New insights on the effects of human-induced environmental change on avian reproduction

Human-induced global change currently represents the greatest threat to global biodiversity (IPPC 2023, Keck et al. 2025). In this context, ever since formal efforts to connect behavioural ecology to conservation began at the end of the 20th century, avian research has provided crucial evidence on how anthropogenic impacts modify animal behaviour (reviews by Gil and Brumm 2013, Murgui and Hedblom 2017, Matuoka et al. 2020). Still, we need a clearer understanding of behavioural responses to such perturbations, their mechanisms and adaptive value to improve predictions of how human-driven global change will affect species and biodiversity.

The goal of this special issue was to provide an updated overview of how human-induced environmental pressures specifically affect avian reproductive behaviour, in order to identify key challenges and potential future directions in this field. The thematic issue features eleven papers: nine field-based studies (one of them based on open-access databases), which span a diverse range of ecological contexts, reproductive traits and species, along with a mini-review and a viewpoint article. In field-based studies, Passerines are the most represented taxonomic group, although one work focusses on a shorebird and another one on a bird of prey. In addition, the article based on open data sources includes almost 300 migratory bird species.

The work of Wheeler and colleagues (2025) investigated a wild zebra finch Taeniopygia castanotis population nesting in New South Wales (Australia). The authors found that parents reduced their hourly rate of parental visits to the nest by 0.91% following each increase of 1°C in daytime temperature. This interesting finding offers a proximate behavioural mechanism for coping with increasing temperatures, which can help to explain body size declines observed in other bird species in response to climate change.

Four studies in this special issue explored direct human disturbances, urbanization and landscape alterations as primary drivers of environmental change, and these were commonly linked to detrimental effects on avian reproductive traits. The long-term study on a population of great tits Parus major breeding in the Netherlands, reported that non-motorized recreational activities such as hiking, biking, pet walking or horseback were associated with reduced reproductive success (i.e. smaller clutch size and reduced nestling body size), the relationship being independent of habitat quality (Urhan et al. 2025). Similarly, in a four-year study, Zhang and colleagues (2025) showed that Chinese blackbirds Turdus mandarinus experienced constrained extra-pair paternity (EPP) in highly urbanized cities of southern China, while low EPP was in turn negatively associated with fitness-related traits. In addition, Lane and colleagues (202) presented data on song sparrows Melospiza melodia breeding in southwestern Virginia (USA), which typically suffer higher rates of brood parasitism in urban than in rural breeding sites. Across four consecutive breeding seasons, they reported that nestlings from urban environments showed shorter telomere length when they shared the nest with a brood parasite, compared with nestlings from unparasitized nests. These findings reveal how urbanization affects animals both directly, via abiotic factors, and indirectly, through shifts in community dynamics or alterations in molecular mechanisms.

Rivers et al. (2025) investigated the nesting preferences of Eurasian curlews Numenius arquata, during three breeding seasons in New Forest National Park (UK). Birds strongly avoided nesting near a major road passing though the study site, despite the habitat being suitable for breeding. These results underscore how human-altered landscape features can override habitat suitability, emphasizing the need for targeted conservation strategies to achieve a successful recovery of threatened species.

The special issue also includes studies showing that some species appear to thrive in anthropogenic environments. This seems to be the case for the pale-breasted thrush Turdus leucomelas. Batisteli and co-workers (2025) discovered that breeding on artificial substrates such as windows or water pipes – within two university campuses in south-eastern Brazil – was associated with higher reproductive success across three study years, compared to nesting on natural substrates. Elaborating on this, at the inter-specific level, Kinnunen et al. (202) performed a wide analysis of the structural and socio-economic features of US in relation with migratory species richness during the breeding season. They found that in urban areas where people commuted longer (i.e. travel time to work in minutes), there was a higher diversity of breeding migrants overall, except for shorebirds. This result may indicate that the resources provided by houses, yards, and diverse plant communities in cities can offer favourable nesting habitats for bird species, which can find refuge in urban areas of certain regions. Other aspects like housing density were less important. An additional four-year study provided insight on the trophic strategy of European honey-buzzards Pernis apivorus breeding in northwestern Spain (Martín-Ávila et al. 2025). The researchers showed that the invasive Asian hornet Vespa velutina became the second most frequently consumed prey by nestlings, although native common wasps remained the preferred diet source. These findings suggest that honey-buzzard parents have learned how to take advantage of a novel resource (introduced in the study area due to human activities) that may mitigate the highly energetic cost of provisioning the young.

Two of the studies included in the special issue addressed the specific effects of pollutants. First, Mari et al. (2025) followed a pied flycatcher Ficedula hypoleuca population breeding close to a smelter in Finland. High levels of heavy metal pollution were found to constrain blue eggshell colouration, a trait linked to female quality in other bird populations. Next, in an original mini-review, Jiménez-Peñuela et al. (202) focussed on one of the most commonly used pesticides worldwide, triazole fungicides. The authors proposed an adverse outcome pathway of triazole effects on the reproductive behaviour and physiology of avian populations from agricultural habitats, and stressed the need to re-evaluate the current risk assessment of these pesticides.

The contribution by Badas et al. (2025) highlights a central theme of this special issue, namely how compensatory strategies might allow birds to cope with human-altered environments. The authors bring into focus that the environmental stress experienced during early life potentially shape, even prenatally, specific physiological mechanisms (i.e. telomere repair maintenance processes and/or hormetic responses –or the process by which a low dose of an environmental stressor might stimulate compensatory processes or have beneficial effects), as well as reproductive strategies (e.g. maternal effects) that can buffer the associated negative effects of human-induced environmental change. Despite parental effects are often considered as a potential mechanism for transgenerational plasticity, there is very little evidence on how human-induced perturbations alter the transference of maternal effects via eggs, and how this modulates the development of behaviour in the offspring. The viewpoint also suggests that experimental manipulations are needed to unravel the specific negative (or positive) effects caused by anthropogenic disturbances and to move this topic forward.

We hope that the articles that we bring together in this special issue inspire future work on the effects of human-induced environmental change on avian reproduction. To further advance in the field, we call for experimental studies, either in natural or captive conditions, including manipulation of specific environmental features, in order to infer causality in the observed response patterns. Some of the studies in this issue clearly indicate that spatial (e.g. large scale) and temporal replicates (e.g. lifelong) will be particularly interesting for identifying general patterns and mechanisms. There is also a need for exploring transgenerational effects of human impacts in this context.

– We thank all authors who contributed to the special issue. We are deeply grateful to Michael Tobler, Jan-Åke Nilsson, and Staffan Bensch for the opportunity to put together this special issue, and for their invaluable support and encouragement from the very beginning.

– This work was supported by projects: PID2022-139166NB-I00 to JM (funded by MCIN/AEI/ https://doi.org/10.13039/501100011033/ and ‘ERDF A way of making Europe') and 2024-T1/ECO-31257 to EPB (funded by Atracción de Talento César Nombela from Comunidad de Madrid – CAM).

Judith Morales: Conceptualization (equal); Writing – original draft (lead); Writing – review and editing (equal). Elisa Pérez-Badás: Conceptualization (equal); Writing – original draft (supporting); Writing – review and editing (equal). Juan Diego Ibáñez-Álamo: Conceptualization (equal); Writing – original draft (supporting); Writing – review and editing (equal).