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Experimental evidence that nestlings adjust their fledging time to each other in a multiparous bird
Abstract
The transition from nestling to fledgling is a key moment in the development of altricial birds. Mortality immediately after fledging is typically high and selection should favour fledging strategies that maximize the chance of survival. While several studies have examined the influence of ecological conditions or nestling development on the timing of fledging, the question whether nestlings influence each other's behaviour has received little attention. We tested how fledging decisions of blue tit, Cyanistes caeruleus, nestlings depend on the behaviour of their nestmates. First, we show that in unmanipulated broods, fledging events within a nest were highly clustered and nestlings fledged closer in time to a sibling than expected if fledging events were independent of one another. We then experimentally tested whether nestlings adjust their timing of nest departure to the behaviour of their nestmates, by translocating nestlings to a brood that differed in age by 2 days. Nestlings that were 2 days younger than their adoptive brood advanced their fledging time such that they fledged close in time to a nestmate. Nestlings that were 2 days older than their adoptive brood significantly delayed their fledging time, but they were often the first to fledge and were not always followed close in time by a nestmate. We conclude that nestling blue tits have a strong propensity to leave the nest close in time to nestmates. The adaptive significance of this behaviour warrants further study.
... Although we did not find any differences in nestlings' body mass at late stage of nestlings' phase, in other Great Tit populations, it was found that fledgling with a higher body mass had greater survival and recruitment chances (Monrós et al. 2002;Naef-Daenzer et al. 2001). It is also possible that light affected nestlings' behavior displayed just before the fledging and strengthened the interaction between nestlings (Santema et al. 2021). It is not clear why SY females preferred to breed in brightened cavities. ...
Natural light plays an important role in many aspects of birds' biology, ecology and behaviour. Wild birds experience various light conditions, both in terms of its intensity and spectral properties, which vary within the nesting habitat of avian species. Recent study has shown that some bird species prefer to build their nests in bright nest sites. Light is one of the major factors affecting early development and condition of nestlings, but to date, this effect has not been tested in wild conditions. This study aims to answer whether birds could benefit from nesting in brighter light environment. Potential benefits may occur in nestlings' condition, growth rate and breeding output. The research was carried out in the population of Great Tits (Parus major) breeding in two types nest boxes which differed with internal illumination. In "dark" boxes, the only source of light was the entrance hole. "Bright" boxes have additional side semi-transparent windows. We conducted two experiments in which light environment in nest box was set after (Experiment I) or before (Experiment II) birds settle in. Our study showed that light environment did not significantly affect nestlings body condition and growth. However, females in their first breeding attempt showed strong preference to the brightened nest boxes. In this group, the offspring were heavier and showed stronger immune responses than nestlings reared in dark nest boxes. Nestlings in bright nest boxes fledged about one day earlier. Nesting in brightened nest boxes may provide potential benefit for adult females in their first breeding attempt. The interaction between maternal effect and light environment is being discussed.
... Collecting nests and replacing them with other nest material is a relatively straightforward procedure and unlikely to affect the nestlings at this late stage. As is customary in nest-box studies of Great and Blue tits, visits to nestlings after day 15, for normally developed broods, is kept to a minimum or avoided altogether to reduce the risk of inducing premature fledging (Jongsomjit et al. 2007, Santema et al. 2021. ...
en The biotic and abiotic environments in bird nests change during the nesting cycle as eggs are laid and incubated and nestlings develop and eventually fledge. Nest-arthropod communities have been studied for many bird species and are commonly sampled after young fledge. However, the population dynamics of arthropods in nests are expected to vary over the nesting cycle as a result of the changing nest environment, in symphony with arthropod life cycles and generation times. Few investigators have examined nest arthropod communities at different stages of the breeding period. We collected nests of Great Tits (Parus major) at the egg stage, nestling stage, and after fledging, and extracted nest arthropods using Berlese funnels and identified them to Primary Taxonomic Groups (PTGs). Total arthropod abundance, as well as abundance of fleas, parasitic mites, and adult predatory beetles, was higher during the nestling stage than after fledging. The abundance of beetle mites decreased from the egg stage to fledging, whereas larval predatory beetles and scavenger flies increased. Thus, our results demonstrate important changes in overall abundance, but also in the trophic structure of nest arthropod communities during the nesting cycle. Our results also suggest that nests collected after fledging may give biased information on the abundance of parasites, or nest-arthropod communities in general, during the nestling stage.
