Uniparental versus biparental incubation and embryonic development in tits

Submitted by Michi on 23 January 2024.

Text by Jianqiang Li

This blogpost is based on the article by Hu et al. about the effects of ambient temperature on embryonic development between biparental incubating black-throated tits and uniparental incubating silver-throated tits.

The temperature experienced by bird embryos is a crucial factor that can shape their growth and the traits they exhibit after hatching. Ambient temperature can affect nest temperature, which directly affects the eggs inside the nest. Ambient temperature can also affect the behaviours of the incubating birds and then indirectly affect the temperature that the eggs experience. The vast majority of bird species are either uniparental incubating where only one parent attends incubation, or biparental incubating where both parents take turns to incubate. As the nests of uniparental incubators are usually left unattended more frequently than the nests of biparental incubators, the effect of ambient temperature on nest temperature and thus on embryonic development and post-hatching phenotype should be greater in uniparental incubators than in biparental incubators. However, this has rarely been investigated in existing studies.

                  Habitat at the study site (Photo: Jianqiang Li).

Our study tested this idea with two congeneric species, the biparental incubating black-throated tits (Aegithalos concinnus) and the uniparental incubating silver-throated tits (A. glaucogularis). Black-throated tits and silver-throated tits are sympatric distributed at our study site in the Dongzhai National Nature Reserve in Henan Province, China, providing an opportunity to study them simultaneously under similar environmental conditions. Using data collected from 2008 to 2022, we compared the effects of ambient temperatures during the incubation period on their nest temperature, incubation period length and hatching success as well as nestling body mass and condition.

                       A black-throated-tit incubating eggs in the nest (Photo: Jiayu Zhang).

We found a negative relationship between incubation period length and ambient temperature in both species, indicating that their embryos developed faster in warmer weather. Moreover, the slope of the relationship between incubation period length and ambient temperature was significantly greater for uniparental incubating silver-throated tits than for biparental incubating black-throated tits. This implied a greater effect of ambient temperature on embryonic development in silver-throated tits, which appeared consistent with the expectation. However, we found this phenomenon was not due to a greater effect of ambient temperature on nest temperature because nest temperatures of the two species had positive relationships with ambient temperature in a similar way. Rather, it suggests a greater response of silver-throated tit embryos to temperature change.

​                       A silver-throated-tit incubating eggs in the nest (Photo: Jiayu Zhang).

In addition, we did not find any effects of the temperature during the incubation period on the two species’ hatching success or nestling body mass and condition.

                        The researchers measuring the nestlings. (Photo: Juanjuan Wang)

Our findings highlight the complex interplay among parental incubation behaviours, embryonic development and environmental factors in birds, and have important implications for our understanding of how birds respond and adapt to changing environments.

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