Vittorio Baglione

Communication structures society, and is likewise shaped by relationships and shared tasks; yet, for most socially complex species, we know little of their full vocal repertoire and its functions. We investigated how communication structures the who, what, and when of social interactions in cooperative carrion crows – group-living birds who rely on coordinated behaviors, as in chick care. Leveraging machine learning to integrate large-scale data from crow-borne audio-loggers and nest cameras, we charted the vocal repertoire across 24 cooperative groups and mapped all discovered call types to behaviors and social context. We found that crows used a rich repertoire across three domains of joint behavior – flocking, chick care, and territorial display. Relatively quiet call types were abundant and included close-range calls that may coordinate chick care by announcing nest visits. Our study demonstrates how combining continuous-capture data and machine learning can reveal a holistic understanding of how vocalizations function across contexts.

Understanding vocal communication is essential to unraveling avian social behavior and cognition; however, audio recording remains particularly challenging in field studies involving wild populations. In this study, we deployed a lightweight, multi-sensor biologging device (MiniDTAG) designed for medium- to large-sized birds. The device integrates a microphone, accelerometer, magnetometer, and pressure sensors into a 12.5 g package, enabling high-fidelity acoustic and behavioral data collection. We deployed 52 MiniDTAGs over three breeding seasons in free-ranging cooperatively breeding carrion crows ( Corvus corone ) in northern Spain. The auto-releasing attachment method allowed the birds to free themselves from the tag after 18.5 days, on average. We recovered 87% tags, collecting over 83 h of data per device on average. Using a machine learning model (Voxaboxen), we detected over 127,000 vocalizations and assigned them to focal tagged individuals, adult conspecifics, crow chicks, and parasitic great spotted cuckoo nestlings ( Clamator glandarius ) with high precision and recall. We also explored the potential of accelerometer data to identify specific behaviors within a cooperative context, namely anti-predator mobbing. To evaluate logger impact, we analyzed 825 h of video from 22 crow groups and found minimal effects on brood feeding rates and reproductive success. Our results highlight the MiniDTAG’s potential to advance the study of animal communication by capturing vocalizations across the whole range of amplitudes. This approach opens new avenues for exploring the mechanisms of cooperation and information exchange in complex social systems and lays the groundwork for future comparative studies in corvid communication.

Climate change affects timing of reproduction in many bird species, but few studies have investigated its influence on annual reproductive output. Here, we assess changes in the annual production of young by female breeders in 201 populations of 104 bird species (N = 745,962 clutches) covering all continents between 1970 and 2019. Overall, average offspring production has declined in recent decades, but considerable differences were found among species and populations. A total of 56.7% of populations showed a declining trend in offspring production (significant in 17.4%), whereas 43.3% exhibited an increase (significant in 10.4%). The results show that climatic changes affect offspring production through compounded effects on ecological and life history traits of species. Migratory and larger-bodied species experienced reduced offspring production with increasing temperatures during the chick-rearing period, whereas smaller-bodied, sedentary species tended to produce more offspring. Likewise, multi-brooded species showed increased breeding success with increasing temperatures, whereas rising temperatures were unrelated to reproductive success in single-brooded species. Our study suggests that rapid declines in size of bird populations reported by many studies from different parts of the world are driven only to a small degree by changes in the production of young.

In group living animals, behavioural interactions with conspecifics strongly modulate an individual’s physiological stress response. Stable social relationships may reduce an individual’s stress response, which in turn can affect the immune system and health. Ultimately, positive health effects of stable social bonds may contribute to maintain group living. We investigated whether, in cooperatively breeding carrion crows ( Corvus corone ), the quality of social relationships correlates with coccidian oocyst and nematode eggs excretion. We repeatably collected behavioural data on dyadic social interactions and individual droppings to quantify parasite eggs and oocysts from 36 individuals in a captive population of carrion crows in northern Spain. Individuals with strong social bonds, living with more relatives and in larger groups excreted a significantly smaller proportion of droppings containing coccidian oocysts. The probability to excrete droppings containing nematode eggs was not affected by social factors. The relationship between social interactions and coccidian oocyst excretion is consistent with the idea that high quality social relationships can positively affects individual’s health, setting the stage for the evolution of stable social living.

Polygamous mating is expected to occur in obligate avian brood parasites because the lack of parental care reduces the need for a stable reproductive bond. Unlike nesting species, an absence of the constraints resulting from raising offspring might also favour a flexible mating system that adjusts to changing ecological conditions. Information on brood parasites' mating systems and their spatio‐temporal variation is, however, still scant. Here we analysed the genetic mating patterns of Great Spotted Cuckoos Clamator glandarius in two populations in northern and southern Spain and compared the results with those of previous studies. Parentage analyses showed high levels of polygamy in both populations that contrast with a prevalence of monogamy previously reported in the southern population. We suggest that the differences arise from an increase in population density, which in turn increases the probability of intraspecific encounters and therefore opportunities for mating. We also found that a greater number of mates increased the number of offspring produced, both in males and in females. The increase in offspring production in females might be the result of enhanced fertilization success during the lengthy laying period. Our data, combined with previous reports, demonstrate plasticity in the genetic mating patterns of the Great Spotted Cuckoo that may be associated with large fluctuations in population density.

Avian brood parasites should target the most profitable host species, but current conditions might locally influence their choice, producing geographic mosaics of coevolution. Throughout Europe, the magpie Pica pica has been invariably reported as the primary host of the great spotted cuckoo Clamator glandarius , whereas the carrion crow Corvus corone is the secondary one. However, we found that this pattern reversed in northern Spain, where up to 70% of carrion crow nests were parasitized versus 20% of magpie nests. In southern Spain, conversely, parasitism increased proportionally in both hosts (up to approximately 90% of available nests) throughout the 3 years of study. Surprisingly, magpies provided the best reproductive output for cuckoos in both areas, in contrast with cuckoo’s preference for the crow host in the north. Genetic data ruled out the presence of different host-specific races in this brood parasite, dismissing the hypothesis that a prevalence of different gentes at the 2 sites explained the observed variability in host choice. Instead, we found that magpie nests in the south were easier to reach and more scattered than in the north, where cuckoos preferentially targeted nests that were less concealed and more isolated. We suggest that the habitat constraints parasitism on magpies in the north, driving cuckoo host choice toward the crows. The coevolutionary scenario therefore includes a 3-way interaction, where the pressure that the parasite puts on a host species in a given place critically depends on the environmentally mediated interaction between the same parasite and a different host.

The Aquatic Warbler (Acrocephalus paludicola) is one of the most threatened migratory passerine birds in the world. The species stops over at both European and African wetlands during its migration. Using data from a long-term ringing program in the restored wetland of La Nava (Spain), we describe several aspects of the species' stopover ecology at this site with special focus on juveniles: (1) timing of migration, (2) population size, (3) fuel reposition rate, (4) stopover duration and (5) site fidelity. We elaborated two Multiple Linear Regressions and a Generalized Linear Model to estimate the determinants of migration phenology, daily fattening rate and abundance of captures in addition to minimum observed stopover duration. Finally, we calculated return rates to estimate stopover site fidelity. We determined that: this stopover site belongs to an Atlantic migration route; juveniles experience delayed migration; and that reduced captures are associated with more restrictive hydrological manag...