Long-Term Variation in Blood Glucose Concentration in Nestling Great Tits ( Parus major )

The main aim of this study was to examine if blood glucose concentration displays any pattern of variation between years and distinct habitats. Bird blood glucose concentration reflects their high metabolic demands and is influenced by a variety of environmental factors. Therefore variation in glucose levels of free-living birds is an important aspect of their functional ecology. We now present results concerning variation in glucose concentration in the blood of Great Tit (Parus major) nestlings (∼ 14-day-old). We also compare the obtained results with variation in blood glucose nestlings Blue Tit (Cyanistes caeruleus) published elsewhere. Our present study was conducted in central Poland in an 8-year period, 2005–12 in two distinct habitat types: an urban parkland and a rural deciduous forest. The most important findings of the study were: (i) mean levels of blood glucose varied markedly between years; (ii) glucose concentrations were significantly higher in the parkland study area; (iii) heavier nestlings were characterised with lower blood glucose levels; (iv) there was a negative relationship between fledging success and per-brood mean glucose concentration in the urban park site but not in the forest site; and (v) Great Tit nestlings were characterised by significantly higher blood glucose levels than Blue Tits nestlings. Variation in glucose concentration of nestling Great Tits shows a consistent spatio-temporal pattern which is generally similar to that found in Blue Tits.