. Mean VAR was significantly related to bird abundance, but no relationship was found between bird abundance and number of days needed to reach a CV lower than 20%. Our results highlight that prior assessment of effort needed to estimate a reliable VAR should be a prerequisite for future monitoring programmes using singing activity indices. We found large differences in the number of monitoring days needed to obtain a reliable VAR in comparison to prior research on seabirds, suggesting that further research should be developed in different taxa and situationsThis is a contribution to the LIFE Ricoti (LIFE15-NAT-ES-000802), supported by the European Commission, the “BBVA-Dron Ricoti”, funded by the BBVA Foundation and the Excellence Network Remedinal 3CM (S2013/MAE2719), supported by Comunidad de Madri

Moderate sheep grazing increases arthropod biomass and habitat use by steppe birds

Open semi-natural ecosystems have been historically shaped by anthropogenic land-use, and the abandonment or intensification of these activities implied a detrimental alteration of their landscapes. Extensive sheep grazing has gradually decreased during the 20th century in Mediterranean steppes, triggering changes across all taxa. Here, we address the effect of sheep grazing on both arthropod biomass and space use by insectivorous steppe birds, using an endangered passerine as a model species. We found that biomass of different arthropod groups peaked at intermediate levels of grazing, and that both short-term grazing (affecting arthropod biomass) and long-term grazing (affecting vegetation structure) explain space use by insectivorous birds, whereas only long-term processes are decisive for bird territory establishment. Our results emphasise the role of sustained moderate grazing intensity in the conservation of steppe biodiversity. In the current decline context of extensive sheep grazing, agricultural policies should prioritise these practices to ensure the persistence of open semi-natural ecosystemsThis study was partially supported by the European Commission (Life Ricotí project LIFE15-NAT-ES-000802) and the BBVA Foundation (BBVA-Dron Ricotí project). JGC was funded through a Postdoc grant by the Education and Research Department of Madrid Autonomous Region Government (REMEDINAL TE; S2018/EMT4338), and this paper contributes to project REMEDINAL TE-CM (P2018/ EMT4338

Prey choice in insectivorous steppe passerines: New insights from DNA metabarcoding

Food availability plays a key role affecting almost every aspect of bird ecology, including bird population, distribution, reproduction, and behavior. Understanding the functional relationship between prey availability and insectivorous birds’ diet is important in the current scenario of habitat loss and declining of insect and bird populations. We used a fecal metabarcoding approach coupled with prey availability sampling (arthropod abundance and biomass) to test for evidence of selective foraging in a shrub-steppe passerine assemblage over the 2017–2019 breeding seasons in semi-natural steppes of central Spain. The results showed that the six bird species selected specific arthropod taxa. Heteroptera, Orthoptera, Araneae, Lepidoptera and some Coleoptera families were the main selected prey taxa, while Formicidae appeared to be avoided, suggesting that shrub-steppe passerines tend to select prey items providing essential nutrients and energy during the breeding season, while poor quality ones are neglected. Our findings highlight the utility of metabarcoding dietary data to assess prey selection patterns in insectivorous passerines and provide valuable information for the development of conservation and management programs to ensure the long-term availability of crucial food resources for shrub-steppe birds and other insectivores.This study was supported by the European Commission LIFE Ricotí (LIFE15-NAT-ES-000802) and LIFE Connect Ricotí (LIFE20-NAT-ES-000133) projects. This is a contribution to the Excellence Network Remedinal TE-CM (S2013/MAE2719). JG-C is funded by a Margarita Salas Postdoctoral Fellowship (CA4/RSUE/2022-00205) provided by the Spanish Ministry of Universities and Universidad Autónoma de Madrid (Spain)

Comparative assessment of satellite- and drone-based vegetation indices to predict arthropod biomass in shrub-steppes