RESUMEN
es Cambios en las comunidades de artrópodos entre estados reproductivos en nidios de Parus major
Los ambientes bióticos y abióticos de los nidos de las aves cambian durante el ciclo de anidación a medida que los huevos son puestos e incubados y los pichones se desarrollan y eventualmente salen del nido. Las comunidades de artrópodos en los nidos han sido estudiadas en muchas especies de aves y son comúnmente muestreadas después de que los pichones abandonan el nido. Sin embargo, se espera que la dinámica poblacional de los artrópodos en los nidos varíe a través del ciclo de anidación, como resultado de cambios en el ambiente del nido, en sincronía con los ciclos de vida de los artrópodos y sus tiempos generacionales. Pocos investigadores han examinado las comunidades de artrópodos en los nidos en diferentes etapas reproductivas. Colectamos nidos de Parus major en la etapa de huevos, en la tapa de pichones y posterior al abandono del nido por los pichones y extrajimos los artrópodos del nido utilizando embudos Berlese y los identificamos hasta los Grupos Taxonómicos Primarios (PTGs). La abundancia total de artrópodos, así como la abundancia de pulgas, piojos parásitos y escarabajos depredadores adultos fue mayor durante la etapa de pichones que después del abandono del nido. La abundancia de escarabajos piojos disminuyó de la etapa de huevos a la etapa de pichones, mientras que larvas de escarabajos depredadores y moscas carroñeras incrementó. Por lo tanto, nuestros resultados demuestran cambios importantes en la abundancia en general, pero también en la estructura trófica de las comunidades de artrópodos en los nidos durante el ciclo de anidación. Nuestros resultados también sugieren que los nidos colectados después de que los pichones han abandonado los nidos pueden dar información sesgada de la abundancia de parásitos o de las comunidades de artrópodos en los nidos en general durante la etapa de pichones.
Radial porosity profiles (RPP) are a new quantitative osteohistological parameter designed to capture the dynamic changes in the primary porosity of limb bones through ontogeny, providing insights into skeletal growth and functional development of extant and extinct vertebrates. Previous work hypothesized that RPP channelization-the intraskeletal alignment of RPPs across different bones resulting from similar cortical compaction patterns-indicates increasing locomotor performance of the developing limbs. By investigating RPPs in ontogenetic series of pheasants, pigeons and ducks representing distinct locomotor developmental strategies, we test this hypothesis here and show that RPPs are indeed powerful osteohistological correlates of locomotor ontogeny. Qualitative and quantitative analyses reveal strong association between RPP channelization and fledging, the most drastic locomotor transition in the life history of volant birds. The channelization signal is less clear in precocial leg function; however, when additional intraskeletal and inter-cohort RPP characteristics are considered, patterns related to leg precocity can also be identified. Thus, we demonstrate that RPPs can be used in future by palaeobiologists to generate breakthroughs in the study of the ontogeny and evolution of flight in fossil birds and pterosaurs. With further baseline data collection from modern terrestrial vertebrates, RPPs could also test hypotheses regarding ontogenetic postural shifts in dinosaurs and other terrestrial archosaurs. This article is protected by copyright. All rights reserved.
Leaving the nest is a key transition in the life of altricial birds, whereby fledging decisions should depend on multiple factors, including the risk of predation. High postfledging predation risk may favour fledging at a more advanced stage of development, if more developed fledglings are better at escaping predation, or together with others. While comparative studies have highlighted the role of predation risk for between-species variation in the timing of fledging, drivers of within-species variation in fledging behaviour remain largely unknown. We presented owl models near blue tit, Cyanistes caeruleus, nests during the first half of the day throughout the fledging period to simulate an increased risk of postfledging predation. Using an automated monitoring system, we then recorded the precise fledging times of 595 nestlings from 105 nests (52 predator-treated, 53 control nests). Contrary to our predictions, the predator presentations did not affect the age at which nestlings fledged, the time of day of fledging or other aspects of fledging behaviour. The tendency to fledge together with siblings was affected, but the effect was in the opposite direction to that expected, with nestlings exposed to the predator treatment being more likely to fledge alone. Parents visited predator-treated nests less often, but this effect diminished over the course of the morning. We suggest several explanations for why the behavioural responses to the predation risk manipulation were generally limited.
In altricial birds, leaving the nest is a key life history transition associated with a high risk of mortality. Studies of numerous species have shown that young typically fledge early in the day, and it is often asserted that early fledging is important for survival; however, evidence for this hypothesis is limited. We used an automated monitoring system to obtain precise fledging times of 1582 young blue tits, Cyanistes caeruleus, from 230 nests. As expected, nestlings primarily fledged early in the day (84% fledged before midday). However, we found no evidence that early fledging was associated with higher postfledging survival (i.e. recorded the following autumn or later). We propose two alternative explanations for the morning peak in fledging. Hypothesis 1 is that some offspring reach a developmental threshold for fledging overnight and leave the nest early the next day. This is supported by our observation that offspring that fledged early in the day tended to be more developed than those that fledged later in the day, that is, they were older and had a high body mass (measured at 14 days of age) for their fledging age. Hypothesis 2 is that the timing of fledging is related to parental provisioning behaviour. Our results do not support this hypothesis. Parents reduced their nest visit rate over the course of the day, but offspring did not fledge earlier when their parents decreased their visit rate more strongly with time of day. In conclusion, our results do not support the notion that the time of fledging affects survival but suggest a link with nestling development.
Significance
Parent–offspring conflict has explained a variety of ecological phenomena across animal taxa, but its role in mediating when songbirds fledge remains controversial. Our analysis of nesting and postfledging survival rates within 18 songbird species found that offspring commonly leave safer nesting environments for riskier postfledging ones—known as postfledging bottlenecks. This timing of fledging incurs a cost for offspring survival, but benefits adults by increasing their likelihood of raising at least one offspring to independence. Parents therefore appear to manipulate offspring into fledging earlier than expected based on the offspring’s ensuing survival prospects. Our results suggest that parent–offspring conflict and associated variation in parental benefits explain variation in fledging age among songbird species and why postfledging bottlenecks occur.
