Interactive effects of parental age and environmental variation on the breeding performance of Tengmalm’s owls

Abstract

Summary1. Two main mechanisms have been proposed to account for the changes in breeding performance of long-lived animals with age: progressive appearance or disappearance of different quality individuals within a cohort and within-individual improvements with age. 2. We studied age-related breeding performance of vole-eating Tengmalm's owls ( Aegolius funereus , L.), whose prey populations fluctuate in a cyclic manner in western Finland. In years of low vole abundance, most yearling owls were not able to breed. In years of initially intermediate but increasing vole abundance, clutch size increased with female age and partners of old males initiated egg-laying earlier than those of young males. In years of initially high but decreasing vole abundance, the differences in laying dates were still detectable, whereas age-related differences in clutch size of females tended to disappear. 3. Within-cohort analyses did not indicate quality differences between surviving and dying males of the same age in years of increasing vole abundance, whereas in years of decreasing vole abundance early breeding males were more likely to survive than late-breeding males. This novel finding indicates that quality differences between individuals may induce observed age-related differences in only some years, and especially that differential mortality may occur in a different year when the difference in breeding performance is detectable. 4. Within-individual analyses showed that individual males advanced their nest initiation with age, and there was a trend that females laid larger clutches with increasing age. In nests of long-lived males, a significant decline in the clutch size from mid-age (2-4 years) to older age (6-10 years) was found. 5. We conclude that environmental variation may mask age-related differences in breeding performance at the population level, since the differences appeared to emerge more clearly in poor and intermediate food conditions. Some evidence for the differential mortality-hypothesis was found for males, which are mainly responsible for subsisting their families during the entire breeding season. Substantial improvements in competence or increased reproductive effort from 1 to 3 years of age, and deteriorated skills due to senescence at older ages may account for within-individual changes in breeding performance of males.

Hatching asynchrony and brood reduction in Tengmalm's owl Aegolius funereus: the role of temporal and spatial variation in food abundance

“…and small passerine birds, but at such times the over-winter survival of owls is low and only experienced high-quality individuals are able to breed (Korpimäki 1988b). The owls are able to breed as yearlings, although yearling males do not breed during years of food scarcity (Korpimäki 1981(Korpimäki , 1988bLaaksonen et al 2002). First eggs are usually laid in late March to early April, and the timing of laying depends largely on winter vole densities (Korpimäki and Hakkarainen 1991).…”

Reproduction and migration in relation to senescence in the barn swallow Hirundo rustica: A study of avian ‘centenarians’

“…Recently, several studies demonstrating senescence in free-living organisms through measurements of age-dependent mortality, reproduction and reproductive value have been published [e.g., Gustafsson and Pärt (1990); Perdeck and Cavé (1992); Newton and Rothery (1997); Bérubé et al (1999); Møller and de Lope (1999); Espie et al (2000); Sanz and Moreno (2000); Pyle et al (2001); Robertson and Rendell (2001); Cam et al (2002); Laaksonen et al (2002); Orell and Belda (2002); Reid et al (2003)]. Several of these studies have investigated patterns of age-specific fecundity and mortality, showing how reproductive performance and survival late in life are related to early performance.…”

Age-related improvement of reproductive success in BluethroatsLuscinia svecica

“…The influence of parental age has been investigated mainly in longliving birds (Coulson 1966, Hamer & Furness 1991, Laaksonen et al 2002 and was not well-known in short-lived species (Green 2001, McGraw et al 2001. The influence of the age of the male remained poorly documented.…”