Many bird species adjust their nest defense behavior according to the type and magnitude of perceived threats. Hosts of brood parasites – species that rely on another species effort to raise its offspring – are particularly suitable for studying such discrimination because they must defend their nests against both parasites and predators. Previous studies have typically compared host responses to brood parasites, which pose no direct threat to host adults, with responses to predators threaten, which threaten both eggs and adults. We tested whether yellow warblers (Setophaga petechia) discriminate between two heterospecific intruders that provide a similar functional cue – namely, the removal of an egg from the nest – by comparing their responses to the brood parasitic brown-headed cowbird (Molothrus ater) and predatory gray catbird (Dumetella carolinensis), which targets only nest contents and does not threaten adult birds. We predicted that cowbird and catbird both would elicit similar responses, and tested it through comparisons between the main behavioral responses in warbler defense repertoire. Our results confirmed a parasite-specific response to cowbirds, including seet calls and nest-protection behavior that differed from those elicited by catbirds. Given that cowbirds and catbirds provide similar informational cues at the nest (i.e., egg removal), it remains unclear how hosts differentially associate these two types of threats. We suggest that including nest predators that are innocuous to host adults as comparative species may help reveal the associative mechanisms underlying such refined discriminatory abilities. Birds must defend their nests against multiple threats, but the optimal defense strategy depends on the type of intruder. Brood parasites, such as the brown-headed cowbird, harm host fitness primarily indirectly: they remove a host egg and, during subsequent visits, lay their own, with the resulting chick eventually monopolizing parental care and substantially reducing host offspring survival. Yellow warblers, an important cowbird host species, may prevent these costs by adopting a nest-defense strategy that may position them close to the parasites without exposing themselves to risk, as cowbirds pose no direct threat to adults. Nest predators, by contrast, may also prey on adults, making close mobbing potentially risky. However, predators that target only eggs or nestlings pose no danger to adults, and in principle, close mobbing may be similarly advantageous. Remarkably, yellow warblers respond differently to cowbirds and to nest-only predators, despite the similar functional cue of egg removal. How hosts form the cognitive association underlying such refined, threat-specific defense remains unknown, revealing a critical gap in our understanding of avian-decision making and threat discrimination.

Parental infanticide followed by cannibalism remains a relatively understudied phenomenon, particularly among birds of prey. This behaviour, where parents kill their own offspring, is often considered an adaptive strategy for brood reduction in response to limited food availability during chick-rearing. In this brief report, we describe a case of siblicide followed by parental infanticide and cannibalism observed in a Golden Eagle (Aquila chrysaetos) nest, monitored via webcam in Nebrodi Regional Park, Sicily (Italy). Using video footage from the entire breeding attempt, we documented the sequence of events in detail, including prey deliveries, feeding frequency for each chick, and the number and intensity of aggressive interactions from hatching to the chicks' deaths. Our analysis suggests that the primary driver of this behavior was a severe shortage of food, likely linked to adverse weather conditions during the nesting period. We conclude that the infanticide and subsequent cannibalism were a result of insufficient prey provisioning caused by unfavorable climatic factors.

Behavioral defenses are a key adaptation across animals, but confirming decay under relaxed selection is challenging. If expression involves decision-making, then defenses may only be expressed when the right environmental cues are available (i.e., cryptic plasticity). Even if defenses wane, they could be quickly restored once selection resumes as animals can learn by observing others (i.e., social memory). Here we tested cryptic plasticity and social memory under relaxed selection in a cuckoo host, the common reed warbler, by manipulating perceived parasitism risk with social information in geographically distinct areas differing in allopatry (100-1,000 years). Despite predicting that social information of a cuckoo vs. a control would elicit otherwise cryptic behavioral defenses, only birds that mobbed model cuckoos prior to manipulation upregulated this defense, and only in the recently allopatric population. Social information also had no effect on low-to-absent rates of foreign egg rejection, a second line of defense common to cuckoo host species. These results contrast with parasitized locations where similar methods provoke mobbing and increase egg rejection 10-fold. Our study therefore suggests that, even when manipulating information to account for reaction norms, behavioral defenses may degrade rapidly under relaxed selection, demonstrating a process facilitating a geographic mosaic of coevolution.

