Publication details
Sex- and age-biased mortality in wild Grey Partridge Perdix perdix populations
| Authors | |
|---|---|
| Year of publication | 2012 |
| Type | Article in Periodical |
| Magazine / Source | IBIS |
| MU Faculty or unit | |
| Citation | |
| Web | Full Text |
| Doi | http://dx.doi.org/10.1111/j.1474-919X.2012.01259.x |
| Field | Zoology |
| Keywords | Cox proportional hazard model; radiotracking; survival |
| Description | Differing reproductive effort, individual qualities and local environmental conditions can lead to uneven mortality risk among individuals within populations, and may result in survival differences according to age and sex. Identification of factors contributing to unequal operational sex ratios has been important for understanding population dynamics and conservation management. In this study, sex- and age-specific mortality was estimated in three wild Grey Partridge populations year round from analysis of radio-tracking data from a total of 168 individuals. Survival days were counted in three periods defined individually for each animal: the pairing period (covey break-up to laying of the first egg); the nesting period (between clutch initiation date and failure of the last nesting attempt, or the date when chicks were 14 days old); and the covey period (the end of the nesting period or joining a group until covey break-up). Predation was the main cause of mortality. A significant effect of age on survival was found during the pairing period, when older individuals paired off faster and survived better. The highest mortality risk overall was found during the nesting period. Furthermore, significantly higher mortality of females was recorded during the nesting period, suggesting that greater investments in reproduction, behaviour at the nest or the quality of nesting habitats can decrease survival of females and cause a male-biased sex ratio. No significant effect of age or sex was found during the covey period, nor for the year as a whole, but there was a significant difference in annual mortality rates between the three study populations. Our results confirm age- and sex-specific variation of adult mortality in a ground nesting bird with biparental care during the year-round cycle, documenting differing sensitivities of various population cohorts to predation. |