Torpor in Three Species of Brazilian Hummingbirds under Semi-Natural Conditions Author(s): Claus Bech, Augusto S. Abe, John Fleng Steffensen, Martin Berger and Jose Eduardo P. W. Bicudo Source: The Condor, Vol. 99, No. 3 (Aug., 1997), pp. 780-788 Published by: University of California Press on behalf of the Cooper Ornithological Society Stable URL: http://www.jstor.org/stable/1370489 . Accessed: 15/01/2014 07:54 Your use of the JSTOR archive indicates your acceptance of the Terms & Conditions of Use, available at . http://www.jstor.org/page/info/about/policies/terms.jsp . JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact [email protected]. University of California Press and Cooper Ornithological Society are collaborating with JSTOR to digitize, preserve and extend access to The Condor. http://www.jstor.org This content downloaded from 186.217.234.34 on Wed, 15 Jan 2014 07:54:58 AM All use subject to JSTOR Terms and Conditions The Condor 99:780-788 C The Cooper Ornithological Society 1997 TORPOR IN THREE SPECIES OF BRAZILIAN HUMMINGBIRDS UNDER SEMI-NATURAL CONDITIONS1 CLAUSBECH Department of Zoology, Norwegian University of Science and Technology, N-7034 Trondheim, Norway, e-mail: [email protected] AUGUSTo S. ABE Departmento de Zoologia, Universidade Estadual Paulista, BR-13506900 Rio Claro, Sp, Brazil JOHN FLENG STEFFENSEN2 Department of Zoophysiology, University of Aarhus, DK-8000 Aarhus C., Denmark MARTIN BERGER Westfiilisches Museum fiir Naturkunde, D-48161 Miinster, Germany JOSEEDUARDO P. W. BICUDO Uhiversidade de Sao Paulo, Instituto de Biociencias, Dept. Fisiol., BR-05508900 Sao Paulo, Brazil Abstract. We measuredbody temperaturesin three species of Brazilianhummingbirds, the VersicoloredEmerald (Amazilia versicolor; body mass 4.1 g), the Black Jacobin(Me- lanotrochilusfuscus; body mass 7.7 g) and the Swallow-tailedHummingbird (Eupetomena macroura;body mass 8.6 g), duringovernight exposure to naturalconditions of photoperiod and ambienttemperatures. All three species entered torpor.In both A. versicolor and E. macroura,individuals entered torpor even if they had access to feeders up to the time of sunset. In contrast,M. fuscus was less proneto entertorpor and did so mainlyif it had been fasting for more than two hoursbefore sunset.Furthermore, M. fuscus often spentthe whole night in torpor,whereas the two other species entered torpor for a variable,often short, period of the night. We observed more than one torporbout during a single night in all three species. We suggest that multiple nocturnaltorpors result from interruptionof the normal torpor patternby some (unknown)external stimuli. Any interruptedtorpor was always followed by a new entry into torpor,supporting the view that there is a body mass thresholdbelow which the hummingbirdsmust enter torpor. Our data also indicatethat these hummingbirdspecies might use torporeven if they are not energeticallystressed. Key words: hummingbirds,Amazilia versicolor,Melanotrochilus fuscus, Eupetomena macroura, torpor, thermoregulation, body temperature. INTRODUCTION Hiebert 1990). Most of the studies on humming- For many small homeotherms,daily torporis an birds suggest that daily torpor is a strategy em- essential mechanism to cope with periods of ployed in situations involving energetic stress. food deprivationand/or severe weather condi- Thus, torpor has less often been reported in ap- tions that pose a challenge to their energeticbal- parently well-fed individuals (Krtiger et al. ance. Torporis known to occur in birds from at 1982, Carpenter and Hixon 1988, Hiebert 1993a, least six differentorders (Procellariiformes,Co- 1993b). lumbiformes, Coliiformes, Caprimulgiformes, Because it is difficult to obtain physiological Apodiformes, and Trochiliformes;see Reinert- information from free-living hummingbirds, sen 1983, Heller 1989, French 1993). Daily tor- most studies have been of birds kept under lab- por has been extensively studied in humming- oratory conditions. Information about the use of birds, in which significantenergetic savings are torpor under natural conditions in hummingbirds correlated with the use of daily torpor (Hain- is consequently scarce (Calder and Booser 1973, sworth et al. 1977, 1981, Beuchat et al. 1979, Carpenter 1974, Calder et al. 1990), as it is for other bird species entering torpor (Brigham 1 1992). The only study that has provided accept- Received 27 June 1996. Accepted 13 March1997. able that need not be en- 2Current address: Marine Biological Laboratory, proof hummingbirds University of Copenhagen,DK-3000 Helsingor,Den- ergetically stressed in order to resort to daily tor- mark. por is that