The duration of the developmental period represents a fundamental axis of life history variation, yet broad insights regarding the drivers of this diversity are currently lacking. Here, we test mechanistic and ecological explanations for the evolution of developmental duration using embryological data and information on incubation and fledging for 3096 avian species. Developmental phases associated primarily with growth are the longest and most variable, consistent with a role for allometric constraint in determining the duration of development. In addition, developmental durations retain a strong imprint of deep evolutionary history and body size differences among species explain less variation than previously thought. Finally, we reveal ecological correlates of developmental durations, including variables associated with the relative safety of the developmental environment and pressures of breeding phenology. Overall, our results provide broad-scale insight into the relative importance of mechanistic, ecological and evolutionary constraints in shaping the diversification of this key life history trait.
Recent advances in animal tracking technology have ushered in a new era in biologging. However, the considerable size of many sophisticated biologging devices restricts their application to larger animals, whereas older techniques often still represent the state-of-the-art for studying small vertebrates. In industrial applications, low-power wireless sensor networks (WSNs) fulfill requirements similar to those needed to monitor animal behavior at high resolution and at low tag mass. We developed a wireless biologging network (WBN), which enables simultaneous direct proximity sensing, high-resolution tracking, and long-range remote data download at tag masses of 1 to 2 g. Deployments to study wild bats created social networks and flight trajectories of unprecedented quality. Our developments highlight the vast capabilities of WBNs and their potential to close an important gap in biologging: fully automated tracking and proximity sensing of small animals, even in closed habitats, at high spatial and temporal resolution.
It is commonly observed in many bird species that dependent offspring vigorously solicit for food transfers provided by their parents. However, the likelihood of receiving food does not only depend on the parental response, but also on the degree of sibling competition, at least in species where parents raise several offspring simultaneously. To date, little is known about whether and how individual offspring adjusts its begging strategy according to the entwined effects of need, state and competitive ability of itself and its siblings. We here manipulated the hunger levels of either the two heaviest or the two lightest blue tit ( Cyanistes caeruleus ) nestlings in a short-term food deprivation experiment. Our results showed that the lightest nestlings consistently begged more than the heaviest nestlings, an effect that was overruled by the tremendous increase in begging behaviour after food deprivation. Meanwhile, the amplified begging signals after food deprivation were the only cue for providing parents in their decision process. Furthermore, we observed flexible but state-independent begging behaviour in response to changes in sibling need. As opposed to our expectations, nestlings consistently increased their begging behaviour when confronted with food deprived siblings. Overall, our study highlights that individual begging primarily aims at increasing direct benefits, but nevertheless reflects the complexity of a young birds’ family life, in addition to aspects of intrinsic need and state.
Should they stay or should they leave? The age at which young transition between life stages, such as living in a nest versus leaving it, differs among species and the reasons why are unclear. We show that offspring of songbird species that leave the nest at a younger age have less developed wings that cause poorer flight performance and greater mortality after fledging. Experimentally delayed fledging verified that older age and better developed wings provide benefits of reduced juvenile mortality. Young are differentially constrained in the age that they can stay in the nest and enjoy these fitness benefits because of differences among species in opposing predation costs while in the nest. This tension between mortality in versus outside of the nest influences offspring traits and performance and creates an unrecognized conflict between parents and offspring that determines the optimal age to fledge.
Phenotypic traits developed in one life-history stage can carryover and affect survival in subsequent stages. For songbirds, carryover effects from the pre- to post-fledging period may be crucial for survival but are poorly understood. We assessed whether juvenile body condition and wing development at fledging influenced survival during the post-fledging period in the Dickcissel (Spiza americana). We found pre- to post-fledging carryover effects on fledgling survival for both traits during the “early part”—first four days—of the post-fledging period. Survival benefits of each trait depended on cause-specific sources of mortality; individuals in better body condition were less likely to die from exposure to adverse environmental conditions, whereas those with more advanced wing development were less likely to be preyed upon. Fledglings with more advanced wing development were comparatively more active and mobile earlier in the post-fledging period, suggesting they were better able to avoid predators. Our results provide some of the first evidence linking development of juvenile phenotypic traits to survival against specific sources of post-fledging mortality in songbirds. Further investigation into pre- to post-fledging carryover effects may yield important insights into avian life-history evolution. This article is protected by copyright. All rights reserved.
