Effects of age,sex, and ENSO phase on foraging and flight performance in Nazca boobies

Age‐related changes in survival and reproduction are common in seabirds; however, the underlying causes remain elusive. A lack of experience for young individuals, and a decline in foraging performance for old birds, could underlie age‐related variation in reproduction because reproductive success is connected closely to provisioning offspring. For seabirds, flapping flight during foraging trips is physiologically costly; inexperience or senescent decline in performance of this demanding activity might cap delivery of food to the nest, providing a proximate explanation for poor breeding success in young and old age, respectively. We evaluated the hypothesis that young and old Nazca boobies (Sula granti), a Galápagos seabird, demonstrate deficits in foraging outcomes and flight performance. We tagged incubating male and female adults across the life span with both accelerometer and GPS loggers during the incubation periods of two breeding seasons (years), during the 2015 El Niño and the following weak La Niña. We tested the ability of age, sex, and environment to explain variation in foraging outcomes (e.g., mass gained) and flight variables (e.g., wingbeat frequency). Consistent with senescence, old birds gained less mass while foraging than middle‐aged individuals, a marginal effect, and achieved a slower airspeed late in a foraging trip. Contrary to expectations, young birds showed no deficit in foraging outcomes or flight performance, except for airspeed (contingent on environment). Young birds flew slower than middle‐aged birds in 2015, but faster than middle‐aged birds in 2016. Wingbeat frequency, flap–glide ratio, and body displacement (approximating wingbeat strength) failed to predict airspeed and were unaffected by age. Sex influenced nearly all aspects of performance. Environment affected flight performance and foraging outcomes. Boobies'' foraging outcomes were better during the extreme 2015 El Niño than during the 2016 weak La Niña, a surprising result given the negative effects tropical seabirds often experience during extreme El Niños.     

Parental age and lifespan influence offspring recruitment: a long-term study in a seabird

Recent studies of wild populations provide compelling evidence that survival and reproduction decrease with age because of senescence, a decline in functional capacities at old ages. However, in the wild, little is known about effects of parental senescence on offspring quality. We used data from a 21-year study to examine the role of parental age on offspring probability of recruitment in a long-lived bird, the blue-footed booby (Sula nebouxii). Offspring probability of recruiting into the breeding population varied over the life of parents and effects age were similar in mothers and fathers. Offspring recruitment was high when parents were roughly 6-12 years old and low before and after then. Effects of parental age on offspring recruitment varied with lifespan (parental age at last reproduction) and previous breeding experience. Offspring recruitment from young and old parents with long reproductive lifespans was greater than that of offspring from parents with short lifespans at young and old ages. For parents with little previous breeding experience recruitment of offspring decreased with their hatch date, but experienced parents were no similarly affected. We found evidence of terminal effects on offspring recruitment in young parents but not in older parents, suggesting that senescence is more likely a gradual process of deterioration than a process of terminal illness. Failure to recruit probably reflects mortality during the first years after independence but also during the fledgling transition to full independence. Our results show effects of parental age and quality on offspring viability in a long-lived wild vertebrate and support the idea that wild populations are composed of individuals of different quality, and that this individual heterogeneity can influence the dynamics of age-structured populations.     

Reduced reproductive performance prior to death in the Black‐legged Kittiwake: senescence or terminal illness?

The breeding of Black-legged Kittiwakes Rissa tridactyla in their last breeding season has been compared with that of pairs which survived to the next breeding season. The time of laying was not affected but the clutch size, breeding success and productivity were significantly lower and a higher proportion of pairs totally failed to rear any young in pairs where one of the partners died before the next breeding season. When both partners died before the next breeding season, the breeding performance was reduced to a greater extent, suggesting an additive influence. The depressive effect on the last breeding attempt was confirmed by comparing the breeding success of individual females in their ultimate and penultimate breeding attempts. The effect was present in breeding birds of all ages, from first time breeders to the oldest individuals, and so could not be interpreted as an effect of senescence. Most of the adults which died apparently did so several months after breeding, during the winter half of the year when the kittiwake is oceanic. It is suggested that this depressive effect on breeding is the result of terminal illness which caused the birds to lose condition progressively over several weeks or months. It is possible that stress in the form of disease or parasite infections is primarily responsible for the death of many of the individuals. Attention is drawn to the possible confusion between the effect reported here and claims that senescence leads to lower reproductive output in old birds. It is suggested that more critical examinations are needed of claims that senescence directly affects the breeding success of birds.     

