Sex-dependent migration of eastern great bustard (Otis tarda dybowskii) in Northeast Asia

Abstract

Background The great bustard (Otis tarda) holds the distinction of the heaviest bird to undergo migration as well as the greatest degree of sexual size dimorphism among living birds. Though the migration of the species has been widely discussed in the literature, researchers know little about the migration patterns of the subspecies in Asia (Otis tarda dybowskii), especially the males. Methods In 2018 and 2019, we captured six O. t. dybowskii (five males and one female) at their breeding sites in eastern Mongolia and tagged them with GPS-GSM satellite transmitters. This constitutes the first time that male great bustards of the eastern subspecies have been tracked. We combined the tracking data of our only female with other three females from central Mongolia, which was published in previous study for analysis. Results We found notable differences between the sexes: 1) males started migration later but arrived early than females in the spring, but not in autumn; 2) males had 1/3 of the migration duration of females (16.44 ± 14.68 days vs. 49.34 ± 21.28 days); 3) males migrated about 1/2 the distance of females (945.13 ± 79.00 km vs. 1922.88 ± 87.08 km). Additionally, we found bustards exhibited high fidelity to their breeding, post-breeding and wintering sites. Indeed, most of the wintering sites found by GPS tracking in this study were also utilized 70 years earlier, according to previous work. For conservation, we found only 22.20% of GPS location fixes of bustards were within protected areas and less than 5.0% for wintering sites and during migration. Conclusions Our findings suggest that the migration patterns of eastern great bustards are sex-specific and more conservation effort is needed for the Asian populations of this threatened species.