12.3.3Disease control
Parasitic disease was once considered to have little impact on most bird species,
only in exceptional circumstances being a major cause of mortality (Lack 1954,
1966). We now know that disease is an important component in the population
limitation of many birds (Newton 1998), while the role of pathogens in threat-
ened bird populations has been reviewed by Cooper (1989). Introduced diseases
may have profound impacts on native hosts, a well known example being the
introduced avian malaria and pox in Hawaii, which limits the endemic honey-
creepers to upland areas where mosquito densities are low (Van Riper et al.
1986). The Pink Pigeon on Mauritius suffers high nestling mortality from tri-
chomoniasis, caused by a flagellate protozoan believed to have been introduced
to Mauritius with exotic doves (Swinnerton 2001).
A knowledge of the disease profile of the focal species is often useful so that:
- The likely effect of disease upon the survival and breeding of the species can
be understood. - The disease can be combated as a cause of poor breeding or survival.
- New diseases can be excluded by quarantine measures.
A health audit of a wild population of a managed critically endangered species
needs to be implemented during the early stages of the project (Stage 2). Surveys
of disease, and knowledge from similar surveys on related species, provide useful
indicators (Joyner et al. 1992; Gilardi et al. 1995). It is important to find what
diseases are present, how these may be influencing survival and productivity, and
how they can be managed to minimize their impact.
The species should be screened for diseases known to be important to closely
related species (where such information is available). For example, pigeons are
prone to trichomoniasis and parrots to several viral infections such as psittacine
beak and feather disease and poliomavirus. There also needs to be a more general
screening for parasitic diseases to look for ecto-parasites, blood parasites, and
endo-parasites. Fecal samples should be screened for pathogenic bacteria, with
selective culture for fungi, yersinia, and chlamydia. All dead adults, chicks, and
eggs should be postmortemed in an attempt to understand the causes, and also
the patterns of mortality (Greenwood 1996).
A careful health audit of both wild and captive birds enables measures to be
taken to avoid transmission of disease from captive to wild populations and vice
versa, or from one species to another. Where there are in situcaptive facilities
ideally these should be for single species only, and where other species are held in
the same place, they should be screened to avoid transmission of disease to the
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