June 2013 was bad for tree swallows. At the Queen’s University Biological Station, over 90% of nests failed as a result of persistent cold, rainy weather.
This happened to be the same year we were conducting an experiment on the hormonal mechanisms of parental care in these birds. The bad weather made for a disastrous field season. Just a couple of weeks in, and we were turning up cold lifeless chicks in nearly every nest. The upside was that it led to some potential insights into the way stress hormones and tough weather conditions interact. My coauthors Jenny Ouyang and Ádám Lendvai have written an excellent blog post about it here:
It was remarkable how closely the nest failure rates tracked the fluctuating air temperature. This could be caused by a couple of factors, with a major one being that tree swallows rely on flying insects to feed their young, and the ability of insects to fly depends on temperature. Persistent cold weather means that parent tree swallows cannot find enough food to support their offspring.
The corticosterone hormone implants made the treatment birds more susceptible to faster brood mortality, even during benign weather. It should be noted that the implants were deployed before the bad weather struck, and we would not have performed this experiment if we had known in advance that this would be such a tough year! Hopefully, though, the results provide some insight into the role of stress hormones as mediators of a sensitive period in the life history of these birds.
Read the study here: