Breeding in the pandemic: short-term lockdown restrictions in a European capital city did not alter the life-history traits of two urban adapters

Humans are transforming natural habitats into managed urban green areas and impervious surfaces at an unprecedented pace. Yet the effects of human presence per se on animal life-history traits are rarely tested. This is particularly true in cities, where human presence is often indissociable from urbanisation itself. The onset of the SARS-CoV-2 outbreak, along with the resulting lockdown restrictions, offered a unique, "natural experiment" to investigate wildlife responses to a sudden reduction in human activity. We analysed four years of avian breeding data collected in a European capital city to test whether lockdown measures altered nestbox occupancy and life-history traits in terms of egg laying date, incubation duration and clutch size in two urban adapters: great tits (Parus major) and blue tits (Cyanistes caeruleus). Lockdown measures, which modulated human presence, did not influence any of the life-history traits investigated. In contrast, the interaction between year and tree cover, a distinct ecological attribute of the urban space, was positively associated with clutch size, a key avian life-history and reproductive trait. This highlights the importance of inter-year variation and habitat quality over human activity on urban wildlife reproduction. We discuss our results in the light of other urban wildlife studies carried out during the pandemic, inviting the scientific community to carefully interpret all lockdown-associated shifts in biological traits.

Supplementary Information

The online version contains supplementary material available at 10.1007/s11252-022-01309-5.

Coping with novelty across an urban mosaic: Provisioning latency increases closer to roads and is associated with species-specific reproductive success in two urban adapters

Most research on urban avian ecology has focused on population- and community-level phenomena, whereas fewer studies have examined how urbanization affects individual behavioral responses to a sudden and novel stimulus, and how those translate to fitness. We measured between-individual variation in provisioning latency in two urban adapters - great tits and blue tits - in response to an infrared camera installed in the nestbox, encountered when offspring in the nest were at the peak of food demand (9-10-days old). For each nestbox, we quantified urbanization as intensity in human activity, distance to road and proportion of impervious surface area. In both species, provisioning latency increased closer to roads. Moreover, increased provisioning latency when exposed to a novel object was associated with higher reproductive success in great tits whose nestboxes were surrounded by high amounts of impervious surface. In contrast, increased provisioning latency was consistently associated with lower reproductive success in blue tits. Our results suggest that provisioning latency changes in relation to the environment surrounding the nest, and may be context- and species-specific when exposed to a novel stimulus, such as a novel object in the nest. To better understand the role of initial behavioral responses towards novelty across an individual's lifetime and, ultimately, its impact on fitness in the urban mosaic, further research explicitly testing different behavioral responses across the entire breeding cycle in wild model systems is needed.

Changes to the gut microbiota of a wild juvenile passerine in a multidimensional urban mosaic

Urbanisation is a major anthropogenic perturbation presenting novel ecological and evolutionary challenges to wild populations. Symbiotic microorganisms residing in the gastrointestinal tracts (gut) of vertebrates have mutual connections with host physiology and respond quickly to environmental alterations. However, the impact of anthropogenic changes and urbanisation on the gut microbiota remains poorly understood, especially in early development. To address this knowledge gap, we characterised the gut microbiota of juvenile great tits (Parus major) reared in artificial nestboxes and in natural cavities in an urban mosaic, employing two distinct frameworks characterising the urban space. Microbial diversity was influenced by cavity type. Alpha diversity was affected by the amount of impervious surface surrounding the breeding location, and positively correlated with tree cover density. Community composition differed between urban and rural sites: these alterations covaried with sound pollution and distance to the city centre. Overall, the microbial communities reflect and are possibly influenced by the heterogeneous environmental modifications that are typical of the urban space. Strikingly, the choice of framework and environmental variables characterising the urban space can influence the outcomes of such ecological studies. Our results open new perspectives to investigate the impact of microbial symbionts on the adaptive capacity of their hosts.

Cross-Context Responses to Novelty in Rural and Urban Small Mammals

The Anthropocene is the era of urbanization. The accelerating expansion of cities occurs at the expense of natural reservoirs of biodiversity and presents animals with challenges for which their evolutionary past might not have prepared them. Cognitive and behavioral adjustments to novelty could promote animals’ persistence under these altered conditions. We investigated the structure of, and covariance between, different aspects of responses to novelty in rural and urban small mammals of two non-commensal rodent species. We ran replicated experiments testing responses to three novelty types (object, food, or space) of 47 individual common voles (Microtus arvalis) and 41 individual striped field mice (Apodemus agrarius). We found partial support for the hypothesis that responses to novelty are structured, clustering (i) speed of responses, (ii) intensity of responses, and (iii) responses to food into separate dimensions. Rural and urban small mammals did not differ in most responses to novelty, suggesting that urban habitats do not reduce neophobia in these species. Further studies investigating whether comparable response patters are found throughout different stages of colonization, and along synurbanization processes of different duration, will help illuminate the dynamics of animals’ cognitive adjustments to urban life.

