The temperature of reptile eggs affects offspring sex, size and running speed. Warmer temperatures usually make for faster reptiles. However, reptiles are ectotherms and cannot produce heat on their own: if it's cold when their running speed is tested, they might just be slower. Birds, in contrast, are endotherms like us. While the temperature of bird eggs affects how long it takes for chicks to hatch, there is little information on how egg temperature affects motor skills in birds. Starlie Belnap and colleagues at Florida International University, USA, recently used bobwhite quail eggs to test whether incubation temperatures influence the way chicks walk.

First, the researchers kept bobwhite quail eggs in three different incubators: one at the optimal temperature (37.5°C) for hatching, a high-temperature incubator at the maximum temperature that the eggs can tolerate (38.1°C) and a low-temperature incubator at the coolest temperature (36.9°C) that the eggs can endure. They then collected chicks that hatched on the same day and found that baby bobwhite quails incubated in cooler temperatures weighed less and had larger leg joint angles than their counterparts. The differences in weight are not surprising, as temperature is known to affect an animal’s metabolism; when endotherms are cold, they burn more energy to keep warm which, over time, can result in weight loss. Additionally, the differences in leg joint angle might mean that the legs are stiffer, decreasing the chicks’ range of motion after they have hatched.

Intriguingly, Belnap and colleagues found that the baby birds from the higher temperature incubator had shorter lower legs than those from the optimal and lower temperature incubators. This is in contrast to their original prediction that warmer temperatures would be beneficial to the chicks, optimizing their bodies for movement and enhancing their coordination. However, bobwhite quails with shorter lower legs have a smaller base of support and might be less stable than bobwhite quails with longer lower legs. And when the scientists checked the coordination of the bobwhite quail chicks from the warmer incubator, they were astonished by the youngsters’ clumsiness. The team enticed the chicks to walk on a runway towards a speaker playing calls from a mother bobwhite quail and found that chicks incubated at the hot and cold temperatures fell more than 3 times as often as chicks incubated at the optimal temperature. This suggests that egg incubation temperature affects the coordination of hatchlings. The scientists’ suspicions were backed up when they noticed that the stride length of the chicks from the cold incubator were very variable, which suggests poor motor control and increases the risk of them tripping and falling over.

However, many features of the chicks’ walks were not affected by their different starts in life. For example, the speed and average size of their steps did not differ significantly between hatchlings from the optimal- temperature incubator and those from the high- or low-temperature incubators. This study provides evidence that incubation temperature affects bobwhite quail chick motor coordination after hatching. If mama birds do not keep their eggs at the optimal hatching temperature, they might end up with some seriously clumsy chicks.

S. C.
J. P.
Prenatal incubation temperature affects neonatal precocial bird's locomotor behavior
Physiol. Behav.