Age and terminal reproductive attempt influence laying date in the thorn‐tailed rayadito

Age‐specific variation in reproductive effort can affect population dynamics, and is a key component of the evolution of reproductive tactics. Late‐life declines are a typical feature of variation in reproduction. However, the cause of these declines, and thus their implications for the evolution of life‐history tactics, may differ. Some prior studies have shown late‐life reproductive declines to be tied to chronological age, whereas other studies have found declines associated with terminal reproduction irrespective of chronological age. We investigated the extent to which declines in late life reproduction are related to chronological age, terminal reproductive attempt or a combination of both in the thorn‐tailed rayadito Aphrastura spinicauda, a small passerine bird that inhabits the temperate forest of South America. To this end we used long‐term data (10 years) obtained on reproductive success (laying date, clutch size and nestling weight) of females in a Chilean population. Neither chronological age nor terminal reproductive attempt explained variation in clutch size or nestling weight, however we observed that during the terminal reproductive attempt older females tended to lay later in the breeding season and younger females laid early in the breeding season, but this was not the case when the reproductive attempt was not the last. These results suggests that both age‐dependent and age‐independent effects influence reproductive output and therefore that the combined effects of age and physiological condition may be more relevant than previously thought.     

The impact of reproductive investment and early‐life environmental conditions on senescence: support for the disposable soma hypothesis

Several hypotheses have been put forward to explain the evolution of senescence. One of the leading hypotheses, the disposable soma hypothesis, predicts a trade‐off, whereby early‐life investment in reproduction leads to late‐life declines in survival (survival senescence). Testing this hypothesis in natural populations is challenging, but important for understanding the evolution of senescence. We used the long‐term data set from a contained, predator‐free population of individually marked Seychelles warblers (Acrocephalus sechellensis) to investigate how age‐related declines in survival are affected by early‐life investment in reproduction and early‐life environmental conditions. The disposable soma hypothesis predicts that higher investment in reproduction, or experiencing harsh conditions during early life, will lead to an earlier onset, and an increased rate, of senescence. We found that both sexes showed similar age‐related declines in late‐life survival consistent with senescence. Individuals that started breeding at a later age showed a delay in survival senescence, but this later onset of breeding did not result in a less rapid decline in late‐life survival. Although survival senescence was not directly related to early‐life environmental conditions, age of first breeding increased with natal food availability. Therefore, early‐life food availability may affect senescence by influencing age of first breeding. The disposable soma hypothesis of senescence is supported by delayed senescence in individuals that started breeding at a later age and therefore invested less in reproduction.     

Evaluating the contributions of change in investment and change in efficiency to age‐related declines in male and female reproduction

It is commonly observed that reproduction decreases with age, often at a different rate in males and females. This phenomenon is generally interpreted as senescence. Such reproductive declines may stem from at least two sources: a change in resource allocation and a decline in the ability to convert resources into offspring. This distinction is important because a shift in resource allocation may be favoured by selection, while reduced efficiency is purely deleterious. We propose a way to distinguish whether a decline in reproduction is purely deleterious based on estimating reproductive investment, output, and their ratio, efficiency. We apply this approach to the hermaphroditic snail Physa acuta and demonstrate that both male and female functions decline with age. The male decline largely stems from reduced investment into male activity while female decline is due to increased reproductive inefficiency. This shows that age‐related declines in reproduction can occur for a number of different reasons, a distinction that is usually masked by the general term ‘senescence’. This approach could be applied to any species to evaluate age‐related reproductive decline. We advocate that future studies measure age trajectories of reproductive investment and output to explore the potential processes hidden behind the observation that reproduction declines with age.     

