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Comparative Study
, 278 (1716), 2311-7

Trapped in the Darkness of the Night: Thermal and Energetic Constraints of Daylight Flight in Bats

Comparative Study

Trapped in the Darkness of the Night: Thermal and Energetic Constraints of Daylight Flight in Bats

Christian C Voigt et al. Proc Biol Sci.


Bats are one of the most successful mammalian groups, even though their foraging activities are restricted to the hours of twilight and night-time. Some studies suggested that bats became nocturnal because of overheating when flying in daylight. This is because--in contrast to feathered wings of birds--dark and naked wing membranes of bats efficiently absorb short-wave solar radiation. We hypothesized that bats face elevated flight costs during daylight flights, since we expected them to alter wing-beat kinematics to reduce heat load by solar radiation. To test this assumption, we measured metabolic rate and body temperature during short flights in the tropical short-tailed fruit bat Carollia perspicillata at night and during the day. Core body temperature of flying bats differed by no more than 2°C between night and daytime flights, whereas mass-specific CO(2) production rates were higher by 15 per cent during daytime. We conclude that increased flight costs only render diurnal bat flights profitable when the relative energy gain during daytime is high and risk of predation is low. Ancestral bats possibly have evolved dark-skinned wing membranes to reduce nocturnal predation, but a low degree of reflectance of wing membranes made them also prone to overheating and elevated energy costs during daylight flights. In consequence, bats may have become trapped in the darkness of the night once dark-skinned wing membranes had evolved.


Figure 1.
Figure 1.
(a) Elimination of 13C label and (b) the reaction progress variable after intraperitoneal injection of 200 mg of 13C-labelled Na-bicarbonate in 11 male C. perspicillata. The solid line indicates the mean values of 13C enrichment above baseline (AP13CE; %) and the ln-converted reaction progress variable, respectively. The grey areas indicate the range ±1 s.d.
Figure 2.
Figure 2.
Carbon dioxide production rate (formula image; ml min−1) measured by indirect calorimetry in relation to formula image (ml min−1) measured by the Na-bicarbonate method. Total bicarbonate pool size was estimated by either the plateau (filled circles) or the intercept method (open circles).
Figure 3.
Figure 3.
(a) Core body temperature (°C) and (b) mass-specific CO2 production rate (ml g−1 h−1) in C. perspicillata flying at night and during the day.

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