DOI: 10.5061/dryad.xksn02vtf
title: Data from: Biparentally incubating Aegithalos concinnus (Black-throated Tit) provide a more stable nest thermal environment than uniparentally incubating A. glaucogularis (Silver-throated Tit)

description: Different parental care modes in birds have been thought to be adaptations
 to different environmental conditions, but their adaptability to
 environments remains underexplored. We predict that the biparentally
 incubating species have a better adaptability to environments than the
 uniparentally incubating species. By comparing two congenic species (the
 uniparentally incubating Silver-throated Tits Aegithalos glaucogularis and
 the biparentally incubating Black-throated Tits A. concinnus) from their
 sympatric populations in central China, we found that Silver-throated Tits
 had shorter on- and off-bouts (i.e., shorter time on and off the nest)
 than Black-throated Tits. When ambient temperature increased, both species
 decreased on-bout duration and increased off-bout duration, but the
 decrease of on-bout duration in Black-throated Tits was to a greater
 degree. Moreover, only Black-throated Tits extended off-bouts after longer
 on-bouts, although both species extended on-bout durations after longer
 off-bouts. In addition, when ambient temperature increased, their daytime
 cumulative nest temperatures increased, whereas nest temperature
 fluctuations decreased. However, despite that their daytime cumulative
 nest temperatures were similar, Silver-throated Tit nests experienced more
 temperature fluctuations. These patterns imply that biparentally
 incubating Black-throated Tits have more flexible strategies in egg care
 and a better ability to maintain a stable nest thermal environment than
 uniparentally incubating Silver-throated Tits. The findings highlight
 different adaptive potentials between biparentally and uniparentally
 incubating birds, shedding light on the evolution of different incubation
 modes in birds.
description: <strong>On-bout duration and off-bout
 duration</strong> Whenever accessible, nests at
 the incubation stage were filmed to observe parental incubation behaviors.
 For the nests involved in this study, they were filmed 1-4 times according
 to field workload and need in the years between 2009 and 2016, and were
 filmed once or twice on the 4th/5th day and/or the 9th/10th day of
 incubation during the years between 2017 and 2019. Cameras were mounted on
 tripods placed at least 0.5 m from the nests. Each video recording lasted
 for an average of 125 ± 45 min (mean ± SD, n = 252 video
 records). Data of on- and off-bout durations (i.e.,
 time on and off the nest) of both species were obtained from the videos,
 including a total of 2551.2 h from 245 ST nests and 2059.8 h from 213 BT
 nests. Through the videos, we recorded the incubating bird’s identity (by
 color rings) and calculated the duration of each on- and off-bout. The
 final data set contained 343 on-bouts (n = 115 nests) and 344 off-bouts (n
 = 115 nests) of STs, and 103 on-bouts (n = 52 nests) and 103 off-bouts (n
 = 52 nests) of BTs. We did not use the temperature logger data for this
 analysis because although using temperature change to identify the on- and
 off-bouts was feasible for the uniparentally incubating ST, it was not for
 biparentally incubating BT as the time interval between one parent’s
 leaving and another’s entering the nest was often short and could not be
 accurately identified from the temperature logger data.
 <strong>Nest temperature</strong>
 We monitored the nest temperatures with the temperature logger
 Lexiang GSP958 (accuracy ± 0.5 °C; Lexiang Electronics Co. Ltd, China) in
 2019, 2021, and 2022. Temperature loggers were usually (in 60 out of 99
 nests) installed between the day when at least three eggs were laid and
 the first day of incubation and were collected until nest failure or after
 nestling hatching. The mean (± SD) number of days that the loggers were
 left in the nests during the incubation stage were 7.75 (± 2.45) days
 (range 2 ~ 13 days). The thermistor was wrapped in an artificial egg that
 was made of paraffin and similar in size to the natural eggs of the two
 species before being placed into the nests. The recording intervals of the
 temperature loggers were set as 1 min. Due to unknown technical reasons of
 the loggers, the temperature data occasionally showed abnormal values at
 certain specific temperatures (e.g., ~11.9 °C and ~31.8 °C), which can be
 identified through an abrupt drop in temperature that differed from a
 normal curve of temperature drop during an off-bout. In such cases, we
 replaced the abnormal values using values calculated by averaging the
 temperatures 1 min before and after the abnormal values.
