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.

How Zebra Finches Choose their Valentines

Like many birds, Zebra Finches tend to pair up and stay paired. However, how they choose their mates is a bit of a mystery. 

Whereas many animals choose their mates for certain physical traits, Zebra Finches don't seem to do so. Malika Ihle and her colleagues at the Max Planck Institute for Ornithology, in Seewiesen, Germany recently published their research into what makes Zebra Finches pair up. 

The studied 160 single Zebra Finches, allowing groups of 20 males and 20 females in an aviary to become acquainted with one another. Grooming is a sign of Zebra Finch courtship, so when pairs started grooming each other, the researchers knew that those birds were capable of pairing. They let half the couples stay together. The other half they divided into "arranged marriages." They caged all the pairs for a few months so they could develop relationships, then released them into a group aviary to raise their families. 

Over the following five months, the researchers observed as the pairs went through three breeding cycles. Then they repeated the experiment, this time allowing only one third of the birds to stay with their mates. 

The results? Couples who had chosen each other had 37% more surviving young than those who had not. Forced couples produced more unfertilized eggs, lost more eggs, and had more chicks die after hatching. Females in forced pairs were not as interested in mating as those who had chosen mates. Males in forced pairs were less interested in caring for chicks and more interested in mating with other females. 

Dr Ihle and her colleagues say that, if the finches were choosing mates for genetic reasons, more embryos would have died from defects caused by interbreeding between such a limited selection of partners. However, the difference in the survival of chicks appeared to depend on how well they were cared for by their parents. The researchers argue that the results they saw indicate that Zebra Finches select their mates based on how well they get along. We here at Talkin' Birds don't think that's a bad way to choose. 



Zebra Finch Pairs Seem to Discuss Child-Rearing Inequalities

Like humans, some bird species mate for life and rear chicks together. But do they squabble like we do when one partner seems to be slacking off? The answer seems to be yes.

A forthcoming article in the Biological Journal of the Linnean Society describes research on vocalizations between Zebra Finch mates (Taeniopygia guttata) when they're incubating eggs. Zebra Finch couples share all chick-rearing responsibilities, including sitting on the nest before the chicks hatch. They sit in shifts about a half-hour long; while one sits, the other goes in search of food. When it's time to change shifts, the finches have what sounds like a conversation. Researchers were curious about whether this finch-to-finch conversation would change if one spouse were late returning to the nest for his or her turn. 

Working with twelve pairs of Zebra Finches incubating eggs in a large aviary, researchers trapped the male of each pair at the beginning of a foraging shift and detained him for an entire hour. Remember, his spouse was home on the nest, expecting him to return in a half hour. She did not leave the nest while waiting. Instead, she and the male had a, um, rapid conversation when he finally returned, vocalizing at each other faster than usual. (We imagine a heated argument.)

Are you wondering whether a female took extra time away from the nest if her spouse came back late? The answer: only if the male didn't talk with her much. If the late-arriving male initiated only a short conversation, the female would fly off for up to an hour. However, if the male took the time to "talk" longer with the female, she'd come back in 30 minutes. In other words, it looked as if the female got back at the male only if both spouses did not talk long enough to sort things out. 

No word on what the unhatched chicks thought about these delayed arrivals and arguments. Perhaps a next-generation study is in order.