Page 264 - Hand rearing birds second

252 Hand-Rearing Birds

Figure 15.1 Hatchling Double-crested Cormorant, note closed eyes and egg tooth. Source: photo courtesy
of International Bird Rescue.

Normal clutch sizes range from one to seven eggs, with an average clutch size of four. The eggs
are generally laid every day over a period of several days, but some cormorant species may take 2–3
days between eggs. Both parents sit on the eggs throughout the incubation period, which averages
30 days across cormorant species. The smallest chicks often do not survive due to sibling competi-
tion for food (Dorr et al. 2014); if larger clutches survive, all chicks may experience slower growth
(Hobson 2013).
Cormorants are altricial, hatching without feathers and with eyes closed (Figure 15.1). The
chicks open their eyes approximately 3 days after hatching and take approximately 12–15 days to
grow a wooly coat of down feathers, which remains until approximately 4 weeks of age. Chicks are
typically able to thermoregulate once down growth is complete. They are cared for by their parents
for approximately 6–8 weeks (Wallace and Wallace 1998; Hobson 2013; Dorr et al. 2014). Chicks at
ground‐nesting cormorant colonies may form nurseries or crèches once they are downy and old
enough to venture from the nest. Adults will seek out their own young to feed within a crèche, and
will rebuff chicks that are not their own. Cormorant chicks voluntarily seek out water when their
plumage is complete, generally at 6–7 weeks of age.

­ Criteria­for Intervention

Because of their communal nesting proclivities, nestling and pre‐fledgling cormorant chicks likely
require intervention only if an active colony is devastated or disturbed – for example, by an oil spill,
man‐made interference (e.g. construction), or a weather event. While it is always in a chick’s best
interest to be raised by its parents, lone chicks may require intervention near such urban rookery
sites as bridges, barges, and pier systems.
Intervention by putting healthy, uninjured, orphaned chicks less than 2 weeks of age to foster
with wild adult parents at ground‐nesting colonies may be successful, but care must be taken to
match chick age and not overburden the parents with more than three total chicks or the smallest
will likely starve. As with any wild foster placement, careful observation before, during, and after
introducing chicks to prospective parents is recommended, and fostering should only be considered
if reintroducing the chick will not disrupt the colony.