Unusual incubation behavior and embryonic tolerance of hypothermia in the Sichuan Partridge ( Arborophila rufipectus )

Incubation is an energetically demanding phase of avian reproduction. Single-sex incubators are often faced with a direct conflict between incubation and foraging. We report an unusual incubation behavior of the Sichuan Partridge (Arborophila rufipectus), with long recesses of females and embryonic hypothermia, at Laojunshan National Nature Reserve, southwest China. The Sichuan Partridge is a globally endangered species that inhabits subtropical evergreen and deciduous broadleaf forests at 1100–2250 m a.s.l. Female Sichuan Partridges incubated eggs alone, and typically took one long incubation recess of 4.5 ± 1.2 h (mean ± SD) day−1. They left the nests at 7:36 a.m. (±50 min) and returned at 12:06 p.m. (±70 min). Nest attentiveness was 81.2 ± 5.2% of the entire incubation period. Females prolonged the recess duration and decreased nest attentiveness significantly in response to high disturbance risk and bad weather. Although eggs experienced ~4.2 h below 26 °C (the physiological zero temperature) for each recess, the total hatching rate was 88.4%, suggesting that embryonic hypothermia had minimal negative effect on the hatching rate. For Sichuan Partridge, the ability to withstand embryonic hypothermia may be an adaptation to cold montane environments.