Is embryonic hypothermia tolerance common in birds?

Avian incubation temperatures oscillate within narrow limits to ensure proper embryonic development. However, field observations and experimental studies have found that some species can tolerate very low incubation temperatures, either regularly or occasionally. We artificially incubated eggs from five domestic species, which represent a range of egg sizes, to examine whether a diversity of avian species could exhibit an unusual hypothermia tolerance, as observed in the field. We found that eggs of the chicken (Gallus gallus domesticus ), pigeon (Columba livia domestica ), Japanese quail (Coturnix japonica ) and budgerigar (Melopsittacus undulatus ) survived the incubation period and hatched after experiencing 10°C hypothermia for 6 h each day. However, embryos of white-rumped munia (Lonchura striata ) died after 10 days of hypothermia. Our results showed that unusual hypothermia tolerance occurs in several avian species. This phenomenon might have been selected through the evolutionary history of birds. Future research should identify the importance of phylogeny, egg size and embryonic stage in tolerance to hypothermia.