Birds that live in our cities can be affected by human activities that alter their natural behaviour. While numerous studies have explored the impact of daily human activities, relatively little attention has been given to the effects of transient events, such as artistic installations, which represent a potential source of disturbance. This study focuses on Video Mapping, a technology that allows video projections on non-homogeneous surfaces, usually on buildings or monuments. Despite its potential to introduce light and sound pollution, no prior investigation, to our knowledge, has examined the ecological implications of this technology. Accordingly, here we tested the impact of Video Mapping on avian urban biodiversity, focusing on an artistic installation that took place in the Botanical Garden of the University of Palermo in summer 2021. Our findings reveal a reduction in bird abundance in the days preceding the event, though no discernible impact was observed during or subsequent to the event. We also quantified the brightness and loudness of single projections, revealing that higher levels of light and sound intensity were associated with reduced local bird abundance and diversity. Our results encourage new investigations into the impacts of transient events or artistic installations in urban green areas. Such inquiries are necessary for the development of evidence-based strategies aimed at mitigating the adverse effects of human activities on urban ecosystems, fostering harmonious relationships between humans and wildlife in urban contexts.-Ciaralli, S., Zaffuto, E., Bellia, E., Ceraulo, M., Dominoni, D. & Campobello, D. (2025). Effects of Video Mapping events on avian biodiversity in an urban botanical Ardeola, 72: 15-31.

Artificial wetlands have become a common conservation approach to contrast the decline of biodiversity globally, as a result of the ongoing loss and fragmentation of natural habitats. Assessments on the trend of the avian biodiversity in artificial wetlands are essential to understand their conservation value. This study aims to analyse temporal changes in the abundance of bird guilds and species in small artificial wetlands in Northern Italy. We surveyed bird populations over the 2005-2019 period from three adjacent wetlands, and examined temporal trends of species as both single species and grouped in guilds. We found the water systems analysed supported a high diversity of species. Overall, we found Swans and Geese, Cormorants, Raptors and Large wading birds had an increasing trend between 2005 and 2019, while Gulls and Terns were stable, Ducks, Rails and Cranes, and Grebes and Divers were uncertain, and Shorebirds decreased. Species-specific trends were revealed: Circus cyaneus (+13.40%) and Falco vespertinus (+21.32%) increased, while Calidris pugnax decreased (-7.91%) and Aythya nyroca was uncertain (+6.30%). Furthermore, dominant species had mainly a stable abundance (e.g. Larus ridibundus and Anas platyrhynchos), while Anas crecca increased (+2.97%), Vanellus vanellus decreased (-3.65%), and Fulica atra had an uncertain trend. We described these local systems as of vital importance to sustain the local and regional avian biodiversity, also urging to ensure national and international functional connectivity between natural and artificial systems.

In the sexual selection framework, nuptial gifts are materials a donor provides to a receiver that can increase the donor's fitness. In specific cases, sharing crucial information may be a nonmaterial nuptial gift. To investigate this hypothesis, we focused on the common cuckoo, Cuculus canorus, an obligate avian brood parasite whose reproduction costs of females are mainly related to finding host nests needed to lay their eggs. Nest searching is assumed to be conducted only by females. We hypothesized that males could contribute by transferring information on nest locations to females as a nonmaterial nuptial gift. Here, we show the results of a first step in this direction, in which we identified any behaviour potentially conveying information on nest abundance in the surrounding area, that is, behaviours whose frequency varied with host nest density. We conducted our investigation in a marshland area within the Po Plain (Italy), where we recorded both visual displays of cuckoos at perching sites, by using camera traps, and nest abundance of two of the most parasitized cuckoo host species, the reed warbler, Acrocephalus scirpaceus, and great reed warbler, Acrocephalus arundinaceus, by systematic nest monitoring. We found that male cuckoos adopted a certain posture, wing drooping, and tended to keep their tails up more frequently in areas with the highest versus lowest host nest densities. This is consistent with these behaviours acting as potential signals codifying information on nest abundance in the area. We finally discuss the implications of our findings for the mating choices of female cuckoos and the study directions warranted to reveal whether these displays and information transfer may be included as new elements of the sexual selection framework.

