Data from: Is embryonic hypothermia tolerance common in birds?

Avian incubation temperatures oscillate within narrow limits to insure proper embryonic development. However, field observations and experimental studies have found that some species can tolerate very low incubational temperatures, either regularly or incidentally. We artificially incubated different-sized eggs from five domestic species, which represent most avian egg sizes, to examine if most 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) could hatch successfully after experiencing 10°C hypothermia for six hours each day during incubation. However, embryos of white-rumped munia (Lonchura striata) died after 10 days of hypothermia manipulation. This suggests that hypothermia tolerance may be related to egg size, with embryos of smaller eggs being less tolerant to hypothermia. Also, tolerance to hypothermia may be less late in the incubation periods. Our results showed that unusual hypothermia tolerance occurs in several avian species. This phenomenon might have been selected through the evolutionary history of birds.