Adult survival probability and body size affect parental risk‐taking across latitudes

Parents faced with a predator must choose between their own safety versus taking care of their offspring. Each choice can have fitness costs. Life‐history theory predicts that longer‐lived species should be less willing than shorter‐lived species to return to care for their offspring after a predator disturbance because they have more opportunities to reproduce in the future. We increased adult predation risk during incubation for 40 bird species in north temperate, tropical, and south temperate latitudes. We found that species with higher adult survival probabilities were more cautious, waiting longer before returning to the nest to provide care. Contrary to other studies, we also found that parents were more risk averse and waited longer to return in smaller than larger species, likely reflecting greater vulnerability of smaller species. Ultimately, the relative risk a predator poses to a species and the probability of future reproduction predict parental risk taking across the world.     

South temperate birds have higher apparent adult survival than tropical birds in Africa

Life history theory predicts an inverse relationship between annual adult survival and fecundity. Globally, clutch size shows a latitudinal gradient among birds, with south temperate species laying smaller clutches than north temperate species, but larger clutches than tropical species. Tropical birds often have higher adult survival than north temperate birds associated with their smaller clutches. However, the prediction that tropical birds should also have higher adult survival than south temperate birds because of smaller clutch sizes remains largely untested. We measured clutch size and apparent annual breeding adult survival for 17 south temperate African species to test two main predictions. First, we found strong support for a predicted inverse relationship between adult survival and clutch size among the south temperate species, consistent with life‐history theory. Second, we compared our clutch size and survival estimates with published estimates for congeneric tropical African species to test the prediction of larger clutch size and lower adult survival among south temperate than related tropical species. We found that south‐temperate species laid larger clutches, as predicted, but had higher, rather than lower, apparent adult survival than related tropical species. The latter result may be an artefact of different approaches to measuring survival, but the results suggest that adult survival is generally high in the south temperate region and raises questions about the importance of the cost of reproduction to adult survival.     

The post‐fledging period in a tropical bird: patterns of parental care and survival

How environmental conditions affect the timing and extent of parental care is a fundamental question in comparative studies of life histories. The post‐fledging period is deemed critical for offspring fitness, yet few studies have examined this period, particularly in tropical birds. Tropical birds are predicted to have extended parental care during the post‐fledging period and this period may be key to understanding geographic variation in avian reproductive strategies. We studied a neotropical passerine, the western slaty‐antshrike Thamnophilus atrinucha, and predicted greater care and higher survival during the post‐fledging period compared to earlier stages. Furthermore, we predicted that duration of post‐fledging parental care and survival would be at the upper end of the distribution for Northern Hemisphere passerines. Correspondingly, we observed that provisioning continued for 6–12 weeks after fledging. In addition, provisioning rate was greater after fledging and offspring survival from fledging to independence was 75%, greater than all estimates from north‐temperate passerines. Intervals between nesting attempts were longer when the first brood produced successful fledglings compared to nests where offspring died either in the nest or upon fledging. Parents delayed initiating second nests after the first successful brood until fledglings were near independence. Our results indicate that parents provide greater care after fledging and this extended care likely increased offspring survival. Moreover, our findings of extended post‐fledging parental care and higher post‐fledging survival compared to Northern Hemisphere species have implications for understanding latitudinal variation in reproductive effort and parental investment strategies.     

Post‐fledging survival of altricial birds: ecological determinants and adaptation

