A global evidence synthesis of outcomes of urban bird conservation interventions

Aalia Irshad Khan , Silvia Colucci, Trina Rytwinski, Edward Cheskey, Autumn Jordan, Rachel Buxton

Avian populations face high concentrations of threats in urban areas. Understanding the outcomes of urban conservation interventions to tackle these threats could inform more effective evidenced-based approaches. Using an evidence synthesis and meta-analysis of peer-reviewed literature on conservation interventions to tackle four leading causes of urban bird mortality in urban areas (cat predation, bird-window collisions, road mortalities, light pollution, and bird-vehicle collisions), we: 1) summarized the current state of the literature on urban threats and conservation interventions for birds, and 2) evaluated the outcomes of interventions aimed at reducing impacts of major urban threats on birds. Our evidence synthesis found that across all threats, few studies (35 out of 522) explored outcomes of conservation interventions compared to those that determined the establishment, magnitude, and drivers of threats. Our meta-analysis of nine types of collar-based interventions to reduce urban cat predation found that rainbow-colored Birdsbesafe™ collars most consistently demonstrated evidence of reduced numbers of dead birds brought home by cats (pooled reduction of 54% compared to controls). However, these results were drawn from a very small number of studies (n=13). To reduce mortality from bird-window collisions, closely spaced vertical stripes and circular or square decals reduced collisions by 98% (n=6) There were no studies that explored outcomes of interventions to reduce light pollution in urban areas. Two studies explored the use of traffic control measures (speed bumps, chicanes and barrier poles) to reduce bird-vehicle collisions, although we could not draw conclusions on their outcomes. Overall findings suggest there is a need for greater research on the effectiveness of conservation interventions for all urban threats.