# Data from: The effect of ambient temperature on bird embryonic development: a comparison between uniparental incubating silver-throated tits and biparental incubating black-throated tits ##### **[Article link: https://doi.org/10.1111/jav.03168](https://doi.org/10.1111/jav.03168)** This dataset (Hu_2023_JAB_Tits_data.xlsx) includes the details of the "nest temperature (°C)", "incubation period length (in days)", "Hatching success", and "nestling body mass (g) & condition" of the silver-throated tits and black-throated tits, which were collected from 2008 to 2022 (except 2020 when COVID-19 pandemic occurred) in the Dongzhai National Nature Reserve of Henan Province, located in central China (31.95 °N, 114.25 °E). It also includes related data about ambient temperature (°C), clutch size, brood size, etc. Nest temperature (Sheet 1): Nest temperature data (°C) were recorded by the temperature loggers. We used temperature data loggers to monitor the nest temperature (i.e. the temperature inside the nest bowl) of the two species for eight years (specifically, from 2008 to 2012 and in 2019, 2021, and 2022). In the earlier years (2008–2010), thermistor probes were directly installed into the centre of the clutches. In the later years (2011, 2012, 2019, 2021, and 2022), the thermistor probe was enclosed in an artificial egg made of paraffin wax (of similar size to the eggs of the real eggs of the studied species) before being placed inside the nest. The temperature loggers were installed into the nests during either the egg-laying period or the incubation stage but were mostly installed on or before the day of clutch completion. The recording intervals of the temperature loggers were mostly set as 1 min, with some exceptions set at 10 s, or at 0.5, 1.5, 2, or 2.5 min. Incubation period length (Sheet 2): Incubation period length (in days) was calculated as the number of days from the day of clutch completion to the day before hatching. Hatching success (Sheet 3): Hatching success was the proportion of hatched eggs relative to clutch size. Nestling data (Sheet 4): Nestling data mainly included the nestlings' body mass (g) and condition. Nestling body condition was calculated as the "scaled mass index" (see Peig and Green 2009 for details) using body mass and tarsus length, which provides a body condition index standardized by body size. ref: Peig, J. and Green, A. J. 2009. New perspectives for estimating body condition from mass/length data: The scaled mass index as an alternative method. – Oikos 118: 1883–1891.

The temperature experienced by avian embryos during development has important impacts on their growth and post-hatching phenotypes. Ambient temperature can directly affect avian nest temperature and indirectly affect it through its impact on parental incubation behaviours. Because the nests of uniparental incubators are usually left unattended more frequently than the nests of biparental incubators whose nests can be attended by another bird when one bird leaves the nest, we predict that the effect of ambient temperature on nest temperature and thus on embryonic development (specifically, incubation period length and hatching success) and post-hatching phenotype (i.e. potential carry-over effect on nestling body mass and condition) should be greater in uniparental incubators than in biparental incubators. To test this prediction, we studied two congeneric species, the biparental incubating black-throated tits (Aegithalos concinnus) and the uniparental incubating silver-throated tits (A. glaucogularis). We found that although the two species’ embryos both developed faster (shorter incubation period length) when ambient temperature was higher, the slope was significantly greater for silver-throated tits than for black-throated tits, consistent with our prediction of a greater effect of ambient temperature on embryonic development in silver-throated tits. However, the result 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. Therefore, it implies a greater response of silver-throated tit embryos to temperature change. In addition, ambient temperature during the incubation stage did not affect either hatching success or nestling body mass and condition in both species. Although our predictions were not fully supported, our findings highlight the different responses of embryonic development to environmental changes between a uniparental incubator and a biparental incubator and suggest further research to explore the mechanisms.