Figure 2: Scatter plots of immune function and Julian day in four bird
species during spring migration. Panels 1-4 show the relationship
between microbial killing ability (% E.coli killed) and Julian day and
panels 5-8 show the relationship between IgY levels (mOD/min) and Julian
day. Dashed lines indicate non-significant correlations. Significant
relationships are depicted in bold lines in the panels 3, 4 and 7
respectively. Please note that the x-axis is differently scaled among
the figure panels
Microbial killing ability was significantly different between the four
species (Figure 3, chi-squared= 20.43, df= 3, P<0.001). A
pairwise Wilcoxon test showed significantly higher microbial killing
ability in Dunnocks when compared to Chaffinches (P=0.004) and Wheatears
(P=0.009). Song thrushes showed a significantly higher microbial killing
ability than Chaffinches (P=0.004) and Wheatears (P=0.009). There was no
significant difference in microbial killing ability between Wheatears
and Chaffinches (P=0.59), and Dunnocks and Song thrushes (P=0.59).
Similarly, immunoglobulin levels were significantly different between
the four species (f=11.25, df= 3, P< 0.001, Figure 3). A Tukey
test revealed that the IgY levels in Dunnocks were significantly lower
than IgY levels in Chaffinches (P=0.001) and Song Thrushes
(P<=0.001). The IgY levels in Wheatears were significantly
lower than that in Song thrushes (P=0.01). There was no difference in
levels of IgY between Song thrushes and Chaffinches (P=0.19), Wheatears
and Chaffinches (P=0.68) or Wheatears and Dunnocks (P=0.07).