Project Bluebird

Researchers

Abstract

Many bird populations are in decline, and one contributing factor is climate change. Shifts in climate can affect the timing of bird migration and breeding, as well as the nest temperatures experienced by eggs. Bird eggs, similar to reptilian eggs, are heavily affected by temperature; because of this, mothers regulate the temperature of the eggs by incubating them. The mothers are so careful in their incubation that species of birds tend to have an average temperature that their eggs are ideally incubated at, down to a tenth of a degree. This is important because even a deviation of 1℃ can affect the weight, probability of hatching, and survival rate of the offspring (Wada et al. 2015). 

Few studies have looked at how incubation temperature affects the immune systems of the offspring. To address this knowledge gap we experimentally manipulated incubation temperatures in Eastern Bluebirds and then assessed how temperature affected the proportion of white blood cell types present in 13-day old offspring. We also investigated whether the presence of mites in the nest influenced white blood cell counts in offspring. We found that birds incubated at cooler temperatures had lower Basophil counts than those incubated at control and higher temperatures. We also found that, of the birds raised in nests with no ectoparasites, those incubated at higher temperatures had significantly higher lymphocyte counts than control nests or nest incubated at lower temperatures. Of the control nests, those with mites present in them, regardless of any other ectoparasites present, had higher lymphocyte counts. Future work should explore if there is a causal relationship between the two, or if another factor is causing both results.

Methods

Results

Discussion

We can see that incubation temperature has at least some effect on the immune system. The presence of nest ectoparasites also correlated with the relative abundance of certain cell types. There are clear differences in heterophil and eosinophil counts, especially when compared with the presence of mites in the nests. This supports previous work (DuRant et al. 2011, Arida et al. 2010) that incubation temperatures can affect some components of offspring immunity. The trends also match counts we would expect to correlate. Ectoparasites feed on host blood and can stimulate immune responses (Owen et al. 2010) such as a surge in eosinophils, which are responsible for protecting the organism from parasites. However, in the present study it is not clear whether mites are altering the proportions of heterophils and eosinophils, or if birds with certain immune profiles are more susceptible to mites.

Acknowledgements

We would like to thank Sydney Horan for the eastern bluebird image and our collaborators in the Knutie lab at the University of Connecticut who assisted with data collection (Ryan Shannon, Sila Inanoglu, Lorraine Pérez-Beauchamp, Carrie Sleath, Carissa Leung, Sarah Knutie).