Geographic distance, landscape heterogeneity and migratory connectivity influence population genetic structure of farmland-dependent wintering birds and their conservation

Understanding the drivers of population structure is a conservation priority for declining species. However, the relative extent to which landscape features in wintering areas and migration route drive population genetic structure for birds is still unclear. The eastern great bustard (Otis tarda dybowskii) is an endangered and declining steppe bird which is heavily dependent on farmland for overwintering. We used noninvasive fecal sampling and molecular genetics to quantify genetic diversity and explore the extent of genetic differentiation among 145 individuals from 7 wintering populations across this subspecies' non-breeding distribution. Genetic analyses revealed low to moderate but significant genetic differentiation, showing three genetic clusters consistent with three migration routes. Landscape genetic analysis based on variance partitioning revealed that 67.4 % of the observed genetic variability was explained through isolation by distance (IBD), and in contrast, 56.5 % was explained by landscape heterogeneity. The low level of genetic diversity and significant population differentiation we discovered, combined with small population size, put the eastern great bustard at risk of inbreeding depression. Our results strengthen evidence for strong migratory connectivity in this subspecies, with significant genetic clustering correlated to known migration routes. The construction of secure nature reserves and improvement of wintering habitats can help to reduce threats on the wintering grounds, and thus associated demographic impacts on tightly connected breeding populations.