Why are my df for year showing up as 1? I've tried different ways to convert it to a factor, yet the df is still 1

Question

I've looked at different posts asking the same question, but I don't understand why it isn't working.

bandingdata$Year <- factor(bandingdata$Year)

As soon as I run an anova, it's like I didn't even do anything the the df for Year is still 1.

model <- aov(FatMass ~ Month + Year, data = bandingdata)
summary(model)

              Df    Sum Sq  Mean Sq F value Pr(>F)    
Month          5  44276958  8855392    49.6 <2e-16 ***
Year           1  31334428 31334428   175.5 <2e-16 ***
Residuals   2579 460451164   178539                   
---
Signif. codes:  0 ‘***’ 0.001 ‘**’ 0.01 ‘*’ 0.05 ‘.’ 0.1 ‘ ’ 1
14 observations deleted due to missingness