Avian incubation provides an opportunity to test how parental behavior and ecological conditions interact to shape variation in offspring traits along geographic gradients. In particular, the duration of the incubation period is shorter at higher latitudes, but the degree to which this pattern arises from genetic divergence in rates of growth and development versus from parentally-mediated variation in egg temperatures is controversial. At higher latitudes parents have higher daytime incubation attentiveness, i.e., they spend a greater proportion of the day on the nest. However, interpreting latitudinal variation in behavior is complicated by latitudinal patterns in ambient temperature and day length. Here, we use 24-hour video recordings to compare the incubation behavior of orange-crowned warblers (Leiothlypis celata) in California and Alaska and test how attentiveness varies between populations and as a function of temperature. Birds in Alaska had higher nest attentiveness during the day, despite experiencing similar ambient temperatures. However, when analyzed over 24-hours, the longer nighttime period in California almost entirely canceled out daytime attentiveness differences between populations, and differences in 24-hour attentiveness were small. Our work highlights how incorporating nighttime incubation behavior qualitatively alters latitudinal patterns of attentiveness, and how lower ambient temperatures cannot account for the higher attentiveness in a high latitude population. These populations differ in their incubation period lengths, and differentiating between evolved versus environmentally-induced variation in offspring growth and development will help understand the fitness consequences of variation in developmental periods.

Data collection details are described in the associated publication (Sofaer et al. Journal of Avian Biology). Data are based on video recordings of orange-crowned warbler (Leiothlypis celata) incubation behavior, and observations of incubation period length. The data on nest attentiveness are summarized from the on and off bout data.

Definitions of data columns:

OCWA_OnOffBouts.csv: This file contains on and off bout data transcribed from video recordings, and associated hourly temperature from nearby weather stations.

• Pop: AK or CA, corresponding to Alaska or California
• NestID: nest identity
• OnDate: date of start of on-bout; format is m/d/yyyy
• OffDate: date of end of on-bout; format is m/d/yyyy
• IncStartTime: time at start of on-bout; format is hh:mm:ss
• IncEndTime: time at end of on-bout; format is hh:mm:ss
• ExcludeON: binary; has value of 1 if on-bout duration should be excluded from analyses (e.g., because incomplete)
• ExcludeOFF: binary; has value of 1 if off-bout duration should be excluded from analyses (e.g., because incomplete)
• NOTES: description of any uncertinaty in video observation or other notes
• Overnight: binary; 1 if the on and off times correspond to an overnight period
• OnMin: duration of on-bout (min.)
• OffMin: duration of off-bout (min.)
• StartHour: integer hour of on-bout start time
• TempC_mean: mean temperature (degrees C) during the hour starting at StartHour
• TempC_max: maximum temperature (degrees C) during the hour starting at StartHour
• TempC_min: minimum temperature (degrees C) during the hour starting at StartHour
• Precip_mm: total precipitation (mm) recorded during the hour starting at StartHour

OCWA_DaytimeAtten.csv: This file contains hourly nest attentiveness during active hours (i.e., excluding the overnight period) and associated weather.

• Pop: AK or CA, corresponding to Alaska or California
• NestID: nest identity
• Date: date of observation; format is m/d/yyyy
• StartHour: integer hour over which atteniveness is summarized
• Atten.min: number of minites on the nest during that hour (maximum of 60)
• TempC_mean: mean temperature (degrees C) during the hour starting at StartHour
• TempC_max: maximum temperature (degrees C) during the hour starting at StartHour
• TempC_min: minimum temperature (degrees C) during the hour starting at StartHour
• Precip_mm: total precipitation (mm) recorded during the hour starting at StartHour

OCWA_IncPeriod.csv: Incubation period duration data

• Pop: AK or CA, corresponding to Alaska or California
• NestID: nest identity
• NumEggs: number of eggs observed in nest
• NumHatched: number of young hatched
• clutch_yearday: day of year of clutch completion date
• hatch_yearday: day of year of first egg hatching
• IncLength: duration of incubation period (number of days)