Notornis, 30 (4), 265-282
Article Type: Paper
The breeding of the South Island Robin at Kowhai Bush, Kaikoura, during the 1977-78 and 1978-79 seasons and the mortality from August 1976 to December 1979 are described. Most robins began laying in August and completed breeding in January. Thirty-four percent of their nests were relined “old” ones built in previous seasons by robins or Turdus species. Average time to build a “new” nest was 3.4 days, followed by a prelay period that averaged 4.2 days.
Eggs were laid at about 24-hour intervals. Mean clutch size was 2.7 eggs (range 2-4), being smallest in July and largest in October. Incubation averaged 17.7 days, and the females spent 81% of daylight time on the eggs; males did not incubate. In the two seasons, 63% of the eggs hatched and 23% were eaten by predators. Hatching success varied between seasons, months and the four age classes of females.
Both parents fed the nestlings, but only the female brooded. Nestlings averaged 20.8 days in the nest, with little or no brooding after day 15. Overall, 42% of the nestlings fledged; most of the rest were eaten by predators. The proportion that fledged decreased as the season progressed because the loss to predators increased. Pairs fledged a mean of 2.1 fledglings in 1977-78 and 2.9 in 1978-79.
Juveniles were fed by their parents from 24 to about 50 days, depending on the .number of juveniles, how many the female cared for and how soon the next clutch hatched.
Mortality was highest in summer for immatures and autumn for adults. Immatures died more in summer, possibly because they were less efficient foragers than adults, but similar proportions of the two age classes died in autumn and winter, perhaps because predation was the main mortality factor.