Canopy bridges as road overpasses for wildlife in urban fragmented landscapes

Abstract

Abstract:The effects of habitat fragmentation and deforestation are exacerbated by some elements, such as roads and power lines, which may become filters or barriers to wildlife movements. In order to mitigate mortality and restore connectivity, wildlife passages are being constructed as linear corridors. The installation of these mitigation measures must be followed by systematic monitoring, in order to evaluate their use and effectiveness, to assist in their management, and to convince stakeholders of their value. In this paper we present the results of a monitoring study of the use of rope overpasses developed near a protected area in Porto Alegre, southern Brazil. The canopy bridges were installed by the Urban Monkeys Program in places where electric hazards and road-kills of brown howler monkeys (Alouatta guariba clamitans Cabrera, 1940) were recorded. Camera traps were installed at each bridge, and local people were selected and trained to monitor overpass use over 15 months, from August 2008 to October 2009. Three species were recorded using canopy bridges: brown howler monkey (Alouatta guariba clamitans Cabrera, 1940), white-eared opossum (Didelphis albiventris Lund, 1840) and porcupine (Sphiggurus villosus Cuvier, 1823). Rope bridges with the highest number of species recorded had more forest cover and lower urban area around them than overpasses little used. Our results indicate that overpasses, in Porto Alegre, work as a linear corridor between forest remnants, although the outcomes for individual survival, group persistence, population demography or gene flow have not been measured. Furthermore, canopy bridges may be important to mitigate the impact of roads and power lines on wildlife, but electric cables also need to be completely isolated when present, to warrant animals' physical integrity. Resumo: Os efeitos do desmatamento e da fragmentação de hábitats são exacerbados por elementos como rodovias e redes elétricas, que podem atuar como filtros ou barreiras aos movimentos da vida silvestre. Com o objetivo de mitigar a mortalidade e restaurar a conectividade, passagens de fauna têm sido construídas como corredores lineares. A instalação dessas estruturas deve ser seguida de monitoramento sistemático, visando à avaliação de seu uso e efetividade e a geração de informações para seu manejo e para convencer os tomadores de decisão sobre seu valor. Neste artigo, apresentamos os resultados do monitoramento do uso de seis pontes de corda, realizado durante 15 meses, entre agosto de 2008 e outubro de 2009, nas imediações da Reserva Biológica do Lami José Lutzenberger, em Porto Alegre, Brasil. As pontes de dossel foram instaladas pelo Núcleo de Extensão Macacos Urbanos em locais com registros de atropelamentos e choques elétricos de bugios-ruivos (Alouatta guariba clamitans Cabrera, 1940). Instalamos armadilhas fotográficas em cada ponte e selecionamos moradores locais para registrarem seu uso. Três espécies foram registradas usando as pontes de corda: o bugio-ruivo (Alouatta guariba clamitans Cabrera, 194...

Effects of Road Density and Pattern on the Conservation of Species and Biodiversity

“…Nevertheless, two studies speculated that crossing structures were still biologically effective as low crossing frequencies may be enough to maintain functional connectivity [105,106]. A study on bear species in Canada supported this theory by revealing that while structures were not frequently used, overall use was sufficient to ensure gene flow between populations [107].…”

A remarkably quick habituation and high use of a rope bridge by an endangered marsupial, the western ringtail possum

“…Many rope bridges, or canopy bridges, have been installed worldwide to mitigate negative impacts on arboreal species, including several opossum, monkey, dormouse and squirrel species (Norwood 1999, Teixeira et al 2013, Sonoda 2014. In the eastern parts of Australia, rope bridges have been built for gliders, possums, and koalas (Phascolarctos cinereus); however, monitoring of the use of these structures by the target species is still limited to a handful of cases (Weston et al 2011, Goldingay et al 2013, Soanes et al 2013, and assessment of factors influencing the use of these structures is lacking.…”

Identification of local factors causing clustering of animal‐vehicle collisions

“…Roads are also fenced at places of frequent AVCs (Forman and Alexander ), audio and optical signal systems are installed to discourage animals from crossing roads (Rowden et al ), and speed limits, warning signals (Al‐Ghamdi and AlGadhi ), and thermal sensors draw the attention of drivers to the presence of large animals (Hirota et al ). Despite many of these measures and constructions, traffic accidents caused by animals are increasing (Iuell et al ) perhaps because systems to identify AVC clusters are often determined separately for different taxonomic groups (Iuell et al , Glista et al ), by different numbers of observers, or with differing frequency and duration of surveys (Teixeira et al ). With differing methodologies, some road kills may be missed and mortality may be underestimated when there is a long time interval between searches for AVCs or species with soft or small bodies, which rapidly decay (Gerow et al , Guinard et al ).…”