Scrambling Eggs' Incubating Temperatures

New research indicates that climate change may affect the development of embryos in birds' eggs, especially if the birds live in a hot climate.

A team of scientists at Australia's Macquarie University studied the effects of warming atmospheric temperatures on in-the-egg development of wild Zebra Finches, Taeniopygia guttata (yes, we're discussing Zebra Finches again).    In the wild, the Zebra Finch breeds in arid and semi-arid regions throughout Australia where atmospheric temperatures regularly exceed 96.8◦F. Like all birds, Zebra Finches can lay only one egg per day. They don't start incubating them until the clutch is complete, which takes about five days.

All the eggs are incubated equally, and they tend to hatch on the same day. Why does this matter? Because the chicks who hatch first grow big first, depriving their smaller siblings of resources. 

The Australian research team suspected that warm temperatures might cause problems during the egg-laying, pre-incubation stage. If the ambient temperature were to become warm enough for eggs to develop even without an adult sitting on them, the earliest-laid eggs would hatch earliest.  They were also concerned that Zebra Finches might be reaching the upper edge of their tolerance for high temperatures--in other words, that heated eggs might not hatch at all.

To test the prediction that warmer nest temperatures trigger early development, the team set up “hot” and “cool” experimental nest chambers. Thirty-three eggs from eight clutches were removed from their parents' nests on the day they were laid and placed into one of the four chambers. They were kept cool or warm while their sibling eggs were laid, then returned to their parents, who incubated the entire clutch until hatching. 

All the experimentally treated eggs hatched following their return to the parental nest, no matter how they had been treated--that's the good news: even the "hot" eggs survived. Overall, the average developmental time was 13 days — shorter for eggs that had been placed in the “hot” nest chambers. Also, as predicted, the eggs laid early in the laying sequence developed and hatched sooner.

Now the bad news: the time to hatching was similar for eggs placed in either the natural nest chambers or in the nest-box nest chambers--just 13 days, when 14 days had been expected. In other words, even though the heat-treated eggs hatched first, ALL the nests were "hot" enough to hatch fast.

What does this mean? That the nests of birds in hot climates are already affected by climate change, and they might suffer more if temperatures increase.