Nightjar superstars!

PhD student Ryan O'Connor has just published brand new research on the record-breaking evaporative cooling prowess of Southern African nightjars. Nightjars roost and nest in the open and experience temperatures 60C + ... but somehow manage to maintain their body temperature near 40C all the same. Read his blog about how they do it:

Can you see her?? Incubating Rufous-cheeked Nightjar. Because of its superb camouflage, the incubating female is very difficult to see, but she is inside of the black circle (full size picture and zoomed in...).

Can you see her?? Incubating Rufous-cheeked Nightjar. Because of its superb camouflage, the incubating female is very difficult to see, but she is inside of the black circle (full size picture and zoomed in...).

“Nightjars are crepuscular and nocturnal aerial insectivores. During the day, some nightjar species will roost and nest in sites that are devoid of shade and consequently are subjected to intense solar radiation. The combination of solar radiation, air temperature, convection and conduction can culminate into an overall heat index known as operative temperature. At some nightjar nest and roost sites, operative temperatures can approach 60 °C. Under these conditions, nightjars must evaporative body water to dissipate internal heat loads and maintain a normal body temperature. So, just how do nightjars tolerate such extremely high operative temperatures? The secret lies in their mechanism for evaporating water. Whereas most birds pant to evaporate water, nightjars, along with some members of other avian groups, evaporate water via a process known as gular fluttering. Gular fluttering consists of rapid movements of the gular region (i.e., throat). The advantage of gular fluttering over panting is that it does not involve the large movements of the thorax that is characteristic of panting. The movement of the thorax during panting demands an increase in energy expenditure. In contrast, when gular fluttering, nightjars can dissipate large heat loads without expending lots of energy. Thus, gular fluttering is typically regarded as an “energetically efficient” evaporative cooling mechanism. In other words, when exposed to operative temperatures far above body temperature, nightjars can dissipate large amounts of heat without large increases in their metabolism. This limits their endogenous heat production and minimizes their overall heat load. For example, O’Connor et al. (2016) found that at an operative temperature of 56 °C, Rufous-cheeked Nightjars dissipated an amount of heat that was equivalent to 515% of metabolic heat produced. This is the highest ratio of evaporative heat loss to metabolic heat produced ever recorded in a bird. At an operative temperature of 52 °C, O’Connor et al. (2016) observed Freckled Nightjars evaporating an amount of heat that was equivalent to 452% of metabolic heat produced. These extraordinary evaporative cooling capacities result in nightjars maintaining body temperatures far below operative temperatures.”