Conservation ecology of kea - Kea Conservation Trust website

abundance caused by heavy beech seeding (Chapter 1; King 1983). We only recorded a
death if a carcass was found; the disappearance of a bird was not regarded as a death.
The intensity of our radio tracking was such that we are confident that the disappearance
of birds was due either to transmitter malfunction, flat batteries or emigration, rather than
to dead birds falling down holes and being undetectable. Most radio-tagged individuals
were monitored for more than one year, giving a total sample of 89 kea-years (70 male
and 19 female). We calculated survivorship by dividing the number of deaths by 89 and
subtracting this from 1.
Adult female survival
All kea in our study area were monogamous. If the sex ratio is uneven in a monogamous
population then it is important to estimate the survivorship of the rarer gender rather than
the more common one. Adult female kea perform all incubation and brooding, which
makes them potentially more prone to mortality by predation than males (Elliott 1996b;
Wilson et al. 1998). It is, therefore, likely that adult female survival is lower than adult
male survival and that the sex ratio is accordingly skewed toward males. Unfortunately,
logistical considerations prevented us from radio-tagging enough adult females to
separately estimate their survival from telemetry data. Instead, we assume that somatic
(non-reproductive) survival among adult females is equal to that measured from the
telemetry data (above), and that overall adult female survival equals somatic survival
minus nesting mortality. We aimed to measure nesting mortality by colour banding adult
females so that we could tell whether they went missing when their nests were preyed
upon.
Juvenile survival
We radio-tagged eleven chicks at fledging time in the 97/98 summer. In January 1999
(one year later) we flew at 7-10 thousand feet, in a radio-telemetry equipped fixed-wing
aircraft (Cessna 172), over all forested mountains within a 50 kilometre radius of the
nests. Following the flight, we visited all of the birds on foot to see if they were alive.
We are confident that we were just as likely to detect a dead bird as a live one, as
reception and coverage from the plane was exceptionally good. For example, one
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