Gestation length

This is the length of time of active foetal growth from fertilization to birth. However this is often poorly recorded and different defintions are used for eutherian and metatherian
mammals. Therefore, this data type has three specialized drop down lists: ‘Start Point’, ‘End Point’ and ‘Growth Type’. Additionally, ‘Date of Birth’should be recorded as precisely as possible; if only month or season are reported then record this information.

Gestation Start Point

• Unspecified
• First observed copulation
• Fertilization
• Birth (marsupials only)
• Implantation
• Palpably pregnant
• Capture (pregnant female caught and kept until she gives birth)
• Laying (monotremes only)

Gestation End Point

• Unspecified
• Fertilization
• Implantation
• Palpably pregnant
• Birth
• End of obligate teat attachment (marsupials only)
• First pouch emergence (marsupials only)
• Permanent exit from pouch (marsupials only)
• Hatching (monotremes only)

Gestation Growth Type

• Active — used only to indicate periods that are reported to entirely consist of active foetal growth.
• Inactive — used only to indicate periods that are reported to have no active foetal development.
• Uncertain — used when a source reports that some of the time period recorded as gestation length includes a period of delay but not when this occurs or for how long.
• Unspecified — used when a source does not record whether foetal growth is known to be active throughout the specified gestation length.

These options can be used to accurately record how a source measures gestation length.
Typically, this will only involve one data point, e.g. 23 days /First observed copulation/ Birth/ Unspecified

However if reproductive delay is reported then separate entries should be made detailing the timespan of periods of active and inactive growth,
e.g. 12 days/ First observed copulation/ Implantation/ Inactive
23 days/ Implantation/ Birth/ Active

If there is more than one pregnancy during the same breeding season (using the same definitions) then the gestation lengths should be averaged.

Generic value types: Data Value, Data Range, Measure, Sample Size, Captivity Status, Units and Source Type.