What shall I do now? State-dependent variations of life-history traits with aging in Wandering Albatrosses

Allocation decisions depend on an organism's condition which can change with age. Two opposite changes in life‐history traits are predicted in the presence of senescence: either an increase in breeding performance in late age associated with terminal investment or a decrease due to either life‐history trade‐offs between current breeding and future survival or decreased efficiency at old age. Age variation in several life‐history traits has been detected in a number of species, and demographic performances of individuals in a given year are influenced by their reproductive state the previous year. Few studies have, however, examined state‐dependent variation in life‐history traits with aging, and they focused mainly on a dichotomy of successful versus failed breeding and non‐breeding birds. Using a 50‐year dataset on the long‐lived quasi‐biennial breeding wandering albatross, we investigated variations in life‐history traits with aging according to a gradient of states corresponding to potential costs of reproduction the previous year (in ascending order): non‐breeding birds staying at sea or present at breeding grounds, breeding birds that failed early, late or were successful. We used multistate models to study survival and decompose reproduction into four components (probabilities of return, breeding, hatching, and fledging), while accounting for imperfect detection. Our results suggest the possible existence of two strategies in the population: strict biennial breeders that exhibited almost no reproductive senescence and quasi‐biennial breeders that showed an increased breeding frequency with a strong and moderate senescence on hatching and fledging probabilities, respectively. The patterns observed on survival were contrary to our predictions, suggesting an influence of individual quality rather than trade‐offs between reproduction and survival at late ages. This work represents a step further into understanding the evolutionary ecology of senescence and its relationship with costs of reproduction at the population level. It paves the way for individual‐based studies that could show the importance of intra‐population heterogeneity in those processes.     

Early reproductive investment,senescence and lifetime reproductive success in female Asian elephants

The evolutionary theory of senescence posits that as the probability of extrinsic mortality increases with age, selection should favour early‐life over late‐life reproduction. Studies on natural vertebrate populations show early reproduction may impair later‐life performance, but the consequences for lifetime fitness have rarely been determined, and little is known of whether similar patterns apply to mammals which typically live for several decades. We used a longitudinal dataset on Asian elephants (Elephas maximus) to investigate associations between early‐life reproduction and female age‐specific survival, fecundity and offspring survival to independence, as well as lifetime breeding success (lifetime number of calves produced). Females showed low fecundity following sexual maturity, followed by a rapid increase to a peak at age 19 and a subsequent decline. High early life reproductive output (before the peak of performance) was positively associated with subsequent age‐specific fecundity and offspring survival, but significantly impaired a female's own later‐life survival. Despite the negative effects of early reproduction on late‐life survival, early reproduction is under positive selection through a positive association with lifetime breeding success. Our results suggest a trade‐off between early reproduction and later survival which is maintained by strong selection for high early fecundity, and thus support the prediction from life history theory that high investment in reproductive success in early life is favoured by selection through lifetime fitness despite costs to later‐life survival. That maternal survival in elephants depends on previous reproductive investment also has implications for the success of (semi‐)captive breeding programmes of this endangered species.     

Similar patterns of age‐specific reproduction in an island and mainland population of great tits Parus major

The process of ageing was long thought to be too infrequent to affect life‐histories in natural populations. Long‐term studies have, however, recently demonstrated ageing to be ubiquitous even in the wild, although confounding factors, such as emigration instead of mortality, or inter‐population variation in rates of ageing have seldom been addressed. Here, we present analyses of female age‐specific reproductive performance in a Dutch island population of great tits Parus major. For this population with limited connectivity to surrounding areas, we show that, between individuals, reproductive lifespan positively co‐varies with recruit production, while within individuals performance improves up to 3 years of age, after which it gradually declines. We also show these patterns to be strikingly similar to those recently found in a less isolated British mainland population of great tits, characterised by different environmental conditions and life‐history strategies, in particular the frequency of multiple breeding. Our results therefore suggest patterns of age‐specific reproductive performance to be robust to both environmental and life‐history variation.     

