Birds feeding on date palm sap during Bengali traditional sap harvesting on Nijhum Dweep, Bangladesh

There is a Bengali tradition of consuming palm "jaggery" (unrefined sugar made from the sap of Indian date palms, Phoenix sylvestris) as a sweetener. To obtain jaggery, people tap Indian date palms to extract the energy-rich phloem sap during the winter. In Bangladesh, people commonly cultivate Indian date palms in traditional agroforestry. We explored which bird species capitalize on the jaggery tradition by consuming sap from tapped Indian date palms on Nijhum Dweep, an island in the Bay of Bengal. Once each day for 30 d between December 2019 and February 2020, we quantified the presence of birds on 120 tapped palms along a 1 km transect. We observed 37 bird species in the palms, and 18 of them (49%) were seen to consume sap. Seven species had not previously been recorded as sap feeders. Among the 18 sap-consuming species, we categorized 5 species (Chestnut-tailed Starling Sturnia malabarica, Asian Pied Starling Gracupica contra, Jungle Myna Acridotheres fuscus, Red-vented Bulbul Pycnonotus cafer, and Black Drongo Dicrurus macrocercus) as constant consumers of date palm sap; 11 species as accidental sap consumers, and 2 species as accessory sap consumers. Insectivorous and omnivorous species accounted for 78% of the sap consumers (39% each), with granivorous and frugivorous species accounting for the remaining 22%. This study highlights date palm sap as a potentially significant winter food source for resident birds, and demonstrates birds' ability to utilize tapped palms as an anthropogenic food resource.