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. Para juveniles altriciales, salir del nido es un paso abrupto hacia un ambiente desconocido. A pesar del incremento en los estudios investigando el periodo posterior a la salida, nuestro conocimiento actual de las causas y consecuencias de la supervivencia luego de salir del nido es fragmentada. Aquí, revisamos la literatura sobre la supervivencia de aves juveniles altriciales posterior a su salida del nido, con el fin de responder las siguientes preguntas principales: es la baja supervivencia luego de salir del nido un cuello de botella en el ciclo reproductivo altricial? Que sabemos sobre los factores causales últimos y proximales, como las relaciones tróficas (comida y depredación), condiciones del hábitat o factores abióticos que influencian el periodo posterior a la salida del nido? Analizamos estimados semanales de supervivencia de 123 series de datos basados en estudios de 65 especies, cubriendo 1–13 semanas posteriores a la salida del nido. Como patrón general, la supervivencia de los volantones fue baja durante la primera semana posterior a la salida (mediana de la tasa = 0.83) y mejoro rápidamente con el tiempo luego de la salida (semana 4 mediana mediana de la tasa = 0.96). Para especies que anidan en el suelo, la supervivencia inmediatamente después de salir del nido fue similar a la supervivencia de huevo a volantón. Para especies que anidan por encima del suelo, supervivencia durante la primera semana posterior a la salida fue substancialmente menor que durante los periodos de anidación y periodos tardíos posteriores a la salida. Consecuentemente, el periodo temprano posterior a la salida del nido es un cuello de botella con una marcada mortalidad elevada para la mayoría de especies altriciales. Depredación fue la principal causa proximal de mortalidad. El hábitat, variación anual y estacional del ambiente y la condición de los volantones han sido reportados como factores que afectan la supervivencia posterior a la salida del nido. La supervivencia individual dependió fuertemente de caracteres físicos como masa, longitud del ala, los cuales probablemente influencian la habilidad de los volantones de escapar a los depredadores. Relaciones tróficas en varios niveles son el factor ultimo de adaptación de caracteres relevantes para la supervivencia durante los periodos previos y posteriores a la salida del nido. La dinámica espacio-temporal de los recursos alimenticios determinan el desarrollo físico de los juveniles y por lo tanto su rendimiento después de salir del nido. Sin embargo, los depredadores pueden causar selección rápida y eficiente para los caracteres de los volantones y de las decisiones de reproducción en los adultos. La intensidad y la duración de la inversión parental posterior a la salida del nido también influencia la supervivencia de los volantones. La mortalidad posterior a la salida del nido es por lo tanto no aleatoria y una perdida inevitable. Los caracteres y las estrategias relacionadas con la salida del nido y la etapa posterior a esta salida, crean diferencias grandes en la aptitud y por lo tanto son una parte integral pero poco comprendida de la estrategia de reproducción altricial.
In species with biparental care, males and females share the benefits of investing in offspring but pay the costs individually. As a result of these evolutionary conflicts of interest between the sexes, it is expected that the two parents should follow different behavioural rules when providing food to the young. Such a discrepancy may be accentuated when parents have to choose between different subsets of offspring (e.g., large and small nestlings). We manipulated the degree of hatching asynchrony in Blue Tits Cyanistes caeruleus and quantified male and female feeding behaviour when nestlings were 7 and 10 days old. First, we tested for a difference in the role of the sexes during the nestling rearing period between experimentally asynchronous and synchronous control broods. We then focused on experimentally asynchronous broods to examine the existence of sex differences in the pattern of food distribution (in terms of number of feedings and prey types) between junior and senior siblings. At the earlier nestling stage (7 days old), experimental females fed their young more often than their mates despite the fact that they were faced with a trade-off between brooding the smallest nestlings and bringing food to the nest. On day 7, there was a skew in favour of senior siblings whereas food was more evenly distributed within the brood when nestlings were older. We found no difference in how male and female Blue Tits distributed feeding visits among junior and senior nestlings. However, we found that females fed the smallest nestlings with a greater amount of spiders in comparison with their senior siblings, which could be related to their more suitable size in comparison with other prey types, their high content of essential nutrients or both. Such pattern could be interpreted as a “cryptic form” of parentally biased favouristism. We compare these findings with previous work on other species and discuss why parents did not feed junior siblings more frequently.
Species in the avian family Alcidae show enormous inter- and intraspecific variation in age and mass at nest departure (hedging). We develop a dynamic programming model of the nest departure decision that incorporates the differential growth benefits and mortality costs of the pre- and postfledging habitats (nest and ocean). The model's most basic prediction is the existence of a negatively inclined fledging boundary in mass-time space: nestlings fledge as their growth trajectory hits the boundary. The consequence is that faster-growing nestlings fledge younger and heavier than slower growers and that later-hatched nestlings fledge younger and lighter. A review of the comparative and experimental data in the literature largely supports these predictions. We use the model to show how a widespread pattern reported in the literature-the seasonal hedging mass decline-arises because of the interaction of growth and hatching date variation with the fledging strategy modeled here. The seasonal decline occurs in the absence of any of the causes most commonly suggested in the literature, particularly the seasonal decline in food availability. A detailed case study of the rhinoceros auklet (Cerorhinca monocerata) strongly supports the mechanism outlined here.
Abstract In altricial birds, siblings raised within a nest usually leave the nest within hours of each other, despite often differing considerably in age. The youngest members of the brood are typically underdeveloped at this time and less likely than their older siblings to survive outside the nest, yet they risk abandonment if they do not fledge with their older siblings. Nest leaving is usually initiated by the older offspring, which may delay this process to provide more time for their younger siblings to mature, increasing the younger siblings' postfledging survival and their own inclusive fitness. We tested this hypothesis in a population of house wrens Troglodytes aedon and found that broods with broad age spans among siblings had longer nestling periods than broods with narrow age spans and that delayed fledging improves the survival and reproductive prospects of younger siblings, although at a potential cost to future siblings. We also manipulated age spans through cross-fostering and found that older foster nestlings postponed fledging when raised with younger broodmates, as predicted if the age of younger nestlings determines the time of fledging. Our results support kin-selection theory and demonstrate that the exact time of fledging is attributable, in part, to sib-sib interactions.
