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62 Hand-Rearing Birds

strategy is to remove eggs for artificial incubation at an appropriate humidity and give the parents
dummy eggs, returning their own eggs just before hatching.
For artificially hatched eggs, the humidity in the hatcher should be increased as soon as eggs are
externally pipped in order to limit the drying of shell membranes, which can restrict the embryos’
movement. The amount of humidity needed varies by species, but those eggs with longer pip‐to‐
hatch intervals are at greatest risk of having dry membranes.

Turning
Eggs must be turned at regular, frequent intervals during incubation to facilitate normal mem-
brane development and nutrient uptake and to prevent the embryo from sticking to the inside of
the shell. Chickens turn their eggs every 35 minutes on average, while most incubators with
automatic turning mechanisms turn eggs hourly. Some machines can be set to turn at longer or
shorter intervals, but hourly turning is generally sufficient for nondomestic species. While com-
mercial poultry eggs are set with their air cells uppermost and rotated around the short axis in
order to maximize the number of eggs that will fit in the incubator, nondomestic species are not
adapted to hatch well in this position. They should be set on their sides and rotated around the
long axis. Eggs must be turned in opposite directions each time to prevent rupture of the chala-
zae and should turn through a radius of at least 90°. Supplemental hand‐turning, usually two to
three times daily through ~180° in opposite directions, may improve hatchability, particularly in
large eggs. In machines that do not turn through at least 90°, additional hand‐turning is essential
to ensure completion of the chorioallantoic membrane (CAM). When automatic turning is not
available and eggs are hand‐turned, they must be turned a minimum of five times daily, prefer-
ably more, but always an odd number of times to prevent eggs from being in the same position
overnight every night.

Ventilation

Because embryos are respiring throughout incubation, they are sensitive to abnormal levels of
oxygen and carbon dioxide in the incubator. In most avicultural settings, only a few eggs are incu-
bated at a time so ambient outdoor oxygen and carbon dioxide concentrations are naturally main-
tained in the incubator as long as the hatchery is adequately ventilated. The exception to this is at
high altitude where the oxygen concentration in the air is lower. In that case, testing and supple-
menting oxygen levels in the incubator can increase hatchability. Commercial incubation facilities,
however, must always work to ensure adequate ventilation, especially late in incubation when eggs
are generating high levels of carbon dioxide. During a power failure with incubators containing
large numbers of eggs, opening the incubator for ventilation within an hour becomes more impor-
tant than keeping it closed to conserve heat.

­ Candling

Candling is the primary method for monitoring embryonic development. Excellent photos of can-
dled eggs, healthy and not, at all stages of development are available on the internet (Ernst et al.
2004a) and in published materials (Jordan 1989; Delaney et al. 1999). Many eggs have pigmented
shells that make candling difficult or even of little value later in incubation. It is important to have