Within minutes of hatching, Japanese quail (Coturnix japonica) chicks are up and about, pecking around for their first snack. However, these independent youngsters aren't entirely self-sufficient. Unable to generate their own body heat, tiny newly hatched chicks still depend on their parents for warmth. ‘Chicks that feed themselves from the first day of life alternate finding food with being warmed up by mum to avoid their body temperature dropping dangerously low’, says Andreas Nord from Lund University, Sweden. And the smaller the chicks, the more they need their parents’ warmth. In addition, Nord and Jan-Åke Nilsson, also from Lund University, knew that the size of the chicks when they hatch depends on the amount of warmth provided by their parents during incubation; even the most devoted quail parents don't spend the entire time brooding. This made the scientists wonder how much of an effect the warmth provided by incubating parents has on the amount of time their hatchlings can spend foraging before returning to warm up.

Incubating quail eggs at temperatures ranging from a cool 35.5°C to a toasty 38.5°C, Nord recorded that the chicks from the warmest eggs hatched after 16 days, while it took the youngsters from the coolest eggs more than 19.5 days to emerge. After collecting the youngsters and transferring them to a cosy pen, complete with heat lamp instead of parents, Nord simulated the effects of the youngsters wandering off at 1 day of age by placing them in a cooler chamber (20°C) for 10 min and checking the youngsters’ body temperature before and after their chilly outing. Repeating the process each day until the chicks were capable of generating enough heat to keep warm (7 days), it was clear that the smallest chicks that had been incubated at the lowest temperature were at a disadvantage when venturing off alone. They lost more heat than the larger chicks that had been incubated at warmer temperatures and they lost it faster.

The chicks’ chillier start might put them at a disadvantage relative to those whose attentive parents kept their eggs warm during incubation. ‘If you have to feed yourself, but are not as good at keeping the fire burning when you do, you probably can't spend as long away from mum's warmth. This means you will find less food than your warmer siblings – a bad start for which you may have to pay a price later’, says Nord.

Low incubation temperature slows the development of cold tolerance in a precocial bird
J. Exp. Biol