C.C. Voigt and Y. Winter. Energetic cost of hovering flight in nectar-feeding bats (Phyllostomidae : Glossophaginae) and its scaling in moths, birds and bats. Journal of Comparative Physiology B-Biochemical Systemic and Environmental Physiology, 169(1):38-48, 1999. (bibtex: Voigt-1999-ECH).