Geographical variation in reproductive ageing patterns and life‐history strategy of a short‐lived passerine bird

We investigated differences in ageing patterns in three measures of breeding performance in populations of barn swallows Hirundo rustica L. from Spain and Denmark differing in breeding latitude and hence migration distance and duration of the breeding season. We found differences in ageing patterns between populations. Generally, young (i.e. yearling) and old females (i.e. ≥ 5 years of age) laid their first eggs later and produced smaller clutches than middle‐aged females (i.e. 2–4 years of age) in both populations. The southernmost population (i.e. Spanish) showing the shorter migratory distance experienced a greater within‐individual increase in timing of breeding and clutch size in early life and a greater within‐individual decrease in laying date but not in clutch size during senescence compared with the northernmost population (i.e. Danish). We also found that the number of fledglings produced annually was related to the age of the two members of the breeding pairs with pairs composed of young and old females performing less well than breeding pairs composed of middle‐aged females. We did not find reproductive senescence for the age of the male while controlling for the age of the female on the number of fledglings produced annually by the breeding pair. Differential survival between individuals did not explain age effects on laying date or annual clutch size in neither population. However, the increase in the number of fledglings produced annually with age was partly explained by the disappearance of poor‐quality members of the pairs, mainly poor‐quality males. Age‐related breeding success (i.e. number of fledglings) was similar for barn swallows from Spain and Denmark. Therefore, the study of ageing patterns and life‐history strategies in free‐ranging animals from more than a single population can throw new light on life‐history theory, population dynamics and evolutionary studies of senescence.     

Age-Related Variation in Foraging Behaviour in the Wandering Albatross at South Georgia: No Evidence for Senescence

Age-related variation in demographic rates is now widely documented in wild vertebrate systems, and has significant consequences for population and evolutionary dynamics. However, the mechanisms underpinning such variation, particularly in later life, are less well understood. Foraging efficiency is a key determinant of fitness, with implications for individual life history trade-offs. A variety of faculties known to decline in old age, such as muscular function and visual acuity, are likely to influence foraging performance. We examine age-related variation in the foraging behaviour of a long-lived, wide-ranging oceanic seabird, the wandering albatross Diomedea exulans. Using miniaturised tracking technologies, we compared foraging trip characteristics of birds breeding at Bird Island, South Georgia. Based on movement and immersion data collected during the incubation phase of a single breeding season, and from extensive tracking data collected in previous years from different stages of the breeding cycle, we found limited evidence for age-related variation in commonly reported trip parameters, and failed to detect signs of senescent decline. Our results contrast with the limited number of past studies that have examined foraging behaviour in later life, since these have documented changes in performance consistent with senescence. This highlights the importance of studies across different wild animal populations to gain a broader perspective on the processes driving variation in ageing rates.     

When Celibacy Matters: Incorporating Non-Breeders Improves Demographic Parameter Estimates

In long-lived species only a fraction of a population breeds at a given time. Non-breeders can represent more than half of adult individuals, calling in doubt the relevance of estimating demographic parameters from the sole breeders. Here we demonstrate the importance of considering observable non-breeders to estimate reliable demographic traits: survival, return, breeding, hatching and fledging probabilities. We study the long-lived quasi-biennial breeding wandering albatross (Diomedea exulans). In this species, the breeding cycle lasts almost a year and birds that succeed a given year tend to skip the next breeding occasion while birds that fail tend to breed again the following year. Most non-breeders remain unobservable at sea, but still a substantial number of observable non-breeders (ONB) was identified on breeding sites. Using multi-state capture-mark-recapture analyses, we used several measures to compare the performance of demographic estimates between models incorporating or ignoring ONB: bias (difference in mean), precision (difference is standard deviation) and accuracy (both differences in mean and standard deviation). Our results highlight that ignoring ONB leads to bias and loss of accuracy on breeding probability and survival estimates. These effects are even stronger when studied in an age-dependent framework. Biases on breeding probabilities and survival increased with age leading to overestimation of survival at old age and thus actuarial senescence and underestimation of reproductive senescence. We believe our study sheds new light on the difficulties of estimating demographic parameters in species/taxa where a significant part of the population does not breed every year. Taking into account ONB appeared important to improve demographic parameter estimates, models of population dynamics and evolutionary conclusions regarding senescence within and across taxa.     

