Loading mixture data on MixSIAR

[CatiaS]

Hi!

Currently I have started using MixSIAR to determine individual diet composition of Lesser black-backed gulls. As part of this analysis, my intent would be to have information on the diet of the gulls at an individual level (not population level). With this in mind, after looking over the examples provided in the manual, I was unsure on what would be the most correct way to load my mixture data.

To do that, so far, I have placed "individual" as a fixed effect in MixSIAR GUI, which also prompted me to select a "Process only" error structure. My first question is, would this be the most correct way to load this type of data?

Additionally, I also have d13C and d15N values in different sections of the same primary feather per chick. In this case, I also want to retrieve information on the diet of each individual (an not the population iteself). Each primary was divided in 3 sections and, across all individuals, section one of bird 1 corresponds to section 1 of bird 2 and so on. With this disign on mind, what would be the best way to load the data?

Should i load this specific data by looking at each section separately, and also placing individual as a fixed effect?

All actual statitical testing and hypothesis inferring will be done after retrieving diet information on these samples (i.e, how individual diet connects to bird body condition and growth). The type of analysis I am planning to do are mainly General/Generalized Linear Models.

Thank you in advance for the help,

Cátia