Methodology for estimating the abundance of rare animals: Seabird nesting on North East Herald Cay

We discuss the problem of estimating the number of nests of different speci es of seabirds on North East Herald Cay based on the data from a 1996 surve y of quadrats along transects and data from similar past surveys. We consid er three approaches based on different plausible models, namely a condition al negative binomial model that allows for additional zeros in the data, a weighting approach (based on a heteroscedastic regression model), and a tra nsform-both-sides regression approach. We find that the conditional negativ e binomial approach and a linear regression approach work well but that the transform-both-sides approach should not be used. We apply the conditional negative binomial and linear regression approaches with poststratification based on data quality and availability to estimate the number of frigatebi rd nests on North East Herald Gay.