Jente Ottenburghs

Why are some birds louder than others? Menezes and Podos (2026) examined vocal amplitude across 123 bird species, revealing substantial variation in how loudly different bird species communicate. Vocal amplitude was primarily associated with body size and beak gape width, whereas ecological factors showed no significant relationships. Despite the potential role of loud calls in attracting mates, the analyses found no clear relationship between vocal amplitude and polygamy.

Hybridization occurs in various groups of vertebrates, although the incidence, frequency and parental divergence times differ. One hypothesis for this difference between taxonomic groups is the so-called viviparity-driven conflict hypothesis, which is built upon the theory that more genetic and immunological mismatches may arise when the zygote spends a longer time within the mother. Accordingly, theory predicts a higher chance of failure of hybridization events between viviparous species compared to oviparous species. In this study, we reviewed hybridization events in both viviparous and oviparous Squamata (lizards, snakes and amphisbaenids) and used the collected data to test the viviparity-driven conflict hypothesis with a phylogenetic generalized linear mixed model. Hybridization was phylogenetically widespread and present among both reproductive modes, although divergence times of parental species were significantly longer in hybridization events between oviparous species. Moreover, the interaction between divergence time and viviparity showed a negative effect on hybridization probability. The results indicate that viviparous species lose the capability of hybridizing more rapidly with increasing divergence time than oviparous species. Hence, our findings provide support for the viviparity-driven conflict hypothesis.

Aim: Rapid climate change is reshaping Arctic ecosystems and altering species' breeding distributions. We assessed climate‐driven breeding range shifts of Arctic birds and examined how functional traits, including morphology, habitat breadth, and thermal niche breadth, influence these shifts. Location: European and North American Arctic. Taxon: Arctic‐breeding bird species in the orders Anseriformes, Charadriiformes and Passeriformes. Method: We quantified range shift metrics (i.e., record‐frequency‐weighted centroid latitude change and moving distance) between past (1960–1999) and current (2000–2024) periods using species occurrence data. Changes in suitable breeding distributions were estimated with species distribution models. The effects of functional traits on range shifts were evaluated using generalized linear models for each of the focal taxonomic groups, with continent‐level PGLS models across all species. Results: Climatic trends differed markedly between the European and North American Arctic, resulting in region‐specific range shift responses. A significant interaction between habitat breadth and thermal niche emerged, as habitat breadth was positively associated with range shifts in species with narrow thermal breadth and lower critical minimum temperature, but negatively associated with shifts in species with broad thermal breadth and higher critical minimum temperature. Morphological traits linked to dispersal ability showed generally weak effects, and migratory strategy and trophic guild exhibited no consistent influence across taxa or regions. Although sensitivity analyses supported the main patterns, uneven sampling coverage, local record clustering, and unequal sample sizes limited our ability to fully disentangle biological range shifts from changes in sampling effort. Main Conclusions: Trait interactions were more influential than single traits, indicating that species' responses to climate change depend on multidimensional trait combinations. Single functional traits provided limited explanatory power for Arctic bird range shifts and were strongly region and taxon‐dependent. Incorporating regional context and trait interactions is therefore essential for improving predictions of biodiversity responses to ongoing climate change.

Avian hybridization has been predominantly studied in natural contexts, such as hybrid zones or the identification of hybrid individuals. However, captive settings offer a complementary framework for understanding the ecological and evolutionary mechanisms underlying hybridization. Artificial conditions might relax premating isolation barriers that typically prevent interspecific breeding in the wild, although certain mate recognition mechanisms could remain effective in captivity. Here, I present a comparative analysis of wild and captive hybrids in owls (order Strigiformes; families Tytonidae and Strigidae) to test two predictions: (1) captivity facilitates hybridization between morphologically more divergent species than observed under natural conditions, and (2) certain premating isolation mechanisms are still effective in captivity, with a focus on iris coloration as a visual cue in species recognition. In total, I compiled an overview of 26 reported cases of owl hybridization. Of these cases, 11 (42%) were supported by reliable documentation, involving 19 species (8% of 244 assessed species). Seven additional cases (27%) remain provisional, and eight (31%) were deemed unreliable. Comparative analyses of morphological traits indicated that captive hybrid pairs showed a broader range of interspecific differences in body mass, tarsus length, and wing length than natural hybrid pairs. No consistent differences were found between captive and natural hybrid pairs in terms of iris coloration, activity pattern, or trophic niche. Overall, hybridization in owls appears rare. The tendency for captive hybrids to involve morphologically divergent species suggests that artificial conditions relax certain constraints on interbreeding. However, the similarity in iris coloration among most hybridizing species supports a potential role for this trait in premating isolation. Future studies integrating genomic data, experimental approaches, and broader comparative datasets will be needed to clarify the impact of captivity on reproductive barriers.

