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- Data packageData from: First three-dimensional tracks of bat migration reveal large amounts of individual behavioral flexibility(2019-05-28) O'Mara, M. Teague; Wikelski, Martin; Kranstauber, Bart; Dechmann, Dina K.N.It is generally assumed that small migrating birds and bats explore wind conditions and then choose a flight altitude, which they then maintain. Because of their high metabolism and flight costs, bats should also minimize energy expenditure during migratory flight, but we know little of how individuals make their migratory journeys. We followed migrating common noctules (Nyctalus noctula) fitted with miniaturized barometric pressure radio transmitters by airplane to record three dimensional migratory movements. Mean airspeeds were 7.2-15.9 m/s and overall climb rates were faster than overall descent rates. While all bats migrated in the same northeasterly direction, they showed flexibility in their altitudes, distances and stopover sites both within and among individuals. This suggests that individuals make decisions to take advantage of wind, landscape, and navigational conditions or other, yet unknown factors, to optimize their nightly flights. Our results once more confirm that the flexibility and behavioral repertoire of individuals in the wild is greater than we assume.
- Data packageData from: Common noctules exploit low levels of the aerosphere(2019-02-21) O'Mara, M. Teague; Wikelski, Martin; Kranstauber, Bart; Dechmann, Dina K.N.Aerial habitats present a challenge to find food across a large potential search volume, particularly for insectivorous bats that rely on echolocation calls with limited detection range and may forage at heights over 1000 m. To understand how bats use vertical space, we tracked one to five foraging flights of eight common noctules (Nyctalus noctula). Bats were tracked for their full foraging session (87.27 ± 24 mins) using high-resolution atmospheric pressure radio transmitters that allowed us to calculate height and wingbeat frequency. Bats used diverse flight strategies, but generally flew lower than 40 m, with scouting flights to 100 m and a maximum of 300 m. We found no influence of weather on height and high-altitude ascents were not preceded by an increase in foraging effort. Wingbeat frequency was independent from climbing or descending flight, and bats skipped wingbeats or glided in 10% of all observations. Wingbeat frequency was positively related to capture mass, and wingbeat frequency was positively related to time of night, indicating an effect of load increase over a foraging bout. Overall, individuals used a wide range of airspace including altitudes that put them at increased risk from human-made structures. Further work is needed to test the context of these flight decisions, particularly as individuals migrate throughout Europe.
- Data packageData from: Tracking post-hibernation behavior and early migration does not reveal the expected sex-differences in a "female-migrating“ bat(2015-03-23) Varga, Katarina; Dechmann, Dina K.N.; O'Mara, M. Teague; Wikelski, MartinLong-distance migration is a rare phenomenon in European bats. Genetic analyses and banding studies show that females can cover distances of up to 1,600 km, whereas males are sedentary or migrate only short distances. The onset of this sex-biased migration is supposed to occur shortly after rousing from hibernation and when the females are already pregnant. We therefore predicted that the sexes are exposed to different energetic pressures in early spring, and this should be reflected in their behavior and physiology. We investigated this in one of the three Central European long-distance migrants, the common noctule (Nyctalus noctula) in Southern Germany recording the first individual partial migration tracks of this species. In contrast to our predictions, we found no difference between male and female home range size, activity, habitat use or diet. Males and females emerged from hibernation in similar body condition and mass increase rate was the same in males and females. We followed the first migration steps, up to 475 km, of radio-tagged individuals from an airplane. All females, as well as some of the males, migrated away from the wintering area in the same northeasterly direction. Sex differences in long-distance migratory behavior were confirmed through stable isotope analysis of hair, which showed greater variation in females than in males. We hypothesize that both sexes faced similarly good conditions after hibernation and fattened at maximum rates, thus showing no differences in their local behavior. Interesting results that warrant further investigation are the better initial condition of the females and the highly consistent direction of the first migratory step in this population as summering habitats of the common noctule occur at a broad range in Northern Europe. Only research focused on individual strategies will allow us to fully understand the migratory behavior of European bats.