The Impact of the Female Immune Challenge on Parental Feeding Rate,Mass and Body Condition Index of Offspring

Reproduction is a resource-demanding period, when trade-offs between investment in immunity versus other functions of an adult organism may exist. This research investigates the potential trade-off between a challenged immune system of a female parent and parental provisioning in free-living Great Tits Parus major and Eurasian Blue Tits Cyanistes caeruleus. In both species, half of females were challenged with sheep red blood cells (SRBC) as an antigen, while the others were injected with phosphate buffer saline (PBS) as a control. Six days later – at the day assumed to be the peak of an immune response in birds treated with SRBC, when nestlings were nine days old – parental feeding rates were recorded. Two days later (and eleven days after hatching), nestling mass and body condition index (BCI) were quantified. SRBC challenge of the female increased feeding rates of Great Tit males and females, but did not change parental provisioning in Eurasian Blue Tits. This may be explained by the different reproductive strategies in these two bird species. Parental provisioning influenced the mass and BCI of offspring. In both species, offspring mass was lower and BCI was higher in the SRBC group than those in the control group. This means that high providers, such as Great Tits with increased feeding rates, do not always raise chicks with high fledgling mass. Parental provisioning is one of the key factors linking reproduction and the immune system.