Blue Tits exhibit extreme variation in clutch size and hatching asynchrony, which is the focus of this study. This paper reports an in-depth study of breeding Blue Tits showing that variation in Blue Tit hatching asynchrony can be explained by a number of phenological variables including particularly, date of bud burst in the local oak tree, which signals caterpillar emergence (34%), also date of first egg (14%) and female weight (8%). Hatching asynchrony explained 9% of the variation in brood mortality in this southern English population. Early incubation relative to clutch completion (incubation asynchrony) in Blue Tits explained 85% of the variation in hatching asynchrony, differs between years and advanced hatching in early and fledging in late laid eggs. Consequently, because fledging is usually synchronous, hatching asynchrony shortens the total time spent in the nest and explained 28% of the variation in nesting time from clutch completion to fledging. I present experimental evidence that brood reduction resulting from hatching asynchrony may be particularly adaptive towards the end of the breeding season, with 91% of the variation in the productivity of asynchronously-hatched broods being explained by, and increased with, date of hatching. About one fifth of birds delayed daytime incubation until after clutch completion, probably in wait for caterpillars to appear. Although the delay period was variable and extended total nesting time it always resulted in synchronous hatching. I propose that Blue Tits may have evolved plastic responses to environmental cues such as oak bud burst, which causes them to incubate at the optimum time to ensure maximum fledging success and chick fitness.
IN animals with parental care, parents rearing offspring of variable ages are typically assumed to exert less effort than those rearing even-aged offspring. This is because spaced births spread out peak loads in the combined food demands of all offspring(1-3). Creating a mixed-size sibship also helps establish a hierarchy among the young which reduces the costs of sibling rivalry(4) and can help efficient elimination of young if food becomes short(5,6). We manipulated hatching spread within broods of the blue tit Parus caeruleus and studied postbreeding survival rate of the adults. We report here that, contrary to current,theory, female parents suffer less when the young are even-aged than when they are of variable ages, whereas the opposite result was found for male parents. Apparently, the male contributes more in synchronous broods, thus lightening the female's total investment burden. In blue tits this sexual conflict over hatching pattern is won by the female because she alone incubates. By delaying incubation until most eggs have been laid, she reduces hatching span.
We present a multivariate model of the post‐fledging survival of juvenile great and coal tits ( Parus major L. , P. ater L. ) in relation to chick body condition and timing of breeding. Radio‐telemetry and colour marks were used to track tit families during 20 days from fledging, that is, the period of post‐fledging dependence. Data on 342 chicks of 68 broods were obtained.
Forty‐seven per cent of juveniles died during the observation period, predation being the main cause of mortality. In the first 4 days after fledging the mortality rate was 5–10% per day.
Survival of juveniles was positively correlated with fledging mass. Furthermore, survival strongly decreased during the season. In the second half of June, mortality was five times the rate of mid‐May. The differential survival resulted in selection for both early fledging and high fledging mass. Juvenile condition was less important for survival in birds that had fledged early in the season. Their survival rates exceeded 70% in all weight classes, whereas in late broods only the heaviest individuals survived equally well. The survival of birds fledging both late and in poor condition was below 20%. Thus, selection for high fledging mass was much stronger in the late season than in early broods.
We conclude that the impact of predation after leaving the nest results in selection for early breeding and, particularly in the late season, for high fledging mass. This may explain why the earliest broods have been found to produce most recruits into the breeding population even if they did not profit from maximum food availability during the nestling period. On the other hand, energetic limitations may constrain the begin of egg laying in adult birds. Thus, counteracting evolutionary responses to the seasonal development of food availability (the caterpillar peak) and to the risk of post‐fledging mortality (the peak in post‐fledging mortality) may have focused the period of optimal reproduction to a narrow time‐window.
The main mechanism to achieve hatching asynchrony (HA) for incubating birds is to start heating the eggs before clutch completion. This might be achieved through partial incubation and/or early incubation. Even in the absence of incubation behaviour during the laying phase, clutches still experience a certain degree of asynchrony. Recent studies have shown that eggs located in the centre of the nest receive more heat than peripheral ones during incubation. As eggs receiving more heat would develop faster, we hypothesized that HA should be shorter in nests where eggs were moved homogeneously along the centre-periphery space during incubation than in those nests where eggs repeatedly remained in the same locations, either centrally or peripherally. We explored the relative roles of egg repositioning and partial incubation in determining HA in wild birds by (1) removing eggs from 20 Great Tit Parus major nests on the day of laying and replacing them with fake eggs to avoid partial incubation, and returning them when full incubation began; (2) monitoring twice a day the position of each individually marked egg relative to the clutch centre during incubation, and estimating the coefficient of variation of the distances; and (3) determining HA in each nest. Preventing partial incubation reduced HA by 51% days in experimental nests. It also caused negative effects for the incubating females (lengthening the full incubation period) and positive effects for the brood (increasing fledging success). However, our hypothesis about the role of egg repo-sitioning on HA was not supported: all the females moved the eggs with remarkable consistency , generally attaining a coefficient of variation of the distances around 33%, and it was not related to the HA experienced. We therefore conclude that partial incubation is an important factor regulating HA, and females compensate for the potential effects of differential heating by moving the eggs homogeneously within the clutch.
