ESTIMATING ADULT SURVIVAL RATES OF NEW-ZEALAND BLACK SWANS BANDED AS IMMATURES

Recovery data from birds banded only as immatures are common, but ther e are no widely accepted methods of estimating age-specific survival r ates from such data. To estimate survival rates of black swans (Cygnus attratus) banded in New Zealand 1974-89, we developed a model that al lows estimation of year-specific adult survival rates from birds bande d only as immatures. Survival rates of immatures were modelled as time invariant, but immature recovery rates, adult recovery rates, and adu lt survival rates varied temporally. Expressions for bias show that vi olation of the assumption of time-invariant immature survival rates bi ases 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 re covery 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 rec overy rates could be explained by variation in daily bag limit, season length, and number of licensed hunters. This suggests that black swan s may be useful candidates for testing assumptions about the effects o f changing hunting regulations on waterfowl demography.