Urbanization enhances body condition, but not innate immune defences, in a common waterbird

Abstract

There is a growing body of evidence that urbanization can affect body condition and immune function in wild birds, although these effects may be complex and taxa-specific. Here, we assessed the effects of urbanization on body condition (size-corrected body mass and haemoglobin concentration) and innate immune defences (haemolysis-haemagglutination assay, haptoglobin concentration and bacterial killing assay) in 136 Eurasian coots (Fulica atra) from three urban and three non-urban populations across Poland. We also quantified the heterophil to lymphocyte ratio to control for the potential effect of physiological stress on immune defences. We found that urban coots showed significantly better condition than non-urban ones. At the same time, we found no relationship between any immune defence and urbanization or condition. Thus, our study offers no support for condition-dependent immune function. Our analyses also revealed significant differences between male and female coots in both condition and immune defences; however, we found no evidence for sex-specific responses to urbanization. In conclusion, our study provides correlative evidence that urban habitat enhances condition, but not immune defences in the Eurasian coot.

Keywords: Eurasian coot; birds; health; innate immunity; urban-rural.

Figure 1.

Conceptual framework showing predictions on the associations between urbanization, condition and immune defences in the Eurasian coot.

Figure 2.

Location of the sampling sites. Urban and non-urban coot populations were marked in yellow and green, respectively.

Figure 3.

Differences in body condition in three urban (yellow) and three non-urban (green) populations of the Eurasian coot. Means (central point), s.e. (box) and 95% confidence intervals (whiskers) of haemoglobin concentration (a) and size-corrected body mass (b) are shown. For the purpose of visualization, size-corrected body mass was calculated as residuals from body mass against wing length.

Figure 4.

Differences in body condition and immune defences between males (M) and females (F) in urban (yellow) and non-urban (green) populations of the Eurasian coot. Means (central point), s.e. (box) and 95% confidence intervals (whiskers) of haemoglobin concentration (a), size-corrected body mass (b), haptoglobin concentration (c), haemolysis (d) and bacterial killing capacity (e) are shown.