For altricial young, fledging is an abrupt step into an unknown environment. Despite increasing numbers of studies addressing the post‐fledging period, our current knowledge of the causes and consequences of post‐fledging survival remains fragmentary. Here, we review the literature on post‐fledging survival of juvenile altricial birds, addressing the following main questions: Is low post‐fledging survival a bottleneck in the altricial reproductive cycle? What is known of proximate and ultimate causal factors such as trophic relations (food and predation), habitat conditions, or abiotic factors acting in the post‐fledging period? We analyzed weekly survival estimates from 123 data series based on studies of 65 species, covering weeks 1–13 post‐fledging. As a general pattern, survival of fledglings was low during the first week post‐fledging (median rate = 0.83), and improved rapidly with time post‐fledging (week 4 median rate = 0.96). For ground‐nesting species, survival immediately after leaving nests was similar to egg‐to‐fledging survival. For species breeding above‐ground, survival during the first week post‐fledging was substantially lower than during both the nestling period and later post‐fledging stages. Thus, the early post‐fledging period is a bottleneck of markedly elevated mortality for most altricial species. Predation was the main proximate cause of mortality. Various factors such as habitat, annual and seasonal variation in the environment, and the physical condition of fledglings have been found to affect post‐fledging survival. Individual survival depended strongly on physical traits such as mass and wing length, which likely influence the ability of fledglings to escape predation. Trophic relationships at various levels are the main ultimate driver of adaptation of traits relevant to survival during the pre‐ and post‐fledging periods. Spatiotemporal dynamics of food resources determine the physical development of juveniles and, in turn, their performance after fledging. However, predators can cause quick and efficient selection for fledgling traits and adult breeding decisions. Parental strategies related to clutch size and timing of breeding, and the age and developmental stage at which young fledge have substantial effects on post‐fledging survival. The intensity and duration of post‐fledging parental investment also influences fledgling survival. Post‐fledging mortality is therefore not a random and inevitable loss. Traits and strategies related to fledging and the post‐fledging stage create large fitness differentials and, therefore, are integral, yet poorly understood, parts of the altricial reproductive strategy.     

Maternal expenditure in the polygynous and monomorphic guanaco: suckling behavior, reproductive effort, yearly variation, and influence on juvenile survival

We investigated patterns of maternal expenditure and its influenceon juvenile survival in the polygynous monomorphic guanaco (Lama guanicoe)in southern Chile from 1990 to 1994. Birth weight and growth rate(until age 1) of males and females were similar. Suckling ratesof males and females were not significantly different, althoughmothers of males rejected suckling attempts more often thanmothers of females during fall and winter. Mothers with sonsterminated suckling bouts in equal proportion as did motherswith daughters. Our estimated level of reproductive effort for guanacosfalls within the range of species exhibiting no sex-biased maternal expenditureon offspring. Mean yearly birth weight was negatively correlated withpopulation density. Mean suckling time throughout the year differedamong cohorts, as did the mean number of suckling attempts andrejected suckling attempts per hour throughout the year. Juvenilesurvival was estimated until age 1. Of the model with five covariatesincluding juvenile sex, birth weight, adult female aggressiontoward taggers, mean suckling time, and population density,only mean suckling time and population density were significantly relatedto survival. The risk ratio for mean suckling time indicatesthat the risk of mortality increases as suckling time increases,whereas the risk ratio for population density indicates thatthe risk of mortality decreases as population density increases.Under some conditions increasing population density may be correlatedwith lower offspring birth weight, yet enhanced juvenile survival.This effect on survival was possibly associated with the numberof predators on the study area from year to year.     

Survival to independence in relation to pre‐fledging development and latitude in songbirds across the globe

Species differ strongly in their life histories, including the probability of survival. Annual adult survival was investigated extensively in the past, whereas juvenile survival, and especially survival to independence, received much less attention. Yet, they are critical for our understanding of population demography and life‐history evolution. We investigated post‐fledging survival to independence (i.e. survival upon leaving the nest until nutritional independence) in 74 species of passerine birds worldwide based on 100 population level estimates extracted from published literature. Our comparative analyses revealed that survival to independence increased with the length of nestling period and relative fledging mass (ratio of fledging mass to adult body mass). At the same time, species with higher nest predation rates had shorter nestling periods and lower relative fledging mass. Thus, we identify an important trade‐off in life history strategies: staying longer in the nest may improve post‐fledging survival due to enhanced flight ability and sensory functions, but at the cost of a longer exposure to nest predators and increased mortality due to nest predation. Additionally, post‐fledging survival to independence did not differ between species from the northern temperate zone vs species from the tropics and southern hemisphere. However, analyses of post‐fledging survival curves suggest that 1) daily survival rates are not constant and improve quickly upon leaving the nest, and 2) species in the tropics and southern hemisphere have higher daily post‐fledging survival rates than northern temperate species. Nevertheless, due to the accumulation of mortality risk during their much longer periods of post‐fledging care, overall survival until independence is comparable across latitudes. Obtaining high‐quality demographic data across latitudes to evaluate the generality of these findings and mechanisms underlying them should be a research priority.     

