Neither forest herbicides nor ambient temperature exert strong effects on reproductive output of a cavity-nesting songbird

Abstract

Land management may combine with air temperature to influence the persistence of animal populations, so both must be evaluated in concert to understand how populations respond to increased forest management intensity and projected climate change. We used a large-scale study that experimentally manipulated herbicide application intensity within regenerating forests to test how herbicide-mediated changes in temperature influenced three components of reproductive output in the House Wren (Troglodytes aedon): nest survival, the number of offspring produced, and nestling body condition. We found no evidence for a consistent herbicide treatment effect on any reproductive measure, although our power to detect effects was modest. Relative to unsprayed controls, nest survival was lowest in the light herbicide treatment, and this measure increased on sites that were subjected to greater herbicide application (i.e., at moderate and intensive herbicide treatments), against our predictions. We also detected no evidence of a temperature effect singly or in combination with herbicide application on wren reproductive output. Although herbicide intensity was more influential on reproductive output than was temperature, we found that neither exerted strong effects in regenerating conifer forests. Given the dearth of studies that combine evaluations of temperature and land management impacts on songbird reproductive output, we suggest researchers continue to expand our understanding of the relative influence of both drivers simultaneously to better formulate conservation strategies in light of expected changes in climate and a heightened global demand for wood products.

Keywords

• forest herbicide
• intensive forest management
• microclimate
• reproductive output
• troglodytes aedon
• temperature