Early-life experience shapes patterns of senescence in a food-caching passerine

Abstract

For many species, breeding performance increases through early adulthood followed by declines later in life. Although patterns of age-specific decline have been shown to vary between individuals, the factors that lead to this individual variation in the intensity of reproductive senescence are yet to be fully understood. We investigated whether early-life social status influenced age-related trends in the breeding performance of male Canada jays (Perisoreus canadensis), year-round residents of North America's boreal and sub-alpine forests. Shortly after young become nutritionally independent, intra-brood dominance struggles lead to one juvenile (Dominant Juvenile) remaining on the natal territory after expelling its subordinate siblings (Ejectees). First, we show via radio tracking that in our declining range-edge population Ejectees either join an unrelated pair (67%), form a breeding pair with another bird (28%) or occupy a territory alone (5%). Second, using 39 years of breeding data, we demonstrate that Ejectee males advanced laying dates and increased the annual number of nestlings until 6 years of age before declining, whereas Dominant Juvenile males advanced laying dates until 11 years and increased annual number of nestlings until 12 years of age before declining. This study documents clear variation in ageing patterns between dominant and expelled young, with implications for the role of early-life experiences and phenotypic quality in determining patterns of ageing.

Keywords: Canada jay; dispersal timing; food hoarding; lifespan.

Figure 1.

The relationship between age and reproductive performance of Dominant Juveniles (blue) and Ejectee (grey) juvenile Canada jay males. Mean reproductive performance is shown (circles ± s.e.). (a) Laying date with a fitted cubic model (±95% CI) for Dominant Juveniles, and a threshold model (±95% CI) for Ejectees and (b) annual number of nestlings with fitted threshold models (±95% CI). The solid bars above the x-axis in (a) and (b) reflect the breakpoints of the top threshold models and the dotted lines indicate 95% confidence intervals [28]. Sample sizes for each age group are indicated for Dominant Juvenile (blue text) and Ejectee (grey text) males.