Torpor in Three Species of Brazilian Hummingbirds under Semi-Natural Conditions

Abstract

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 support@jstor.org.. Abstract. We measured body temperatures in three species of Brazilian hummingbirds, the Versicolored Emerald (Amazilia versicolor; body mass 4.1 g), the Black Jacobin (Melanotrochilus fuscus; body mass 7.7 g) and the Swallow-tailed Hummingbird (Eupetomena macroura; body mass 8.6 g), during overnight exposure to natural conditions of photoperiod and ambient temperatures. 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 prone to enter torpor and did so mainly if it had been fasting for more than two hours before sunset. Furthermore, M. fuscus often spent the 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 torpor bout during a single night in all three species. We suggest that multiple nocturnal torpors result from interruption of the normal torpor pattern by some (unknown) external stimuli. Any interrupted torpor was always followed by a new entry into torpor, supporting the view that there is a body mass threshold below which the hummingbirds must enter torpor. Our data also indicate that these hummingbird species might use torpor even if they are not energetically stressed. University of California Press and

Heterothermy in an Australian passerine, the Dusky Woodswallow (Artamus cyanopterus)

“…The pattern of torpor by Dusky Woodswallows that we report here is similar to that observed in other diurnal birds such as hummingbirds or martins (Bartholomew et al 1957;Dawson and Hudson 1970;Prinzinger and Siedle 1988;Hiebert 1992;Bech et al 1997;McKechnie and Lovegrove 2002;Schleucher 2004). Nevertheless, long-term seasonal data on diurnal birds as provided by our study are scant.…”

Prey availability affects daily torpor by free-ranging Australian owlet-nightjars (Aegotheles cristatus)

“…We know of only two studies that have experimentally examined the response of birds to reduced food abundance; however, both relied strongly on artificial conditions in field situations. Bech et al (1997) caught three species of hummingbirds at artificial feeders and deprived them of food for varying periods until sunset, then kept them in cages overnight to examine torpor use. All three species entered torpor, but torpor frequency and duration were positively related to the duration of the fasting time before sunset.…”

Influence of Normal Daytime Fat Deposition on Laboratory Measurements of Torpor Use in Territorial versus Nonterritorial Hummingbirds

“…It follows, then, that any factor causing energy stores to drop below a critical threshold should result in torpor initiation. This is supported by the fact that captive birds increase torpor use when food is restricted (Hiebert 1991;Bech et al 1997). It is likely that when food is restricted for free-living birds, torpor will be used more frequently as well.…”

“…Several studies during the past 40 years have attempted to clarify patterns of torpor use in hummingbirds (e.g., Lasiewski 1963;Wolf and Hainsworth 1972;Krüger et al 1982;Bech et al 1997). However, data from these studies are variable and difficult to interpret because energy budgets were not considered.…”