洋县野生朱Huan的繁殖

朱鹮(Nipponia nippon)的繁殖状况 ,尤其是种群数量的变化 ,一直受到国内外的关注。本文收集分析了 1 981～ 1 997年 1 7年朱繁殖资料 ,进一步研究了朱的繁殖及其数量 ,以期为朱保护 ,采取行之有效的措施 ,提供科学依据。1　研究方法自 1 981年朱被重新发现后 ,至 1 997年 ,每年3～ 6月繁殖期 ,固定人员 ,2～ 3人为 1组 ,在每个巢区设立观察点 ,进行跟踪观察 ,并详细统计每窝产卵数、孵化数、雏鸟成活数和死亡数。并结合平常的跟踪监护 ,调查分析种群数量动态 ,统计成鸟死亡数 ,然后进行整理分析。2　结果与讨论2 .1　种群数量1 98…     

Increased adult mortality and reduced breeding success with age in a population of common guillemot Uria aalge using marked birds of unknown age

Although there is general consensus about the existence of senescence in vertebrates, empirical evidence of senescence in demographic parameters in wild populations is limited. Data on breeding success and survival of breeding common guillemots Uria aalge were collected over 20 years on the Isle of May (Scotland) using a pool of individuals marked as adults. Because the years of hatching of individuals were not known, we used the time (years) elapsed since first capture (TFC) as a measure of age. The use of this proxy did not create any bias in estimating senescence in the case of a linear decline, nor did it greatly decrease the power of a test for senescence. Breeding success declined significantly from 0.81 (95% CI: 0.77–0.84) to 0.62 (0.54–0.68) over the study period. It also varied in relation to age, initially increasing (from 0.62 (0.54–0.68) at TFC of 0 year to 0.76 (0.73–0.79) at TFC of 9 years) up to a plateau (from TFC of 9 years with 0.76 (0.73–0.79) until TFC of 13 years with 0.77 (0.74–0.79) before declining in later life to 0.70 (0.61–0.78) at TFC of 19 years). Survival was generally high and varied significantly from year to year. It also declined with TFC: survival of birds marked in 1982 decreased from 0.92 (0.85–0.96) at a TFC of 0 year to 0.88 (0.82–0.92) at a TFC of 19 years. Resighting probabilities also declined with TFC suggesting that the oldest birds do not come back to the colony to breed as regularly as younger individuals. These findings indicate that individual common guillemots on the Isle of May showed both actuarial and reproductive senescence.     

Life history of breeding partners alters age‐related changes of reproductive traits in a natural population of blue tits

Reproductive senescence, an intra‐individual decline in reproductive function with age, is widespread, but proximate factors determining its rate remain largely unknown. Most studies of reproductive senescence focus on females, leaving senescence in male function and its implications for female function largely understudied. We constructed linear mixed models to explore the interactive effects of paternal and maternal age and a life‐history trait (i.e. age at first reproduction) on four fitness components (i.e. laying date, clutch size, number of fledglings and number of recruits) measured in a wild, breeding population of blue tits Cyanistes caeruleus ogliastrae where individual breeding success has been followed for over 30 years (our dataset spanned 29 years). Previous studies have shown that, across female lifespan, laying date decreases and subsequently increases; earlier laying dates result in higher fitness because hatchlings have greater access to a seasonal food source. Our analyses reveal that females that initiate reproduction early in life show a greater delay in laying date with old age. In addition to delayed laying dates, older females lay smaller clutches. However, the magnitude of female age effects was influenced by the age at first reproduction of their breeding partners. Senescence of laying date and clutch size was reduced when females mated with males that reproduced early in life compared to males that delayed reproduction. We confirmed that both laying date and clutch size were significantly correlated with reproductive fitness suggesting that these dynamics early in the breeding cycle can have long‐term consequences. These complex phenotypic interactions shed light on the proximate mechanisms underlying reproductive senescence in nature and highlight the potential importance of cross‐sex age by life‐history interactions.     

