Young survival input file and age covariate

[michaelnv]

Hello,

I’m interested in using the “Lukacs Young Survival from Marked Adults” model in MARK to apply to an avian species with precocial young (attending females are radio marked). I’ve read the corresponding chapter and searched the forum but can’t seem to find answers to a few very basic questions,

1. I’m trying to fit age as an individual covariate and model it in a similar way as was done in the nest survival chapter, using the add function in the design matrix to compute age at the first day of the study. However, I suspect the relationship between survival and chick age is non-linear (e.g. low but increasing survival over first 10 days, then leveling off after like a threshold). I’m not sure how to model this. I tried imbedding the add function in a min function (e.g. min(add(ageday1, 1), 10) for first row of DM) and it works, but I don’t know if it’s doing what I think it’s doing, and I'm unsure how to graph survival as a function of age using this model. Does this approach seem reasonable or am I going over the cliff edge?

2. I’ve considered altering the input file to match the example plover file in chapter 19 where all broods are observed on the first day of the study (i.e. there’s a count for every brood on the first encounter in the infile). This makes modeling chick age very easy (as can be seen in section 19.3), but it really complicates using the design matrix for group-level covariates like weather (e.g. chicks during encounter occasion 3 experience different weather unless they are the same age). Complications of group-level covariates in the DM aside, is altering the input file in the way I suggest valid?

Thanks so much for any suggestions you can provide!