Arthropod biomass is a key element in ecosystems functionality, and basic food item for many species, which must be estimated through traditional costly field sampling in normally just a few sampling points. Arthropod biomass and plant productivity should be narrowly related, as a great majority of arthropods are herbivorous, and others depends on these. Quantifying plant productivity with satellite or aerial vehicles imagery is an easy and fast procedure already tested and implemented in agriculture and field ecology. However, the ability of satellite or aerial vehicles imagery for quantifying arthropod biomass and its relationship with plant productivity has been scarcely addressed. Here, we used Unmanned Aerial Vehicle (UAV) and satellite Sentinel-2 (S2) imagery to establish relationship between plant productivity and arthropod biomass estimated through ground-truth field sampling in shrub-steppes. We UAV sampled 7 plots of 47.6-72.3 ha at 4 cm pixel resolution, and afterwards downscaling spatial resolution to 50 cm resolution. In parallel, we used S2 imagery from same and other dates and locations at 10 m spatial resolution. We related several vegetation indices (VI) with arthropod biomass (epigeous, coprophagous, and four functional consumer groups: predatory, detritivore, phytophagous and diverse) estimated in 41-48 sampling stations for UAV flying plots, and in 67-79 sampling stations for S2. VI derived from UAV were consistently and positively related with all arthropod biomass groups. Three out of seven, and six out of seven S2-derived VI were positively related with epigeous and coprophagous arthropod biomass, respectively. BNDVI and ENDVI showed consistent and positive relationships with arthropod biomass, regardless of the arthropod group and the spatial resolution. Our results point out that UAV and S2-VI imagery data may be a viable and cost-efficient alternative to quantify arthropod biomass at large scales in shrub-steppes. The relationship between VI and arthropod biomass is probably habitat-dependent and thus, future research should address this relationship including several habitats to validate vegetation indices as proxies of arthropod biomass.This study was partially supported by the European Commission (Life Ricotí project LIFE15-NAT-ES-000802 and Life Connect Ricotí project LIFE20-NAT-ES-000133) and the BBVA Foundation (BBVA-Dron Ricotí project). This paper contributes to project REMEDINAL-3 from CAM

Selecting the best: Interspecific and age-related diet differences among sympatric steppe passerines

Parental food provisioning is crucial for the growth and survival of offspring. Growth rate depends on food quality and food supplied to offspring may differ from what adults use for their own. In the case of steppe passerine birds, detailed characterization on nestling dietary composition, as well as prey choice and resource partitioning among species, is a pending subject. Dietary differences between nestlings and adults remain also largely unexplored. By using faecal DNA metabarcoding, we described the diet of nestlings and adults of five shrub-steppe passerine species over the 2017–2019 breeding seasons in central Spain. We also monitored arthropod availability in the field to assess dietary selection. We expected interspecific dietary differences to limit competition for food resources among sympatric species, as well as parental selection of high quality prey for nestlings. We also predicted age-related differences, with nestlings being fed nutrient-rich prey more frequently than adults. The main arthropod orders provisioned to nestlings were Orthoptera, Julida, Araneae and Lepidoptera. Nestlings of the different species showed high interspecific diet overlap, indicating both a coincidence in growth needs among bird species and no or little limitation of the most profitable resources during the breeding season. Adults of all species showed higher diet richness than nestlings, and age-related differences in prey composition were mainly driven by the selection of the most easily digestible, larger protein- and calcium-rich prey for nestlings, which may favour their rapid growth, and avoiding highly sclerotized and less nutritional prey such as ants. Our study sheds light on the basic ecology and conservation of these declining steppe birds, indicating that interspecific competition may not be a major factor during the breeding season. Given the current global decline of arthropods, further long-term research would be necessary, along with the implementation of effective conservation measures that ensure a sufficient availability of resources identified as key prey in the diet of steppe bird nestlings.This study was supported by the European Commission LIFE Ricotí (LIFE15-NAT-ES-000802) and LIFE Connect Ricotí (LIFE20-NAT-ES-000133) projects. This is a contribution to the Excellence Network Remedinal TE-CM (S2013/MAE2719). JG-C is funded by a Margarita Salas postdoctoral fellowship (CA4/RSUE/2022–00205) provided by the Spanish Ministry of Universities and Universidad Autónoma de Madrid (Spain). CPG acknowledges support from Ministerio de Educación y Formación Profesional through the Beatriz Galindo Fellowship (Beatriz Galindo-Convocatoria 2020) and JZ acknowledges support from Ministerio de Universidades through the predoctoral FPU fellowship program