of Carpenter and Hixon (1988), who [780] This content downloaded from 186.217.234.34 on Wed, 15 Jan 2014 07:54:58 AM All use subject to JSTOR Terms and Conditions TORPORIN BRAZILIANHUMMINGBIRDS 781 demonstratedtorpor in a free-living, well-fed, (Mettler,accuracy 0.01g) and then placed indi- Rufous Hummingbird Selasphorus rufus. In the vidually in smaller overnight cages (approxi- same species, but under laboratoryconditions, mately 12 X 12 X 20-cm cardboardboxes) pro- Hiebert(1993a, 1993b) reportedincreased inten- vided with a perch. Usually the birds roosted sity of torporduring periods of food restriction, quietly on the perch during the night, although but when body mass nonetheless showed an in- in some cases they apparentlyhad spent the crease. In S. rufus the use of torporwas highest night sitting on the floor of the cage. The cages in the autumn, suggesting a function of torpor (up to six used each night) were placed outdoors as a strictly energy saving mechanism, thereby duringthe night. The walls and top of each cage minimizing the time required for premigratory were equipped with holes, to ensure that the fattening. In this case torpor is not correlated hummingbirdswere exposed to natural varia- with inadequate food intake (Carpenteret al. tions in both ambienttemperature and photope- 1993, Hiebert 1993a). However, it is still an riod. open question whether hummingbirdsnormally The small size of hummingbirdsmakes the need to be energy-stressedin order to enter tor- measurementof body temperature(Tb) a difficult por under naturalconditions (Calder 1994). task. We used a copper-constantanthermocouple We examined the use of torporby three spe- (California Fine Wire Company, type 0.005) cies of Brazilianhummingbirds kept undersemi- placed subcutaneouslyand laterally on the pec- naturalconditions. We asked whetherthese spe- toral muscle for measurementsof body temper- cies would entertorpor under conditions as close ature.The thermocouplewas fixed in place with to naturalas possible. We also wanted to study small pieces of adhesive tape. During measure- the influence of short-termchanges in their en- ment, the subcutaneouslyplaced tip of the ther- ergetic status on the use of torpor.The energetic mocouplewas covered by the wing. Pilot studies status of the hummingbirdswas manipulatedby of all three species indicatedthat such measure- experimentallydepriving them of food from the ments of pectoral temperaturedid not differ by time of captureuntil sunset. more than 0.2-0.30C from simultaneous mea- surementsof rectaltemperature. A thermocouple METHODS was placed inside one of the cages to recordthe The study was carriedout at the Museu de Biol- actual ambient temperature(Ta) to which the ogia, at SantaTeresa in the state of EspiritoSan- birds were exposed. All thermocoupleswere ex- to, Brazil (19055'S, 40036'W; about700 m above tended by using large-diametercopper-constan- sea level). We studied three species of hum- tan thermocouples(Bicc Cables, U.K., 4-5 m mingbirds, the Versicolored Emerald Amazilia length) that went to a nearby house where the versicolor (- 4.1 g), the Black Jacobin Melan- data-acquisitionequipment was placed. otrochilus fuscus (- 7.7 g), and the Swallow- Body temperatureswere measured every 40 tailed Hummingbird Eupetomena macroura (- sec throughout the night. The thermocouple 8.6 g). We did not determinesexes in any of the wires were connectedto a Data Translation(DT three species, all of which are common breeding 2805) A/D converter, via a DT-757 terminal birds in the study area (Ruschi 1982). board, and processed by a computer using a We conductedthe study from 2-20 December Labtech Notebook data acquisition program. 1987. The length of the nights did not vary Each night, up to six individuals were studied much, being approximately11 hr long. Sunrise simultaneously. We consistently used at least changed from 05:53 to 05:59 and sunset from two differentspecies, as well as variablefasting 19:10 to 19:19 duringthe studyperiod. All times times, each night. After arousal of the birds, are given in Rio de Janeirosummertime. which usually occurredbetween 06:00 and 07: The hummingbirdsin the study area are ac- 00, they were removed from their cages and re- customed to feeding at artificialfeeders. Hence, leased again after removing the thermocouples individuals of all three species were easily and re-weighing. caught at the feeders duringthe afternoon.After The total time spent in torporduring a night capture they were kept individually, at normal was calculated as the time Tb was below 350C ambient temperature,in ca. 0.5 m3 cages and during that particularnight.