An integrated approach to life-cycle evolution using selective landscapes

A model which defines fitness in terms of the intrinsic rate of increase of phenotypes is used to analyse which life cycles are appropriate to which ecological circumstances. The following predictions are made for asexual animals and those sexual animals producing on average more than one daughter per brood. If there are no behavioural or physiological interactions between variables, then number of offspring per breeding should be maximized, survival until first/next breeding should be maximized, and time to first/next breeding should be minimized. If interactions occur such that altering one life-cycle variable affects another, then there are trade-offs between variables and the optimum trade-off will maximize fitness.Number of offspring per breeding will generally affect adult survivorship until next breeding. Given certain reasonable assumptions about this trade-off, high juvenile survivorship selects towards semelparity (many offspring per brood), low juvenile survivorship selects towards iteroparity (few offspring per brood). If juvenile survival depends on adult feeding, as in altricial birds, then juvenile survivorship declines as clutch size is increased. Optimal clutch size maximizes the number of surviving offspring per brood.Two trade-offs involve parental care. If parents guard their offspring they should take more risks if brood size is larger. The amount that parents feed their offspring should depend on how effective feeding is in enhancing growth. Growth may also be enhanced by taking risks, in juveniles or adults. The extent of risk-taking should depend on how effective risk-taking is in enhancing growth.If the number of offspring per brood is related to growing conditions for offspring, the prediction is that more offspring per brood should be produced if growing conditions for offspring are better. If the adult can protect the offspring, for example by encapsulating them, the amount of protection provided should depend on how effective the protection is in increasing offspring survivorship.     

Sex allocation and sex‐specific parental investment in an endangered seabird

Biased offspring sex ratio is relatively rare in birds and sex allocation can vary with environmental conditions, with the larger and more costly sex, which can be either the male or female depending on species, favoured during high food availability. Sex‐specific parental investment may lead to biased mortality and, coupled with unequal production of one sex, may result in biased adult sex ratio, with potential grave consequences on population stability. The African Penguin Spheniscus demersus, endemic to southern Africa, is an endangered monogamous seabird with bi‐parental care. Female adult African Penguins are smaller, have a higher foraging effort when breeding and higher mortality compared with adult males. In 2015, a year in which environmental conditions were favourable for breeding, African Penguin chick production on Bird Island, Algoa Bay, South Africa, was skewed towards males (1.5 males to 1 female). Males also had higher growth rates and fledging mass than females, with potentially higher post‐fledging survival. Female, but not male, parents had higher foraging effort and lower body condition with increasing number of male chicks in their brood, thereby revealing flexibility in their parental strategy, but also the costs of their investment in their current brood. The combination of male‐biased chick production and higher female mortality, possibly at the juvenile stage as a result of lower parental investment in female chicks, and/or at the adult stage as a result of higher parental investment, may contribute to a biased adult sex ratio (ASR) in this species. While further research during years of contrasting food availability is needed to confirm this trend, populations with male‐skewed ASRs have higher extinction risks and conservation strategies aiming to benefit female African Penguin might need to be developed.     

Family dynamics through time: brood reduction followed by parental compensation with aggression and favouritism

Parental food allocation in birds has long been a focal point for life history and parent–offspring conflict theories. In asynchronously hatching species, parents are thought to either adjust brood size through death of marginal offspring (brood reduction), or feed the disadvantaged chicks to reduce the competitive hierarchy (parental compensation). Here, we show that parent American coots (Fulica americana) practice both strategies by switching from brood reduction to compensation across time. Late‐hatching chicks suffer higher mortality only for the first few days after hatching. Later, parents begin to exhibit parental aggression towards older chicks and each parent favours a single chick, both of which are typically the youngest of the surviving offspring. The late‐hatched survivors can equal or exceed their older siblings in size prior to independence. A mixed allocation strategy allows parents to compensate for the costs of competitive hierarchies while gaining the benefits of hatching asynchrony.     