Contrasting effects of the COVID-19 lockdown on urban birds' reproductive success in two cities

The ubiquitous activity of humans is a fundamental feature of urban environments affecting local wildlife in several ways. Testing the influence of human disturbance would ideally need experimental approach, however, in cities, this is challenging at relevant spatial and temporal scales. Thus, to better understand the ecological effects of human activity, we exploited the opportunity that the city-wide lockdowns due to the COVID-19 pandemic provided during the spring of 2020. We assessed changes in reproductive success of great tits (Parus major) at two urban habitats affected strikingly differently by the ‘anthropause’, and at an unaffected forest site. Our results do not support that urban great tits benefited from reduced human mobility during the lockdown. First, at one of our urban sites, the strongly (− 44%) reduced human disturbance in 2020 (compared to a long-term reference period) did not increase birds’ reproductive output relative to the forest habitat where human disturbance was low in all years. Second, in the other urban habitat, recreational human activity considerably increased (+ 40%) during the lockdown and this was associated with strongly reduced nestling body size compared to the pre-COVID reference year. Analyses of other environmental factors (meteorological conditions, lockdown-induced changes in air pollution) suggest that these are not likely to explain our results. Our study supports that intensified human disturbance can have adverse fitness consequences in urban populations. It also highlights that a few months of ‘anthropause’ is not enough to counterweight the detrimental impacts of urbanization on local wildlife populations.

Connecting the data landscape of long-term ecological studies: The SPI-Birds data hub

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. Furthermore, 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-term 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 year and a half since the establishment, SPI-Birds has recruited over 120 members, and currently hosts data on almost 1.5 million individual birds collected in 80 populations over 2,000 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 the principles 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.

Little parental response to anthropogenic noise in an urban songbird, but evidence for individual differences in sensitivity

Anthropogenic noise exposure has well-documented behavioral, physiological and fitness effects on organisms. However, whether different noise regimes evoke distinct responses has rarely been investigated, despite implications for tailoring noise mitigation policies. Urban animals might display low responsiveness to certain anthropogenic noise regimes, especially consistent noise (e.g. freeway noise), but might remain more sensitive to more diverse noise regimes. Additionally, whether individuals differ in noise sensitivity is a rarely explored issue, which is important to fully understand organismal responses to noise. To address these knowledge gaps, we used a field experiment to measure how urban great tits (Parus major) altered parental behaviors in response to two noise regimes: consistent freeway noise, and a diverse anthropogenic noise regime that incorporated variability in noise type and temporal occurrence. We also evaluated whether sex, age, or a well-described personality trait, novel environment exploration behavior, were associated with responses to noise, although our power to assess individual differences in responses was somewhat limited. We found no evidence for mean population-level changes in nestling provisioning behaviors during either noise treatment. However, despite this overall canalization of behavior, there was evidence for individual differences in noise sensitivity, particularly during the diverse noise treatment. Females and birds that explored a novel environment more rapidly (fast explorers) reduced nestling provisioning rate more relative to baseline levels than males and slow explorers during the diverse urban noise, but not during the consistent freeway noise. Furthermore, first year breeders and fast explorers displayed larger increases in latency to return to the nest box relative to baseline conditions during the diverse noise only. Results suggest that urban animal populations might become overall tolerant to anthropogenic noise, but that certain individuals within these populations nonetheless remain sensitive to certain types of noise exposure. CAPSULE: In an urban songbird, we found no population-level changes in nestling provisioning behavior during noise exposure, but did find evidence for individual differences in noise sensitivity.

Bertalanffy-Pütter models for avian growth

This paper explores the ratio of the mass in the inflection point over asymptotic mass for 81 nestlings of blue tits and great tits from an urban parkland in Warsaw, Poland (growth data from literature). We computed the ratios using the Bertalanffy-Pütter model, because this model was more flexible with respect to the ratios than the traditional models. For them, there were a-priori restrictions on the possible range of the ratios. (Further, as the Bertalanffy-Pütter model generalizes the traditional models, its fit to the data was necessarily better.) For six birds there was no inflection point (we set the ratio to 0), for 19 birds the ratio was between 0 and 0.368 (lowest ratio attainable for the Richards model), for 48 birds it was above 0.5 (fixed ratio of logistic growth), and for the remaining eight birds it was in between; the maximal observed ratio was 0.835. With these ratios we were able to detect small variations in avian growth due to slight differences in the environment: Our results indicate that blue tits grew more slowly (had a lower ratio) in the presence of light pollution and modified impervious substrate, a finding that would not have been possible had we used traditional growth curve analysis.

Growing in the city: Urban evolutionary ecology of avian growth rates

INTRODUCTION

Rapid environmental change driven by urbanization offers a unique insight into the adaptive potential of urban-dwelling organisms. Urban-driven phenotypic differentiation is increasingly often demonstrated, but the impact of urbanization (here modelled as the percentage of impervious surface (ISA) around each nestbox) on offspring developmental rates and subsequent survival remains poorly understood. Furthermore, the role of selection on urban-driven phenotypic divergence was rarely investigated to date.

