It has been hypothesized that parents increase their fitness by biasing the sex ratio of extra-pair offspring (EPO) towards males. Here, we report a male bias among EPO in a wild population of blue tits (Cyanistes caeruleus). This resulted from a decline in both the proportion of males and EPO over the laying order of eggs in the clutch. However, previous studies suggest that, unlike the decline in EPO with laying order, the relationship between offspring sex ratio and laying order is not consistent between years and populations in this species. Hence, we caution against treating the decline in proportion of males with laying order, and the resulting male bias among EPO, as support for the above hypothesis. Variable patterns of offspring sex and paternity over the laying order may explain inconsistent associations between offspring sex and paternity, between and within species.
The data package contains one dataset:
- Laying order, sex and paternity of blue tit hatchlings in 2009
Laying order, sex and paternity of 743 blue tit hatchlings in 2009, from 68 broods.
|Datum van beschikbaarheid||11-sep-2013|
|Uitgever||University of Groningen|
|Datum van data-aanmaak||2009|
|Geografische dekking||The Netherlands|