Differences in seasonal survival suggest species‐specific reactions to climate change in two sympatric bat species

Long‐lived animals with a low annual reproductive output need a long time to recover from population crashes and are, thus, likely to face high extinction risk, if the current global environmental change will increase mortality rates. To aid conservation of those species, knowledge on the variability of mortality rates is essential. Unfortunately, however, individual‐based multiyear data sets that are required for that have only rarely been collected for free‐ranging long‐lived mammals. Here, we used a five‐year data set comprising activity data of 1,445 RFID‐tagged individuals of two long‐lived temperate zone bat species, Natterer's bats (Myotis nattereri) and Daubenton's bats (Myotis daubentonii), at their joint hibernaculum. Both species are listed as being of high conservation interest by the European Habitats Directive. Applying mixed‐effects logistic regression, we explored seasonal survival differences in these two species which differ in foraging strategy and phenology. In both species, survival over the first winter of an individual's life was much lower than survival over subsequent winters. Focussing on adults only, seasonal survival patterns were largely consistent with higher winter and lower summer survival but varied in its level across years in both species. Our analyses, furthermore, highlight the importance of species‐specific time periods for survival. Daubenton's bats showed a much stronger difference in survival between the two seasons than Natterer's bats. In one exceptional winter, the population of Natterer's bats crashed, while the survival of Daubenton's bats declined only moderately. While our results confirm the general seasonal survival pattern typical for hibernating mammals with higher winter than summer survival, they also show that this pattern can be reversed under particular conditions. Overall, our study points toward a high importance of specific time periods for population dynamics and suggests species‐, population‐, and age class‐specific responses to global climate change.     

Fledgling Bachman’s Sparrows in a longleaf pine ecosystem: survival,movements, and habitat selection

Fledgling ecology remains understudied for many passerine species, yet information about the fledgling life stage is critical for understanding full-annual life cycles and population recruitment. We examined the survival, habitat selection, and movements of fledgling Bachman’s Sparrows (Peucaea aestivalis) in a longleaf pine-wiregrass (Pinus palustris-Aristida stricta) community managed with frequent prescribed fire. We captured and marked 36 fledglings on the day of fledging and used radio-telemetry to relocate them daily until independence during three breeding seasons (2014–2016). We visually confirmed the status of fledglings as live or dead during daily relocations and determined causes of mortality. We measured vegetation characteristics at fledgling locations and compared them to the characteristics of vegetation at the locations of adult males. We used a Known Fates analysis in Program MARK to estimate fledgling survival, and generalized linear mixed effect models to determine habitat selection. Estimated fledgling survival until independence was 0.31 (SE = 0.08), with most mortality during the first 4 d post-fledging. Fledglings with longer wing chords had higher rates of survival than those with shorter wing chords, possibly due to an increased ability to evade predators. Fledgling movements were restricted primarily to natal territories. Fledgling Bachman’s Sparrows were located in areas with greater woody plant, forb, and grass cover and less bare ground than available in natal territories. Similar to fledglings of other songbirds, understory woody and herbaceous plants appear to provide critical cover for fledgling Bachman’s Sparrows, and maintenance of such cover should receive consideration in management plans for longleaf pine communities.     

