Institute of Avian Research

Rapid environmental change due to urbanization poses novel challenges to animals. Behavioral change and individual plasticity are generally hypothesized to be the key to adapting to these challenges. One commonly observed behavioral change is higher observed aggression levels in urban animals, perhaps because anthropogenic noise disrupts effective acoustic communication during conflicts, leading to greater use of physical aggression. We investigated the hypothesis that urban noise drives aggression by performing repeated simulated territorial intrusion experiments on rural and urban chaffinches (Fringilla coelebs). We expected urban chaffinches to be more aggressive, change their aggression levels more between trials, and for aggression to increase with noise levels, irrespective of the habitat. We found that while aggression did not differ between habitats in the initial trial, rural chaffinches decreased their aggression level in the second trial and thus were less aggressive than the urban chaffinches, which did not change their response. That is, urban birds were less flexible in responding to an intruder than rural birds, contrary to previous findings in other songbirds. Moreover, aggression levels correlated positively with ambient noise levels. Given our small sample size and lack of spatial replicates, our results should be interpreted with caution. Nevertheless, as a lack of flexibility in aggression is potentially costly, our results highlight the importance of studying the plasticity in aggressive behavior in human-impacted landscapes.

Telomeres are regarded as key markers of cellular ageing and physiological state. Oxidative stress, which can accelerate telomere shortening, is thought to increase during energetically demanding processes such as bird migration. However, their study in the context of migratory behaviour is limited. Here we compared telomere length (TL) and mitochondrial DNA copy number (mitoDNAcn) between migratory and resident Eurasian blackbirds on the island of Helgoland, a migratory stopover site. Contrary to expectations, we found migrants had longer TLs despite similar mitochondrial densities. These findings reinforce the idea that migratory individuals may possess specific physiological adaptations, such as enhanced antioxidant defences, that help preserve telomere integrity. Overall, our results underscore the complex interactions between migratory behaviour and cellular maintenance and point to the need for broader comparative studies across species and migratory strategies.

Ticks are blood-sucking arthropods which can vector various, pathogenic microorganisms between humans and domestic or wild animal hosts. In Cameroon, little is still known about the diversity of ticks and tick-borne pathogens found feeding on these various hosts. This study investigates the frequency of positive pools of Borrelia spp. and Rickettsia spp. in 415 DNA pools arising from 1148 collected ticks belonging to five genera and twenty-five tick species collected from both domestic and wild animals in Cameroon. Tick species were identified morphologically and confirmed molecularly when necessary. All tick pools were tested for Rickettsia spp. and Borrelia spp. using molecular methods of which 18.01 % and 10.38 % of tick pools tested positive for Rickettsia or Borrelia DNA, respectively. This is the first Borrelia spp. detection in ticks collected from wild animals in Cameroon. Three species of Rickettsia were found in ticks feeding on domestic animals, namely, Rickettsia africae, Rickettsia aeschlimannii, and Rickettsia massiliae. Borrelia spp. in Cameroon are closely related to Candidatus Borrelia javanensis from China, as well as Candidatus Borrelia africana and Candidatus Borrelia ivorensis from the Ivory Coast. Although the risk this Borrelia species could pose to humans or animals is currently not known, both Rickettsia species are known to cause human disease warranting continuous monitoring and future research to determine the overall public health risk these microorganisms could pose.