Social information use by cuckoo-hosts provides an excellent example of how social interactions within species can influence selection on another. Neighbours observe each other’s mobbing behaviour towards cuckoos, and then adjust costly defences back at their own nest in response. This may even allow naïve juveniles to ‘learn’ to recognise cuckoos, suggesting that ‘social responsiveness’ must play a key part in determining how hosts respond to changing rates of brood parasitism. However, if the ‘cultural memory’ of cuckoos is lost, can this plasticity in defences be rescued? This is fundamental for cuckoo-host coevolution, as the rates at which host defences are lost, gained, or retained determines evolutionary dynamics. Using populations of reed warblers at the northern- and southernmost extents of their range, we designed a field experiment to test whether populations allopatric to cuckoos (i) still recognise cuckoos as a threat, (ii) respond to social cues to upregulate defences, and (iii) vary in their strength of social responsiveness. We found defences and social responsiveness to be weaker in the south, where there is a much longer history of allopatry. In the north, only birds that retained recognition of cuckoos showed social responsiveness: social information about cuckoos did not increase hosts’ propensity to attack (whereas it doubled in the range core), but it did increase the strength of mobbing in the 30% of birds that recognised the cuckoo at the northern range front. Most importantly, however, experimental cuckoo eggs remained in the nest, whereas in previous experiments elsewhere the same social information increased egg rejection ten-fold. This suggests that social responsiveness is more limited at the range edges, under relaxed selection, and this would incur little immediate cost to cuckoos’ fitness if they (re)invade. Our study provides a rare example of geographic variation in social information use and highlights how current range expansions may influence the outcome of future species interactions.### Competing Interest StatementThe authors have declared no competing interest.

ABSTRACT Capsule The Eurasian Reed Warbler Acrocephalus scirpaceus from breeding sites in Italy has little genetic variability in the mitochondrial cytochrome b gene but shows morphological variation suggesting isolation of some populations. Aims To investigate the morphometric and genetic trait variation of Eurasian Reed Warbler populations at a large temporal and spatial scale. Methods We analysed morphometric traits and the mitochondrial cytochrome b (cyt b) gene of samples collected over 25 years, from populations at seven sites across the Italian peninsula and islands. Results While we found no genetic differences, we detected significantly smaller body sizes in individuals breeding in Sicily and Sardinia compared to those from mainland Italy. There were also significant body size differences between two Sicilian populations: one larger breeding on the southern coast and the other smaller at an inner highland site. Conclusion The morphometric data, together with the site fidelity of individuals, are consistent with there being isolation of some populations. Specifically, our results are consistent with an example of polyphenism, morphological plasticity, in the populations of the main Italian islands, Sicily and Sardinia.

Our aim was to investigate the among-populations diversity of prey composition in Eurasian Reed Warblers’ diets via their droppings, both to assess the ecological validity of this sampling method and to test whether the prey species most abundant in fecal samples were also the most present in the Italian study site. We collected fecal samples at four sites throughout Italy, for a total of 144 samples. Within reedbeds, the breeding habitat of the Eurasian Reed Warbler, we also collected arthropods by carrying out entomological sweepings at one of the study sites. Within the fecal samples, we identified dozens of prey species, belonging mainly to Araneae, Coleoptera, Diptera, Hymenoptera and Aphidoidea taxa, whose compositions were not statistically different among sites. The commonest prey species were Coleoptera in the droppings (68.5%) and Diptera in the reedbeds (31.3%), although the latter was less numerous in the fecal samples. The diets of different Italian populations of Eurasian Reed Warbler emerging from our study underline a strong Coleopteran presence, without differences across Italy. Fecal samples appear to be an exhaustive method to study variation in Eurasian Reed Warbler diet and its ecological importance; however, although potential caveats do exist, such as the possible under-representation of Diptera.

Because of its parasitic habits, reproduction costs of the common cuckoo (Cuculus canorus) are mostly spent in pre-laying activities. Female costs are limited to searching host nests and laying eggs, whereas, males spend time in performing intense vocal displays, possibly with territorial purpose. This last aspect, together with a sexual plumage dimorphism, points to both intra- and inter-sexual selections operating within this species. One element triggering sexual selection is a differential fitness accrued by different phenotypes. Before analyzing possible sexual selection mechanisms operating in cuckoos, it is therefore necessary to verify whether there is a variability among male secondary characters by describing and quantifying them. Here we aimed to quantitatively characterize the main two potential candidates of sexual selection traits, i.e., calls and displays, shown by males at perches. During the 2019 breeding season, in a site within the Po Plain, we both audio and video recorded cuckoo males at five different perches. We analyzed acoustic variables as well as display sequences searching for potential correlations. We found a significant variation among calls that could be clustered into four vocal types. We also found that no visual displays were associated with vocal displays; cuckoo males were either vocal and motionless or soundless and active. We discuss our results under the perspective of the potential value of sexual selection in brood parasites and its role in its parasitic habit.

