in which y = vector of observations for the ith trait (i = 1 or 2),
bi = vector of section-year-season effect for the ith trait,
ai = vector of random animal effects for the ith trait,
ei = vector of random residual effects for the ith trait,
Xi = incidence matrices relating records of the ith trait to fixed effects,
Zai = incidence matrices relating records of the ith trait to random animal effects, and
Zpi = incidence matrices relating records of the ith trait to random pen effects.