Modeling survival of fledglings after leaving the nest

[Germán López]

Hello,
I'm analyzing a data set of magpie fledglings marked with color rings that were followed weekly after leaving the nest. The 48 fledglings come from 11 nests in two years and they were followed for one year. One particularity of this data set is that apparently all live individuals were detected every week, i.e. recapture stories are always series of 1 until a bird disappears. Thus, these data resemble to known fate data and perhaps could be modeled in this way.
However, I have seen that the program MARK do not allows for the inclusion of age effects in known fate models. Since age effect may be obviously important when young birds are involved I'm modeling survival with live recapture models but fixing recapture probability to be 1. I would acknowledge any comment and suggestion about if this would be a correct approach.
Further details and problems of the analyses:
- I'm using two age classes to represent the periods before (6 weeks) and after independence of the parents.
- Given the high number of recapture occasions (51 weeks) I have reduced the number of survival parameters to be estimated by forcing the survival of each four consecutively weeks to be the same.
I have estimated c-hat with the procedures described in the introductory guide to MARK (Cooch and White) and values obtained are not too high (1.2 - 1.3). However bootstrap GOF are significant in all models, thus showing lack of fit to the data. This lack of fit could be due to violation of model assumptions if survival probability of fledglings from the same nest are not independent. But in this case I think that greater values of c-hat would be expected due to overdispersion. Is this correct?
To try to avoid this problem I have also fitted models with a different survival probability for individuals from each nest (so, nests are groups) during the parent dependent period, and time varying survival (but equal to all birds whatever the nest of origin) after independence. But again bootstrap GOF is significant although c-hat = 1.21. I would acknowledge also any suggestion about this.
Thanks!
Germán López