Wintering throughout lower Central America and north-western South America, the Tennessee Warbler (Leothlypis peregrina) both prepares for migration and stops over in our study region. In northern Colombia, the wintering population in the Sierra Nevada de Santa Marta is joined by thousands of birds arriving from further south in March and April, with birds forming remarkable single-species flocks over 100 birds strong. Roving flocks seek trees with small fruits that they pierce and extract the juices from, allowing them to fatten for onward journeys of >1500 km (see Bayly et al. 2019 in Publications).