2023 Author: Bryan Walter | [email protected]. Last modified: 2023-05-21 22:24
Wide-eared folded lip (Tadarida teniotis) with a backpack transmitter.
Wide-eared folded lips are able to rise up to 1600 meters above the ground, using ascending air currents, due to the features of the relief. This helps them find food faster and travel long distances with less energy, according to an article for the journal Current Biology. Previously, it was believed that such a method of movement was unavailable for bats, since the night air currents are not as strong as the daytime ones used by birds of prey.
Many bird species use updrafts, either thermal or terrain, to climb to great heights and soar for extended periods. This strategy helps to dramatically reduce flight energy consumption. Most often, predators and scavengers rely on updrafts: for example, thanks to them, the Andean condors (Vultur gryphus) can cover distances of up to 172 kilometers without a single flap of their wings.
At night, the sun does not heat the surface of the earth, as a result of which heat flows are weakened. In addition, it becomes more difficult to spot relief features that generate updrafts. Based on this, scientists have long assumed that nocturnal birds and bats are not capable of passive flight due to ascending currents.
Nevertheless, some bats rise hundreds and even thousands of meters above the ground at night. A team of experts led by M. Teague O'Mara from the University of Southeast Louisiana decided to find out how they do it. To do this, the researchers traveled to a mountainous area in northeastern Portugal and tagged eight female broad-eared folded lips (Tadarida teniotis) with GPS trackers that recorded the three-dimensional position of bats every thirty seconds. The movements of each individual were monitored for one to three nights, an average of six hours per night.
O'Mara and his co-authors found that folded lips leave the caves where they spend daylight hours, on average, 47 minutes after sunset. During the whole night bats hunt, after which they return to the place of the day - the original one or one of the alternative ones. Although most of the time, folded lips move along relief features, sometimes they quickly rise to great heights. For example, one of the individuals rose to 1,680 meters above ground level in just twenty minutes. Most folded lips, having reached their maximum flight altitude, soon descend to a height of about one hundred meters above the ground, but some are at an altitude of more than a kilometer for up to twenty minutes (an average of about eight minutes).
Researchers have divided all the episodes of the upward flight of the fold-lips into two categories. The first included forty-eight cases when bats climbed especially high (an average of 564 meters above the ground). The second category included three hundred thirty-five climbs to a moderate height (on average up to 115 meters, maximum - 334 meters). Comparison showed that fold-lips rise to higher heights faster than moderate ones, but their average flight speed is lower. Most often, these bats climb to great heights along the steep southern and western slopes, where winds blow up the ridges.
The data obtained indicate that fold-lipped lips, like birds, use the updrafts of air created by mountainous terrain. Due to the combination of relief and winds, they can quickly rise to considerable heights. The easiest way to do this is for bats that are in the valleys. The authors hypothesize that folded lips are capable of making a mental map that allows them to navigate in ascending currents.
The researchers found that fold-lipped lips can reach speeds of up to 135 kilometers per hour, but they tend to fly more slowly. With the support of a tailwind, the bats' own speed decreases, and at high altitudes, where the wind strength weakens, on the contrary, it increases.
In spring and autumn, wide-eared folded lips from southern Europe actively hunt migratory Lepidoptera, which accumulate in the air layers 200-600 meters above the ground. O'Mara and his colleagues conducted their study in August, when insect migration had already begun, and noted that bats are most active at these altitudes. According to the authors, updrafts allow foldlips to make energy-efficient exploration forays in search of prey accumulations. In some cases, insects concentrate on the leeward side of the slopes - and in order to get here, a bat just needs to "ride" the wind and wait for it to bring it to a rich source of food.
However, at heights of more than a kilometer, migratory insects are not found, so that the highest rises of the folded lips require a different explanation. Perhaps taking advantage of the updrafts of air, these bats simply save energy when traveling long distances, for example, between places for daytime. At the same time, their flight resembles the trajectory of a roller coaster car: when they reach the slope, the folded lips rise in an ascending stream, and then slowly descend, after which the cycle repeats.
Close relatives of wide-eared folded lips, Brazilian folded lips (T. brasiliensis) in horizontal flight can reach speeds of up to 160 kilometers per hour. This is higher than any bird. Even peregrine falcons develop a higher speed only during a dive.