Dietary niche overlap and resource partitioning among six steppe passerines of Central Spain using DNA metabarcoding

Trophic niche partitioning is a mechanism that facilitates the coexistence of ecologically similar species by sharing their resource use. However, detailed information of the trophic niche in insectivorous birds is usually limited by the lack of accurate identification of consumed food resources. The use of DNA metabarcoding has proved useful for molecular identification of the taxa present in bird faecal samples. Here, we used this molecular technique to study the diets of six steppe passerine species distributed in two Special Protection Areas in central Spain, and to characterize the dietary niche overlap and the prey composition differences between bird species. In total, we distinguished 112 diet items, covering 39 arthropod families of 13 orders. Although significant dietary differences existed in prey species composition, our results indicated a 74% overlap in steppe bird dietary niche, mostly due to high consumption of abundant arthropod prey such as beetles, grasshoppers and spiders in the breeding season by all bird species. The lowest overlap was found for the dietary niches of the Greater Short-toed Lark Calandrella brachydactyla and Dupont's Lark Chersophilus duponti, a scarce and threatened species, which appeared to be the species with the most distinct dietary niche within the community. Our results make a significant contribution to the knowledge of shrub-steppe bird diets and their trophic interactions, indicating that some extent of interspecific resource partitioning occurs in the study area, notably between Dupont's Lark and the Greater Short-toed Lark. Our study demonstrates the value of DNA metabarcoding in the assessment of passerine diets and provides useful ecological results for the design of biodiversity conservation programmes in the increasingly scarce and threatened steppe habitatsThis study was supported by the European Commission LIFE Ricot ı (LIFE15-NAT-ES-000802) and LIFE Connect Ricot ı (LIFE20-NAT-ES-000133) projects, and the BBVA Foundation Dron Ricot ı project. This is a contribution to the Excellence Network Remedinal 3CM (S2013/MAE2719). Lu ıs P. da Silva and Vanessa A. Mata were funded by Fundac ~ao para a Ci^encia e Tecnologia (FCT) through the research contract CEECIND/02064/ 2017 and 2020.02547.CEECIND, respectivel

First documented case of Tawny Pipit Anthus campestris nest parasitism by common cuckoo Cuculus canorus in Spanish steppes

Primo caso documentato di parassitismo di un nido di calandro Anthus campestris da parte del cuculo Cuculus canorus nelle steppe spagnole. Il parassitismo interspecifico della covata o del nido è un comportamento riproduttivo relativamente comune negli uccelli. Attraverso questa tattica riproduttiva, i parassiti di cova evitano i costi associati all’allevamento e al mantenimento dei pulcini deponendo le uova nei nidi della specie ospite nella quale sono specializzati. Il cuculo (Cuculus canorus) segue questa strategia di parassitismo di cova. Le femmine di cuculo depongono le uova nei nidi di altre specie di uccelli, imitando la forma, le dimensioni e il colore delle uova della specie ospite. In questo lavoro riportiamo il primo caso documentato di parassitismo di nidi di calandro da parte del cuculo in habitat steppici spagnoli, dove finora non sono stati registrati casi di parassitismo su questa speci

Range contraction and population decline of the European Dupont’s lark population

