Perhaps the most challenging task in managing a captive flock of birds, especially a flock that consistently demonstrates the reproductive anomalies consistent with inbreeding, is how to get an egg to lose the proper amount of weight.
All avian eggs must lose weight in order to hatch successfully. The loss of weight is a result of the transfer of gases and moisture from inside the egg, through the shell, into the environment. The captive flock of `alala lay eggs that often have shells that are either too porous, or not porous enough, hence eggs that either lose too much weight or not enough weight.
In an effort to control the weight loss of those eggs with “difficult shells,” we adjust the humidity in the incubators and manage the adult’s diet (especially calcium levels). We also have several techniques that aim to fine-tune the passage of moisture and gases across the shell. In the case of too great a weight loss, biologists will actually “paint” the shell with a thin coating of non-toxic glue or fingernail polish, or even wrap the egg in a thin layer of paraffin, being careful to leave a band of exposed shell which allows the chick to “pip” the shell when it is ready to hatch. In the case of an egg that doesn’t lose enough weight, the shell can be lightly sanded or even incubated on a bed of silica gel, a well-known, non-toxic desiccant.
The results of these techniques, although not always successful, can help maximize the number of chicks that successfully hatch. In 2004, 12 `alala chicks hatched, a new record for the Hawaii Endangered Bird Conservation Program.
Alan Lieberman is the program director for the San Diego Zoo’s Hawaii Endangered Bird Conservation Program.
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