Env Exp Biol (2014) 12: 7–14

Migrating Nathusius’s pipistrelles Pipistrellus nathusii (Chiroptera: Vespertilionidae) optimise flight speed and maintain acoustic contact with the ground

Abstract

Populations of Nathusius’s bats Pipistrellus nathusii breeding in north-eastern Europe migrate seasonally to and from hibernation sites in central Europe. Characteristic flight speeds of P. nathusii were calculated based on aerodynamic theory (C.J. Pennycuick and U.M. Norberg) and morphometric data of captured individuals. Actual flight speeds and altitudes of migrating individuals were measured in the field at the Baltic coast of Latvia. The bats flew on average 11.5 m above the ground. The average flight speed ranged from 11.2 up to 13.1 m s^–1 (40.3 and 47.2 km h^–1) and exceeded the predicted minimum power and maximum range speeds, indicating that P. nathusii minimise the cost of transport or perhaps the duration of the autumn migration flight. The length of the inter-pulse intervals was correlated with the flight height, indicating that P. nathusii adjust the sonar according to the flight altitude to maintain acoustic contact with the ground.