Nocturnal hypothermia impairs flight ability in birds: a cost of being cool

Abstract

Many birds use regulated drops in night-time body temperature (T b ) to conserve energy critical to winter survival. However, a significant degree of hypothermia may limit a bird's ability to respond to predatory attack. Despite this likely energy-predation trade-off, the behavioural costs of avian hypothermia have yet to be examined. We thus monitored the nocturnal hypothermia of mourning doves (Zenaida macroura) in a laboratory setting in response to food deprivation. Nocturnal flight tests were used to quantify the flight ability of hypothermic doves. Many hypothermic doves (39% of tests) could not fly while carrying a small weight, but could do so after quickly warming up to typical daytime T b . Doves that were unable to fly during their first test were more hypothermic than those that could fly, with average T b reductions of 5.38C and 3.38C, respectively, but there was no overall indication of a threshold T b reduction beyond which doves were consistently incapable of flight. These results suggest that energy-saving hypothermia interferes with avian antipredator behaviour via a reduction in flight ability, likely leading to a trade-off between energy-saving hypothermia and the risk of predation.

Thermal dependence of sprint performance in the lizard Psammodromus algirus along a 2200-meter elevational gradient: Cold-habitat lizards do not perform better at low temperatures

“…For example, the sprint speed of lizards of the genus Takydromus peaks at 30-32°C of body temperature, diminishing gradually towards warmer or cooler temperatures (Chen et al, 2003;Xiang et al, 1996). Similar results have been found in ants (Hurlbert et al, 2008), fish (Wilson, 2005), a number of other ectotherms (Bennett, 1990), and even endotherms (Carr and Lima, 2013;Rojas et al, 2012).…”

A temperate endotherm trades thermoregulation for self-preservation: stress-induced changes in surface temperature as thermoregulatory trade-offs

“…At temperatures below thermoneutrality, declines in core body temperature can reduce the metabolic demand of Black-Capped Chickadees by as much as 10% (Reinertsen & Haftorn, 1986), but in doing so, enzymatic activity and neuromuscular response times are also likely to fall (discussed in Brodin, Nilsson, & Nord, 2017), owing to Q 10 effects. In both Morning Dove ( Zenaida macroura ) and Blue Tits ( Cyanistes caeruleus ), such declines in neuromuscular response times during hypothermia have been anecdotally and empirically supported, with hypothermic individuals exhibiting reduced flight capacity when compared with normothermic conspecifics (Carr & Lima, 2013;Haftorn, 1972). Consequently, whilst permitting core body temperature to fall under stress exposure and resource limitation may be an energetically favourable strategy in the cold, long-term fitness consequences with respect to predator avoidance may be high.…”

High ambient temperatures induce aggregations of chimney swifts Chaetura pelagica inside a roost

“…Restricted food availability has been shown to initiate torpor as an energy conservation strategy in many bird species Lovegrove 2002, Ben-Hamo et al 2010). However, torpor may incur other costs, such as rewarming time and increased predation risk, so huddling may be a preferred strategy in social birds (Wojciechowski et al 2011, Carr andLima 2013). For example, food-deprived speckled mousebirds maintained a higher rest-phase body temperature if they huddled compared to single individuals (McKechnie et al 2006).…”

“…Alternative physiological strategies, such as torpor, can conserve energy by down-regulating metabolism, and thus body temperature, in response to low ambient air temperatures or decreased energy availability Lovegrove 2002, Geiser 2004). However, these strategies require inactivity and reduced responsiveness, which means animals cannot allocate energy to other fitness-enhancing behaviors, such as vigilance or social interactions, and may be more susceptible to predation (Gilbert et al 2010, Carr andLima 2013).…”