November 2015
Read about the white-capped albatross mark recapture sample size analysis for Disappointment Island.


This study assessed the effect of alternative mark-recapture sampling approaches to a potential mark-resighting study of white-capped albatross on the estimation of demographic rates.

A data simulator was used to create dummy mark-resighting observations for a single banding year with alternative scenarios of: banded sample size (150, 300 or 600 breeding individuals); number of subsequent consecutive resighting years (2, 3, 4, 5 or 10 years); and resighting probability of breeders (0.6 or 0.4) and non-breeders (0.0 or 0.1).

The SeaBird demographic modelling software was then used to determine variability in the estimates of survival and breeding rate using the dummy mark-resighting observations. This assessment assumed that demographic rates were constant with respect to year and age and variability of demographic rates of wild populations are likely to be greater than those obtained by this assessment.

Increasing the banded sample size from 150 to 600 individuals led to an increase in the precision (c.v.) of annual survival breeding rate estimates. With an input survival rate of 0.95 and a banded population of 150 individuals, the range of survival estimates was wide with 5 years of resighting effort (range from 0.91-0.99, x̄ = 0.95), though was much narrower with 10 years of resighting effort (0.93-0.96, x̄ = 0.95). With a banded sample size of 600 individuals, the range of survival estimates was narrow with 5 years of resighting effort (0.93-0.97, x̄ = 0.95).

The precision of demographic rate estimates was not greatly affected by reducing the resighting probability of breeders from 0.6 to 0.4, though reducing the resighting probability of non-breeders from 0.10 to 0.00 produced imprecise estimates that were for some samples very different from input values. 

Publication information

Roberts, J., Doonan, I., & Thompson, D. 2015. Mark-recapture sample size effects on demographic rate estimation of white-capped albatross - Simulation Modelling. Report prepared by the National Institute of Water and Atmosphere for the New Zealand Department of Conservation, Wellington. 12p. 


Conservation Services Programme
Department of Conservation
PO Box 10-420
Wellington 6143


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