Comparative survival and recovery of Ross's and lesser snow geese from Canada's central arctic

Large increases in several populations of North American arctic geese have resulted in ecosystem-level effects from associated herbivory. Consequently, some breeding populations have shown density dependence in recruitment through declines in food availability. Differences in population trajectories of lesser snow geese (Chen caerulescens caerulescens; hereafter snow geese) and Ross's geese (C. rossii) breeding in mixed-species colonies south of Queen Maud Gulf (QMG), in Canada's central arctic, suggest that density dependence may be limiting snow goose populations. Specifically, long-term declines in age ratios (immature:adult) of harvested snow geese may have resulted from declines in juvenile survival. Thus, we focused on juvenile (first-year) survival of snow and Ross's geese in relation to timing of reproduction (annual mean nest initiation date) and late summer weather. We banded Ross's and snow geese from 1991 to 2008 in the QMG Migratory Bird Sanctuary. We used age-structured mark-recapture models to estimate annual survival rates for adults and juveniles from recoveries of dead birds. Consistent with life history differences, juvenile snow geese survived at rates higher than juvenile Ross's geese. Juvenile survival of both species also was lower in late seasons, but was unrelated to arctic weather measured during a 17-day period after banding. We found no evidence of density dependence (i.e., a decline in juvenile survival over time) in either species. We also found no interspecific differences in age-specific hunting vulnerability, though juveniles were more vulnerable than adults in both species, as expected. Thus, interspecific differences in survival were unrelated to harvest. Lower survival of juvenile Ross's geese may result from natural migration mortality related to smaller body size (e.g., greater susceptibility to inclement weather or predation) compared to juvenile snow geese. Despite lower first-year survival, recruitment by Ross's geese may still be greater than that by snow geese because of earlier sexual maturity, greater breeding propensity, and higher nest success by Ross's geese. © 2012 The Wildlife Society.     

Increased lifetime reproductive success of first‐hatched siblings in Common Kestrels Falco tinnunculus

Order of birth has profound consequences on offspring across taxa during development and can have effects on individuals later in life. In birds, differential maternal allocation and investment in their progeny lead to variance in the environmental conditions that offspring experience during growth within the brood. In particular, laying and hatching order have been proposed to influence individual quality during the growing period, but little is known about the fitness consequences that these two factors have for offspring from a lifetime perspective. We explored the effect of laying and hatching order on post‐fledgling survival (measured as recruitment probability) and lifetime reproductive success (LRS) in Common Kestrels Falco tinnunculus, using a long‐term and individual‐based dataset. First‐hatched chicks showed higher survival probability and LRS than their siblings. This effect was not due to body condition of the individuals at adulthood, the quality of their mates or the reproductive outcome compared with later‐hatched individuals. Instead, first‐hatched chicks had a higher recruitment probability. This could be explained by the higher body condition attained by first‐hatched chicks at the end of the nesting period, perhaps due to an enhanced competitive advantage for food over their siblings at the time of hatching. Laying order, in contrast to hatching order, appeared to have little or no effect on LRS. Our results suggest that hatching order within siblings predicts fitness, and that better early‐life conditions during growth experienced by first‐hatched chicks improve first survival and then recruitment, resulting in an enhanced LRS.     

Season of birth affects juvenile survival of giraffe

Variation in timing of reproduction and subsequent juvenile survival often plays an important role in population dynamics of temperate and boreal ungulates. Tropical ungulates often give birth year round, but survival effects of birth season for tropical ungulate species are unknown. We used a population of giraffe in the Tarangire Ecosystem of northern Tanzania, East Africa to determine whether calf survival varied by season of birth. Variation in juvenile survival according to season of birth was significant, with calves born during the dry season experiencing the highest survival probability. Phenological match may confer a juvenile survival advantage to offspring born during the dry season from greater accumulated maternal energy reserves in mothers who conceive in the long rainy season, high-protein browse in the late dry-early short rainy seasons supplementing maternal and calf resources, reduced predation due to decreased stalking cover, or some combination of these. Asynchrony is believed to be the ancestral state of all ungulates, and this investigation has illustrated how seasonal variation in vegetation can affect juvenile survival and may play a role in the evolution of synchronous births.     

