GLM for proportional data

#1
Hi,
I'm hoping someone can help me sort out question about how the proportion comparisons in GLM works in R.

I'm trying to compare hatch success among years (and later, sites). I've used a GLM to compare among years by making a txt file where the success column contains the number of chicks that hatched, and failures are the number of eggs in each nest that didn't hatch. Each row corresponds to a nest.

The code looks like this:

y<-cbind(success,fail)

hsmodel1<-glm(y~year,binomial)

This will give me hatch success as #of chicks hatched/eggs laid, correct? Not # of chicks hatched /nest?

Secondly, if my species lays up to 2 eggs, is using this proportional method still valid, since there could be 0, 1 or 2 successes or failures? I'm pretty sure it is, but I am starting to doubt myself from a question a colleague asked today.

Thanks!
Mog
 
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