Chiroptera Neotropical, 13 (2), December 2007
Initiating flight directly from the ground by Tadarida brasiliensis (Chiroptera:Molossidae) in Barbacena, state of Minas Gerais, Brasil
Leonardo Víctor De Knegt1,* and Márcio Heitor S. da Silva2 1. Programa de Treinamento em Epidemiologia Aplicada aos Serviços do SUS, Episus / GTDER / CGDT / DEVEP / SVS / Ministério da Saúde. SCS Quadra 4 Bloco A, Edifício principal, 6º andar. Brasília, DF. Brasil. CEP 70304-000. 2. Gerência de Vigilância Ambiental / SE / Secretaria de Estado da Saúde de Minas Gerais. Avenida Afonso Pena, 2300, 8º andar. Bairro Funcionários. Belo Horizonte, MG. Brasil. CEP 30130-007. * Corresponding author. Email:
[email protected]
Abstract It is generally assumed that Molossids cannot take flight directly from the ground, needing a drop of approximately three meters in order to initiate flight. This is frequently referred as related to their long wingspan, which would prevent them from taking off from the ground. A total of 600 Tadarida brasiliensis were collected from a roof colony and put on on the ground in an Eucaliptus field; success or failure in initiating flight was observed. Most bats (592 or 98.7%) were able to initiate flight directly from the ground, and the rest had success after climbing up to 30cm on a tree trunk. This shows that gaining momentum through free fall in Molossids may be a strategy with other finalities, such as energy saving, rather than a consequence of physical limitations. Keywords: behavior, Free-tailed bat
execute flight-initiation jumps among bats was referred exclusively to Desmodontinae, particularly to Desmodus rotundus (Schutt et al. 1997). However, the authors’ field observations suggest the opposite, that other phyllostomid species, as well as one molossid (Eumops sp.) are sometimes capable of using such leaps and jumps to take off directly from ground level. The objective of this study was to observe if T. brasiliensis was capable of initiating flight from the ground.
Introduction Flight characteristics and style in bats depend heavily on species, feeding biology and roosting habits (Vaughan 1970; Canals et al. 2001). Although flight can be highly expensive in terms of energy, there are mechanisms that can be used to save energy while flying, such as gliding instead of flapping (Bennet 1985), and bat flight is generally considered a less expensive energetically than bird or insect flight (Swartz et al. 2007). Tadarida brasiliensis is a relatively small molossid bat (mean total length 103-109mm, mean forearm length 42-45mm, body mass 11 to 15g) (Wilkins 1989). It is an insectivore bat, and its diet is comprised mostly by moths (Wilkins 1989). In urban environments, T. brasiliensis roosts mostly in house roofs and cellars, as well as in dilation joints in buildings, forming colonies that range from few individuals up to thousands of them (Pacheco and Marques 1995; Fabián and Marques 1996; Esbérard et al. 1999). It has been traditionally referred that molossid bats needs a vertical drop of about three meters in order to initiate flight, thus requiring an adequate “take off” site. This is frequently referred as related to the long wingspan normally observed in insectivorous bats, which would not allow the beginning of the flapping process while in contact with the ground (Dietz 1973; Texas Tech University 1994; Chebes 2002). The ability to
Material and Methods A total of 600 T. brasiliensis individuals were captured from a colony of approximately 1,200 individuals, with the use of gloves and butterfly nets. The colony was located in a roof in the city of Barbacena, state of Minas Gerais, southeastern Brazil, in 2005. Roof coordinates were 21º 15’ 10” S; 43º48’ 24” W. Species identification was conducted with the use of an identification key (Gregorin and Taddei 2002). After capture, each individual was set on a horizontal surface on the ground, and success or failure in initiating flight was observed and noted. Individuals who were not capable of initiating flight directly from the ground were allowed to climb a tree trunk freely, and results on climb height and flight success/failure were also observed.