Life‐history tradeoffs revealed by seasonal declines in reproductive traits of Arctic‐breeding shorebirds

Seasonal declines in breeding performance are widespread in wild animals, resulting from temporal changes in environmental conditions or from individual variation. Seasonal declines might drive selection for early breeding, with implications for other stages of the annual cycle. Alternatively, selection on the phenology of nonbreeding stages could constrain timing of the breeding season and lead to seasonal changes in reproductive performance. We studied 25 taxa of migratory shorebirds (including five subspecies) at 16 arctic sites in Russia, Alaska, and Canada. We investigated seasonal changes in four reproductive traits, and developed a novel Bayesian risk‐partitioning model of daily nest survival to examine seasonal trends in two causes of nest failure. We found strong seasonal declines in reproductive traits for a subset of species. The probability of laying a full four‐egg clutch declined by 8–78% in 12 of 25 taxa tested, daily nest survival rates declined by 1–12% in eight of 22 taxa, incubation duration declined by 2.0–2.5% in two of seven taxa, and mean egg volume declined by 5% in one of 15 taxa. Temporal changes were not fully explained by individual variation. Across all species, the proportion of failed nests that were depredated declined over the season from 0.98 to 0.60, while the proportion abandoned increased from 0.01 to 0.35 and drove the seasonal declines in nest survival. An increase in abandonment of late nests is consistent with a life‐history tradeoff whereby either adult mortality increased or adults deserted the breeding attempt to maximize adult survival. In turn, seasonal declines in clutch size and incubation duration might be adaptive to hasten hatching of later nests. In other species of shorebirds, we found no seasonal patterns in breeding performance, suggesting that some species are not subject to selective pressure for early breeding.     

Age-related improvement in reproductive performance in a long-lived raptor: a cross-sectional and longitudinal study

In numerous iteroparous species, mean fecundity increases with age. Such improvement has been explained by: a) progressive removal of inferior breeders from the breeding population (selection‐hypothesis); b) delayed breeding of higher‐quality phenotypes (delayed‐breeder‐hypothesis); c) longitudinal enhancement of skills associated with age per se (age‐hypothesis); d) progressive improvement in the capability to conduct specific tasks facilitated by accumulated experience (breeding‐experience‐hypothesis); and e) increasing parental investment promoted by declining residual reproductive values (restraint‐hypothesis). To date, there have been few comprehensive tests of these hypotheses. Here, we provide such a study using a long‐term dataset on a long‐lived raptor, the black kite Milvus migrans (maximum lifespan 23 yr). Kites delayed breeding for 1–7 yr and all measures of breeding performance increased linearly or quadratically up to 11 yr of age. There was no support for the delayed‐breeder‐hypothesis: superior phenotypes did not delay breeding longer. Superior breeders were retained longer in the breeding population, consistent with the selection‐hypothesis. All measures of breeding performance increased longitudinally within individuals, supporting the age‐hypothesis, while some of them increased with accumulated previous experience, supporting the breeding‐experience‐hypothesis. Some analyses suggested the existence of trade‐offs between reproduction in the early years of life and subsequent survival, partially supporting the restraint‐hypothesis. The pattern of age‐related improvements in breeding rates observed at the population‐level could be ascribed to the combined effect of the progressive removal of inferior phenotypes from the breeding population and the individual‐level lack of specific skills which are progressively acquired with time and experience. It was also compatible with a longitudinal increase in reproductive investment. Results from previous studies suggest that different mechanisms may operate in different species and that age‐related improvements in reproduction may be frequently promoted by the complex interplay between longitudinal improvements and changes in the relative frequency of productive phenotypes in the breeding population.     

