by Piter Kehoma Boll
The zebra finch, Taeniopygia guttata, is an Australian bird that is often used as a model for behavioral studies focused on their vocalization.
Recently, a research team from Australia discovered a new call in this species and named it “incubation call”. This particular vocalization was identified as occurring during the last five days of incubation when one of the birds, either the male or the female, was alone with the eggs, and only when temperatures were above 26°C. This raised the hypothesis that this call is used by the parents to communicate to the embryos that the environmental temperature is high and that this information would be used by the nestlings to adapt their behavior and metabolism to higher temperatures.
An experimental study was conducted where eggs were kept in incubators under a constant temperature and exposed (test) or not (control) to recorded incubation calls. The results indicated that nestlings that were exposed to incubation calls grew faster in high temperatures than those that were not exposed to the calls. The mean difference in nestling mass between different temperatures and treatments was of about 2 g only, although the difference in mass between two randomly selected nestlings could be as much as 6 g. Additionally, the R² value of the analyses, which tells how much of the variation is explained by the measured variable, was only 0.1, i.e., temperature explained only 10% of the growth differences between different temperatures in both treatments.
One of the most intriguing aspects, however, was the fact that the incubation call was produced at temperatures as low as 26°C, which is not particularly hot in the natural environment of the zebra finch. Thus, another team conducted new studies to understand better how and when the “incubation call” was produced. They decided to rename this call as the “v-call” because their shape is an inverted V in spectrograms. They discovered that the v-call is related to panting, when the birds breathes quickly with its bill open to help reduce body temperature and is likely a side effect of panting and not a deliberate directed call. It is also not produced only during the last 5 days of incubation, but during the whole incubation period and the chick rearing, and some birds are more likely to v-call than others. The results suggest that the v-call is unlikely to have evolved as an incubation call and is more likely a side effect of panting. There is, however, the possibility that embryos can use this information to modulate their growth, although more studies are needed.
Other recent studies with the zebra finch indicate that elevated temperatures can have negative effects on the bird’s reproductive fitness. Temperatures around 40°C reduce sperm quality in male zebra finches and reduce the ability of females to discriminate between songs produced by males of the same species and males of different, distantly related species. A combination of these two effects can lead to a severe decrease in reproductive success by reducing the mating events and reducing sperm ability to fertilize eggs.
A physiological modulation in embryos to deal with the adverse effects of higher temperatures, as suggested by the use of the v-calls, would be certainly benefitial. Maybe this is a behavior still under selection? Let’s see what further studies tell us.
– – –
Coomes CM, Danner RM, Derryberry EP (2019) Elevated temperatures reduce discrimination between conspecific and heterospecific sexual signals. Animal Behavior 147: 9–15. https://doi.org/10.1016/j.anbehav.2018.10.024
Hurley LL, McDiarmid CS, Friesen CR, Griffih SC, Rowe M (2018) Experimental heatwaves negatively impact sperm quality in the zebra finch. Proceedings of the Royal Society B: Biological Sciences 285(1871): 20172547. https://doi.org/10.1098/rspb.2017.2547
Mariette MM, Buchanan KL (2016) Prenatal acoustic communication programs offspring for high posthatching temperatures in a songbird. Science 353(6301): 812–814. https://doi.org/10.1126/science.aaf7049
McDiarmid CS, Naguib M, Griffith SC (2018) Calling in the heat: the zebra finch “incubation call” depends on heat but not reproductive stage. Behavioral Ecology 29(6): 1245–1254. https://doi.org/10.1093/beheco/ary123
– – –
* This work is licensed under a Creative Commons Attribution-Share Alike 2.0 Generic License.