Insights into the phenology of migration and survival of a long migrant land bird

Abstract

The process of migration stems from an adaptation of climatic seasonality and animals have developed various strategies to complete the journey between a wintering and breeding ground. Understanding the migratory behavior and determining when and where mortality occurs during the annual cycle is fundamental to understand population dynamics and implement appropriate conservation measures. Based on a big data set and advanced statistical methods, we inspected the phenology of migration of a polygynous land bird, the Macqueen s bustard, Chlamydotis macqueenii. We explored its migration strategies between sex, age, season and geographical origin. We show that departure for migration depended on age in the fall with juveniles being the first to leave and on age and sex in the spring with juveniles departing later and males induced to arrive early in spring to secure high-quality territories. Birds breeding at higher latitudes were the first to leave in the fall and more likely to perform longer stopovers. Bustards exhibited different strategies for spring and fall migrations: spring migration was significantly longer than fall migration with more but shorter stopovers. Survival was lower for juveniles experiencing their first migration and for all birds during fall migration and on their wintering ground. Experience linked to social hierarchical pressures and environmental conditions might be the key drivers of migration strategies and survival in long-distance polygynous migrants.

Releases of Asian houbara must respect genetic and geographic origin to preserve inherited migration behaviour: evidence from a translocation experiment

“…However, although based on limited sample size (n = 5), migratory behaviour of experimentally translocated birds indicated a potentially considerable heritable component to the differing migration strategies. This would signify finer-scale adaptation than suggested for Asian houbara by neutral genetic markers [34] or broader-scale migration studies [31,33].…”

“…7: 200250 date from the post-breeding grounds; bearing from post-breeding area to wintering-site; wintering-site latitude and longitude; migratory distance (the straight-line displacement from post-breeding to wintering-site); wintering-site fidelity; and fidelity after return migration to breeding/release site [31,32,37]. We did not compare stop-over locations and timings, speed or migratory efficiency, as these are probably influenced by weather and certainly by age [32,33]. Only tracks that could provide reliable estimates of each migratory parameter were included (sample sizes are shown in figure 2; details of telemetry data processing and criteria for identifying stop-over and wintering sites are described in electronic supplementary material, methods S1).…”

“…Analyses considered both males and females from the eastern population, but only males from the central and western populations as it was not possible to trap females in these areas. Previous analysis found no difference between male and female adult houbara for first-step bearing, departure date, migration distance, wintering latitude, or breeding-site fidelity [32,33]. However, as a precaution we also examined analyses repeated while excluding females from the eastern population.…”

“…Wild adults and juveniles from the eastern population primarily migrate along a south/southwesterly route [32] passing the Iran/Turkmenistan border between the Hindu Kush (maximum 7690 m elevation) and the Kopet Dag mountains within the Turkmen-Khorasan range (maximum 3190 m: forming a broad west-east topographic obstacle to the north-south migration), to winter in southern Iran and Pakistan (figure 1). Migration routes of central and western populations had not been characterized previously, but we a priori hypothesized that western individuals may follow a similar migration route to Asian houbara breeding to the northwest (on the Turanian Plain in western Kazakhstan), which initially migrate south over the Ustyurt Plateau, then southwest to west crossing the Kopet Dag mountains, which do not appear to act as a barrier to their migration [31,33], to winter southwest of the Caspian Sea predominantly in southern Iran and Iraq.…”

“…The species undertakes long-distance migrations and is subject to large-scale captive breeding and release programmes to reinforce threatened migratory populations throughout its range [30]. Observational studies suggest that migration orientation and distance are heritable [31,32] and differ across the range [31], with juveniles migrating independently of their mothers [32] and probably also of experienced adults, as they leave earlier than adults, migrate more slowly flying fewer kilometres per day [32], and spend longer on stop-overs [33]. Treating migratory Central Asian populations as a single unit for management therefore risks homogenizing and potentially compromising population-specific migratory strategies [31].…”