METHODS AND RESULTS

Data on nestling development and body mass were analysed in a gradient of urbanization set in Warsaw, Poland, in two passerine species: great tits (Parus major) and blue tits (Cyanistes caeruleus). Increasing levels of impervious surface area (ISA) delayed the age of fastest growth in blue tits. Nestling body mass was also negatively affected by increasing ISA 5 and 10 days after hatching in great tits, and 10 and 15 days in blue tits, respectively. High levels of ISA also increased nestling mortality 5 and 10 days after hatching in both species. An analysis of selection differentials performed for two levels of urbanization (low and high ISA) revealed a positive association between mass at day 2 and survival at fledging.

DISCUSSION

This study confirms the considerable negative impact of imperviousness-a proxy for urbanization level-on offspring development, body mass and survival, and highlights increased selection on avian mass at hatching in a high ISA environment.

Human recreation reduces clutch size in great tits Parus major regardless of risk-taking personality

Recreation negatively affects wildlife by influencing animal behavior vital to reproduction and survival. Such nonconsumptive effects of perceived predation risk are mainly studied in ground-breeding birds. However, if antipredator responses characterize bird species generally, so should nonconsumptive effects of perceived predation associated with human recreation. Moreover, as individuals consistently differ in behaviors linked to antipredator responses, they should also differ in responses to recreation, with bolder birds being less affected. To test this key prediction, we quantified effects of human recreation pressure on a cavity-breeding passerine. We uniquely quantified human recreation pressure over a substantial (8-year) period within 12 nest box populations of the great tit Parus major, assayed annually for reproductive parameters. We detected considerable spatial variation in recreation pressure. In plots with high recreation pressure, we found strong support for birds breeding further away from highly frequented paths and birds producing smaller clutches; we also found moderate support for birds producing fewer fledglings. These detrimental effects did not vary with behavioral proxies of an individual’s risk-taking phenotype (exploratory activity). This implies that effects of recreation pressure apply to the average bird, and extend to species (like forest birds) not previously considered.

Quantifying human presence in a heterogeneous urban landscape

Humans are a keystone species in urban ecosystems. Although the impact of human activities is increasingly reported in behavioral and evolutionary ecology, little is known about the effects of physical human presence per se. Of particular relevance is the extent to which human presence (sometimes referred to as human disturbance), is repeatable across the urban mosaic over time. We quantified human presence at fixed locations—here in a 15-m radius of great tit nestboxes—within six urban and suburban study sites. While overall human presence did not differ between urban sites, it was significantly higher than in the suburban village. Moreover, considerable variance between fixed locations was observed within each site. We reported overall high repeatability of human presence for all sites (0.57 < R < 0.88, mean: 0.76, median: 0.77). We further simulated datasets of human presence made of an increasing number of counts, and demonstrated that 10 counts of human presence (each 30 s long) made at each fixed location can generate a highly reliable indicator of human presence (R ≥ 0.6) for any urban site. We thus confirm that human presence is repeatable across the urban mosaic, thereby offering consistent cues to urban wildlife of human presence or absence in space and time. Importantly, our approach of human presence quantification allows for an effort-efficient approach to understand the effects of physical human presence at designated temporal timeframes, thereby allowing to reliably test the effects of human presence on the behavior and ecology of urban wildlife.

A New Framework for Urban Ecology: An Integration of Proximate and Ultimate Responses to Anthropogenic Change

As urban areas continue to grow, understanding how species respond and adapt to urban habitats is becoming increasingly important. Knowledge of the mechanisms behind observed phenotypic changes of urban-dwelling animals will enable us to better evaluate the impact of urbanization on current and future generations of wildlife and predict how animals respond to novel environments. Recently, urban ecology has emerged not only as a means of understanding organismal adaptation but also as a framework for exploring mechanisms mediating evolutionary phenomena. Here, we have identified four important research topics that will advance the field of urban ecology and shed light on the proximate and ultimate causes of the phenotypic differences commonly seen among species and populations that vary in their responses to urbanization. First, we address the ecological and socio-economic factors that characterize cities, how they might interact with each other, and how they affect urban species. Second, we ask which are the proximate mechanisms underlying the emergence over time of novel traits in urban organisms, focusing on developmental effects. Third, we emphasize the importance of understanding the ultimate causations that link phenotypic shifts to function. This question highlights the need to quantify the strength and direction of selection that urban individuals are exposed to, and whether the phenotypic shifts associated with life in the city are adaptive. Lastly, we stress the need to translate how individual-level responses scale up to population dynamics. Understanding the mechanistic underpinnings of variation among populations and species in their responses to urbanization will unravel species resilience to environmental perturbation, which will facilitate predictive models for sustainability and development of green cities that maintain or even increase urban biodiversity and wildlife health and wellbeing.