Effects of repeated investigator disturbance on corticosterone concentrations and the immune system in chicks of Black-Legged Kittiwake (Rissa tridactyla)

Repeated exposure to investigator disturbance increases the corticosterone levels and can give detrimental effects on the growth and immune system in nestlings. As the offspring is developing, they need to invest in different life history components. Since the resources are limited, the investment has to be a trade-off between components like immune system and growth. The immunity is divided into the innate immune system with initial non-specific protection and the acquired immune system with specific pathogen protection. The acquired immune system is considered to be the more costly to develop. The present study examined the effects of repeated investigator disturbance on the nestlings of the Black-Legged Kittiwakes during the nestling season at Svalbard. The objective was to test if repeated disturbance caused an increase in the baseline corticosterone levels, increased the heterophil to lymphocyte (H/L) ratio or altered the growth of the nestlings of the experimental group. Blood samples were taken of the experimental group and the control group at day 6 and 31 after hatching. The experimental nestlings were removed from their nests and the biometrics were measured every second day for 25 days, while the controls were only measured at day 6 and 31. The nestlings of the experimental group did not increase their baseline corticosterone levels or H/L ratio compared to the control group. There were also no significant differences on the body condition index (BCI) or the biometric measurement between the two groups either. The results of the present study suggest therefore that the nestlings of the Black-Legged Kittiwake are resilient to and do not perceive the investigator disturbance as a stressor. A significant correlation between the H/L ratio and the body condition index (BCI) of the nestlings was found, proving a relationship between nestlings with low BCI having a high H/L ratio. Differences in H/L ratio between the sexes were also proven, with the females having a higher H/L ratio than the males. These results are consistent with previous studies