Tree cavity availability across forest, park, and residential habitats in a highly urban area

Public safety considerations constraint the conservation of large old trees and their crucial ecological heritage in urban green spaces

Large old trees in urban public green spaces deliver a diversity of values essential for human well-being, including biodiversity conservation. Yet, the conservation of large old trees bearing key wildlife microhabitats interferes with safety considerations. This intuitive notion, however, is backed by an insufficient and scattered body of evidence. Here, we empirically examined this process using data on 5974 trees across 510 sample plots, organized as quintuplets within 102 sample sites, including urban parks, cemeteries, recreational forests, and historic reserves in the urban agglomeration of Kraków, Poland. Our analyses demonstrate that trees situated in areas frequently visited by people, or those near walking paths, benches, or playgrounds, have elevated accident hazards and, therefore, necessitate intensive tree surgeries (pruning and logging) to remain harmless. Large old trees, which bear the most diverse microhabitats and pose greater risks when they collapse, are especially affected by these measures. Accordingly, we found that the co-occurrence of large trees with elevated accident hazards results in significant losses of dead and sloped trees, and trees with cavities, injuries, crown deadwood, fungal fruiting bodies, or epiphytes, particularly in parks and, to a lesser extent, in recreational forests. Apparently, some tree-related microhabitats, such as injuries, cavities, and microsoils, also emerge in risky spots after pruning. Our findings underscore that the conservation of large old trees and their ecological functions faces significant challenges due to safety considerations. To address conservation challenges and harmonize human coexistence with biodiversity, we recommend enhancing environmental awareness and reevaluating arboricultural and planning policies. This would involve establishing strategic and pocket reserves on city peripheries and interiors, allowing larger older trees to thrive and develop important microhabitats without compromising public safety. Otherwise, we risk losing many large old trees and/or their superior value for wildlife, which will regenerate over decades, if not centuries.

Urban landscape organization is associated with species-specific traits in European birds

Urbanization is one of the main current drivers of the global biodiversity loss. Cities are usually developed in a gradient between land-sharing (low density housing with small and fragmented green areas) and land-sparing areas (high density housing with large and non-fragmented green patches) depending on the spatial organization of urban attributes. Previous studies have indicated differences in biodiversity between these two urban development types, but mechanisms underlying these differences are inadequately understood. In this context, the landscape features of each urban development type may select for organisms with specific traits. To analyze it, we quantified birds in 9 European cities during the breeding and wintering season, collected species-specific traits and performed Bayesian comparative analyses. We found that birds living in land-sparing areas had a higher reproductive investment and a higher nesting specialization than birds living in land-sharing areas during the breeding season. Typical birds from land-sparing urban areas during winter are fast-lived species. Our results indicate that urban development type could have an important role selecting animal traits and provides useful information on how to build more biodiversity-friendly cities.

Alien vs. Predator: Impacts of Invasive Species and Native Predators on Urban Nest Box Use by Native Birds

Many bird species in Australia require tree hollows for breeding. However, assessing the benefits of urban nest boxes to native birds requires frequent monitoring that allows to assess nesting success. To better understand the benefits of nest boxes for native birds, we examined the impact of local habitat characteristics, invasive species (common myna, Acridotheres tristis), and native mammalian predators on urban nest box use and nesting success of native birds. We installed 216 nest boxes across nine locations in southeastern Australia (S.E. Queensland and northern New South Wales) in both long-invaded sites (invaded before 1970) and more recently invaded sites (after 1990). We monitored all boxes weekly over two breeding seasons. We recorded seven bird species and three mammal species using the nest boxes. Weekly box occupancy by all species averaged 8% of all boxes, with the species most frequently recorded in the nest boxes being the common brushtail possum (Trichosurus vulpecula), a native cavity user and nest predator. We recorded 137 nesting attempts in the boxes across all bird species. The most frequent nesting species were the invasive alien common mynas (72 nesting attempts). We recorded an average nesting failure rate of 53.3% for all bird species. We did not record any common mynas evicting other nesting birds, and found that several native species used the same box after the common myna completed its nesting. We recorded native possums in 92% of the boxes, and possum occupancy of boxes per site was negatively correlated with bird nesting success (p = 0.021). These results suggest that when boxes are accessible to invasive species and native predators, they are unlikely to significantly improve nesting opportunities for native birds. To ensure efficient use of limited conservation resources, nest boxes should be designed to target species of high conservation importance and limit other species of both predators and competitors.

Big City Living: A Global Meta-Analysis Reveals Positive Impact of Urbanization on Body Size in Lizards

Urban environments pose different selective pressures than natural ones, leading to changes in animal behavior, physiology, and morphology. Understanding how animals respond to urbanization could inform the management of urban habitats. Non-avian reptiles have important roles in ecosystems worldwide, yet their responses to urbanization have not been as comprehensively studied as those of mammals and birds. However, unlike mammals and birds, most reptiles cannot easily move away from disturbances, making the selective pressure to adapt to urban environments especially strong. In recent years, there has been a surge in research on the responses of lizards to urbanization, yet no formal synthesis has determined what makes an urban lizard, in other words, which phenotypic traits are most likely to change with urbanization and in which direction? Here, we present a qualitative synthesis of the literature and a quantitative phylogenetic meta-analysis comparing phenotypic traits between urban and non-urban lizard populations. The most robust finding from our analysis is that urban lizards are larger than their non-urban counterparts. This result remained consistent between sexes and taxonomic groups. Hence, lizards that pass through the urban filter have access to better resources, more time for foraging, and/or there is selection on attaining a larger body size. Other results included an increase in the diameters of perches used and longer limb and digit lengths, although this may be a result of increased body size. Urban lizards were not bolder, more active or exploratory, and did not differ in immune responses than non-urban populations. Overall, studies are biased to a few geographic regions and taxa. More than 70% of all data came from three species of anoles in the family Dactyloidae, making it difficult to generalize patterns to other clades. Thus, more studies are needed across multiple taxa and habitats to produce meaningful predictions that could help inform conservation and management of urban ecological communities.

Chicago’s Urban Cemeteries as Habitat for Cavity-Nesting Birds

Although not explicitly managed for conservation, urban cemeteries may provide a reserve of dead and dying trees for cavity-nesting birds. However, the ability of urban cemeteries to support these birds on current landscapes is largely unknown. We surveyed cavity-nesting birds and their habitat in 18 cemeteries in Chicago, Illinois (USA). At each location, we examined vegetation, availability of gravestones and monuments for perches, and landscape-level environmental conditions. We tested the importance of these variables for presence of individual bird species, and for overall richness of native cavity-nesting birds. We also assessed the availability and characteristics of tree cavities and their distribution among different tree species. We found that most cemeteries contained at least one dead or dying tree. Across all sampled areas, we detected 207 naturally-occurring and 77 excavated tree cavities. Tree species generally supported cavities in proportion to their abundance. We observed 12 native and two non-native cavity-nesting bird species in the cemeteries. Cavity-nesting bird species richness was best explained by landscape-level variables such as canopy cover and distance to water, but local-level variables (e.g., number of graves in a 50 m radius) influenced habitat selection for some species. Based on our results, we make suggestions for how both existing cemeteries and new “green” cemeteries can support biodiversity conservation.