Author Institution: Central State College, Wilberforce, Ohi

Agee, Robert

Craft, Thomas J.

Edmondson, Marian I.

The Ohio Journal of Science

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A COMPARATIVE STUDY OF THE MECHANICS OF FLYINGAND SWIMMING IN SOME COMMON BROWN BATSTHOMAS J. CRAFT, MARIAN I. EDMONDSON, AND ROBERT AGEECentral State College, Wilberforce, OhioAlthough bats made their appearance upon the earth more than a millionyears ago, the first known reports of North American bats having the ability toswim were reported by Craft and Dexter (1955) and Patten and Patten (1956).The data reported here attempt to give comparative measurements of some ofthe anatomical mechanics involved in flying and swimming in Myotis sodalisand Eptesicus fuscus. It is also apparent that this situation presents an excellentopportunity to compare some of the physiological differentials of an animal perform-ing a function for which it is accustomed and primarily adapted, with one forwhich it is neither accustomed to performing nor primarily adapted. A compara-tive study of some physiological stresses evidenced during flying and swimmingin bats is currently under study in our laboratory.MATERIALS AND METHODSThe Myotis sodalis used in this investigation were collected from Carter Caveslocated in northeastern Kentucky. Seventeen specimens were collected January 6,1956, and thirteen specimens were collected March 25, 1956. Twenty-threespecimens of Eptesicus fuscus were collected from a stock barn in Greene County,Ohio during October 1956. It was standard procedure to determine the sex,weight, body length (snout to vent) and the forearm length of each animal. Theanimals were not fed during the tour of investigation. The bats were stored at4±2°C. One hour prior to any given test the specimens to be tested were removedfrom the temperature of 4±2°C to one of 22±2°C. Burbank and Young (1934),Evans (1938), and Hock (1951) have agreed that the body temperature of batsremains within one or two degrees centigrade of the atmospheric temperaturewhen the bat is inactive. We found sixty minutes to be sufficient time for thetemperature to change from one of approximately 4 to 6°C to one of 22 to 24°C.We also found 22°C to be sufficient temperature to allow normal flight by thebats tested. However, Larsell and Dow (1935), as a result of observations madeon a Cory norhinus sp., listed four stages of emerging from winter sleep, namely:(1) when the temperature is below 0°C, rigidity is evidenced. Only thegrasping reflex of the hindfeet is slightly evidenced.(2) stage of medula reflexes, grasping reflex is fully exhibited, (atmospherictemperature above 0°C).(3) at approximately 10°C, marks the beginning of cerebral activity andprotective movements are evidenced.(4) at approximately 35°C, marks the stage of awakening, all muscularactivities are regained.The bats were allowed to fly in a laboratory 10x7x3.3m. They were allowedto swim in a tank 1.5 x 1 m containing approximately 6 ft3 of tap water. Theanimals performed the operations of flying and swimming on different days.Observations on the mechanics of flying and swimming were made by motionpicture photography. Pictures were taken at sixty-four frames per second.RESULTS AND DISCUSSIONIn the collections of M. sodalis sixty-three percent were male and thirty-sevenpercent were female. The collections of E. fuscus contained sixty-nine percentTHE OHIO JOURNAL OF SCIENCE 58(4): 245, July, 1958.246 THOMAS J. CRAFT, MARIAN I. EDMONDSON AND ROBERT AGEE Vol. 58male specimens and thirty-one percent female. The results of the observationsmade on their capacities to fly and swim have been tabulated in table 1.Eisentraut (1936) showed in a set of motion picture figures that a large mouse-eared bat found in Germany made eleven or twelve wing beats (flying strokecycles) per second while flying and in this time traveled about 420 cm. Theflying and swimming stroke cycles are divided into a propulsion phase, which isresponsible for the animals forward movement, and a recovery phase. Theduration of the flying stroke cycle was observed to be the same in M. sodalis andE. fuscus, this being 0.109 second in each group. The propulsion phase required0.062 second