The long shadow of senescence: age impacts survival and territory defense in loons

Abstract

Senescence, increased mortality that occurs among animals of advanced age, impacts behavior and ecology in many avian species. We investigated actuarial, reproductive, and behavioral senescence using capture, marking, and resighting data from a 26‐year study of common loons Gavia immer. Territorial residents of both sexes exhibited high annual survival (0.94) until their mid 20s, at which point survival fell to 0.76 and 0.77 in males and females, respectively. Sexual symmetry in actuarial senescence is somewhat surprising in this species, because males make a substantially greater investment in territory defense and chick‐rearing and because males engage in lethal contests for territory ownership. Survival of displaced breeders (0.80) was lower than that of territorial residents in both young and old individuals. Old males and females also experienced slightly higher annual probability of eviction (0.16 for males; 0.17 for females) than prime‐aged breeders (0.13 for both sexes), indicating senescence in territory defense. Prime‐aged males reclaimed territories at a high rate (0.49), in contrast to females of the same age (0.33). However, old males resettled with success (0.35) similar to old females (0.31), suggesting that males decline in competitive ability as they age. Nonetheless males, but not females, showed an apparent increase in breeding success over the entire lifetime, a possible indication that very old males make a terminal investment in reproductive output at the cost of survival.

Aging and Senescence across Reproductive Traits and Survival in Superb Fairy-Wrens (Malurus cyaneus)

“…The ageing of these traits was highly asynchronous, with variable rates and durations of both early-adulthood improvements and late-life declines, with some traits not showing any period of maturation in early adulthood, and others not showing senescence. Our results add to the growing body of empirical evidence that traits do not senescence synchronously within an individual (Nussey et al 2009;Froy et al 2013;Hayward et al 2013Hayward et al , 2015Zhang et al 2015;Piper et al 2017;Tompkins and Anderson 2018). Below we discuss how the patterns of ageing in fairy-wrens fit with theory and empirical research on ageing, and consider how the distinctive ecological and evolutionary forces faced by this species may be driving these patterns.…”

“…In recent years, it has become possible to characterize this "generalized deterioration" by measuring the ageing of multiple fitness-related traits in wild animal populations. However, the empirical evidence to date suggests that, rather than senescing in unison, either the onset of senescence, or the rates of senescent declines often vary between different phenotypic traits (for example, Bouwhuis et al 2012;Massot et al 2011;Preston et al 2011;Froy et al 2013;Hayward et al 2013;Berger et al 2015a;Zhang et al 2015;Hammers et al 2015;Kervinen et al 2015;Piper et al 2017). In a recent review, Bouwhuis and Vedder (2017) show that, amongst longitudinal studies of ageing in wild bird populations, performance declines are most often reported for physiological traits (89% of which show a decline), and less so for traits involved in reproductive performance (67%) or traits associated with sexual selection (50%).…”

Ageing and senescence across reproductive traits and survival in superb fairy-wrens (Malurus cyaneus)

“…The ageing of these traits was highly asynchronous, with variable rates and durations of both early-adulthood improvements and late-life declines, with some traits not showing any period of maturation in early adulthood, and others not showing senescence. Our results add to the growing body of empirical evidence that traits do not senescence synchronously within an individual (Nussey et al 2009;Froy et al 2013;Hayward et al 2013Hayward et al , 2015Zhang et al 2015;Piper et al 2017;Tompkins and Anderson 2018). Below we discuss how the patterns of ageing in fairy-wrens fit with theory and empirical research on ageing, and consider how the distinctive ecological and evolutionary forces faced by this species may be driving these patterns.…”

Common Loons respond adaptively to a black fly that reduces nesting success

“…The lack of an impact of male age on abandonment provides an interesting contrast to females and sheds more light on the sexual difference in breeding success with age among loons. Both sexes senesce, as annual survival rate falls steeply when loons reach their mid-20s, but fledgling production increases with age in males, while showing no clear change in females (Piper et al 2017). The fact that old males resist nest abandonment better than old females is consistent with the conclusion that males, but not females, might make a terminal investment in incubation that accounts, at least in part, for their greater fledgling production (Piper et al 2017).…”

“…Recent work has shown that loons of both sexes senesce once they reach their mid-20s (Piper et al 2017). Since old birds of many species show declines in reproductive performance with age (e.g., Reed et al 2008, Sergio et al 2011, Pardo et al 2013, the strong tendency for pairs containing old females to abandon nests is perhaps not surprising.…”