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(see Chapter 3). Eggs from this species, particularly from older females, may have difficulty losing
sufficient weight even in a dry incubator running at 30% RH or less. If left under the incubating
parent for 7–14 days before being removed for artificial incubation, such eggs usually establish an
appropriate weight loss trend that can be maintained in the incubator with sufficient care. Rarely,
eggs that have not received parental incubation or otherwise do not lose sufficient weight may
require drastic measures such as sanding or drilling a small hole in the shell over the air cell. In
addition to machine turning every 2 hours, eggs are hand turned through ~180° twice daily in
opposite directions to ensure optimal membrane development.
Signs the hatching process has begun may be observed on candling as early as day 49 but more
typically on day 50–51 with the air cell beginning to draw down. Between this stage and the inter-
nal pip, the egg is transferred to a separate hatcher set at 97.5 °F (36.4 °C) and 50% RH and is no
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longer turned. It is important to use a soft but nonslip substrate, such as Grip Liner (Con-Tact ), to
prevent abrasions and leg splaying after hatching. Internal pip usually occurs on day 53 and exter-
nal pip on day 54. Once the egg is externally pipped, humidity is increased to 80% RH or more to
prevent the shell membranes and extraembryonic membranes from drying out during the pro-
tracted hatching process. Hatching usually occurs on day 57. Healthy self-hatches have occurred in
as little as 45 hours after external pip or as long as 96 hours. Condor eggs are easily candled, which
facilitates frequent monitoring during the entire hatching process at intervals of 2–6 hours depend-
ing on the stage and progress of the egg. Chorioallantoic vessels can be seen gradually receding and
yellowing. Unlike most bird species, California Condor embryos typically defecate in the shell
shortly before hatching. The small amount of dark green feces may also be visible on candling and,
along with absence of active vessels, is a good indicator that hatching should be imminent. The
embryo will respond to tapping and vocalization as it would to the parent during this stage. This
can encourage the embryo to make progress toward hatching. Embryos that do not make sufficient
progress at this stage may require assistance.
Andean Condor eggs are also incubated at 98.0 °F (36.7 °C) and started at 45–55% RH; and
hatched at 97.5 °F (36.4 °C) and 70% RH. Because this species has been reared at many different
facilities, incubation temperatures of 97.5–99.5 °F (36.4–37.5 °C) have been used with success, but
incubating at 98.0 °F (36.7 °C) gives the most consistently healthy hatches. Their incubation term
is 60 days ±2 days with a similar pattern of internal pip 4 days prior to hatching and external pip 3
days prior. The incubation term for eggs from specific females is usually consistent from egg to egg.
In other words, a female whose egg hatches at 59 days of incubation will likely have future eggs
that hatch on day 59.
King Vulture eggs are incubated at 98.5 °F (36.9 °C) and started at 50–60% RH and hatched at
98.0 °F (36.7 °C) and 70% RH. Their incubation term is 55 days ±1 day with a similar pattern of
internal pip 4 days prior to hatching and external pip 3 days prior. Both Andean Condor and King
Vulture eggs are also easily candled.
Eggs of Gyps species, as well as those of other large Accipitrid vultures (Red-headed, Cinereous,
Bearded, Lappet-faced, and White-headed), are incubated at 98.5 °F (36.9 °C) and started at 45–55%
RH and hatched at 98.0 °F (36.7 °C) and 70% RH. Their incubation term is 54–56 days, depending
on species, ±1 day, with a similar pattern of internal pip 4 days prior to hatching and external pip 3
days prior. Accipitrid vulture eggs, like all eggs from species in this family, are difficult to candle.
Gyps vulture eggs are white-shelled and typically unmarked, so early embryonic development can
be readily observed, although this will appear less distinct than in Cathartid eggs. By ¼–⅓ of incu-
bation, the progression of the chorioallantoic membrane lining the inside of the shell will make the
egg virtually opaque below the air cell. It is difficult to assess viability after this. One method, for
eggs past mid-incubation, is to place the egg on a hard, flat surface, guarding it carefully to prevent