Los autores de la UAM pertenecen al Terrestrial Ecology Group (TEG-UAM)Artículo escrito por un elevado número de autores, solo se referencian el que aparece en primer lugar, los autores pertenecientes a la UAM y el nombre del grupo de colaboración, si lo hubiereThe Dupont’s lark (Chersophilus duponti) is an endangered passerine typical of Mediterranean shrub-steppes, whose European distribution is restricted to Spain. Here, we update the population size and distribution range of the species at a European scale and evaluate (i) the current status; (ii) the change in population size and distribution range of the species from 2004 to 2009 to the current period (2017–2022); and (iii) the effectiveness of the current network of special protection areas (SPAs) for protecting the Dupont’s lark. The European Dupont’s lark population showed a decrease of 29.9%, declining from ca. 3267 to 2289 territorial males from 2004 to 2009 to the current period. Moreover, the species has suffered a contraction in its distribution range of 35.9%, with only 39.3% of the species’ territories located within the current network of SPAs. Our findings agree with the previously described decline of the Dupont’s lark in Europe. The population decline was even larger in peripheral regions, which suggests that the species is suffering a centripetal process of contraction and extinction. These results indicate that if there is no change in present-day declining forces, several peripheral populations will reach extinction in a few decades and the overall population size of the species will continue decreasing. Our study should be considered as a last call for action and used for implementing urgent conservation measures to protect the species and its habitat. Future studies should focus on analyzing and managing the factors driving the species’ extinction and future actions for the conservation of the species should focus on increasing the percentage of the Dupont’s lark territories within protected areas, since the data are alarmingly low for a species that is facing clear risk of extinctionThis study was partially funded by the LIFE programme (LIFE Ricotí LIFE15-NAT-ES000802 and LIFE Connect Ricotí LIFE20-NAT-ES-000133), by the European Commission, Levantina y Asociado de Minerales, S.A., with the project “Estudios de investigación aplicado a la conservación de las poblaciones de alondra ricotí (Chersophilus duponti) en el entorno del municipio de Vallanca”, by the Dirección General de Política Forestal y Espacios Naturales de la Junta de Comunidades de Castilla La Mancha with the project “SSCC/046/2017 Censo de Alondra ricotí en la provincia de Guadalajara. Año 2017” and by the Junta de Castilla y León with the project “Estudio para la Mejora del Conocimiento de las Poblaciones de Alondra Ricotí Chersophilus duponti en Castilla y León”. Censuses in Catalonia were carried out with the support of the Generalitat of Catalonia. CPG acknowledges the support from the Ministerio de Educación y Formación Profesional through the Beatriz Galindo Fellowship (Beatriz Galindo—Convocatoria 2020). JGC is funded by a Margarita Salas postdoctoral fellowship (CA4/RSUE/2022-00205) provided by the Spanish Ministry of Universities and Universidad Autónoma de Madrid (Spain

Veränderungen im Leukozytenprofil der Dupontlerche ( Chersophilus duponti ) in Spanien und Marokko

