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

Doucette, Lisa I.; Brigham, R. Mark; Pavey, Chris R.; Geiser, Fritz

doi:10.1007/s00442-011-2214-7

Cited by 43 publications

(29 citation statements)

References 52 publications

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“…These results corroborate other findings that the environment plays an important role in T b expression at an intraspecific level, both within and between populations (McKechnie et al 2007, Glanville and Seebacher 2010, Smit et al 2011, Doucette et al 2012, Glanville et al 2012.…”

Section: Fig 5 Daily Heterothermy Index (Hi)supporting

confidence: 91%

Adaptive thermoregulation during summer in two populations of an arid‐zone passerine

Smit

Harding

Hockey

et al. 2013

Ecology

112

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Abstract. Heterothermy plays an important role in lowering the costs of thermoregulation in endotherms by reducing water and energy requirements. We tested predictions that birds in arid habitats should express fine-scale variation in their thermoregulatory patterns as a function of prevailing climatic conditions. We assessed effects of air temperature (T air ) and water vapor pressure deficit (D) on body temperature (T b ) in free-living White-browed Sparrow-Weavers (Plocepasser mahali ) during summer in two arid habitats in the Kalahari Desert, South Africa, using data from a dry period at a hot, desert site (n ¼ 7 birds), and during a dry period (n ¼ 4 birds) and a wet period (n ¼ 5 birds) at a milder, semi-desert site. The desert birds maintained a significantly higher set-point T b (41.58 6 0.28C, mean 6 SD) than semi-desert birds (40.28 6 0.28C). During the warmest part of day (12:00-18:00 hours), T b increased significantly during periods of high T air and/or high humidity, and mean and maximum T b were up to 1.48 and 2.38C, respectively, above normal levels. However, as T air increased, birds at the desert site maintained T b at or below set-point levels for a greater proportion of the time than birds at the semi-desert site. Birds at the desert site also expressed a greater magnitude of daily heterothermy (heterothermy index, HI ¼ 2.48 6 0.38C, mean 6 SD) than birds at the semi-desert site: the latter population showed a greater magnitude of heterothermy during a dry period (HI ¼ 2.18 6 0.38C) than during a wet period (HI ¼ 1.68 6 0.28C). Birds continued foraging throughout the warmest part of the day, despite the fact that heat dissipation (percentage of time spent panting and wing-spreading) increased significantly with increasing T air . Our findings reveal that populations can vary in their thermoregulatory responses in both space and time and suggest that small changes in T air can have significant effects on thermoregulation in free-ranging desert birds, even when T air , T b . These data have important implications for assessing vulnerability of species to climate change, suggesting that sensitivity should be assessed at the population, rather than species, level.

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Section: Fig 5 Daily Heterothermy Index (Hi)supporting

confidence: 91%

Adaptive thermoregulation during summer in two populations of an arid‐zone passerine

Smit

Harding

Hockey

et al. 2013

Ecology

112

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“…However, recent reports on free-living birds support the relationship between torpor and food availability. For example, moon phase, and presumably foraging efficiency, was a stronger predictor of torpor than ambient temperature in Freckled Nightjars [32] and prey availability similarly predicted the use of heterothermy in free-living Owlet-Nightjars [9]. In contrast, others argue that while food availability may contribute, it is not the sole determinant of heterothermy [28].…”

Section: Discussionmentioning

confidence: 85%

Energy savings due to the use of shallow body temperature reduction in overwintering Northern Cardinals