Does Foraging Performance Change with Age in Female Little Penguins (Eudyptula minor)?

Age-related changes in breeding performance are likely to be mediated through changes in parental foraging performance. We investigated the relationship of foraging performance with age in female little penguins at Phillip Island, Australia, during the guard phase of the 2005 breeding season. Foraging parameters were recorded with accelerometers for birds grouped into three age-classes: (1) young, (2) middle age and (3) old females. We found the diving behaviour of middle-aged birds differed from young and old birds. The dive duration of middle age females was shorter than that of young and old birds while their dive effort (measure for dive and post-dive duration relation) was lower than that of young ones, suggesting middle-aged birds were in better physical condition than other ones. There was no difference in prey pursuit frequency or duration between age classes, but in the hunting tactic. Females pursued more prey around and after reaching the maximum depth of dives the more experienced they were (old > middle age > young), an energy saving hunting tactic by probably taking advantage of up-thrust momentum. We suggest middle age penguins forage better than young or old ones because good physical condition and foraging experience could act simultaneously.     

Individual covariation in life-history traits: seeing the trees despite the forest

We investigated the influence of age on survival and breeding rates in a long-lived species Rissa tridactyla using models with individual random effects permitting variation and covariation in fitness components among individuals. Differences in survival or breeding probabilities among individuals are substantial, and there was positive covariation between survival and breeding probability; birds that were more likely to survive were also more likely to breed, given that they survived. The pattern of age-related variation in these rates detected at the individual level differed from that observed at the population level. Our results provided confirmation of what has been suggested by other investigators: within-cohort phenotypic selection can mask senescence. Although this phenomenon has been extensively studied in humans and captive animals, conclusive evidence of the discrepancy between population-level and individual-level patterns of age-related variation in life-history traits is extremely rare in wild animal populations. Evolutionary studies of the influence of age on life-history traits should use approaches differentiating population level from the genuine influence of age: only the latter is relevant to theories of life-history evolution. The development of models permitting access to individual variation in fitness is a promising advance for the study of senescence and evolutionary processes.     

Individual changes underlie age-specific pattern of laying date and egg-size in female common terns Sterna hirundo

It has been suggested that breeding performance differs between young and old birds due to the appearance and disappearance of phenotypes through differential survival (selection hypothesis) or differential recruitment (delayed breeding hypothesis) of high-quality individuals, but each bird may show constant breeding performance over its life. We tested constant egg-volume and laying date by modelling their variability on the basis of the 109 known-age females of common tern Sterna hirundo with data available from 1 to 9 years. Longitudinal analyses showed a significant advancement of laying date, as well as a steady increase in egg-volume, in young age classes from 2 to 5–7 years old, indicating individual intrinsic changes in performance with age. In our model, female effect accounted for 74% and 8% of variance in egg-volume and laying date, respectively, suggesting that if correlation between breeding performance and survival or recruitment exists, population patterns of age-specific performance may emerge. However, we found no evidence that birds that did not return to breed during young age classes laid later or smaller eggs than returned breeders. Likewise, we found no evidence that recruiting birds laid earlier or larger eggs than same aged birds recruited in preceding years. Thus, this study shows that age-specific patterns in timing of breeding and egg-size in common terns result from individuals intrinsic changes, and we reject the selection and the delayed breeding hypotheses as a major factor shaping age-specific patterns at population level.Communicated by F. Bairlein     

Age-related fledgling production in great cormorants Phalacrocorax carbo: influence of individual competence and disappearance of phenotypes

Age-related reproductive performance of great cormorants Phalacrocorax carbo sinensis was studied in a tree nesting colony in Denmark in relation to age-related improvements of competence and progressive disappearance of phenotypes. Within-individual changes in fledgling production were measured, and cross-sectional analyses were applied. The within-individual analyses showed that competence improved with age and/or that individuals showed restraint to optimize their reproductive effort. The within-individual improvements were three to six times higher among individuals that survived and returned to breed beyond the fourth breeding attempt than among individuals disappearing from the breeding population before the fourth breeding attempt. Taking this into account the within-individual improvements explained 70–90% of the age-effect observed in the population over the youngest ages. Effects of breeding experience were significant for females, but only within the group of individuals that were present in the breeding population beyond the age of five years. In males, improvements arose because of unknown factors related to age. Individual great cormorants that bred beyond the age of five years had higher reproductive success, on average, than birds disappearing from the breeding population earlier in life. This supports the differential survival hypothesis. However, the effect on the population mean was partly counterbalanced by late recruitment of other inferior breeders. It is concluded that the enhancement in fledgling production with increasing age was primarily an effect of age-related improvements of competence and secondly an effect of progressive disappearance of phenotypes.     