Age‐specific reproduction and disposable soma in an urban population of Common Blackbirds Turdus merula

The mechanism of senescence is an important subject of current research, but our knowledge of the factors influencing the rate of ageing in naturally occurring populations remains rudimentary. Evolutionary theories of senescence predict that investment in reproduction in early life should come at the cost of reduced somatic maintenance and thus result in earlier or more rapid senescence. We use data on the complete reproductive histories of 431 Common Blackbirds (222 males and 209 females) collected during a 19‐year study of the ecology of an urban population of this species to test the main hypotheses addressing the issue of senescence. On average, the birds in this population survived for 3.7 (± 1.9 sd) years. Reproductive success in females peaked at the age of 4, but in males remained stable until the 5th year of life. We observed declines in reproductive success, indicative of senescence, after the peak years in both sexes. The mechanism of age‐related changes in the reproduction of females confirms the individual improvement and selective disappearance hypotheses. In the case of males, the increase in reproductive performance comes as a consequence of the disappearance of poor reproducers. The parental investment associated with early life fecundity (the first two breeding seasons in males and females) impairs the breeding success of females later on. Contrary to expectations, there was no negative impact of high early life fecundity on either mortality or lifespan. Individuals of both sexes with a high early life fecundity had a higher lifetime reproductive success than those in which early life fecundity was low. Hence, the most profitable strategy is to maximize reproductive effort in the early stages of life. This yields the highest lifetime reproductive success, despite the increased impact of senescence, especially in females. These results are consistent with the disposable soma hypothesis.     

Improvement of reproductive performance with age and breeding experience depends on recruitment age in a long‐lived seabird

Reproductive success increases with age in many species, however, the underlying mechanisms remain unclear and several hypotheses have been proposed to explain age‐related improvements in reproductive output. In this contribution we investigated the effects of age, recruitment age, breeding experience and sex on reproductive performance during the early breeding career in the common tern Sterna hirundo using long‐term individual‐based data. We used measurements of performance, which spanned the entire breeding process: clutch size, hatching success, fledging success and fledglings per pair. Longitudinal analyses within individuals showed a clear increase with age in all performance measures. Furthermore, a significant change in reproductive performance was found between first time‐ and experienced breeders. Recruitment age had a strong influence on hatching and fledging success: two‐year‐old recruits had significantly lower reproductive success than birds which recruited at older ages, but the increase in breeding performance with experience was stronger in young recruits. Comparing age and experience effects, age effects were more pronounced during the first breeding attempts, whereas experience effects were also visible in subsequent breeding attempts. The degree of intra‐individual improvements in reproductive performance is due to a complex interplay of age at first breeding and experience. The results strongly support the constraint hypothesis.     

Paternal inheritance of growth in fish pursuing alternative reproductive tactics

In species with indeterminate growth, age‐related size variation of reproductive competitors within each sex is often high. This selects for divergence in reproductive tactics of same‐sex competitors, particularly in males. Where alternative tactics are fixed for life, the causality of tactic choice is often unclear. In the African cichlid Lamprologus callipterus, large nest males collect and present empty snail shells to females that use these shells for egg deposition and brood care. Small dwarf males attempt to fertilize eggs by entering shells in which females are spawning. The bourgeois nest males exceed parasitic dwarf males in size by nearly two orders of magnitude, which is likely to result from greatly diverging growth patterns. Here, we ask whether growth patterns are heritable in this species, or whether and to which extent they are determined by environmental factors. Standardized breeding experiments using unrelated offspring and maternal half‐sibs revealed highly divergent growth patterns of male young sired by nest or dwarf males, whereas the growth of female offspring of both male types did not differ. As expected, food had a significant modifying effect on growth, but neither the quantity of breeding substrate in the environment nor ambient temperature affected growth. None of the environmental factors tested influenced the choice of male life histories. We conclude that in L. callipterus growth rates of bourgeois and parasitic males are paternally inherited, and that male and female growth is phenotypically plastic to only a small degree.     