An increase in the perceived risk of predation triggers many behavioural changes in prey species, which can have consequences for their reproductive success. Perceived predation risk may also influence investment in extrapair activities and, as a result, the frequency of extrapair paternity (EPP), but this possibility remains largely untested. Here we report on a study of a small passerine bird, the blue tit, Cyanistes caeruleus, in which we experimentally manipulated perceived predation risk by intermittently broadcasting predator calls throughout the breeding season. We found no evidence that the treatment affected two behavioural indices of extrapair activity (extrabox visits and the time of emergence from the nestbox in the morning during the fertile period) or the rate of EPP itself. The treatment also had no significant effect on clutch size, hatching success or most reproductive behaviours. However, nests in the predator playback treatment produced more fledglings, which was mainly due to a lower frequency of complete brood mortality. We discuss potential explanations for this finding, as well as for the lack of evidence for other effects of the predator playback treatment on blue tit reproductive behaviour. Several measures of reproductive performance suggest that the year in which the experiment took place was an unusually poor one and further work is therefore needed to assess the generality of our findings.
Blood sampling from the brachial vein and sub-cutaneous implantation of PIT-tags (‘passive integrated transponders’) are techniques widely practiced in ornithological research. Longer-term consequences of these procedures (across months or years) have been studied in detail. However, it remains largely unknown how blood sampling and PIT-tagging affect birds during and immediately following the procedure. Here, we test the impact of these procedures on respiration rate and on behavioural correlates of avian pain, stress, and discomfort in the Blue Tit Cyanistes caeruleus. Ten wild-caught Blue Tits were divided in two groups: five were measured, ringed, blood sampled and implanted with a PIT tag (‘treatment birds’); the other five were handled in the same way, but blood sampling and PIT-tagging were conducted as a sham-procedure (‘control birds’). Treatment and control birds did not differ in respiration rates during handling, but treatment birds showed behaviours indicative of an acute stress event associated with brief and moderate pain. Following release in an aviary, treatment and control birds did not differ in behaviour. Birds showed no indication of pain or stress. Instead, they foraged, preened and explored the aviary immediately after handling. Individuals spent much of their time pecking at their new rings. Our results suggest that blood sampling and implantation of PIT-tags have limited short-term effects on Blue Tits. However, the process of handling and ringing itself may have substantial behavioural consequences, which may be relevant for animal welfare and the quality of collected data.
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.
Nestling Troglodytes aedon in lowland central Panama normally hatch asynchronously but, after 6-7 days in the nest at asymptotic weight, fledge synchronously when oldest nestlings are c19 days old. Entire broods of asynchronously hatched nestlings were forced to fledge synchronously when oldest nestlings were 16 days old. Fledgling survival was similar for experimental and control broods except that youngest siblings in experimental broods survived less well than those in control broods, especially in the largest broods. Oldest siblings, which appear to initiate fledging without parental manipulation, had similar survival rates as nestlings and as fledglings between ages 16-19 days. By delaying fledging to increase survival of younger siblings, oldest siblings increase their inclusive fitness. Kin selection may shape fledging behavior. -Author
Despite several decades of intensive research on the breeding biology of birds, very little is known about the behaviour of parents and young during the nest-leaving phase. Factors responsible for the initiation of nest-leaving may have bearings upon a potential conflict between parents and their offspring. Certain nest-leaving behaviours have been assumed in the nest failure hypothesis as an explanation for asynchronous hatching (Clark and Wilson 1981).
This is the first re-appraisal in 50 years of concepts of development made in birds. This book is a case study in evolutionary diversification of life histories. Although birds have a rather uniform body plan and physiology, they exhibit marked variation in development type, parental care, and rate of growth. Altricial birds are fully dependent on their parents for warmth and nutrition and begin posthatching life in a more or less embryonic condition. At the other extreme, such superprecocial species as the megapodes are independent of all parental care from hatching, and the neonate, able to fly, resembles an adult bird. This book thus attempts to present an integrative perspective of organism biology, ecology, and evolution.
The process of nest leaving (fledging) in hole-breeding passerines is largely unexplored, although it is potentially an important facet of reproduction. We used the great tit, Parus major, to investigate whether fledging timing and order were affected by nestling development and sex, as well as the sex ratio in the brood the nestlings were raised in. Because of the difference in size and competitiveness between male and female nestlings, we expected to find an effect of sex and brood sex ratio (BSR) on the process of fledging. To explore its effect on fledging experimentally, we manipulated BSR by swapping 6-day-old nestlings of both sexes. We implanted transponders in all 14-day-old nestlings to determine timing and order of fledging. The brood age at fledging was best explained by average wing length of the brood (negative), average body mass of the brood (positive) and hatching date (negative). In contrast to our hypothesis, BSR did not affect fledging time. Also, the asynchrony of fledging within broods did not depend on BSR. Within broods, fledging order was not affected by sex or by the interaction between sex and BSR. Nestlings with long wings on day 14 fledged earlier than nestmates with shorter wings. Although females were lighter at day 14, they had similar length wings as their male nestmates. Nestlings should keep up with their nestmates during development, because developmental status relative to nestmates, rather than sex-specific competition, influenced the process of fledging.
