Most nests observed in the field were in open situations where they would receive the direct rays of the sun for at least part of the day; the shorter average incubation periods (59 and 70 days, respectively), observed in 1955 and 1956, therefore, more nearly reflect the time of incubation under natural conditions than does the excessively long period (125 days at 75 degrees) observed in 1957 under cooler, more nearly even temperatures. TABLE 1.--The Relationship of Temperature and Duration of Incubation Period as Determined from Laboratory Studies of 49 Eggs of _T. ornata_. =============+===================+=========+========+================= Average | Period of | Number | Number | daily | incubation (Days) | of | of | Remarks temperature |--------+----------|clutches | eggs | (Fahrenheit) | Mean | Range | | | -------------+--------+----------+---------+--------+----------------- | | | | | Wide daily 91 | 59 | 56-64 | 6 | 24 | fluctuations in | | | | | temperature -------------+--------+----------+---------+--------+----------------- | | | | | Wide daily 82 | 70 | 67-73 | 4 | 21 | fluctuations in | | | | | temperature -------------+--------+----------+---------+--------+----------------- | | | | | Temperature 75 | 125 | 124-127 | 2 | 4 | thermostatically | | | | | controlled -------------+--------+----------+---------+--------+----------------- Sixty-five days seems to be a realistic estimate of a typical incubation period under natural conditions; eggs laid in mid-June would hatch by mid-August. Even in years when summer temperatures are much cooler than normal, eggs probably hatch by the end of October. Hatchlings or eggs would have a poor chance of surviving a winter in nests on exposed cut-banks or in other unprotected situations. Overwintering in the nest, hatchlings might survive more often than eggs, since hatchlings could burrow into the walls and floor of the nest cavity. Unsuitable environmental conditions that delay the nesting season and retard the rate of embryonic development may, in some years, be important limiting factors on populations of ornate box turtles.