322
Chiroptera Neotropical, 13 (2), December 2007
(Chiroptera:Vespertilionidae), representantes de dos diferentes patrones de vuelo. Revista Chilena de Historia Natural 74: 699-704. Chebes L. 2002. Eumops perotis. Animal Diversity Web. Accessed November 01, 2007. http://animaldiversity.ummz.umich.edu/site/acc ounts/information/Eumops_perotis.html. Dietz C.L. 1973. Bat walking behavior. Journal of Mammalogy 54: 790-792. Esbérard C.E.L.; Luz E.M. and Chagas A.S. 1999. Uso de residências para refúgios por morcegos no Estado do Rio de Janeiro (Mammalia:Chiroptera). Revista Brasileira de Medicina Veterinária 21: 17-20. Fabián M.E. and Marques R.V. 1996. Aspectos de comportamento de Tadarida brasiliensis (I. Geoffroy, 1824) em ambientes urbanos. Biociências 4: 65-86. Gregorin R. and Taddei V.A. 2002. Chave artifical para identificação de molossídeos brasileiros (Mammalia, Chiroptera). Journal of Neotropical Mammalogy 9: 12-32. Pacheco S.M. and Marques R.V. 1995. Observações sobre o parto em Tadarida brasiliensis (I. Geoffroy, 1824) (Mammalia, Chiroptera, Molossidae) em Porto Alegre, Rio Grande do Sul, Brasil. Comunicações do Museu de Ciência e Tecnologia PUCRS, Série Zoologia 8: 3-11. Riskin D.K.; Bertram J.E. and Hermanson J.W. 2005. Testing the hindlimb-strength hypotesis: non-aerial locomotion by Chiroptera is not constrained by the dimensions of the femur or tibia. The Journal of Experimental Biology 208: 1309-1319. Schutt W.A.; Altenbach J.S.; Chang Y.H.; Culliane D.M.; Hermanson J.W.; Muradali F. and Betram J.E. 1997. The dynamics of flightinitiating jumps in the common vampire bat Desmodus rotundus. The Journal of Experimental Biology 200: 3003-3012. Swartz S.M.; Iriarte-Diaz J. and Riskin D.K. 2007. Wing structure and aerodynamic basis of flight in bats. American Institute of Aeronautics and Astronautics, Providence. Texas Tech University. 1994. The Mammals of Texas - Online Edition. Accessed October 10, 2007. http://www.nsrl.ttu.edu/tmot1/eumopero.htm Vaughan T.A. 1970. Flight patterns and aerodinamics. In: Biology of bats vol.I (edited by Wimsatt W.A.), pp.195-216. Academic Press, New York. Wilkins K.T. 1989. Tadarida brasiliensis. Mammalian Species 331: 1-10.
Results From the total of 600 individuals, 592 (98.7%) were capable of taking off directly from the ground. Eight individuals (1.3%) were not capable of initiating flight directly from the ground. These were allowed to climb a tree trunk, in order to attain the necessary free fall. All of them climbed from one to 30cm, and then started flying. Discussion The results of this experiment seem to contradict previous observations on the flight characteristics of T. brasiliensis (Dietz 1973; Texas Tech University 1994; Chebes 2002). The free fall was not necessary in most cases, and the few individuals who needed it used only about 10% of the traditionally required height (Dietz 1973). Rather than only a morphological problem regarding wingspan, the free fall may be a mechanism for saving energy, since initiating flight is an energy consuming activity, and starting it while already in the air (i.e. gliding) should save energy compared to taking off from the ground (Bennet 1985; Canals 2001). We conclude that T. brasiliensis can initiate flight without the need of a free fall. We suggest further studies using force-sensitive platforms (Riskin et al. 2005; Schutt et al. 2007) to measure the force used in leaps preceding flight, preferably comparing flight success/failure and used force in times right before foraging hours (i.e., low energetic availability) and in different moments during the day. Acknowledgements The authors would like to acknowledge the State Health Secretariat of Minas Gerais (Secretaria de Estado da Saúde de Minas Gerais) and the Zoonosis branch of the Municipal Health Secretariat of Barbacena (Secretaria Municipal de Saúde de Barbacena) for logistic support. This study was conducted under permit number 234/04 – NUFAS/MG, issued by DIFAP/IBAMA. References Bennet A.F. 1985. Energetics and locomotion. In:Functional vertebrate morphology (edited by Hildebrand M.; Bramble D.M.; Liem K.F. and Wake D.B.), pp.173-184. Harvard University Press, Cambridge. Canals M.; Iruiarte-Diaz J.; Olivares R. and Novoa F. 2001. Comparación de la morfologia alar de Tadarida brasiliensis (Chiroptera:Molossidae) y Myotis chiloensis
323