Although sleep is fundamental for survival, not much is known about sleep behaviour in free-living animals and between-individual variation in sleep patterns has hardly been studied, except in humans. We analysed sleep behaviour in a free-living population of blue tits in southern Germany. We recorded individuals roosting in nestboxes between November and April using infrared-sensitive cameras. We investigated the following sleep parameters: time of entering and leaving the nestbox, sleep onset, awakening time, sleep duration, midpoint of sleep, latency to sleep and frequency and duration of nocturnal awakenings. Sleep onset, awakening time and sleep duration followed seasonal changes in daylength. Blue tits slept ca. 4.8 h longer in winter than in spring. During the night, birds woke up between 23 and 230 times, but this did not change seasonally. Local light conditions influenced awakening time: birds at brighter locations woke up earlier. Females slept on average 15 min longer per night than males and this sex difference became more pronounced in early spring. Although females spent a greater proportion of the night awake than males, they still slept more overall. First-year birds spent more time in the nestbox after waking up and left the nestbox later in the morning than older individuals. Repeatability estimates showed that individuals were consistent in their sleep behaviour over the 2-year study period. Our results indicate that sleep patterns are individual-specific traits in blue tits. We suggest that the observed sex difference in sleep duration is caused by sexual selection.
Many taxa have evolved complex life cycles featuring a dramatic shift in habitat or resource use at metamorphosis. Despite their prevalence and unique characteristics, we understand little about the adaptive properties and evolution of these life histories. I offer a conceptual framework that considers how size-specific growth and mortality rates in both habitats interact with size at metamorphosis to affect lifetime fitness. This model predicts the size at metamorphosis that maximizes fitness, and I use this framework to interpret the wide variation in the life history structure of the amphibians. In particular, I speculate on the adaptive significance of the tadpole stage of the anurans and on the cause of variation in the size at metamorphosis both between and within anuran families. Further, I predict the conditions under which direct development or paedomorphosis will be selected for, and I offer hypotheses on the selective factors that may contribute to the three-stage life history of the newts. Fin...
Grouped individuals are less vigilant for predators than solitary conspecifics because: 1) grouping increases the likelihood of predator detection (detection effect) and 2) grouping makes it less likely that any given individual will be preyed upon (dilution effect). The author presents 2 models of vigilance behaviour and test them using data on the vigilance of elk Cervus elaphus. The 1st model, based on the detection effect alone, is implicit in many published formulations of the relationship between vigilance and group size. Although it predicts the direction of the relationship between vigilance and group size, it provides a poor explanation of the form of the relationship. The 2nd model incorporates both detection and dilution effects. Regression analysis on this "security model' indicates that the model provides a good prediction of both the direction and the form of the relationship between vigilance and group size, explaining 69% of the variance in vigilance frequency. The security model demonstrates that both detection and dilution are important in determining the frequency of vigilance behaviour but that the relative importance of these two effects changes across group size, with detection providing relatively less benefit as group size increases. -from Author
1. We studied the significance of hatching asynchrony in blue tits Parus caeruleus during a 4-year period at Oslo, Norway, by comparing breeding success of broods manipulated to hatch over a shorter or longer period than average.
2. Nestling mortality was high and mainly caused by starvation. Mean body mass of fledglings on day 14 was significantly higher for asynchronous than for synchronous broods.
3. No significant difference was found in the mean number of young fledged between the treatment groups, nor in the number of offspring recruited into the local breeding population, even in a year with heavy nestling mortality. However, the number of recruits was few.
4. The results are consistent with the view that asynchronous hatching ensures high quality of some offspring (the offspring quality assurance hypothesis). This benefit is achieved even when no brood reduction occurs.
5. We suggest a potential cost to hatching asynchrony (the diminishing return hypothesis): in asynchronous broods, early hatched offspring may require so much food that their own subsequent survival is reduced or at least no further improved. Resources may therefore be wasted on first hatched offspring that might have improved the growth of younger siblings.
6. Female parents had lower post-breeding survival with asynchronous than with synchronous hatching; the opposite result was found for male parents. We propose the exploitation of mate hypothesis to explain this result. The hypothesis presumes there is sexual conflict over the amount of parental investment in current versus future reproduction, and over the investment in particular offspring within the brood. We suggest that with asynchronous hatching, females have to invest more to keep less competitive, late-hatching nestlings alive.
Various studies have reported that extrapair young outperform their within-pair half-siblings in fitness-relevant traits, suggesting indirect benefits of extrapair copulations for females. Recent studies, however, suggest that potential confounding maternal effects such as laying and hatching order may have been overlooked. In this study on blue tits, Cyanistes caeruleus, we investigated fledging behaviour, a potentially fitness-relevant trait, in relation to the paternity status of the offspring. We tested whether extrapair young differed from within-pair young in fledging order per se and after we controlled for hatching order, a potential confounding maternal effect. We found that male, but not female, extrapair young fledged earlier than their within-pair nestmates. This effect was partly mediated by the higher body mass of extrapair young, which is a major determinant of fledging order independent of paternity status. However, even when we controlled for body mass, a correlate of hatching order, male extrapair young still fledged earlier than their same-sex half-siblings, indicating that male extrapair nestlings may be at an advantage over their siblings. (c) 2012 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.
