Effects of breeding habitat loss on a threatened East Asia migratory forest bird

Migratory landbird population trends and threats in the East Asian-Australasian Flyway (EAAF) are poorly understood. To fill this knowledge gap, we investigated the effect of breeding habitat loss on the population trend for the Fairy Pitta (Pitta nympha), a migratory forest-breeding bird in the EAAF categorized as Vulnerable on the IUCN Red List. It has been assumed that this species is declining rapidly due to deforestation in its breeding range in Taiwan. We analyzed the change in Fairy Pitta population density across Taiwan from 2001 to 2017, and tested the effect of forest cover change on the species' abundance. We detected an average of 4.32 (95% CI: 1.96-6.68) individuals per km(2) in 2001, which has declined at an average annual rate of -8.31% (95% CI: -15.50%--1.16%) during the study, and a minor change in forest cover (-0.22%) in Taiwan during this period. We found no significant effect of the forest cover trend on the population trend of the Fairy Pitta. This suggests that the drivers of population decline may not be related to deforestation in the breeding range, but potentially to breeding habitat degradation, habitat loss in the non-breeding range, or factors unrelated to habitat loss. Further studies are required to assess the major threats to this globally threatened species.