A group of researchers from Trent University have discovered that certain methods of logging elevate stress in developing birds, and that females breeding in these logged areas lay eggs that are more likely to contain males than females, according to a study published today in the journal PLoSONE.

“We weren’t surprised that logging was stressful for nestlings, but that logging caused mothers to produce more sons than daughters has never been reported before,” said Ms. Rhiannon Leshyk, the lead author on the study and a recent graduate from the Environmental and Life Sciences Master’s program at Trent.

The researchers measured the stress hormone corticosterone and molecularly determined the sex of nestling Ovenbirds, small forest songbirds, within forest stands subjected to logging. Not surprisingly, logging was shown to be a stressor, with developing birds exhibiting higher stress hormone levels in the cut sites than the unharvested ones.

What was unexpected was that nests within the cut sites had more male offspring per nest than those in the non-logging sites, and that this increase in males appeared to be proportional to the amount of logging.

Equally striking was that in sites where there was no logging, mothers produced more daughters than sons, which the researchers propose may be to offset increased mortality of females on the wintering grounds. Because so few studies determine the sex of nestlings, the researchers suggest that many species may have female-biased nests when in good environmental conditions.

Ms. Leshyk, together with Drs. Erica Nol and Gary Burness, professors in the Department of Biology at Trent University, and collaborator Dr. Dawn Burke from the Ontario Ministry of Natural Resources, hypothesize that daughters are more sensitive to disturbance than males, and because of this, mothers produce more sons in the logged sites to increase nestling survival.

Posted on Thursday, March 15, 2012.