Leukocyte profiles reveal sex and age differences in immune investment in a polygynous bat.

Land conversion forces humans and animals into close contact on a planetary scale (Ma et al., ; Nyhus, ). Mitigating impacts on wildlife requires a deep mechanistic understanding of the effects of human activity on animal behaviour (Ellis‐Soto et al., ; Gomez et al., ). The survival of individual animals, and ultimately entire populations, depends on their ability to move efficiently across the landscape, to access key resources, like food, shelter and breeding sites (Abrahms et al., ; Nathan et al., ). Yet movement can be compromised by both land modification (fragmented habitat, roads, fences, buildings and other infrastructure) and human mobility (the movement of people and their vehicles) (Doherty et al., ; Ellis‐Soto et al., ; Meekan et al., ; Rutz, ; Tucker et al., ). Disentangling the effects of these static and dynamic components of human activity is crucial for mechanistic interpretation, but challenging, since they are usually confounded, and experimental manipulations are impossible to achieve at scale (Gomez et al., ; Rutz et al., ). With urban expansion projected to surge over the coming decades (Angel et al., ; Huang et al., ; Seto et al., ), investigating the impact of human settlements on wildlife movement is of particular importance. Vertebrate biodiversity declines steeply along gradients of urbanisation (McKinney, ; Newbold et al., ), but it remains unclear—for the reasons outlined above—if wildlife predominantly struggles with the built environment itself or the presence of humans and moving vehicles. Although under tragic circumstances, the COVID‐19 lockdowns of early 2020 provided an unprecedented opportunity to address this long‐standing question (Rutz, ; Rutz et al., ). In many areas, government restrictions caused a sudden, short‐term reduction in human mobility levels, while the distribution of buildings, roads and other infrastructure remained effectively unchanged—dissociating key stressors in a quasi‐experimental manner (Bates et al., ; Rutz, ; Rutz et al., ). A growing body of research documents lockdown impacts on the natural world (Bates et al., ; Gill et al., ; Tucker et al., ). While some species seem to have benefited from reduced levels of human mobility, others have come under increased pressure (e.g. because of reductions in anthropogenic food sources), and in many cases, no effects were detectable (Bates et al., ; Mikula et al., ). Two studies conducted pioneering global‐scale assessments of potential changes in the movement behaviour and activity of terrestrial mammals. Analyses of GPS tracking data for 2300 tagged individuals revealed that animals tended to venture closer to roads during lockdowns in areas of high human footprint (compared to 2019), and moved larger distances in areas experiencing particularly strict lockdowns (Tucker et al., ). Camera trapping data from 102 projects worldwide provided critical context for these findings, demonstrating that changes in the amount and timing of animals' activity varied across taxa and environmental contexts (Burton et al., ).