Morphological changes during postnatal growth and reproduction in the brown long-eared bat Plecotus auritus: implications for wing loading and predicted flight performance

Patterns of postnatal growth, and changes in mass and wing loading during reproduction were studied in captive free-flying brown long-eared bats (Plecotus auritus, Linnaeus, 1758). The bats were fed on noctuid moths occasionally supplemented with mealworms. Growth in body mass was best described by the von Bertalanffy model (n=5 individuals), while growth in forearm length, wingspan and wing area, were best described by the logistic equation (n=5 individuals). Because the wings developed more rapidly than body mass, wing loading decreased from high levels following birth to a minimum at around 30 days of age. Predicted mechanical power requirements for flight (minimum power P-mp and maximum range power P-mr) and the corresponding flight speeds (V-mp and V-mr) as well as the minimum theoretical radius of a banked turn (r(min)) also reached minima at this time. At 30 days of age juveniles could fly with lower predicted power requirements and were more manoeuvrable (could fly more slowly at minimum power and make tighter turns) than adults. These minima corresponded to the time when juveniles first left the roost box to Ay. Reproductive females (n=6) displayed a near two-fold increase in body mass and wing loading over 50 days prior to birth. This resulted in a three-fold increase in the predicted mechanical power requirements for flight (P-mp and P-mr), and a decrease in predicted flight manoeuvrability. Non-reproductive individuals (n=22) had a similar pattern but increased in body mass and wing loading to a lesser extent. Over days 1 to 40 postpartum, both mass and wing loading declined in lactating females, but continued to increase in the non-reproductive bats.