for its completion while the duration of the recovery phase was0.047 second. There was a difference in the rate of execution of the swimmingstroke cycle between the M. sodalis and E. fuscus. The pattern of the swimmingstroke cycle was the reverse of the flying stroke cycle in that the recovery phasewas 0.016 second longer than the propulsion phase. In M. sodalis the swimmingstroke cycle lasted 0.172 second (fig. 1 to 11). The propulsion and recoveryphases lasted 0.078 and 0.094 second, respectively. In E. fuscus the swimmingstroke cycle lasted 0.203 second; the duration of the propulsion phase was 0.094second, and the duration of the recovery phase was 0.109 second.TABLE 1Flying and swimming in batsAverage DataWeightCombined length of headand bodyLength of forearmRate of flyingWing beatsDistance/wing beatRate of swimmingWing beatsDistance/wing beatNumber ofobservations292929151515252525M. sodalis8.8 gm81.9 mm39.4 mm2,986 mm/sec9.1 /sec328 mm295 mm/sec5.8/sec53 mmNumber ofobservations232323181818212121E, fuscus21.75 gm106.85 mm46.8 mm3,671 mm/sec9.1/sec403 mm308 mm/sec4.9 /sec61 mmDuring the swimming propulsion phase (fig. 1 to 5), the lateral extensionof the uropatagium (fig. 1, B) increased as the wing unfolded latero-posteriad.The lateral extension of the uropatagium decreased during the recovery phase(fig. 6 to 11) and at this time the anterior appendages moved dorso-medio-anteriad.In M. sodalis, the distance traversed by the distal extremity of one forearm duringa single swimming stroke cycle was equal to 88 percent of the body length. InE. fuscus, the distance traversed by the distal extremity of one forearm during asingle swimming stroke cycle was equal to 87 percent of the body length.During flight the tip of the uropatagium was curved ventrad thereby producinga dorsal arch on the body of the uropatagium. Such a position enabled theuropataguim to serve as a rudder. When the bat was swimming, the tip of theuropatagium was curved dorsad which produced a ventral arch in the body ofthe uropatagium (fig. 1 to 11). This position reduced the resistance of the waterupon the forward movement of the bats' s body as well as increasing the buoyancyeffect upon its body. The ventral arch was deeper in the best swimmers. Withoutsufficiently ventral arched uropatagium the caudal end of the animal had a tendencyto become submerged in the water at which time the animal began to flounder.The bats tested did not swim with equal facility. Velocity was selected as aFlying and Swimming in BatsThomas J. Craft, Marian I. Edmondson and Robert AgeePLATE IThe photographs were taken with a Bolex 35 mm motion picture camera at sixty-fourframes per second. Myotis sodalis completing the cycle of a swimming stroke.1 to 5 show the propulsion phase of the swimming stroke cycle.A—wing B—uropatagium6 to 11 show the recovery phase of the swimming stroke cycle.247248 THOMAS J. CRAFT, MARIAN I. EDMONDSON AND ROBERT AGEE Vol. 58basis for evaluation of the bats capacity to fly and swim. Three classificationsof the ability to fly and swim were arbitrarily established as shown in table 2.In both species of bats tested, the style of swimming closely resembled the butterflystroke employed by human swimmers. While both species resembled the butterflystroke, the movements of E. fuscus resembled this style of swimming more closelythan did those of M. sodalis. The forearms served as rudders during swimming.Both species were able to float without apparent difficulty. When floating, thewings were folded alongside the body; the uropatagium remained arched ventrad.Upon comparing the distance traveled per wing beat to length of body, wefound that based on the average rates of all members of M. sodalis tested, theyflew 4 times the length of their body per stroke and swam 0.64 of their body lengthper stroke cycle. The members of M. sodalis, classified as good flyers, traveledTABLE 2Classification of swimming and flying in batsGeneraMyotisEptesicusOperation' [Flying \{fSwimming \[ {f (Flying <{{Swimming sImm/sec3,360-4,5402,210-3,3501,320-2,200400-520220-390100-2103,360-4,5402,210-3,3501,320-2,200400-520220-390100-210RatingGoodAveragePoorGoodAveragePoorGoodAveragePoorGoodAveragePoor% of animalsin