[R-sig-ME] correlation of fixed effects coefficients all close to +/-1

[Alessandra Bielli]

Dear list,

I am fitting the mixed effect model:
 > lmer(log(percapita_day) ~ Type_residuo + (1|boatID), data=all)

 where percapita_day is a non-negative continuous response variable (on the
log scale to have residuals normally distributed), Type_residuo is a
categorical explanatory variable and boatID is a random effect with 4
levels.

I have found values very close to +/-1 in the correlation of fixed effects
matrix below, and after some research I learnt that the coefficients are
not about the correlation of the variables but the expected correlation of
the regression coefficients.

Correlation of Fixed Effects:
            (Intr) Tp_rsM Tp_rsdOr Tp_rsdOt Tp_Pyc Tp_rsP Tp_rsR
Type_rsdMtl -0.944
Tp_rsdOrgnc -0.951  0.945
Typ_rsdOtrs -0.959  0.953  0.959
Tp_rsdPplyc -0.926  0.919  0.925    0.933
Tp_rsdPlstc -0.951  0.945  0.951    0.958    0.925
Type_resdRd -0.870  0.867  0.873    0.878    0.850  0.872
Type_rsdVdr -0.954  0.949  0.955    0.962    0.928  0.954  0.876

However I still can't explain why all coefficients are so close to +/-1 and
I was wondering if these are indicators that something is wrong with my
model?
Is that due to the presence of outlayers in the response variable (see
attached)?

Thanks,

Alessandra