Studying the timing of the seasonal movements of migratory birds, known as migration phenology, is crucial for managing and conserving migratory bird populations. This is particularly important for migratory game bird populations in Europe because, according to the EU, migratory birds should not be hunted during their breeding season or during return movements to breeding grounds (pre‐breeding or pre‐nuptial migration). To effectively protect these species during these critical periods, it is vital to employ reliable methods for assessing their migration phenology. Citizen science, which involves the participation of skilled volunteers in scientific data gathering, is a valuable resource for migration studies. It allows the collection of large amounts of data across extensive geographic areas, overcoming some limitations of other datasets and analytical methods. In this study we analysed pre‐ and post‐breeding migration phenology of 23 game bird species in Italy, using citizen science data from the www.Ornitho.it portal. We then compared our findings on pre‐breeding migration onset with published migration timing data from ringing records and found a close match. Additionally, we compared our results with the pre‐breeding migration onset determined for Italy in the ‘Key Concepts Document' (KCD) published by the European Commission that plays a central role in the regulation of hunting activities in EU countries. For 19 species (83%), we estimated an earlier pre‐breeding timing compared to that reported in the last KCD for Italy (2021, amended in 2025 for four species), highlighting a potential risk of these species being hunted during their pre‐breeding migration. These findings highlight the value of citizen science data in obtaining migration timing and the importance of employing multiple methods to estimate it. This approach is particularly valuable for species subject to hunting, which require well‐informed management.

The Northern Wheatear (Oenanthe oenanthe) is a long-distance migratory bird that has become a model species for the study of the phenomenology and molecular aspects of avian migration. Here, we analysed transcriptomic data related to the lipid metabolism in the liver of wheatears during the development and termination of the migratory fattening. In parallel, we partially characterised their plasma phospholipidome. Based on transcriptomic data, we found evidence of a fine-scale regulation of the lipogenesis/lipolysis rate and over the fatty acid composition during the migratory season. Furthermore, our results suggest a regulated production of oxylipins, signaling lipids derivatives of polyunsaturated fatty acids (PUFAs). Regarding the plasma phospholipid profiling, different lipid species showed a significant differential abundance among migratory stages: lysophosphatidylcholine (LPC 18:0), sphingomyelin (SM 34:1;O2) and phosphatidylinositols (PI 36:4 and PI 38:4). The liver transcriptomic and plasma lipidomic data agree well, showing the relevance of the liver in controlling the lipid metabolism in relation to migration. We hope that the results discussed in this publication would open the door for future functional genetic and metabolic studies regarding avian migration.

Abstract Highly pathogenic avian influenza (HPAI) has become a critical threat to wildlife, shifting from a seasonal epizootic to a persistent, year-round panzootic with global consequences. Here, we summarize the origin, evolutionary mechanisms, and expanding host range of the current H5N1 virus (clade 2.3.4.4b) and assess its impact on wildlife. Over the past five years, HPAI has caused the deaths of millions of wild birds, causing dramatic population declines in several seabird species. However, comprehensive quantitative mortality data remain scarce, as existing records are often anecdotal, focus on localized mass die-offs, and thus represent only a fraction of the true magnitude of mortality. This gap in data limits the ability to predict outbreak dynamics and mitigate long-term consequences. Using the Northwestern European Sandwich Tern ( Thalasseus sandvicensis ) population as a case study, we demonstrate the value of integrating mortality data with ecological, serological and genetic data before, during and after an outbreak. This approach uncovered age-specific vulnerability, selective mortality, and population immunological responses. In addition, insights gained with respect to the role of breeding density, carcass removal, and host adaptation in modulating outbreak dynamics are likely to be generalizable across seabird species. The absence of a centralized and standardized wildlife mortality monitoring framework, on the other hand, remains a major barrier to effective outbreak forecasting and conservation planning. We argue that integrating field-based mortality data, population monitoring, serological assays, and genetic analyses within a One Health framework is essential to enable early detection, targeted mitigation, and robust evaluation of outbreak impacts. Without a proactive and data-driven approach to conservation, HPAI will continue to threaten global wildlife populations, with cascading ecological, economic and public health consequences.

Human-wildlife conflicts are generally tackled using single-species studies and ensuing management solutions, ignoring species interactions that may moderate or augment these issues. We investigate the effects of interactions between four goose species foraging in the province of Friesland, the Netherlands, on species distributions, energetics, and consequent economic costs of agricultural damages and management, using an individual-based model. In Friesland, geese are allowed to graze on (semi-)natural grasslands and selected agricultural grasslands (accommodation areas), while they are scared off other agricultural grasslands (scaring areas). We show that interspecific competition and facilitation drive spatial redistribution of goose species. With increasing population sizes, most species are forced to increase foraging in the scaring areas, leading to more scaring events and more additional foraging to compensate for energy spent on fleeing behaviour. Our modelling results underline that careful consideration should be given to how management may affect the spatial distribution of foraging geese.Supplementary InformationThe online version contains supplementary material available at 10.1007/s13280-025-02206-9.

