Parental care and bird embryonic metabolism: A comparison between uniparentally incubating silver-throated tits and biparentally incubating black-throated tits

Studies have shown that organisms may adjust metabolic rates in response to thermal variability, highlighting metabolic plasticity as a key adaptive mechanism. Understanding the extent of metabolic plasticity of an organism is key to predicting its adaptation to climate change. In birds, the embryos from the uniparentally incubating species are more frequently exposed to intermittent cooling due to the parents’ repeated absences from the nest than the embryos from the species with biparental incubation. Such pressure may favour them to evolve a better ability to cope with the physiologically suppressive effects of low temperatures and temperature fluctuations. We compared embryonic heart rate, a proxy for embryonic metabolic rate, and its response to egg temperature change between two closely-related species, the biparentally incubating Black-throated Tit (Aegithalos concinnus) and the uniparentally incubating Silver-throated Tit (A. glaucogularis). We also conducted an interspecific eg..., Research species and fieldwork
This study was conducted in Zhanglou Village of Luoshan County, which is near the Dongzhai National Nature Reserve of Henan Province, China (31.95° N, 114.25° E). The two species, Black-throated Tit and Silver-throated Tit, occur sympatrically in this region and breed synchronously. They typically begin nest-building in late January or early February. Their nests are dome-shaped and similar in size, although slightly different in outer-layer nest materials (Li et al., 2012). Egg-laying generally starts in late February or early March, with one egg laid per day. Clutch sizes typically range from 4 to 8 eggs in Black-throated Tits and 5 to 9 eggs in Silver-throated Tits (Hu et al., 2024), with both species most frequently laying 7-egg clutches (Li et al., 2012). The average egg mass (mean ± SE) of Silver-throated Tits (0.85 ± 0.01 g) is heavier than that of Black-throated Tits (0.72 ± 0.01 g) (Li et al., 2012).
Both species usually initiate incubation on the..., # Data from: Parental care and bird embryonic metabolism: A comparison between uniparentally incubating silver-throated tits and biparentally incubating black-throated tits

Dataset DOI: [10.5061/dryad.9w0vt4bvs](https://doi.org/10.5061/dryad.9w0vt4bvs)

## Description of the data and file structure

Dataset DOI: [10.5061/dryad.9w0vt4bvs](https://doi.org/10.5061/dryad.9w0vt4bvs)

### Files and variables

**File: Hu_et_al_2026_Functional_Ecology_EHR_data.csv**

##### Variables

* NestID: Nest ID for each nest.
* EggID: Egg ID for each egg.
* EggType: Black-throated Tits’ not-fostered eggs (BTN), Black-throated Tits’ fostered eggs (BTY), Silver-throated Tits’ not-fostered eggs (STN), and Silver-throated Tits’ fostered eggs (STY), with fostered eggs meaning those incubated by another species (see Table 2 for sample sizes).
* Year: Research years.
* Species: Black-thoated Ti (BT) and Silver-thorated Tit (ST).
* AdultID: Adult ID for each nest.
* Treatment: Not-fostered eggs (N) and fostered...,