Moult of Malayan Barn Owls Tyto alba

Moult in Malayan Barn Owls Tyto alba was studied in two pairs of wild collected captive birds and from feathers taken from nest sites throughout peninsular Malaysia.
Post-juvenile captive birds moulted nearly to completion prior to first breeding, beginning with P6 at a mean age of 301.5 days. This contrasted with the only other study of moult in captive Barn Ow-Is in Germany when moult began at an age of 400 days, and then continued for a protracted period of two years separated by a suspension of moult during the normal breeding season.
The complex sequence of moult in primaries and secondaries both in the Malayan and German birds was similar.
Moult among adult Malayan birds in the wild showed a broad and somebyhat irregular seasonal trend With lower incidence during peak breeding periods.     

The forms and fitness cost of senescence: age-specific recapture, survival, reproduction, and reproductive value in a wild bird population

Longitudinal studies of senescence accumulate rapidly from natural populations. However, it is largely unknown whether different fitness components senesce in parallel, how reproductive and survival senescence contribute to declines in reproductive value, and how large the fitness cost of senescence is (the difference between the observed reproductive value and the hypothetical reproductive value, if senescence would not occur). We analyzed age-specific survival in great tits Parus major and combined our results with analyses of reproductive senescence to address these issues. Recapture probability of breeding females declined with age, suggesting age-specific increases in skipped or failed breeding and highlighting an important bias that studies of senescence in wild populations should incorporate. Survival probability also declined with age and in parallel with recruit production. Reproductive value decreased 87% between age 1 and age 9 but at a fitness cost of only 4%; the proportion of the contribution of reproductive senescence versus survival senescence to this cost was 0.7. For 11 other species, we estimated fitness costs of senescence of 6%-63% (average: birds, 9%; mammals, 42%), with relative contributions of reproductive senescence of 0.0-0.7 (average: birds, 0.4; mammals, 0.3). We suggest that understanding when and why reproductive and survival senescence differ will help in the identification of proximate mechanisms underlying variation in rates of senescence and its evolution.     

Reproductive senescence in a long-lived seabird: rates of decline in late-life performance are associated with varying costs of early reproduction

Evolutionary theories of senescence predict that rates of decline in performance parameters should be shaped by early-life trade-offs between reproduction and somatic maintenance. Here we investigate factors influencing the rate of reproductive senescence in a long-lived seabird, the common guillemot Uria aalge, using data collected over a 23-year period. In the last 3 years of life, individual guillemots had significantly reduced breeding success and were less likely to hold a site or attempt to breed. Females senesced at a significantly faster rate than males. At the individual level, high levels of reproductive output earlier in life were associated with increased senescence later in life. This trade-off between early- and late-life reproduction was evident independent of the fact that as birds age, they breed later in the season. The rate of senescence was additionally dependent on environmental conditions experienced earlier in life, with evidence that harsh conditions amplified later declines in breeding success. Overall, individuals with intermediate levels of early-life productivity lived longer. These results provide support for the antagonistic-pleiotropy and disposable-soma theories of senescence and demonstrate for the first time in a wild bird population that increased rates of senescence in reproductive performance are associated with varying costs of reproduction early in life.     

Influence of breeding on foraging behaviour and diet of Crowned Cranes

Gichuki, N. 2000. Influence of breeding on foraging behaviour and diet of crowned cranes. Ostrich 71 (1 & 2): 74–79.