ABSTRACTThe way individuals respond to novel stimuli may provide insight into their ability to thrive in different situations, or into their role, for example during reproduction. Here, we analyze variation in the behavioral response of common terns (Sterna hirundo) when confronted with such novel stimuli. We quantify the latency to return to the nest upon facing a novel stimulus, and test for short‐term repeatability, whether variation in this trait is explained by sex, age, and reproductive phase, and whether there is evidence for assortative mating with respect to this trait. We find a repeatability of 32% across the responses recorded during incubation and chick‐rearing. Moreover, females take a longer time to return to the nest than males, and this latency is longer during incubation than during early chick rearing. Variation in this trait is not related to age, and responses are not correlated between the two members of a breeding pair. We suggest the sex effect reflects role differences during parental care, while the vulnerability of the offspring may dictate the effect of reproductive phase. Finally, we assess exploratory behavior during the incubation phase, and find that it does not vary with sex, age, or the response to the novel stimulus. Further work should assess the long‐term repeatability of the two traits we assessed, as well as elucidate whether connections to other repeatable behaviors observed in these birds exist.

Heligoland is an island located in the North Sea, where vegetation was almost destroyed as a result of heavy bombardment during and after the Second World War. However, over the past 70 years, the vegetation has developed from scrub towards bushy or even forested environments. This change has most likely altered habitat suitability for various organisms, including many species of ticks. Ticks can act as major vectors for various pathogens of humans and animals; thus, characterizing the occurrence of a tick population and associated microorganism on the island is of great importance in relation to public and animal health. For this characterization on Heligoland, we flagged ticks at four different locations during June 2023 and 2024. In 2024, ticks were opportunistically sampled from house pets living on the island and during the annual ringing of common murre (Uria aalge) fledglings. In total, 267 ticks were collected over the 2 years which were identified morphologically, and confirmed molecularly if needed, to four species: Ixodes ricinus (n = 132), Haemaphysalis punctata (n = 47), Ixodes uriae (n = 3), and Alectorobius maritimus (n = 85), which for the latter represents the first report in Germany. Questing tick samples positive for Borrelia burgdorferi sensu lato, Rickettsia spp., Anaplasma phagocytophilum, and Babesia spp. were found in one or both years. Subsequent sequencing showed the presence of two Rickettsia species (R. helvetica, R. aeschlimannii), multiple Borrelia species (B. garinii, B. valaisiana, B. bavariensis, B. afzelii), and two Babesia species (Ba. venatorum, Ba. capreoli). Our research highlights a diverse tick and associated microorganism population on the island, which could pose public and animal health risks that will need to be monitored in the future.

Inbreeding is known to have deleterious effects on offspring performance, but the extent to which such inbreeding depression acts on traits is widely variable. In particular, condition-dependent traits that are subject to directional selection are expected to show stronger inbreeding depression. However, while inbreeding effects on primary determinants of fitness have been thoroughly investigated, the impact of inbreeding on other potentially condition-dependent traits such as behavioural and “personality” traits remain little studied. Here, we performed experimental matings between full-siblings and unrelated individuals of Japanese quail (Coturnix japonica) and tested the effect of inbreeding on eight behavioural traits hypothesized to be linked to “personality” differences. Structural equation modelling revealed that these traits were part of a behavioural syndrome involving two a priori hypothesised latent variables, described as emotivity and neophobia. These were underlying all the measured behavioural traits and covaried negatively. Yet, we found no behavioural differences between inbred and outbred offspring, except for tonic immobility, which was longer in inbred offspring. We therefore conclude that inbreeding only has limited effects on behavioural traits linked to personality, suggesting that variation in these behaviours is not underlain by rare recessive deleterious alleles, as predicted when a trait is not condition dependent.