# T-test
boxplot(logMass ~ Aquatic, data=bird, ylab=expression("log"[10]*"(Bird Mass)"),
        names=c("Non-Aquatic","Aquatic"),
        col=c("yellowgreen","skyblue"))
        
# First, let's test the assumption of equal variance 
# Note: we do not need to test the assumption of normally distributed data since 
# we already log transformed the data above 
tapply(bird$logMass,bird$Aquatic,var)
var.test(logMass~Aquatic,data=bird)

# We are now ready to run the t-test        
ttest1 <- t.test(Mass~Aquatic, var.equal=TRUE, data=bird)

# or equivalently
ttest1 <- t.test(x=bird$logMass[bird$Aquatic==0], y=bird$logMass[bird$Aquatic==1], var.equal=TRUE)
ttest1