Details

Autor(en) / Beteiligte

• Barker, Richard J.
• Buchanan, Ian M.

Titel

Estimating Adult Survival Rates of New Zealand Black Swans Banded as Immatures

Ist Teil von

• The Journal of wildlife management, 1993-07, Vol.57 (3), p.549-555

Ort / Verlag

Bethesda, MD: The Wildlife Society

Erscheinungsjahr

1993

Beschreibungen/Notizen

• Recovery data from birds banded only as immatures are common, but there are no widely accepted methods of estimating age-specific survival rates from such data. To estimate survival rates of black swans (Cygnus attratus) banded in New Zealand 1974-89, we developed a model that allows estimation of year-specific adult survival rates from birds banded only as immatures. Survival rates of immatures were modelled as time invariant, but immature recovery rates, adult recovery rates, and adult survival rates varied temporally. Expressions for bias show that violation of the assumption of time-invariant immature survival rates biases adult survival rate estimates. However, if variation in immature survival rates is small, bias is also small. Estimated annual survival rates of adult black swans averaged 0.84 (SE = 0.030) and immature recovery rates 0.10 (SE = 0.005). There was no evidence that parameters differed between sexes, but immature recovery rates and adult survival rates appeared to vary through time. Annual variation in immature recovery rates could be explained by variation in daily bag limit, season length, and number of licensed hunters. This suggests that black swans may be useful candidates for testing assumptions about the effects of changing hunting regulations on waterfowl demography.