TDK conference 2009

House sparrow populations have been decreasing over the world in the past decades especially in cities by unknown reasons. Previous studies have demonstrated that the more urbanized the habitats, the leaner the house sparrows there, suggesting that the body condition of sparrows may be worse in cities than in more natural habitats. To explore whether the decrease of urban populations may be due to chronic stress effects of urbanization (e.g. environmental pollution, junk food), physiological studies are needed. Chronic stress is known to induce a number of characteristic changes in birds’ physiology, such as anaemia, heterophilia and lymphopenia.

As one of the first steps of a monitoring program, in this study I investigated body mass index (BMI; body mass controlled for tarsus length) and some easily measured physiological parameters: hematocrit, proportion of heterophil granulocytes to lymphocytes (H:L ratio), and plasma corticosterone concentrations in house sparrow populations at various habitats along the urbanization gradient. If the lower BMI of urban sparrows is due to chronic stress, then lower hematocrits and higher H:L ratios and corticosterone levels are expected in individuals in urban than in less-urban habitats.

My results confirmed that house sparrows’ BMI is lower in cities and suburbs than in rural habitats. Hematocrit was lower in the molting season and in juveniles than in winter and in adults, respectively; however it did not differ among different habitat types. I found a statistically non-significant tendency that H:L ratio increased from rural habitats to the most urbanized habitats; furthermore it increased with the time spent between capture (an acute stress effect) and blood sampling (rising after ca. 40 minutes). Males had higher baseline corticosterone concentrations than females, but we found no effect of habitat type either on baseline or on acute corticosterone levels. These results do not support that urban house sparrows are exposed to greater chronic stress than rural sparrows; however, the study is worth extending by increasing sample size.