This study investigated the effects of breeding on the foraging behaviour and diet of Grey Crowned Cranes Balearica regulorum in the Kitale area, western Kenya. During the study period (July 1994 to June 1996), 86 pairs successfully bred in 290 ha of wetlands. Egg-laying extended from July to November, indicating that the timing of nesting was flexible. Breeding and non-breeding adult cranes as well as immature birds foraged in grasslands, crop stubble, sown fields and wetlands. These habitats were not used according to the available proportions. Breeding commitments restricted parental adults to habitats within their territories while non-parental adults and sub-adults exploited a wider range of habitats. Further, breeding adults and juveniles had smaller foraging range sizes than those of non- breeding adults and sub-adults. Reduced foraging ranges by breeding birds appear to be a trade-off between energy expenditure in self-maintenance and reproduction. The diet of breeding and non-breeding adults was generally similar consisting of graminoid seeds and arthropods. Breeding birds, however, increased consumption of protein rich animal food and non-seed plant material. Selectivity of food items was greatest among breeding adults. Overall, breeding commitments resulted in reduced foraging range and variety of food items available but the major components of the diet remained the same for all adults and immature birds.     

Telomere length reflects phenotypic quality and costs of reproduction in a long-lived seabird

Telomere length is associated with cellular senescence, lifestyle and ageing. Short telomeres indicate poor health in humans and reduced life expectancy in several bird species, but little is known about telomeres in relation to phenotypic quality in wild animals. We investigated telomere lengths in erythrocytes of known-age common terns (Sterna hirundo), a migratory seabird, in relation to arrival date and reproductive performance. Cross-sectional data revealed that, independent of age, individuals with short telomeres performed better: they arrived and reproduced earlier in the season and had more chicks in the nest. The latter effect was stronger the older the brood and stronger in males, which do most of the chick provisioning. Longitudinal data confirmed this pattern: compared with birds that lost their brood, birds that raised chicks beyond the 10th nestling day experienced higher telomere attrition from one year to the next. However, more detailed analysis revealed that the least and most successful individuals lost the fewest base pairs compared with birds with intermediate success. Our results suggest that reproductive success is achieved at the expense of telomeres, but that individual heterogeneity in susceptibility to such detrimental effects is important, as indicated by low telomere loss in the most successful birds.     

Fitness and feather wear in the Collared Flycatcher Ficedula albicollis

Individual variation in the degree of feather wear is potentially a useful marker of individual quality or fitness, but next to nothing is known about causes and fitness consequences of feather wear in birds. We studied the effects of sex, age, year and experimental manipulation of brood size on primary feather wear in Collared Flycatchers Ficedula albicollis , and related variation in degree of feather wear to differences in fitness (viz. recruitment, survival). At the end of the breeding period, females and young birds had more worn flight feathers than males and adult birds, and the sexual difference in the degree of feather wear was particularly pronounced in one of the two study years. Experimental reduction of brood size reduced the degree of primary feather wear, whereas experimental enlargement of brood size did not lead to increased feather wear. In both sexes, there was a clear tendency for very old (>5 years old) birds to have more worn feathers than middle aged birds. The individual differences in the degree of feather wear were not correlated with individual differences in recruitment rate of young, but survival probability to the next breeding season increased with increasing degree of feather wear.     

Status and structure of the griffon vulture (Gyps fulvus) population in Crete

Griffon vulture (Gyps fulvus) population surveys were conducted during 1996–2002 in the island of Crete (Greece) to document population status and structure. Fieldwork was carried out during the breeding period when birds could be monitored in their colonies. Total population size was estimated at 379 individuals (range = 341–417) with adult birds comprising 63%. The breeding population was estimated at 141 pairs, which were distributed on an average in 23 colonies per year (range = 16–30) while the mean number of breeding pairs that laid eggs was 98 (range= 64–126). Crete thus supports the largest insular population of the species in the world and hosts 70–80% of the breeding population of the species in Greece. Population density was estimated at 6.9 individuals/100 km², 2.6 breeding pairs/100 km² and 1.8 nesting pairs/100 km². The average home range of an occupied colony (i.e., breeding group) was estimated at ca. 204 km² producing a theoretical foraging range of 8 km radius around the breeding cliff. No trends in the total number of individuals and breeding pairs appeared to exist, although significant differences in population size of individual colonies occurred between the years. The majority of the population was concentrated in small-sized colonies, which showed a low occupancy rate. The number of abandoned sites and the colonization of new ones could represent a shift of breeding pairs to alternative colonies provoked by local food abundance and conspesific attraction.