Use of the Barker model in an experiment examining covariate effects on first-year survival in Ross's geese (Chen rossii) : A case study /

Includes bibliographical references (pages 507-508).

The Barker model provides researchers with an opportunity to use three types
of data for mark- recapture analysesÐ recaptures, recover ies, and resightings. This model
structure maximizes use of encounter data and increases the precision of parameter
estimates, provided the researcher has large amounts of resighting data. However, to our
knowledge, this model has not been used for any published r inging studies. Our objective
here is to repor t our use of the Barker model in covar iate-dependent analyses that we
conducted in Program MARK. In particular, we wanted to descr ibe our exper imental
study design and discuss our analytical approach plus some logistical constraints we
encountered while conducting a study of the eþ ects of g rowth and parasites on survival of
juvenile Ross’s Geese. Birds were marked just before ¯ edging, alternately injected with
antiparasite drugs or a control, and then were re-encountered dur ing migration and
breeding in following years. Although the Barker model estimates seven parameters, our
objectives focused on annual sur vival only, thus we considered all other parameters as
nuisance terms. Therefore, we simpli® ed our model structures by maintaining biological
complexity on survival, while retaining a very basic structure on nuisance parameters.
These analyses were conducted in a two-step approach where we used the most parsimonious
model from nuisance parameter analyses as our star ting model for analyses of covar iate
eþ ects. This analytical approach also allowed us to minimize the long CPU times associated
with the use of covar iates in earlier versions of Program MARK. Resightings made up
about 80% of our encounter history data, and simulations demonstrated that precision
and bias of parameter estimates were minimally aþected by this distribution. Overall, the main source of bias was that smaller goslings were too small to retain neckbands, yet were
the birds that we predicted would have the lowest sur vival probability and highest
probability for parasite eþ ects. Consequently, we considered our results conservative. The
largest constraint of our study design was the inability to par tition survival into biologically
meaningful per iods to provide insight into the timing and mechanisms of mortality.