Assessing population dynamics| 321estimated. One way to calculate a sustainable harvest for eggs would be to insert
the maximum growth rate calculated from the structured population model into
equation (13.4), using the minimum estimate of the number of eggs laid as Nmin.
This is a reasonable place to start, but may be unnecessarily conservative, since the
PBR method ignores differences in reproductive value and density-dependence
among classes within a population. To develop an assessment of sustainable har-
vest of eggs specific to this life-history would require additional information
about the density-dependence of some of the life-history parameters, particularly
hatching success and survival of hatchlings to maturity.
Unfortunately, the unique life-history of megapodes makes many of those
parameters difficult to estimate. The hatchlings, which are completely indepen-
dent of their parents from the moment they emerge, are highly vulnerable to pre-
dation, and are thus extremely secretive. The adults also are secretive, living in the
forest except when they come to the communal nesting sites. The estimated
number of eggs laid per female is 8–12 per breeding season (Dekker 1990). The
hatching success rates in predator-proof hatcheries built at nesting grounds have
been between 55% and 75% ( Jones et al. 1995). Post-emergence mortality rates
are not known. In the Australian Brush-Turkey (Alectura lathami), a “very rough
estimate” of the mortality from emergence to sub-adult was 90–97% ( Jones
1988). Maleo become sexually mature in their second or third year ( Jones et al.
1995). There is no estimate of the adult survival rate. Thus, the data do not
currently permit a quantitative determination of the potential growth rate or the
sustainable harvest rate of eggs. To estimate growth rate, the two critical parame-
ters that would have to be measured are: hatchling survival to maturity, perhaps
by banding or otherwise marking hatchlings released from incubation programs;
and adult survival, again by banding or marking, with subsequent recovery,
recapture, or resighting of those marks (see Chapter 5). To estimate the sustain-
able harvest rate without the assumptions of the PBR calculation, additional
information on the density-dependence of the life-history parameters would
be needed.
Even if such monitoring programs can be initiated, it will take a number of
years to obtain enough data to estimate reliably the parameters needed. As an
alternative, an experimental or adaptive approach (see 13.7.2 and 13.7.3) could
be taken, where portions of communal nesting grounds are completely protected
from egg harvesting, and the number of pair-visits, the number of eggs harvested,
and, if possible, the number of hatchlings emerged are monitored. Such an
approach should be designed to assess what level of protection is needed, to pro-
duce an increase in population size, while still allowing some harvest. A good
place to start is the level of protection afforded under traditional egg-harvesting
methods (Argeloo and Dekker 1996).