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Anthropogenic activities generate different forms of environmental pollution, including artificial light at night (ALAN) and airborne toxic chemicals (ATCs). Nocturnally migrating birds are attracted to ALAN during migration and if ALAN occurs in unison with ATC, the chances of ground-level ATC contamination occurring at stopover sites could increase. Here, we document the relationship between ALAN and ATC within the contiguous United States based on 479 toxic chemicals from 15,743 releasing facilities. Using weekly diurnal estimates of relative abundance for 165 nocturnally migrating passerine (NMP) bird species, we assess how the species richness and relative abundance of NMP species are correlated with ALAN and ATC across the annual cycle. The concentration of ATC increased with increasing ALAN levels, except at the highest ALAN levels. The species richness of NMP species was positively correlated with ATC during the non-breeding season and migration, and negatively correlated during the breeding season. The relative abundance of NMP species was negatively correlated with ATC during the breeding and non-breeding seasons and the correlation did not differ from zero during migration. Through the disorienting influence of ALAN, our findings suggest large numbers of NMP species are being exposed to higher ATC concentrations at stopover sites. Outside of migration, large numbers of NMP species that winter along the US Gulf Coast are being exposed for an extended period of time to higher ATC concentrations. Initiatives designed to decrease ALAN during migration have the potential to reduce the acute and chronic effects of ATC contamination, lower the maternal transfer of toxic chemicals to eggs, and decrease the biologically mediated transport of toxic chemicals across regions. However, these initiatives will not benefit species that experience prolonged ATC exposure during the non-breeding season along the US Gulf Coast, a region that could be a significant source of ATC contamination for North American birds.

Cities can host significant biological diversity. Yet, urbanisation leads to the loss of habitats and, potentially, to local extinctions. Understanding how multiple taxa respond to urbanisation globally is essential to promote and conserve biodiversity in cities and surrounding landscapes. Using a dataset with site-level occurrence and trait data of 5302 species from six terrestrial fauna taxonomic groups across 379 cities on 6 continents, we show that urbanisation produces taxon-specific changes in trait composition, with traits related to reproductive strategy consistently showing the strongest response. The effect of urbanisation on community trait composition is strongest at the largest spatial scale considered, and more closely linked to landscape composition (% urban) than arrangement (aggregation), although latitude and climatic variables remain a stronger influence. This study did not find evidence in support of a global urban taxa syndrome, but instead we suggest that there are four general urban trait syndromes, with resources associated with reproduction and diet likely to be driving patterns in traits associated with mobility and body size. Functional diversity measures showed a wide range of responses, leading to a shift in trait space that is most likely driven by the distribution and abundance of critical resources, and the urban trait syndrome displayed by individual species within a community. Further research is required to understand the interactions between the four general urban trait syndromes, resource distribution and abundance and changes in functional diversity of taxa at different spatial and temporal scales. Maximising opportunities to support species within taxa groups with different urban trait syndromes should be pivotal in conservation and management programmes within and among cities. This will reduce the likelihood of biotic homogenisation at the taxa level, and helps ensure that urban environments have the ecological capacity to respond to challenges such as climate change, further habitat fragmentation and loss, and other disruptions. These actions are critical if we are to reframe the role of cities in global biodiversity loss.

Since the 1990s, recognition of urban biodiversity research has increased steadily. Knowledge of how ecological communities respond to urban pressures can assist in addressing global questions related to biodiversity. To assess the state of this research field in meeting this aim, we conducted a systematic review of the urban biodiversity literature published since 1990. We obtained data from 1209 studies that sampled ecological communities representing 12 taxonomic groups. While advances have been made in the field over the last 30 years, we found that urban biodiversity research has primarily been conducted in single cities within the Palearctic and Nearctic realms, within forest remnants and residential locations, and predominantly surveys plants and birds, with significant gaps in research within the Global South and little integration of multi-species and multi-trophic interactions. Sample sizes remain limited in spatial and temporal scope, but citizen science and remote sensing resources have broadened these efforts. Analytical approaches still rely on taxonomic diversity to describe urban plant and animal communities, with increasing numbers of integrated phylogenetic and trait-based analyses. Despite the implementation of nature-based solutions across the world's cities, only 5% of studies link biodiversity to ecosystem function and services, pointing to substantial gaps in our understanding of such solutions. We advocate for future research that encompasses a greater diversity of taxonomic groups and urban systems, focusing on biodiversity hotspots. Implementing such research would enable researchers to move forward in an equitable and multidisciplinary way to tackle the complex issues facing global urban biodiversity.

Despite the critical role parasites play in ecosystem functioning and their considerable influence on human society, little is known about their variations in abundance on a global scale. This gap in knowledge is amplified by a lack of holistic understanding on how the abundance of parasites of wildlife and humans varies across environmental and socioeconomic gradients, despite a need to integrate study of parasites across social and environmental spheres. Free-roaming companion animals (e.g., domestic cats (Felis catus) and dogs (Canis lupus familiaris)) share pathogens and have frequent contact with humans and wildlife. Thus, they are an effective model to understand how parasite and pathogen prevalence of humans and wildlife varies across environmental and socioeconomic gradients. Through a global systematic review and analysis of socioeconomic and environmental variables, including per capita GDP, income disparity, sanitation, biodiversity, island habitation, and latitude, we find that sanitation and island habitation best explained free-roaming companion animal parasite and pathogen prevalence. Sanitation was significantly associated with parasite and pathogen prevalence in free-roaming companion animals, such that for every 10% increase in the proportion of the human population with improved sanitation access, parasite and pathogen prevalence in free-roaming companion animals decreased by 12% (5-19%, 95% C.L.; p = 0.0023). Since companion animals share many parasites with humans and wildlife, these results suggest that actionable interventions to improve sanitation access could reduce parasite and pathogen exposure risks from companion animals to humans and wildlife.Significance StatementIn addition to playing a critical role in ecosystem functioning, parasites also influence human health, behavior, and society. Further, parasites are also impacted by human activities, as much as by ecological phenomena in natural environments. Despite these dualities, little is known about their variations in abundance on a global scale across environmental and socioeconomic gradients. Using free-roaming companion animals (e.g., domestic cats (Felis catus) and dogs (Canis lupus familiaris)) as a model system, we find that access to safely managed sanitation services is strongly associated with parasite and pathogen prevalence. This finding underscores improvements to sanitation as an actionable One Health intervention that could reduce parasite and pathogen exposure risks from companion animals to humans and wildlife.