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254 Hand-Rearing Birds

Metabolic­Bone­Disease­(MBD)
Metabolic bone disease (MBD) (secondary nutritional hyperparathyroidism) is caused by an imbal-
ance of calcium, phosphorus, and vitamin D 3 . In growing birds, MBD, which typically manifests as
a malformation of growing long bones, is almost always caused by a deficiency of dietary calcium
during the rapid growth phase. Once a bird is identified as having MBD (i.e. bones palpate soft or
rubbery, bird has trouble standing when old enough to do so, folding fractures are found on radio-
graphs), it is considered to be a medical patient whose bones and ambulation need to be closely
monitored and whose diet needs to be re‐assessed. Administration of additional amounts of cal-
cium or a vitamin D supplement may be needed. Some fish species used to feed piscivores in cap-
tivity have been found to have low calcium to phosphorus ratios (McRoberts Fish Company,
unpubl. data) and/or to be deficient in vitamin D 3 (Hoopes and Clauss 2016). There is a likely role
of contaminants such as mercury and PCBs in the development of skeletal abnormalities (Ludwig
et al. 1996).

Aspergillosis

Cormorants, like many seabirds, are susceptible to aspergillosis, an infection caused by Aspergillus
fumigatus, a ubiquitous fungus found in decomposing organic matter. Aspergillosis is caused by
fungal spores invading the respiratory system of immune‐compromised animals, including those
suffering from another illness, malnutrition, or stress. Diagnosis is commonly achieved at nec-
ropsy, although symptoms include anorexia, labored breathing, depressed activity, reduced preen-
ing, and chronic anemia. Healthy cormorant chicks are typically not treated prophylactically with
antifungal medication, but if a chick is being treated with other medications, such as antibiotics for
a wound, addition of an antifungal (such as itraconazole or voriconazole) is prudent.

Disease
Some geographic areas may see fledgling Double‐crested Cormorants presented for care with neu-
rologic clinical signs due to infection with Newcastle disease. This disease is caused by avian para-
myxovirus‐1 and is quite deadly to affected chicks while also being highly contagious and of
concern to regulatory agencies due to its deadliness to poultry (White et al. 2015). Suspected
infected chicks should be quarantined away from other patients, humanely euthanized, and sub-
mitted to a diagnostic lab for necropsy and testing. Areas and caging that were in contact with the
chick should be thoroughly disinfected with bleach.

­ Avoiding­Imprinting­and Habituation

Double‐crested Cormorants are highly susceptible to imprinting (if they have been hatched in
captivity) and habituation (if they have lived some time with their parents). Knowing about this
high susceptibility, it is important to plan ahead to avoid these problems, since they are very diffi-
cult to correct. The following techniques have resulted in fledglings that appropriately fear humans
and fly off at release without looking back.
The first technique is to stage cormorant decoys (Knutsons Decoys) in each enclosure to ensure
that all visual stimuli are related to cormorants, not people. It is important to conceal all human
shapes and sounds during every encounter with the chicks (Figures 15.2 and 15.3). This can be