Hosts of brood parasitic cuckoos often employ mobbing attacks to defend their nests and, when mobbing is costly, hosts are predicted to adjust their mobbing to match parasitism risk. While evidence exists for fine-tuned plasticity, it remains unclear why mobbing does not track larger seasonal changes in parasitism risk. Here we test a possible explanation from parental investment theory: parents should defend their current brood more intensively as the opportunity to replace it declines (re-nesting potential), and therefore “counteract” any apparent seasonal decline to match parasitism risk. We take advantage of mobbing experiments conducted at two sites where reed warblers (Acrocephalus scirpaceus) experience (in Italy), or do not experience (in Finland), brood parasitism. We predicted that mobbing of cuckoos should be higher overall in Italy, but remain constant over the season as in other parasitised sites, whereas in Finland where cuckoos do not pose a local threat, we predicted that mobbing should be low at the beginning of the season but increase as re-nesting potential declined. However, while cuckoos were more likely to be mobbed in Italy, we found little evidence that mobbing changed over the season at either the parasitized or non-parasitized sites. This suggests that re-nesting potential has either little influence on mobbing behavior, or that its effects are obscured by other seasonal differences in ecology or experience of hosts.

The integration and synthesis of the data in different areas of science is drastically slowed and hindered by a lack of standards and networking programmes. Long-term studies of individually marked animals are not an exception. These studies are especially important as instrumental for understanding evolutionary and ecological processes in the wild. Further, their number and global distribution provides a unique opportunity to assess the generality of patterns and to address broad-scale global issues (e.g. climate change). To solve data integration issues and enable a new scale of ecological and evolutionary research based on long-terms studies of birds, we have created the SPI-Birds Network and Database (www.spibirds.org) – a large-scale initiative that connects data from, and researchers working on, studies of wild populations of individually recognizable (usually ringed) birds. Within a year of the establishment, SPI-Birds counts 120 members working on more than 80 populations, with data concerning breeding attempts of almost a million individual birds over a 1700 cumulative years, and counting. SPI-Birds acts as a data hub and a catalogue of studied populations. It prevents data loss, secures easy data finding, use and integration, and thus facilitates collaboration and synthesis. We provide community-derived data and meta-data standards and improve data integrity guided by of Findable, Accessible, Interoperable, and Reusable (FAIR), and aligned with the existing metadata languages (e.g. ecological meta-data language). The encouraging community involvement stems from SPI-Bird's decentralized approach: research groups retain full control over data use and their way of data management, while SPI-Birds creates tailored pipelines to convert each unique data format into a standard format. We outline the lessons learned, so that other communities (e.g. those working on other taxa) can adapt our successful model. Creating community-specific hubs (such as ours, COMADRE for animal demography, etc.) will aid much-needed large-scale ecological data integration.

We present a quantitative analysis of the data reported in the only published review of parasitism frequency on hosts of Common Cuckoo Cuculus canorus in a Mediterranean area. We first eliminated a bias potentially introduced by the method by which data were recorded. Of the initial potential 70 species parasitized in Italy, only 44 were confirmed as host species, of which only 10 species had more than 10% of their total nests parasitized. We highlighted differential parasitism on host species according to geographic area, but the analysis suggested results were strongly biased because nest location was generally not reported and the number of records steeply decreased from North to South.

Wounds in living organisms trigger tissue-repair mechanisms. The sea cucumber (Holoturia tubulosa) is an excellent model species for achieving a better understanding of the humoral and cellular aspects involved in such healing processes. Consequently, this study assesses data on its morphometric, physiological and humoral responses 1, 2, 6, 24 and 48h after wound induction. In particular, morphometric data on the weight, width, length and coelomic-fluid volume of the species were estimated at different times during our experiments. In addition, the humoral aspects related to the enzymatic activity of esterase, alkaline phosphatase and peroxidase, as well as the cytotoxic activity of cell lysates (CL) and cell-free coelomic fluids (CfCf) are evaluated for the first time. Our results reveal a significant decrease in body length and weight, along with time-dependent, significant changes in the esterase, alkaline phosphatase, peroxidase and cytotoxic activity in both the CL and CfCf. The data obtained lead to the pioneering finding that there is an important time-dependent involvement of morphometric (changes in weight and length) and humoral (enzymatic and cytotoxic) responses in wound healing.