A comparison of life‐history and parental care in temperate and tropical wrens

Comparing closely related species that live in different environments is a powerful way to understand selective pressures that influence life‐history evolution. We examined a suite of life‐history traits and parental care in neotropical buff‐breasted wrens Cantorchilus leucotis and north‐temperate Carolina wrens Thryothorus ludovicianus (Family Troglodytidae), to test hypotheses about life‐history evolution. As expected, buff‐breasted wrens exhibited smaller clutch sizes and higher annual adult survival than Carolina wrens. We found minimal support for the nest predation hypothesis, as nest survival and age‐corrected provisioning rates to whole broods were similar between species, and number of breeding attempts and breeding season length were greater in temperate wrens. Critical predictions of the food limitation hypothesis were not supported; in particular age‐corrected provisioning rates per nestling were higher in the tropical than temperate species. The adult survival and offspring quality hypothesis garnered the most support, as buff‐breasted wrens exhibited greater age‐corrected provisioning rates per nestling, a longer nestling period, longer re‐nesting intervals following nest success, and lower annual fecundity than Carolina wrens. Despite similarly prolonged breeding seasons, reproductive strategies differ between species with buff‐breasted wrens investing considerably in single broods to optimize first‐year survival and Carolina wrens investing in multiple small broods to optimize annual fecundity.     

Behavioral modifications lead to disparate demographic consequences in two sympatric species

Life‐history theory suggests species that typically have a large number of offspring and high adult mortality may make decisions that benefit offspring survival in exchange for increased adult risks. Such behavioral adaptations are essential to understanding how demographic performance is linked to habitat selection during this important life‐history stage. Though studies have illustrated negative fitness consequences to attendant adults or potential fitness benefits to associated offspring because of adaptive habitat selection during brood rearing, equivocal relationships could arise if both aspects of this reproductive trade‐off are not assessed simultaneously. To better understand how adaptive habitat selection during brood rearing influences demographics, we studied the brood survival, attendant parental survival, and space use of two sympatric ground‐nesting bird species, the northern bobwhite (hereafter: “bobwhite”; Colinus virgininanus) and scaled quail (Callipepla squamata). During the 2013–2014 breeding seasons, we estimated habitat suitability across two grains (2 m and 30 m) for both species and determined how adult space use of these areas influenced individual chick survival and parental risk. We found the proportion of a brood's home range containing highly suitable areas significantly increased bobwhite chick survival (β = 0.02, SE = 0.006). Additionally, adult weekly survival for bobwhite was greater for individuals not actively brooding offspring (0.9716, SE = 0.0054) as compared to brooding adults (0.8928, SE = 0.0006). Conversely, brood habitat suitability did not influence scaled quail chick survival during our study, nor did we detect a survival cost for adults that were actively brooding offspring. Our research illustrates the importance of understanding life‐history strategies and how they might influence relationships between adaptive habitat selection and demographic parameters.     

Nestling telomere shortening,but not telomere length,reflects developmental stress and predicts survival in wild birds

Developmental stressors often have long-term fitness consequences, but linking offspring traits to fitness prospects has remained a challenge. Telomere length predicts mortality in adult birds, and may provide a link between developmental conditions and fitness prospects. Here, we examine the effects of manipulated brood size on growth, telomere dynamics and post-fledging survival in free-living jackdaws. Nestlings in enlarged broods achieved lower mass and lost 21% more telomere repeats relative to nestlings in reduced broods, showing that developmental stress accelerates telomere shortening. Adult telomere length was positively correlated with their telomere length as nestling (r = 0.83). Thus, an advantage of long telomeres in nestlings is carried through to adulthood. Nestling telomere shortening predicted post-fledging survival and recruitment independent of manipulation and fledgling mass. This effect was strong, with a threefold difference in recruitment probability over the telomere shortening range. By contrast, absolute telomere length was neither affected by brood size manipulation nor related to survival. We conclude that telomere loss, but not absolute telomere length, links developmental conditions to subsequent survival and suggest that telomere shortening may provide a key to unravelling the physiological causes of developmental effects on fitness.     

