To determine relative survival rates of small birds occupying small, linear
strips of woodland compared with large patches of woodland, marked populations
of red-capped robins were monitored over a two-year period. In total, 196 male
robins were banded with unique colour combinations in 10 woodland remnants and
censused by song playback at half-yearly intervals. The
Cormack–Jolly–Seber method was used to calculate half-yearly
survival probabilities for birds in the two habitat configurations and the
strongest model included separate survival parameters for summer (36.2%
5.1) and autumn (88.9% 13.5) half-years, but a constant recapture
probability (50.5% 7.2). The inclusion of separate parameters for the
large and linear habitat configurations reduced the strength of the model,
indicating that there was no significant difference between the survival rates
of birds occupying small, linear strips of woodland and birds occupying large
patches of woodland. The mean annual survival, determined by multiplying the
half-yearly survival probabilities, was 32%, which is low, compared
with the annual survival of other Petroica robins. Although no banded birds
were located away from the banding site, we suspect that much of the
‘mortality’ represented emigration during the summer half-year.
Under this scenario a better estimate of annual survival (79%) might be
achieved by extrapolation of survival over the winter half-year. This study
provides no data to support the contention that adult mortality is higher in
small, linear strips of habitat, although further data on the fate of birds
that disappear from remnants is required before this is conclusive. In
addition, to detect a 20% difference in survival using similar methods
to the present study, with their accompanying sources of variation, at least
10 times the number of birds would need to be monitored. This might most
effectively be done as a co-operative banding project.
Climate anomalies affect annual survival rates of swifts wintering in sub‐Saharan Africa