assessment of numbers and distribution, and if possible also of productivity and
survival.
These various components of species restoration may seem self-evident, but a
surprisingly large number of restoration projects have proceeded without a clear
and coherent knowledge of the problems and a plan of how to address them.
Often the ultimate goal is clear but the intermediate steps are less evident. A clear
step-by-step approach to species conservation allows managers to plan the work as
a series of short-term achievable goals, where the roles of managers, technicians,
consultants, and scientists can be clearly defined.
12.3 Broad population management approaches
Within their particular habitats, most bird populations are naturally limited by
a relatively few variables, of which availability of food and safe nest-sites, preda-
tion, competition, and disease are among the most important (Lack 1954, 1966;
Newton 1998). In the absence of human impact, it can be assumed that one, or an
interaction of several such factors, will be limiting the size of most bird populations.
The species may respond to a broad approach simultaneously addressing several of
the more likely limiting factors. In declining or very small populations, productiv-
ity or survival may be enhanced by management without fully understanding the
causes of population decline. This approach was applied to the Chatham Island
Black Robin Petroica traversiand Echo Parakeet Psittacula equesrestoration pro-
grams. The species’ extreme rarity was addressed by providing some supplemental
food, enhancing and protecting nest-sites, controlling/excluding predators, com-
petitors, and parasites around nest-sites (Butler and Merton 1992; Jones and Duffy
1993). These management actions were implemented, even though it was not
known at the time what was limiting Black Robin and Echo Parakeet populations,
and which actions were the most important. In very small populations, empirical
evaluation of the factors affecting numbers can often be the most efficient
approach for understanding the causes of decline or rarity, reacting to problems as
they are identified. The Chatham Island Black Robin, Mauritius Kestrel Falco
punctatus, Pink Pigeon Nesoenas mayeri, and Echo Parakeet had declined to such
low numbers that there was no other option available.
When attempting to restore a population, the temptation to focus exclusively
upon the causes of past decline may not always be necessary (Goss-Custard 1993;
Green 1995). This might in any case not be correctable in the short-term, as with
habitat loss. But a species that is declining due to high adult mortality may be
saved by boosting its productivity, and this may be achieved by improving its
food supply or nest-sites.
272 |Conservation management of endangered birds