Browsing by Author "Kranstauber, Bart"
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- 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: 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: True navigation in migrating gulls requires intact olfactory nerves(2015-11-24) Wikelski, Martin; Arriero, Elena; Gagliardo, Anna; Holland, Richard; Huttunen, Markku J.; Juvaste, Risto; Mueller, Inge; Tertitski, Grigori; Thorup, Kasper; Wild, Martin; Alanko, Markku; Bairlein, Franz; Cherenkov, Alexander; Cameron, Alison; Flatz, Reinhard; Hannila, Juhani; Hüppop, Ommo; Kangasniemi, Markku; Kranstauber, Bart; Penttinen, Maija-Liisa; Safi, Kamran; Semashko, Vladimir; Schmid, Heidi; Wistbacka, RalfDuring migratory journeys, birds may become displaced from their normal migratory route. Experimental evidence has shown that adult birds can correct for such displacements and return to their goal. However, the nature of the cues used by migratory birds to perform long distance navigation is still debated. In this experiment we subjected adult lesser black-backed gulls migrating from their Finnish/Russian breeding grounds (from >60°N) to Africa (to < 5°N) to sensory manipulation, to determine the sensory systems required for navigation. We translocated birds westward (1080 km) or eastward (885 km) to simulate natural navigational challenges. When translocated westwards and outside their migratory corridor birds with olfactory nerve section kept a clear directional preference (southerly) but were unable to compensate for the displacement, while intact birds and gulls with the ophthalmic branch of the trigeminal nerve sectioned oriented towards their population-specific migratory corridor. Thus, air-borne olfactory information seems to be important for migrating gulls to navigate successfully in some circumstances.