Sex‐specific patterns of reproductive senescence in a long‐lived reintroduced raptor

Abstract

For many species, there is evidence that breeding performance changes as an individual ages. In iteroparous species, breeding performance often increases through early life and is expected to level out or even decline (senesce) later in life. An individual's sex and conditions experienced in early life may also affect breeding performance and how this changes with age. Long-term monitoring of individuals from reintroduced populations can provide unique opportunities to explore age-related trends in breeding performance that might otherwise be logistically challenging. We used a unique dataset from a reintroduced population of white-tailed eagles Haliaeetus albicilla in Scotland, which has been intensively monitored since their initial reintroduction in 1975, to study age- and sex-specific trends in two measures of breeding performance. This monitoring provided data on the breeding performance of known individuals ranging in age from 3 to 26 years. We also explored changes in breeding performance in relation to early life experience (i.e., whether they were released or fledged in the wild). Breeding performance increased with age in early life in a similar manner for both sexes. We found stronger evidence for senescence in breeding performance in males than females. However, late-life female breeding success was associated with early life experience, while male senescent trends were not apparently impacted by conditions experienced during early life. Sexual differences in senescence mean that older males are less likely to breed successfully compared to older females, and this may influence females' mate changes later in life. This difference may suggest a linked sexual difference in survival rates or the possibility of proactive partner change by females in later life in this typically monogamous biparental species.

The role of parasitism in the energy management of a free-ranging bird

“…However, we found no effect of age on RMR in females. Sex-specific senescence occurs in a number of wild vertebrate populations, possibly due to different trade-offs existing with age in males and females (Clay et al, 2018; Froy et al, 2013, 2017; Murgatroyd et al, 2018).…”

Landscape homogenization due to agricultural intensification disrupts the relationship between reproductive success and main prey abundance in an avian predator

“…Age was hence included as a two-level factor variable in our analyses. In raptors, young breeders usually start egg-laying later (e.g., [30, 50]) and have lower breeding success (e.g., [31, 32]). As mentioned before, the high turn-over and divorce rate in our study population does not leave us with many ringed adults that would allow a more exact age estimation.…”

“…Another commonly used individual quality measurement is the age of the breeding adults, that relates to breeding experience, and is well known to influence both the timing of breeding and breeding success (as for example documented in our study system, e.g. : [30–32]).…”

Distinguishing within- from between-individual effects: How to use the within-individual centering method for quadratic patterns

“…In the case of age patterns, the among-individual effect may be generated by both selective appearance and disappearance effects (van de Pol and Verhulst 2006), making estimation of the among-individual effect more complicated. In addition, several studies strongly suggest moving away from polynomial models in favour of threshold models when studying aging patterns (Berman et al 2009; Froy et al 2017; Murgatroyd et al 2018; Rodríguez-Muñoz et al 2019). In this context, an interesting alternative method closely related to the within-individual centering is the use of age at first and last reproduction as fixed covariates (van de Pol and Verhulst 2006).…”