GSTM1 and infection: In our linear mixed model analyses to examine factors influencing Hb levels in parasite-specific infected bird models, parasite intensity was selected as an important predictor in mixed infection birds, however, parasite intensity showed negative significant effect in Leucocytozoon infected birds with confidence intervals for the parameter estimates included zero, so there was little evidence that Leucocytozoon parasite had any effect on Hb levels.