classification226612304624691615215326a distance equal to 4.7 times their body length and those classified as good swimmersswam a distance equal to 0.98 of their body length. Based on the average ratesof all members of E. fuscus tested, they flew 3.8 times their body length per strokecycle and swam 0.57 of their body length. The members of E. fuscus classifiedas good flyers flew 4.4 times their body length. A good swimmer of the humanspecies is expected to propel himself a distance equal to the length of his body perstroke cycle.The bats did not improve their rates of swimming with practice. Thoseclassified as good swimmers swam readily and did not flounder about the sidesof the tank. Instead they swam on a straight course, with strong, graceful strokes,and with a deep ventral arch in their uropatagium. The hair of the good swimmersdid not wet as easily as did the hair of the animals falling into other classifications.Apparently the sebaceous glands secreted a more resistant coating of oil onto theroot sheath of the hair. This is in keeping with observations that have beenmade on aquatic birds. If the feathers of aquatic birds are not adequately preened,the birds fail in their attempts to swim. The weight and body length of the batsdid not have a direct effect upon the rate at which they flew or swam.It was observed in both species that females swam faster than males andthat they had shorter forearms. The data in table 2 show that 50 percent of allanimals tested flew and swam equally well: 33 percent flew better than they swam;and 16 percent swam better than they flew.No. 4 FLYING AND SWIMMING JN BATS 249SUMMARY1. Animals classified as good swimmers evidenced a deeper ventral arch in theiruropatagium.2. The hair of animals classified as good swimmers wetted less easily than thehair of those bats falling into other classifications.3. Females of Myosis sodalis and Eptesicus fuscus swam faster than the malesof the respective species.4. The females of each species had an average forearm length that was shorterthan that of the males in their species.5. There was no apparent direct effect of body length and weight upon thebat's rate of flying and swimming.6. The recovery phase of the flying stroke cycle of both species was 0.016 secondshorter than the propulsion phase, but was 0.016 second longer than thepropulsion phase during the swimming stroke cycle.7. (a) According to our classification, 50 percent of all animals swam and flewequally well; (b) 33 percent flew better than they swam; and (c) 16 percentswam better than they flew.ACKNOWLEDGMENTSMiss Marian Edmondson and Mr. Robert Agee were undergraduate assistantsduring 1955-56 and 1956-57 respectively. Mr. Agee's present address is MeharryMedical College, Nashville, Tennessee.The authors wish to thank the Central State College Committee on FacultyResearch for financial support of this investigation. We also wish to thankProfessors Ralph Dexter and Elizabeth Smith for advice and assistance in securingspecimens, Mr. Theodore Green for his technical assistance with the photography,and Professor William C. Lucas, Jr., Central State College swimming coach forhis observations on the swimming style exhibited by the bats.LITERATURE CITEDBurbank, R. C. and J. Z. Young. 1934. Body temperature, sleeping, bats. Jour. Physiol.83:459-467.Craft, T. J. and R. W. Dexter. 1955. Swimming ability of the little brown bat. Jour. Mamm.35: 452-454.Eisentraut, M. 1936. Beitrag zur Mechnik des Fledermaus fluges. Zeitschr. f. wiss. Zool.148: 159-188.Evans, C. A. 1938. Hibernation, body temperature, bats. Amer. Nat. 72: 480-484.Hock, R. J. 1951. The metabolic rates and body temperatures of bats. Biol. Bull. 101:289-299.Larsell, O. and R. S. Dow. 1935. The development of the cerebellum in the bat. (Corynorhinussp. and certain other mammals) Jour. Comp. Neuro. 62: 443-468.Patten, B. C. and M. A. Patten. 1956. Swimming ability of the little brown bat. Jour. Mamm.37: 440-441.

A Comparative Study of the Mechanics of Flying and Swimming in Some Common Brown Bats

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A Comparative Study of the Mechanics of Flying and Swimming in Some Common Brown Bats

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