Adult survival and reproductive rate are linked to habitat preference in territorial,year‐round resident Song Sparrows Melospiza melodia

Individual animal fitness can be strongly influenced by the ability to recognize habitat features which may be beneficial. Many studies focus on the effects of habitat on annual reproductive rate, even though adult survival is typically a greater influence on fitness and population growth in vertebrate species with intermediate to long lifespans. Understanding the effects of preferred habitat on individuals over the annual cycle is therefore necessary to predict its influences on individual fitness. This is particularly true in species that are resident and territorial year‐round in the temperate zone, which may face potential trade‐offs between habitat that maximizes reproduction and that which maximizes non‐breeding season (‘over‐winter’) survival. We used a 37‐year study of Song Sparrows Melospiza melodia residing territorially year‐round on a small island to examine what habitat features influenced adult over‐winter survival, how site‐specific variation in adult survival vs. annual reproductive rate influenced long‐term habitat preference, and if preferred sites on average conferred higher individual fitness. Habitat features such as area of shrub cover and exposure to intertidal coastline predicted adult over‐winter survival independent of individual age or sex, population size, or winter weather. Long‐term habitat preference (measured as occupation rate) was better predicted by site‐specific annual reproductive rate than by expected over‐winter survival, but preferred sites maximized fitness on average over the entire annual cycle,. Although adult over‐winter survival had a greater influence on population growth (λ) than did reproductive rate, the influence of reproductive rate on λ increased in preferred sites because site‐specific variation in reproductive rate was higher than variation in expected over‐winter survival. Because preferred habitats tended to have higher mean site‐specific reproductive and adult survival rates, territorial birds in this population do not appear to experience seasonal trade‐offs in preferred habitat but are predicted to incur substantial fitness costs of settling in less‐preferred sites.     

Cooperative breeding shapes post‐fledging survival in an Afrotropical forest bird

For avian group living to be evolutionary stable, multiple fitness benefits are expected. Yet, the difficulty of tracking fledglings, and thus estimating their survival rates, limits our knowledge on how such benefits may manifest postfledging. We radio‐tagged breeding females of the Afrotropical cooperatively breeding Placid greenbul (Phyllastrephus placidus) during nesting. Tracking these females after fledging permitted us to locate juvenile birds, their parents, and any helpers present and to build individual fledgling resighting datasets without incurring mortality costs or causing premature fledging due to handling or transmitter effects. A Bayesian framework was used to infer age‐specific mortality rates in relation to group size, fledging date, maternal condition, and nestling condition. Postfledging survival was positively related to group size, with fledglings raised in groups with four helpers showing nearly 30% higher survival until independence compared with pair‐only offspring, independent of fledging date, maternal condition or nestling condition. Our results demonstrate the importance of studying the early dependency period just after fledging when assessing presumed benefits of cooperative breeding. While studying small, mobile organisms after they leave the nest remains highly challenging, we argue that the telemetric approach proposed here may be a broadly applicable method to obtain unbiased estimates of postfledging survival.     

“Closer‐to‐home” strategy benefits juvenile survival in a long‐distance migratory bird

Human‐induced changes in the climate and environment that occur at an unprecedented speed are challenging the existence of migratory species. Faced with these new challenges, species with diverse and flexible migratory behaviors may suffer less from population decline, as they may be better at responding to these changes by altering their migratory behavior. At the individual level, variations in migratory behavior may lead to differences in fitness and subsequently influence the population's demographic dynamics. Using lifetime GPS bio‐logging data from 169 white storks (Ciconia ciconia), we explore whether the recently shortened migration distance of storks affects their survival during different stages of their juvenile life. We also explore how other variations in migratory decisions (i.e., time, destination), movement activity (measured using overall body dynamic acceleration), and early life conditions influence juvenile survival. We observed that their first autumn migration was the riskiest period for juvenile white storks. Individuals that migrated shorter distances and fledged earlier experienced lower mortality risks. In addition, higher movement activity and overwintering “closer‐to‐home” (with 84.21% of the tracked individuals stayed Europe or North Africa) were associated with higher survival. Our study shows how avian migrants can change life history decisions over only a few decades, and thus it helps us to understand and predict how migrants respond to the rapidly changing world.