Variation in parental rearing expenditure triggers short‐term physiological effects on offspring in a long‐lived seabird

Parental care in long‐lived bird species involves a trade‐off between the benefits of increasing the effort expended on current offspring and the costs that this represents for future reproductive output. Under regimes of high environmental variability, long‐lived seabirds can adjust their breeding effort to buffer the negative effects of this variability on their offspring. However, the potential impacts of variation in breeding effort on offspring physiology in the short term and on longer‐term survival are poorly understood. In this study, we manipulated brood age through a cross‐fostering experiment to assess whether increasing or decreasing parental reproductive expenditure led to costs in Blue‐footed Booby Sula nebouxii chicks. Specifically, we tested the consequences of altered parental reproductive expenditure on the offspring's physiological condition (plasma metabolites, heterophil to lymphocyte ratio (H/L) and body condition index (BCI)) and survival. Offspring from broods in which parental investment was experimentally increased showed a lower BCI and lower alkaline phosphatase levels and higher H/L ratios than controls. Conversely, offspring showed the opposite pattern when reproductive expenditure was experimentally decreased. We observed no effects of manipulation of parental investment on triglyceride levels or on survival rates. Although our findings suggest that Blue‐footed Booby parents have the ability to adjust their breeding effort according to the demands of their offspring, parental effort could influence the effect of hatching order by suppressing the aggressive tendency of the senior chick.     

Age-dependent terminal declines in reproductive output in a wild bird

In many iteroparous species individual fitness components, such as reproductive output, first increase with age and then decline during late-life. However, individuals differ greatly in reproductive lifespan, but reproductive declines may only occur in the period just before their death as a result of an age-independent decline in physiological condition. To fully understand reproductive senescence it is important to investigate to what extent declines in late-life reproduction can be explained by age, time until death, or both. However, the study of late-life fitness performance in natural populations is challenging as the exact birth and death dates of individuals are often not known, and most individuals succumb to extrinsic mortality before reaching old age. Here, we used an exceptional long-term longitudinal dataset of individuals from a natural, closed, and predator-free population of the Seychelles warbler (Acrocephalus sechellensis) to investigate reproductive output, both in relation to age and to the time until the death of an individual (reverse-age approach). We observed an initial age-dependent increase in reproductive output that was followed by a decline in old age. However, we found no significant decline in reproductive output in the years directly preceding death. Although post-peak reproductive output declined with age, this pattern differed between terminal and non-terminal reproductive attempts, and the age-dependence of the terminal breeding attempt explained much of the variation in age-specific reproductive output. In fact, terminal declines in reproductive output were steeper in very old individuals. These results indicate that not only age-dependent, but also age-independent factors, such as physiological condition, need to be considered to understand reproductive senescence in wild-living animals.     

Plasma mammalian leptin analogue predicts reproductive phenology,but not reproductive output in a capital‐income breeding seaduck

To invest in energetically demanding life history stages, individuals require a substantial amount of resources. Physiological traits, particularly those related to energetics, can be useful for examining variation in life history decisions and trade‐offs because they result from individual responses to environmental variation. Leptin is a protein hormone found in mammals that is proportional to the amount of endogenous fat stores within an individual. Recently, researchers have confirmed that a mammalian leptin analogue (MLA), based on the mammalian sequence of leptin, is present with associated receptors and proteins in avian species, with an inhibitory effect on foraging and body mass gain at high circulating levels. While MLA has been both quantified and manipulated in avian species, little is currently known regarding whether plasma MLA in wild‐living species and individuals is associated with key reproductive decisions. We quantified plasma MLA in wild, Arctic‐nesting female common eiders (Somateria mollissima) at arrival on the breeding grounds and followed them to determine subsequent breeding propensity, and reproductive phenology, investment, and success. Common eiders are capital‐income breeding birds that require the accumulation of substantial fat stores to initiate laying and successfully complete incubation. We found that females with lower plasma MLA initiated breeding earlier and in a shorter period of time. However, we found no links between plasma MLA levels and breeding propensity, clutch size, or reproductive success. Although little is still known about plasma MLA, based on these results and its role in influencing foraging behaviors and condition gain, plasma MLA appears to be closely linked to reproductive timing and is therefore likely to underlie trade‐offs surrounding life history decisions.     

Within‐season increase in parental investment in a long‐lived bird species: investment shifts to maximize successful reproduction?

