This Addendum updates results from previous papers using random effects
instead of fixed effects models for the year factors. Results are now given for Bird
and St Croix islands in addition to those for Dassen and Robben islands. The
results from random effects models are qualitatively unchanged from those given
earlier from the fixed effects models, except that the periods required to obtain
statistically significant results are extended somewhat as a result of the removal
of the negative bias in the residual variance estimates for the earlier fixed effects
models