 As the two species’ incubation behaviors mainly differ during the
 daytime, we focused our analyses on the effects of daytime ambient
 temperature on nest temperature. According to the nest temperature data,
 we found that among all ST nests, the latest time when the birds left
 nests after nighttime incubation in the morning and the earliest time that
 they returned to nests for nighttime incubation in the afternoon were 7:50
 and 16:44, respectively. The latest time when the birds left nests in the
 morning (7:50) was determined by a criterion of an off-bout’s continuous
 temperature drop of ≥ 1 °C lasting for ≥ 9 min, which was obtained by
 matching the temperature logger data to corresponding video data at ST
 nests where they were both available (n = 15 nests and 95.1 h). The
 earliest time that the birds returned to nests for nighttime incubation in
 the afternoon (16:44) was determined by a continuous temperature increase
 following an off-bout, after which the temperature remained relatively
 stable and no off-bout could be identified based on the off-bout
 criterion. We thus defined daytime for STs as 8:00–16:30 to enable
 comparison of temperature across nests, because by choosing this period,
 all birds in the analyses were during the period of daytime incubation. As
 it was hard to accurately identify BTs’ off-bouts from the temperature
 logger data, we were unable to determine their latest time when they left
 nests in the morning and the earliest time that they returned to nests for
 nighttime incubation. We therefore assumed their daytime period to be the
 same as STs (i.e., 8:00–16:30). In total, nest
 temperature data from 298 nest days of 35 ST nests and 469 nest days of 64
 BT nests were available for the analyses after excluding those that could
 not be used (i.e., data did not reflect incubation rhythm but fluctuations
 of ambient temperature) and when there were knowable disturbances (e.g.,
 checking nest, filming nest and capturing parents). The effects of ambient
 temperature on daytime nest temperature were analyzed in two aspects,
 including cumulative temperature and temperature fluctuations. Cumulative
 nest temperature was calculated as daytime average nest temperature × 8.5
 h (8:00–16:30). Nest temperature fluctuations, which reflected the
 stability of nest temperature, were calculated as the number of times when
 nest temperature continuously dropped by ≥ 1 °C (a minimum temperature
 drop of an off-bout confirmed by videos), followed by an increase of ≥ 1
 °C.
description: # [Data from:
 ](https://datadryad.org/dataset/doi:10.5061/dryad.18931zd8c)Biparentally
 incubating *Aegithalos concinnus* (Black-throated Tit) provide a more
 stable nest thermal environment than uniparentally incubating *A.
 glaucogularis* (Silver-throated Tit) Dataset DOI:
 [10.5061/dryad.xksn02vtf](10.5061/dryad.xksn02vtf) ## Description of the
 data and file structure This dataset include the details of the “On-bout
 duration (min)”, “Off-bout duration (min)”, and “Nest temperature (°C)” of
 the Silver-throated Tits and Black-throated Tits, which were collected
 from 2009 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, such as
 ambient temperature (°C), clutch size, and lay date (in days), among
 others. **On-bout duration** * Nest_ID: Nest ID * Adult_ID: Incubating
 adults' ID * Sex: Incubating adults' sex *
 Species: Silver-throated Tit or Black-throated Tit * Year: Research year *
 Lay_date: First-egg laid date of each nest * Clutch_size: Clutch size of
 each nest * Day_of_incubation: Day of incubation for each nest (in days) *
 Filming_length: video length for each incubation behavior recording (min)
 * Ambient_temperature: mean ambient temperature during each on-bout
 duration (°C) * On-bout_duration: time length that adults on the nest of
 each bout (min) * Prior_off-bout_duration: time length that adults are off
 the nest before each on-bout (min) * Feeding: Whether the male ST fed the
 female ST during each on-bout (Y: yes, N: no). **Off-bout duration** *
 Nest_ID: Nest ID * Adult_ID: Incubating adults' ID * Sex: Incubating
 adults' sex * Species: Silver-throated Tit or Black-throated Tit *
 Year: Research year * Lay_date: First-egg laid date of each nest *
 Clutch_size: Clutch size of each nest * Day_of_incubation: Day of
 incubation for each nest (in days) * Filming_length: video length for each
 incubation behavior recording (min) * Ambient_temperature: mean ambient
 temperature during each off-bout duration (°C) * Off-bout_duration: time
 length that adults off the nest of each bout (min) *
 Prior_on-bout_duration: time length that adults are on the nest before
 each off-bout (min) * Feeding: Whether the male ST fed the female ST
 during each prior on-bout (Y: yes, N: no). **Nest temperature** * Nest_ID:
 Nest ID * Species: Silver-throated Tit or Black-throated Tit * Year:
 Research year * Lay_date: First-egg laid date of each nest *
 Clutch_size: Clutch size of each nest * Day_of_incubation: Day of
 incubation for each nest (in days) * Ambient_temperature: daytime average
 ambient temperature during 8:00–16:30 (°C) *
 Nest_temperature_fluctuations: the number of times when nest temperature
 continuously dropped by ≥ 1 °C, followed by an increase of ≥ 1 °C *
 Cumulative_nest_temperature/1000: daytime average nest temperature × 8.5 h
 (8:00–16:30) (°C) * Mean_egg_mass: averaged clutch mass of each nest (g)