[EN] Stress in birds has been widely studied through the measurement of heterophil-to-lymphocyte ratio (H/L ratio). In this study we aimed to assess for the first time the potential variation of stress, measured as H/L ratio, associated to geography (between-country variation) and seasonality (between seasons and within the breeding season), as well as the leukocyte profiles, in the threatened Dupont’s Lark (Chersophilus duponti), using samples from Spain and Morocco. Furthermore, we tested whether variation in H/L ratio was associated with variables such as population density, presence of blood parasites and individual body condition. We found that H/L ratio did not vary between countries, but individuals captured during the breeding season showed higher values of H/L compared to non-breeding ones. Neither male density, nor date within the breeding season had an effect on the H/L ratio. In Spain, individuals with higher body condition showed lower H/L ratio regardless of whether they were malaria-infected. In Morocco, malaria-infected individuals showed higher values of H/L ratio than the non-infected birds. Moreover, we found that our average values of H/L ratio in Morocco were within the ranges of other passerines, but not in Spain. Individuals with higher H/L ratios may be more stressed or present higher capability to face stressful situations. Although H/L ratio is a useful and relatively easy way to obtain measure of stress, the impact that the environment might have on stress and the way it is explained by H/L ratio must be addressed carefully. This study provides new insight for this species’ biology and provides useful reference information to test the status and survival of other populations.[DE] Stress bei Vögeln ist durch die Messung des Verhältnisses von Heterophilen zu T-Lymphozyten (H/L-Verhältnis) umfassend untersucht worden. In dieser Studie wollten wir zum ersten Mal die potentiellen Veränderungen des Stresses in Verbindung mit der Geografie (Unterschiede zwischen einzelnen Ländern) und der Saisonalität (zwischen den Jahreszeiten und innerhalb der Brutsaison), gemessen als H/L-Verhältnis, sowie die Leukozytenprofile bei der bedrohten Dupontlerche (Chersophilus duponti) anhand von Proben aus Spanien und Marokko bewerten. Darüber hinaus haben wir untersucht, ob das H/L-Verhältnis mit Variablen wie der Populationsdichte, dem Vorhandensein von Blutparasiten und der individuellen physischen Verfassung zusammenhängt. Wir stellten fest, dass das H/L-Verhältnis zwischen den einzelnen Ländern nicht variierte, aber die während der Brutzeit gefangenen Tiere höhere H/L-Werte aufwiesen als nicht brütende Tiere. Weder die Dichte an Männchen, noch der Zeitpunkt innerhalb der Brutsaison hatten einen Einfluss auf das H/L-Verhältnis. In Spanien wiesen Tiere mit einer besseren physischen Verfassung ein niedrigeres H/L-Verhältnis auf, unabhängig davon, ob sie mit Malaria infiziert waren. In Marokko zeigten malariainfizierte Vögel höhere Werte des H/L-Verhältnisses als nicht infizierte. Außerdem stellten wir fest, dass unsere Durchschnittswerte für das H/L-Verhältnis in Marokko innerhalb der Werte für andere Sperlingsvögel lagen, nicht aber in Spanien. Tiere mit einem höheren H/L-Verhältnis sind möglicherweise gestresster oder besser in der Lage, mit Stresssituationen umzugehen. Obwohl das H/L-Verhältnis ein nützliches und relativ einfach zu beschaffendes Maß für Stress ist, muss der eventuelle Einfluss der Umwelt auf Stress und die Möglichkeiten, diesen durch das H/L-Verhältnis zu erklären, sorgfältig untersucht werden. Diese Untersuchung bietet neue Einblicke in die Biologie dieser Art und liefert nützliche Referenzinformationen für die Bestimmung des aktuellen Status und für das Überleben anderer Populationen.Open Access funding provided thanks to the CRUE-CSIC agreement with Springer Nature.This study was partially funded by the authors, the Spanish Ministry of Environment (MMA; J.J. Areces and B. Heredia), the Spanish Agency for International Cooperation (AECI), and the LIFE Ricoti (LIFE15-NAT-ES-000802), supported by the European Comisison. D.B.R. was supported by FPI-UAM fellowship from the Universidad Autónoma de Madrid (UAM), and the collaboration of the Instituto de Investigación en Recursos Cinegéticos (IREC-CSIC-UCLM). We wish to thank the Servicio de Vida Silvestre of Conselleria D’infraestructures, Territori i Medi Ambient (Generalitat Valenciana) and the Moroccan government for ringing permits and supporting our work. We thank V. Garza, A. Ramírez, R. del pozo, E. Juarez, E.L. García de la Morena, F. Suárez, M. Radi, M. Znari and M. Alouí, and the Colectivo Ornitológico Cigüeña Negra for their help during fieldtrips and arrangements. We also thank two anonymous referees whose helpful comments contributed to improve the paper. This work was approved by the Local Ethical Committee for Animal Experiments of the Autónoma University of Madrid (CEI80-1468-A229).Peer reviewe