In nest‐building species predation of nest contents is a main cause of reproductive failure and parents have to trade off reproductive investment against antipredatory behaviours. While this trade‐off is modified by lifespan (short‐lived species prioritize current reproduction; long‐lived species prioritize future reproduction), it may vary within a breeding season, but this idea has only been tested in short‐lived species. Yet, life history theory does not make any prediction how long‐lived species should trade off current against future reproductive investment within a season. Here, we investigated this trade‐off through predator‐exposure experiments in a long‐lived bird species, the brown thornbill. We exposed breeding pairs that had no prior within‐season reproductive success to the models of a nest predator and a predator of adults during their first or second breeding attempt. Overall, parents reduced their feeding rate in the presence of a predator, but parents feeding second broods were more risk sensitive and almost ceased feeding when exposed to both types of predators. However, during second breeding attempts, parents had larger clutches and a higher feeding rate in the absence of predators than during first breeding attempts and approached both types of predators closer when mobbing. Our results suggest that the trade‐off between reproductive investment and risk‐taking can change in a long‐lived species within a breeding season depending on both prior nest predation and renesting opportunities. These patterns correspond to those in short‐lived species, raising the question of whether a within‐season shift in reproductive investment trade‐offs is independent of lifespan.     

The Influence of Age on Male Mate‐Searching Behaviour in Thornbug Treehoppers

One prediction from life‐history theory is that males should increase investment in reproductive effort as they age because the opportunity for future reproductive events declines. However, older males may not be able to increase their reproductive effort if condition declines with age. The effect of age‐related changes in condition may be especially important for energetically costly activities such as moving within and between habitat patches while searching for mates. Although such searching is a component of many mating systems, the relationship between age and active mate searching has not been investigated. We investigated whether mate‐searching effort increased with age in the thornbug treehopper, Umbonia crassicornis (Hemiptera: Membracidae). In this species, males search for females using a ‘fly‐call‐walk’ strategy consisting of three phases: (1) flying from one plant to another; (2) walking and signalling while on a plant; and (3) close‐range courtship of encountered females. We measured several aspects of mate‐searching behaviour over the month‐long period of a male’s reproductive lifetime. Over the relevant period of male sexual activity (19–33 d), male condition remained stable. However, older males (25–33 d) did not search more actively than younger males as predicted; instead, younger males (19 d) had greater plant‐to‐plant flight activity and found females faster. Within‐plant walking rates and courtship duration did not differ among age classes. These results suggest that thornbug males may be investing so heavily in mate searching at younger ages that they are unable to increase investment in searching effort when they get older. As a result, older males are likely to be at a competitive disadvantage when active searching is required to locate sparsely distributed females.     

Aging in personal and social immunity: do immune traits senesce at the same rate?

How much should an individual invest in immunity as it grows older? Immunity is costly and its value is likely to change across an organism's lifespan. A limited number of studies have focused on how personal immune investment changes with age in insects, but we do not know how social immunity, immune responses that protect kin, changes across lifespan, or how resources are divided between these two arms of the immune response. In this study, both personal and social immune functions are considered in the burying beetle, Nicrophorus vespilloides. We show that personal immune function declines (phenoloxidase levels) or is maintained (defensin expression) across lifespan in nonbreeding beetles but is maintained (phenoloxidase levels) or even upregulated (defensin expression) in breeding individuals. In contrast, social immunity increases in breeding burying beetles up to middle age, before decreasing in old age. Social immunity is not affected by a wounding challenge across lifespan, whereas personal immunity, through PO, is upregulated following wounding to a similar extent across lifespan. Personal immune function may be prioritized in younger individuals in order to ensure survival until reproductive maturity. If not breeding, this may then drop off in later life as state declines. As burying beetles are ephemeral breeders, breeding opportunities in later life may be rare. When allowed to breed, beetles may therefore invest heavily in “staying alive” in order to complete what could potentially be their final reproductive opportunity. As parental care is important for the survival and growth of offspring in this genus, staying alive to provide care behaviors will clearly have fitness payoffs. This study shows that all immune traits do not senesce at the same rate. In fact, the patterns observed depend upon the immune traits measured and the breeding status of the individual.     

