Forest fragmentation is associated with primary brood sex ratio in the treecreeper (Certhia familiaris)

Abstract

We studied the primary brood sex ratio of an old-growth forest passerine, the Eurasian treecreeper (Certhia familiaris), along a gradient of forest fragmentation. We found evidence that male nestlings were more costly to produce, since they suffered twofold higher nestling mortality and were larger in body size than females. Furthermore, the proportion of males in the brood was positively associated with the provisioning rate and the amount of food delivered to the nestlings. During the first broods, a high edge density and a high proportion of pine forests around the nests were related to a decreased production of males. The densities of spiders, the main food of the treecreeper, were 38% higher on spruce trunks than on pine trunks. This suggests that pine-dominated territories with female-biased broods may have contained less food during the first broods. The observation was further supported by the fact that the feeding frequencies were lower in territories with high proportions of pines. In the second broods, territories with a high forest patch density produced female-biased broods, whereas high-quality territories with a large amount of deciduous trees and mixed forests produced male-biased broods. Our results suggest that habitat quality as measured by habitat characteristics is associated with sex allocation in free-living birds.

Birds bias offspring sex ratio in response to livestock grazing

“…The proportion of sons was lowest in the ungrazed and intensively grazed treatments and highest in treatments grazed at low intensity (by sheep or a mixture of sheep and cattle). This research supports growing evidence that birds manipulate offspring sex ratio in response to local habitat conditions [10] and that too much grazing, or the complete removal of livestock from upland areas, is detrimental to common breeding birds. While additional research is necessary to understand the observed variation in sex ratio, the most likely explanation relates to the effect of grazing manipulation on the quality of the breeding environment.…”

Fluctuating feather asymmetry in relation to corticosterone levels is sex-dependent in Eurasian treecreeper (Certhia familiaris) nestlings

“…Male development owing to higher energetic demand (e.g. parental provisioning rate is higher in male-biased broods, Suorsa et al 2003b) is probably more sensitive to environmental stressors like food restriction, resulting in a stronger association (or faster response to) between corticosterone levels and FA. Such sex-related associations between stress and FA have rarely been studied and documented.…”

“…¼ 31.2 + 12.0 ng ml 21 , min ¼ 10.1, max ¼ 81.1) were corrected for autolysis (Suorsa et al 2003a) by using studentized residuals from the regression of corticosterone on the total handling time of plasma (from bleeding to storing of plasma) as estimates of nestling corticosterone levels. The extracted blood cells of the same samples were also used for nestling sex determination applying DNA molecular methods (Suorsa et al 2003b).…”

Forest clearing and sex ratio in forest-dwelling wood ant Formica aquilonia

“…To date, the effects of human altered sex ratios in natural animal populations have been mostly disregarded. Our study together with the study of Suorsa et al (2003) is one of the first showing that anthropogenic forest loss can alter sex ratios in forest-dwelling animals.…”