Abstract
Long-term and short-term changes in ambient temperature can cause stress in birds, leading to changes in the level of hematological parameters. The H:L ratio (heterophil-to-lymphocyte ratio) is a hematological index that allows for the assessment of the stress induced by environmental changes, including weather conditions. In this paper, we examined the influence of temperatures and the sum of precipitation on the health of nestling pied flycatchers (Ficedula hypoleuca) by using the H:L ratio reflecting the body’s response to stress. All examined temperature indicators influenced the H:L ratio, yet the average value of daily minimum temperature during the first 12 days of nestling life had the strongest influence, maximum temperature had the weakest effect, while precipitation had no significant influence. Our research indicates that even a small increase in temperature caused a stress reaction in nestling pied flycatchers, which was reflected by an increase in the H:L ratio. The increase in the stress index (H:L ratio) was probably a result of poor weather conditions (precipitation, low temperature), which prevented the adult birds from actively foraging and properly feeding the nestlings.
Highlights
Birds are vulnerable to changes in ambient temperatures due to their small body size (McKechnie and Wolf 2010)
We examined the influence of year, the temperature indicators, the sum of precipitation, and wing length on the H:L ratio
We found that temperature during the first 12 days of nestling development significantly positively affected the H:L ratio of nestling pied flycatchers, as shown by analyses of the temperature indicators: we found the strongest effects of Tmin_12 and weaker effects for Tmean_12 and Tmax_12
Summary
Birds are vulnerable to changes in ambient temperatures due to their small body size (McKechnie and Wolf 2010). Air sacs promote the circulation of air on the lung surface, contributing to increased gas exchange and leading to heat loss through evaporation (Fedde 1998). Studies conducted on nestling great tits (Parus major) show that days with average temperatures above 12 °C (classified as hot) contributed to increased parental costs of feeding nestlings. This may have been due to the increased food requirements of young birds to compensate for thermoregulatory costs (Royama 1966; Barba et al 2009)
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