A multi-perspective understanding of population change in migratory species: A case study with pied avocets (Recurvirostra avosetta) in East Asia

Understanding the population dynamics of migratory species is crucial for their conservation. However, researchers often encounter challenges due to insufficient data, especially when monitoring migratory species throughout their annual cycle. One solution to this issue is to combine multiple types of data. Here we develop and test such an approach, using the Pied Avocet, a migratory waterbird species in East Asia, as a case study. We integrate count data, presence-only records, satellite tracking data, and species distribution models.

Our findings reveal an 85 % increase in the annual population of Pied Avocets in East Asia over the past 13 years, despite inconsistent trends across their four major wintering sites. Tracking data indicated that the species experiences low migratory mortality and a moderate to high overall survival rates, with survival not differing significantly between first-year birds and adults. We estimated a 109 % increase in suitable wintering habitat extent and a 42 % increase in breeding habitat extent for Pied Avocets over the past 20 years. These changes are primarily attributed to the proliferation of artificial wetlands, with climate change also contributing to the expansion of wintering habitats.

We conclude that multi-dimensional sources of evidence can be combined to assess and explain population changes even though data of any particular type are relatively limited. We emphasize the effectiveness and importance of using diverse methods to obtain comprehensive information on the population dynamics of migratory species, while concurrently establishing and improving long-term monitoring networks.