Is it a bird? It is plane? No, it’s a free-tailed bat.
Biologists have suggested for years that in the evolutionary battle for flight between the bat and the bird, the bird had won. However a new study might have just recorded the fastest flight speed ever recorded for a bat, teetering it equal in flight speed to some of the fastest bird species.
Birds are often recorded to migrate long distances as well as remain airborne for long periods of time. As mentioned in a previous article, common swifts are now known to remain airborne for up to 10 months during the winter period and wandering albatrosses can remain at sea for years at a time. However this sort of prolonged aerial lifestyle is very rarely, or indeed never, observed in bats leading biologists to presume that bats are both less energy efficient and slower flyers than birds.
Additionally, previous studies have consolidated this opinion, suggesting that birds were indeed generally more energy efficient by being more aerodynamic thus creating more lift and less drag. They also appeared to be a lot faster in flight than their mammal counterparts with the common swift reaching speeds up to 31.1 m/s.
Small Nb. Some diving raptors are capable of reaching a vertical speed of 50 m/s but this is due to a helping hand in gravity and they would not be capable of achieving this for a ground speed.
Indeed bats were inherently thought to be considerably less efficient and also slower in flight, with a wing morphology that created more drag. Additionally it is thought that external facial structures, like nose and ears, essential for echolocation could disrupt airflow over the body and hinder aerodynamic efficiency further. However this new study has proven other wise.. At least in the case of the Brazilian free-tailed bat…
The Brazilian free-tailed bat (Tadarida brasiliensis), weighing in at just 12 grams, is well known for its capacity for quick long-distance flight, chasing insects up to 1 kilometre of altitude above ground level.
Prior studies regarding this species flight species have provided mixed results: one study recorded one group leaving leaving their cave roost at a ground speed of over 14.7 m/s whilst a 1950s study estimated their flight speed at over 18 m/s using a helicopter. However another study estimated maximum flight ground speeds at 26.8 m/s. This last recording led some scientists to think that flight performances of bats have somewhat been overlooked by science and that bats could in fact be in the same league as some birds.
To test this hypothesis a group of scientists recorded the flight duration, speed and wing beat frequency of 7 free flying Tadarida brasiliensis. For this they placed radio trackers on the bats and then recorded their flight using an airplane equipped with radio wave emitters and receivers. The bats covered between 54 and 112 kilometers in a recording session.
The median individual ground speed achieved by the group was between 5.4 m/s and 17m/s, falling within the range of speeds reported for several bats and birds, including the morphologically similar European free-tailed bat, (Tadarida teniotis) which has previously been recorded with an average ground speed of 13.9m/s.
However the team also recorded spikes in the bat’s ground speed: During these, recorded ground speeds went up as high as 44.5 m/s and maximum individual ground speeds were between 27.2m/s and 44.5m/s. These spurts of rapid flight turned out to be the faster than any other previously recorded data.
It is thought that Brazilian free-tailed bats, occupying a morphological extreme amongst bats with their long and thin wings, have adopted a flight strategy known as ‘flap-gliding’. The adoption of this strategy is well documented for birds such as the swift or the swallow however this technique has very rarely been recorded in bats. This particular flight strategy allows Brazilian free-tailed bats to reach a maximum speed with minimal effort and would explain why the wingbeat data suggested a strong positive association between higher ground speeds and increasing wingbeat ‘pauses’ (associated with the ‘glide’ part of the strategy).
So it appears that the Brazilian free-tailed bat could, despite prior expectations, give the Common swift a run for its money if it ever came to a ‘sprint off’. These observed speeds do though only represent a finite amount of the animal’s flight time: Same as for the fastest ground mammal, the cheetah, it would be energetically unsustainable to use this ‘sprint’ phase continuously.
McCracken, G. F. Safi, K. Kunz, T. H. Dechmann, D. K. N. Swartz, S. M. and Wikelski, M. (2016) ‘Airplane tracking documents the fastest flight speeds recorded for bats’ Royal Society of Open Science 3 : 160398.
Read the full paper here: http://rsos.royalsocietypublishing.org/content/3/11/160398
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