2015

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Background: Northern Cardinals (Cardinalis cardinalis) are able to endure drastic seasonal variations in ambient temperature. Many endotherms in these conditions utilize heterothermy (e.g., torpor) to conserve energy by adjusting their body temperatures according to changing environmental conditions. Previous research shows that cardinals reduce energy expenditure during winter nights. By examining whole-animal function, we asked whether this reduced metabolism was a result of decreased activity or an induced state of torpor. We measured body mass, percent fat content, metabolic rate (V O 2 ) across a range of ambient temperatures and body temperature (T b ) using data loggers during both summer (August to early September) and winter (December to January) conditions. We hypothesized that: (a) daily winter T b fluctuations would reveal an induced torpor, and (b) alterations of insulation would play a significant role in thermoregulation.Results: Although insulation in the form of fat stores was higher in the winter, there was no seasonal difference in whole body conductance. We found no evidence for torpor, but found a slight depression in overall circadian temperature rhythms for the winter animals compared to summer animals, resulting in a predicted 10-16 % savings in daily energy expenditure. Conclusions:Our findings support recent work showing that thermoregulatory mechanisms are not as fixed as previously thought and, while fat deposits may function to increase insulation, they are more likely important for fuel storage. These data identify subtle changes in the homeostatic set point for body temperature and show that these slight alterations can have significant impacts on daily energy expenditure in wild birds.

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“…Globally, non-passerines and particularly nocturnal species are more likely to be heterothermic, and much thermoregulatory research has focused on these species (e.g. Brigham, 1992;Körtner et al, 2001;Lane et al, 2004;McKechnie et al, 2007;Smit and McKechnie, 2010;Doucette et al, 2011Doucette et al, , 2012. However, only a handful of studies have documented the nocturnal energetic strategy of free-ranging passerines, and even fewer have measured core T b .…”

Section: Discussionmentioning

confidence: 99%

“…For sedentary, insectivorous species, not only does winter present thermal challenges but also the increased energetic demand must be met when prey availability is reduced or unpredictable (Smit and McKechnie, 2010;Doucette et al, 2012). A small body size poses further energetic challenges.…”

Section: Introductionmentioning

confidence: 99%

“…A small body size poses further energetic challenges. These factors are associated with widespread torpor use by Australia's small mammals (Geiser, 1998(Geiser, , 2004Munn et al, 2010), but although torpor is a thermal strategy for some insectivorous non-passerines (Körtner et al, 2001;Doucette et al, 2012;McKechnie et al, 2007;Smit and McKechnie, 2010), there is currently little quantitative evidence for torpor amongst southern hemisphere passerines. Other adaptations to a harsh and unpredictable climate such as aseasonal and cooperative breeding (Russell, 1989;Astheimer and Buttemer, 2002) suggest that torpor may be likely, together with the fact that many small Australian insectivorous birds are sedentary (Recher and Davis, 1997;Morris and Wooller, 2001).…”

Section: Introductionmentioning

confidence: 99%

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Avian torpor or alternative thermoregulatory strategies for overwintering?

Douglas

Cooper

Withers

2017

Journal of Experimental Biology

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It is unclear whether torpor really is uncommon amongst passerine birds. We therefore examined body temperature and thermoregulatory strategies of an Austral passerine, the white-browed babbler (Pomatostomus superciliosus), which has characteristics related to a high probability of torpor use; it is a sedentary, insectivorous, cooperative breeding species, which we studied during winter in a temperate habitat. Wild, free-living babblers maintained normothermy overnight, even at sub-zero ambient temperatures, with a mean minimum body temperature of 38.5±0.04°C that was independent of minimum black bulb temperature. Physiological variables measured in the laboratory revealed that babblers had a low basal metabolic rate and evaporative water loss, but their body temperature and thermal conductance were typical of those of other birds and they had a typical endothermic response to low ambient temperature. Huddling yielded significant energy savings at low temperatures and a roost nest created a microclimate that buffered against low temperatures. Low basal energy requirements, communal roosting and the insulation of a roost nest confer sufficient energetic benefits, allowing babblers to meet energy requirements without resorting to heterothermia, even in their depauperate, low-productivity landscape, suggesting that passerine birds use alternatives to torpor to balance their energy budgets when possible.

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

Cited by 43 publications

References 52 publications

Adaptive thermoregulation during summer in two populations of an arid‐zone passerine

Adaptive thermoregulation during summer in two populations of an arid‐zone passerine

Energy savings due to the use of shallow body temperature reduction in overwintering Northern Cardinals

Avian torpor or alternative thermoregulatory strategies for overwintering?

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