Sympatric species derive benefits by attending to information conveyed by heterospecifics. Our previous finding of reduced vigilance among jackdaws and lesser kestrels residing in mixed-species colonies suggested a reliance on interspecific communication of information regarding predatory threats. To test for interspecific communication of threat, we first determined whether jackdaw and lesser kestrel call structure varied with perceived threat. In this call production phase of our study, free-living birds in mixed-species colonies were presented with models representing a potential nest predator (European magpie) or with non-threatening stimuli (wood pigeon or wooden dowel) in proximity to nests. We recorded and subsequently analysed those calls to determine if any temporal or frequency-related call parameters differed by model type. In a second, perceptual phase of our study, we tested whether receivers perceive threat-related variation in both conspecific and heterospecific call structure by playing back call exemplars recorded in response to the predator model or to innocuous control stimuli, to determine whether free-living jackdaws or lesser kestrels respond differentially to playbacks of the different call types. We detected differences in vocalizations of both jackdaws and lesser kestrels relative to the model type presented, with more broadband (lesser kestrel) or noisy calls (jackdaws) in response to magpie versus innocuous model types. We also detected differential behavioural responses to call playbacks, with both jackdaws and lesser kestrels increasing vigilance and alarm calling in response to magpie-elicited jackdaw calls, but not to other call types. Taken together, our results suggest that jackdaw, but not lesser kestrel vocalizations, communicate enhanced threat associated with European magpies as possible nest predators. This interspecific alarm communication benefits both jackdaws and lesser kestrels, and, at least in part, explains asymmetric responses of jackdaws and lesser kestrels to magpies attending mixed-species colonies in nature.

Farmland bird species have suffered dramatic declines in recent decades, especially in Mediterranean areas. The intensification of agricultural practices has led to reduced invertebrate prey, which represent the bulk of the diet of many farmland birds. In this study, we investigated the spatial and temporal variation in the diet of the lesser kestrel (Falco naumanni) during the breeding season, monitored over a five-year period between 2006 and 2013 in the Gela Plain (Sicily). Our aim was to understand whether, and to what extent, farming practices affected the reproductive outputs of this predominantly insectivore bird in order to find a profitable compromise between conservation of farmland birds and farming practices. During our study, lesser kestrel diet varied among farmland habitats, in terms of ingested biomass, prey items/pellet and diet breadth. This has reflected in the reproductive output because colonies characterised by a higher ingested biomass fledged more chicks than the others. The artichoke and grassland fields were found to provide the most beneficial dietary parameters. Unexpectedly, the intensive and high-profit artichoke farming might turn out to be suitable for lesser kestrels. Artichoke fields are chiefly used when abandoned after harvest, providing high prey availability and accessibility for kestrels during the brood raising stage of their breeding season. A mosaic of grassland and artichoke fields can thus be recommended for Mediterranean agricultural areas of the Natura2000 network, in which some intensive farming and lesser kestrels can coexist, if adequately framed in a friendly-to-wildlife agriculture policy. Such a potential optimal trade-off between avian population persistence and economic sustainability for farmers we have found, should be planned in alternative management of agro-ecosystems, enhancing the functioning of trophic chains. For our study area, we suggest at least farmers be: i) informed on the role of predators as biological agents for pest control; ii) granted to reduce the high level of chemicals currently used during cultivation in favour of organic farming; and iii) granted to maintain the artichoke fields until June, following completion of the harvest.

Avian nest defence, which is expected to serve both antiparasite and antipredator functions, may benefit or be detrimental to birds, although selective forces that potentially operate on nest defence have not been quantified as a whole. Together with fitness values, we analysed two traits of nest defence, intensity and plasticity, in two distantly related passerine species, yellow warbler (Setophaga petechia) in North America and reed warbler (Acrocephalus scirpaceus) in Europe, both favourite host species for brood parasites. Breeders that escaped parasitism were the most vocal among reed warblers, whereas there was no specific defence phenotype that predicted prevention of parasitism in yellow warblers. Breeders that escaped nest predation were, in both species, those with the most distractive response at the first exposure to a nest-threatening event, such as the experimental predation or parasitism simulated at the nest. However, increasing defence intensity benefited yellow warblers but was detrimental to reed warblers, because intense defence responses attracted predators. Adaptiveness of nest defence was revealed by nest defence phenotypes when examined in concert with the seasonal fitness (i.e. measures of reproductive success). Results revealed selective forces favoured yellow warblers with strong defence phenotypes. Opposite forces were instead revealed among reed warblers whose favoured phenotypes were strong, yet less flexible, defenders.