Habitat Composition and Connectivity Predicts Bat Presence and Activity at Foraging Sites in a Large UK Conurbation

Abstract

BackgroundUrbanization is characterized by high levels of sealed land-cover, and small, geometrically complex, fragmented land-use patches. The extent and density of urbanized land-use is increasing, with implications for habitat quality, connectivity and city ecology. Little is known about densification thresholds for urban ecosystem function, and the response of mammals, nocturnal and cryptic taxa are poorly studied in this respect. Bats (Chiroptera) are sensitive to changing urban form at a species, guild and community level, so are ideal model organisms for analyses of this nature.Methodology/Principal FindingsWe surveyed bats around urban ponds in the West Midlands conurbation, United Kingdom (UK). Sites were stratified between five urban land classes, representing a gradient of built land-cover at the 1 km2 scale. Models for bat presence and activity were developed using land-cover and land-use data from multiple radii around each pond. Structural connectivity of tree networks was used as an indicator of the functional connectivity between habitats. All species were sensitive to measures of urban density. Some were also sensitive to landscape composition and structural connectivity at different spatial scales. These results represent new findings for an urban area. The activity of Pipistrellus pipistrellus (Schreber 1774) exhibited a non-linear relationship with the area of built land-cover, being much reduced beyond the threshold of ∼60% built surface. The presence of tree networks appears to mitigate the negative effects of urbanization for this species.Conclusions/SignificanceOur results suggest that increasing urban density negatively impacts the study species. This has implications for infill development policy, built density targets and the compact city debate. Bats were also sensitive to the composition and structure of the urban form at a range of spatial scales, with implications for land-use planning and management. Protecting and establishing tree networks may improve the resilience of some bat populations to urban densification.

Drivers of Vegetation Species Diversity and Composition in Urban Ecosystems

“…The regional distribution of vegetation patches in urban environments mediates the importance of local habitat for arthropods (Sattler et al 2010;Vergnes et al 2012), birds (Marzluff and Ewing 2001;White et al 2005;Litteral and Wu 2012) and mammals (FitzGibbon et al 2007;Gomes et al 2011;Hale et al 2012), all of which use plants for food and cover. Species respond to patch connectivity and size differently depending on their functional characteristics (e.g Sattler et al 2010;Litteral and Wu 2012).…”

Patterns of Bat Distribution and Foraging Activity in a Highly Urbanized Temperate Environment

“…These areas are novel ecosystems in several ways: they are saturated with light, so patterns of nocturnal biodiversity are likely to be significantly disrupted [7, 8]; the food supply is quite different from natural areas, with an abundance of resources even in winter for granivores or other generalist animals [9, 10] but a reduced supply of invertebrates for insectivores [11–13]; an abundance of potential roosts [14, 15]; a harsh matrix between foraging areas [16, 17]; and increased warmth in all seasons [18]. …”

Temporal and spatial distribution and habitat associations of an urban population of New Zealand long-tailed bats (Chalinolobus tuberculatus)

“…This indicates that gullies and waterways are important for urban bats, possibly because they provide habitat connectivity which was also positively related to bat presence. Habitat connectivity has been shown to allow bats access to resources by reducing the isolation between larger resource patches (Estrada & Coates-Estrada 2001;Hale et al 2012). This can reduce the energetic demands on commuting bats by providing stopover foraging opportunities and resting sites (Verboom & Spoelstra 1999;Murray & Kurta 2004;Menzel et al 2005).…”

“…Other species may require the presence of habitat corridors before they are able to exploit city habitats. Edge species such as Pteronotus parnellii and Sturnira lilium use corridors for stopover foraging and resting when patches of resources are distant from each other (Estrada & Coates-Estrada 2001) and connectivity provided by tree networks are thought to be beneficial for urban Pipistrellus pipistrellus (Hale et al 2012). Habitat requirements can also change with time, over seasons, with the reproductive cycle or due to hibernation.…”