Homoploid hybrid speciation continues to be debated, particularly regarding the role of hybridization in generating reproductive isolation. Lima et al. (2026) present genetic evidence for an admixed lineage in the Black-cheeked Gnateater (Conopophaga melanops). Notably, patterns of isolation by distance, clinal plumage variation, and discordant signals in mitochondrial and nuclear markers complicate this interpretation. These findings highlight the difficulty of distinguishing hybrid speciation from secondary gene flow and underscore the reticulated nature of evolution.

Bird vocalizations can be influenced by different ecological and evolutionary factors. For example, the ‘morphological constraint’ hypothesis predicts a negative correlation between body size and song frequency, while the ‘acoustic adaptation’ hypothesis predicts that organisms in dense habitats sing lower-frequency songs compared with organisms inhabiting more open areas. However, little is known about how song structure is influenced under different lek mating systems. Here, we used 61 cotinga (Aves: Cotingidae) species to investigate fundamental relationships between morphology, ecology and mating system by compiling a dataset on song, morphological and environmental traits as well as different lek mating systems. We found that both peak frequency and frequency range correlate negatively with body size. Moreover, our results suggest a positive (albeit marginally significant) correlation between lek presence and frequency range. Our results thus support the ‘morphological constraint’ hypothesis, while environmental factors barely influence cotinga songs. These findings suggest that cotinga species are vocally constrained by body size, probably because of the limitation on the sound-producing organs, while evolution might have favoured a broad frequency song in avian lek mating systems.

Predicting evolutionary outcomes remains a central challenge in biology. Using three replicate hybrid zones in the Western Andes of Colombia, Castaño et al. (2026) assessed the repeatability of introgression between Lemon-rumped and Flame-rumped Tanagers. Genomic cline analyses revealed heterogeneous patterns of neutral introgression, but deterministic introgression at a plumage-associated locus on chromosome 22. Together, these patterns show that introgression reflects a balance of chance and necessity, with selection generating predictable outcomes amid substantial genomic contingency.

Speciation involves the build-up of reproductive isolation through prezygotic or postzygotic barriers. Research on avian speciation has emphasized the role of prezygotic barriers, whereas postzygotic barriers have remained underappreciated. Revisiting the hybrid zone between two grosbeak species with genomic data, DeRaad et al. (2025) detected ongoing hybridization but strong selection against later-generation hybrids, consistent with mitonuclear incompatibilities. These results demonstrate that postzygotic isolation, whether intrinsic or extrinsic, can be essential in maintaining a hybrid zone.

Migratory birds often traverse thousands of kilometers, yet some individuals may abandon migration and form sedentary populations—a process termed ‘migratory drop-off’. A key limitation in studying this phenomenon is the inability to distinguish between individuals from different populations, particularly when they share part of their range. We aimed to solve this problem for the Barnacle Goose ( Branta leucopsis ), a species with both migratory and sedentary breeding populations along its flyway. We developed a genetic tool aimed at distinguishing individuals from migratory and sedentary populations. Using genome-wide single-nucleotide polymorphisms (SNPs), we assigned geese wintering in the Netherlands to their breeding populations (i.e., the Netherlands and Russia). While complete assignment accuracy is likely unachievable—with potentially up to 20% of individuals misassigned due to ongoing gene flow and limited genetic differentiation—our results suggest that this error can be managed by focusing on high-confidence assignments or by studying traits with pronounced ecological or physiological differences. In the end, we refined a dataset of over 400,000 SNPs to approximately 1000 candidate markers for potential use in a diagnostic tool. Integrating these genetic markers with other methods, such as stable isotopes or morphological traits, may enhance assignment accuracy and offer novel insights into the ecological and evolutionary consequences of migratory drop-off.