Knowledge gaps and research directions in migration ecology for advancing the conservation of migratory songbirds

Understanding migration ecology is essential for effective conservation of migratory species. To achieve a comprehensive understanding of the ecology of migrating species, it is necessary to study how species react to the complex interplay of intrinsic and extrinsic conditions when optimizing their migratory journey in terms of survival, energy and time. Nocturnal migratory songbirds, which often migrate alone and alternate migratory endurance flights with stopovers, provide an excellent group for studying such individual decisions. Specifically, the decision to interrupt the migratory flight and land and the decision to depart from a stopover are critical for the success of migration. We screened 1490 studies, of which 286 studies were eligible, using a systematic literature review, to identify five significant knowledge gaps in the migration ecology of songbirds: (i) exploring when and where bird mortality occurs during migration; (ii) inferring stopover functions from landing decisions; (iii) assessing the consequences of migration distance on migratory decisions; (iv) measuring how predation danger affects bird decisions; and (v) studying the consequences of habitat quality on the migratory decisions. To address these knowledge gaps, we propose novel frameworks that integrate methods applied at different spatial and temporal scales to study songbird decisions in flight and at stopovers. We also discuss testable hypotheses and future directions to stimulate research for enhancing the understanding of migration ecology and advancing the conservation of threatened migratory songbird species.