Abstract
Silviculture (logging) creates a disturbance to forested environments. The degree to which forests are modified depends on the logging prescription and forest stand characteristics. In this study we compared the effects of two methods of group-selection (“moderate” and “heavy”) silviculture (GSS) and undisturbed reference stands on stress and offspring sex ratios of a forest interior species, the Ovenbird (Seiurus aurocapilla), in Algonquin Provincial Park, Canada. Blood samples were taken from nestlings for corticosterone and molecular sexing. We found that logging creates a disturbance that is stressful for nestling Ovenbirds, as illustrated by elevated baseline corticosterone in cut sites. Ovenbirds nesting in undisturbed reference forest produce fewer male offspring per brood (proportion male = 30%) while logging with progressively greater forest disturbance, shifted the offspring sex ratio towards males (proportion male: moderate = 50%, heavy = 70%). If Ovenbirds in undisturbed forests usually produce female-biased broods, then the production of males as a result of logging may disrupt population viability. We recommend a broad examination of nestling sex ratios in response to anthropogenic disturbance to determine the generality of our findings.
Highlights
Natural selection should favour those parents who invest in both sexes [1]
In most monogamous and polygynous species males compete for females, females will nearly always reproduce while males may not be chosen for mating or may be unable to compete against other, better quality males [3]
106 nestlings from 23 nests were used in analyses of brood sex ratios, while 55 nestlings from 17 nests were used in corticosterone analysis
Summary
Natural selection should favour those parents who invest in both sexes [1]. when the quality of the investing parent is lowered, equal investment in both sexes may not result in the highest fitness [2]. Anthropogenic disturbances modify the landscape and alter environmental quality Such disturbances may cause stress in wildlife, resulting in elevated levels of the stress hormone corticosterone (e.g. tourism [12], pollution [13], habitat removal/ disturbance [12,13]). With group-selection silviculture (GSS), small clear-cuts (gaps, 0.03–0.07 ha) are made throughout a stand with the quantity and layout of the gaps differing across logging prescriptions. This method creates larger canopy gaps than those created through the single-tree selection system, a method applied frequently in hardwood forests [20]. We predicted nestling Ovenbirds from harvested sites would have elevated baseline corticosterone levels
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