Assessing and improving the analysis of migration count data for population monitoring

Counts of birds passing a geographic location during migration to or from their breeding grounds are often used to estimate long-term population change. However, birds often stop at count sites for several days to fatten for their next migratory flight, affecting probability of detection. The migratory path followed might also vary among years. The influence of such factors on population estimates are unknown. We will use simulated migration count data to test the influence of birds stopping at a site and of variation in migratory route among years on our ability to estimate population size and change. We will also assess whether population estimates can be improved by alternative sampling or analysis techniques that mitigate the effects of stopover or shifts in migration route – for example, by combining data from multiple sites to better distinguish real population change from variation in counts from alternative factors. 

Tara Crewe
Faculty Supervisor: 
Dr. Phil Taylor & Dr. Chris Guglielmo