Moving across the border: A conservation modeling approach for migratory bat populations

Background/Question/Methods

One of the greatest challenges for bat conservation is that many species migrate across international borders and between habitats with varying levels of protection.  However, bat migration remains poorly understood due to limited data and difficulties in tracking migrants.  An understanding of migratory routes and major roost sites is important for conservation efforts, and is critical to coordinating habitat protection across borders.  We present a migratory network model for the Mexican free-tailed bat (Tadarida brasilliensis) that simulates migration between winter sites in central Mexico and summer maternity sites in northern Mexico and southwestern United States.  This novel modeling approach assesses the migratory linkages between summer and winter bat populations and estimates the relative contribution of different regions to the maintenance of migratory bat populations.

Results/Conclusions

Specific routes contained the largest flows of migrants from winter to summer breeding sites and several sites were the most connected to other sites, representing regional hubs.  The removal of sites from the model indicated that several are quite important for the maintenance of the free-tailed bat population; our results suggested that their elimination would cause substantial declines in population size.  This network modeling approach is a useful tool for furthering our understanding of bat migration, and can be easily applied to other species.  It helps focus conservation efforts to areas that are influential for bat populations, identifies how additional monitoring data may be collected to improve understanding of migratory patterns, and can help harmonize conservation efforts across the U.S. Mexico border.