Genome‐wide prediction of age at puberty and reproductive longevity in sows

Traditional selection for sow reproductive longevity is ineffective due to low heritability and late expression of the trait. Incorporation of DNA markers into selection programs is potentially a more practical approach for improving sow lifetime productivity. Using a resource population of crossbred gilts, we explored pleiotropic sources of variation that influence age at puberty and reproductive longevity. Of the traits recorded before breeding, only age at puberty significantly affected the probability that females would produce a first parity litter. The genetic variance explained by 1‐Mb windows of the sow genome, compared across traits, uncovered regions that influence both age at puberty and lifetime number of parities. Allelic variants of SNPs located on SSC5 (27–28 Mb), SSC8 (36–37 Mb) and SSC12 (1.2–2 Mb) exhibited additive effects and were associated with both early expression of puberty and a greater than average number of lifetime parities. Combined analysis of these SNPs showed that an increase in the number of favorable alleles had positive impact on reproductive longevity, increasing number of parities by up to 1.36. The region located on SSC5 harbors non‐synonymous alleles in the arginine vasopressin receptor 1A (AVPR1A) gene, a G‐protein‐coupled receptor associated with social and reproductive behaviors in voles and humans and a candidate for the observed effects. This region is characterized by high levels of linkage disequilibrium in different lines and could be exploited in marker‐assisted selection programs across populations to increase sow reproductive longevity.     

Divergent patterns of age-dependence in ornamental and reproductive traits in the collared flycatcher

Sexual ornaments are predicted to honestly signal individual condition. We might therefore expect ornament expression to show a senescent decline, in parallel with late-life deterioration of other characters. Conversely, life-history theory predicts the reduced residual reproductive value of older individuals will favor increased investment in sexually attractive traits. Using a 25-year dataset of more than 5000 records of breeding collared flycatchers (Ficedula albicollis) of known age, we quantify cross-sectional patterns of age-dependence in ornamental plumage traits and report long-term declines in expression that mask highly significant positive age-dependency. We partition this population-level age-dependency into its between- and within-individual components and show expression of ornamental white plumage patches exhibits within-individual increases with age in both sexes, consistent with life-history theory. For males, ornament expression also covaries with life span, such that, within a cohort, ornamentation indicates survival. Finally, we compared longitudinal age-dependency of reproductive traits and ornamental traits in both sexes, to assess whether these two trait types exhibit similar age-dependency. These analyses revealed contrasting patterns: reproductive traits showed within-individual declines in late-life females consistent with senescence; ornamental traits showed the opposite pattern in both males and females. Hence, our results for both sexes suggest that age-dependent ornament expression is consistent with life-history models of optimal signaling and, unlike reproductive traits, proof against senescence.     

Tawny Owl Strix aluco as an indicator of Barn Owl Tyto alba breeding biology and the effect of winter severity on Barn Owl reproduction

In the temperate zone, food availability and winter weather place serious constraints on European Barn Owl Tyto alba populations. Using data collected over 22 years in a Swiss population, we analysed the influence of early pre‐breeding food conditions and winter severity on between‐year variations in population size and reproductive performance. To estimate pre‐breeding food conditions, we attempted a novel approach based on an index that combines Tawny Owl Strix aluco reproductive parameters and the occurrence of wood mice Apodemus sp. in their diet. Tawny Owls breed earlier in the season than Barn Owls and are strongly dependent on the abundance of wood mice for breeding. This index was strongly positively associated with the number of breeding pairs and early breeding in the Barn Owl. Winter severity, measured by snow cover and low temperatures, had a pronounced negative influence on the size of the breeding population and clutch size. Food conditions early in the breeding season and winter severity differentially affect the Barn Owl life cycle. We were able to use aspects of the ecology and demography of the Tawny Owl as an indicator of the quality of the environment for a related species of similar ecology, in this case the Barn Owl.