We describe the use of subcutaneous passive integrated transponder (PIT) tags in nestling and adult Great Tits Parus major. We investigated whether subcutaneous PIT tags affected fledging success, winter condition, survival and/or recruitment. We found no negative effects of PIT tags on any of these measures either in juveniles or in adults. Subcutaneous PIT tags have the advantage that the risk of tag loss is negligible and that further data collection can be automated. The subcutaneous implantation of PIT tags provides a promising technique for researchers aiming at gathering short or long-term data without the need to handle or disturb small birds after implantation.
The outcome of sibling competition for food is often determined by variation in body size within the brood and involves trade-offs; traits that enhance competitive ability within the nest may be developed at the expense of traits that enable effective flight at fledging, or vice versa. We quantified growth of skeletal, body mass and feather traits in male and female Blue Tit Cyanistes caeruleus nestlings. Males were significantly heavier, had longer tarsi and tended to have greater head–bill lengths than females, whereas females were similar to males in wing flight feather growth. These differences in growth may result from sexual differences in selection of the traits. Females are likely to prioritize feather growth to facilitate synchronized fledging with the rest of the brood, and to enhance escape from predators. We suggest that males are heavier and develop longer tarsi because body size is an important determinant of male reproductive success.
Passive integrated transponders (PITs) are increasingly used to study behaviour in small passerines. However, to ensure the reliability of such studies, knowledge of long-term fitness consequences of equipping passerines with PITs is crucial. We quantify the effects of fitting PITs, injected subcutaneously or glued to colour rings, on fitness in house sparrows Passer domesticus. Relative annual fitness was assessed with the delifing method as an individual's annual contribution to population growth rate. We found no evidence for adverse fitness effects in individual birds fitted with PITs compared with individuals without PITs, independent of the methods of fitting the tags. Our results provide a solid basis for the assumption that such logging devices are safe to use in small passerines and that PITs will most probably not affect the outcome of studies with respect to population dynamics and fitness components.
A feeding planktonic larval stage may be viewed as a migration into the plankton during early development for feeding and safety. The extensive dispersal is an accidental by-product that increases gene flow and geographic range and hence affects speciation, extinction and degree of adaptation to local conditions. Though the dispersal has profound evolutionary consequences, it does not appear to be selection for dispersal that maintains a feeding larval stage in life histories. Trades between investment per offspring, rate of growth and risk are constrained by the capabilities of very conservative larval forms, and these trades are differently constrained among higher taxa. Brooding is associated with small adult size in many taxa, perhaps because small adults can ventilate and hold all the young that they can produce. Thus physical constraints on parental care may link large adult size and a feeding larval stage, and thereby link the complexes of traits associated with adult size (age at maturation, longevity) and larval feeding (parental investment per offspring, dispersal). Conservative features of body plans influence the capacity to brood young. Most feeding larval forms are extremely ancient and conservative. Moreover, loss of a feeding larval stage is an absorbing state for most taxa.-from Author
Evolutionary conflicts of interest between family members are expected to influence patterns of parental investment. In altricial birds, despite providing the same kind of parental care, patterns of investment in different offspring can differ between parents, a situation termed parentally biased favoritism. Previous explanations for parentally biased favoritism have received mixed theoretical and empirical support. Here, we test the prediction that in blue tits, Cyanistes caeruleus, females bias their food allocation rules to favor the smallest offspring during the nestling stage. By doing so, females could increase the subsequent amount of paternal care supplied by their partner during the fledging period, as a previous study showed that males feed the largest fledglings. When size differences within the brood are less pronounced, all offspring will require similar amounts of postfledging care, and thus, the male parent will lose the advantage of caring for the largest offspring that are closest to independence. In this study, we controlled the hunger of the smallest and largest nestlings in the brood and compared the food allocation rules of the 2 parents. We found that the male parent had a stronger preference than the female to feed the closest nestlings and made no distinction between nestlings based on size, whereas the female provisioned small hungry nestlings more when they were at intermediate distances from her. These differences in parental food allocation rules are consistent with predictions based on sexual conflict over postfledging parental investment. Copyright 2007, Oxford University Press.
A growing body of work suggests that breeding birds have a significant capacity to assess and respond, over ecological time, to changes in the risk of predation to both themselves and their eggs or nestlings. This review investigates the nature of this flexibility in the face of predation from both behavioural and reproductive perspectives, and also explores several directions for future research.
Most available work addresses different aspects of nest predation. A substantial change in breeding location is perhaps the best documented response to nest predation, but such changes are not always observed and not necessarily the best strategy. Changes in nesting microhabitat (to more concealed locations) following predation are known to occur. Surprisingly little work addresses the proactive avoidance of areas with many nest predators, but such avoidance is probably widespread. Individual birds could conceivably adopt anti-predator strategies based on the nest predators actually present in an area, but such effects have yet to be demonstrated. In fact, the ways in which birds assess the risk of nest predation is unclear. Nest defence in birds has historically received much attention, but little is known about how it interacts with other aspects of decision-making by parents.
Other studies concentrate on predation risk to adults. Some findings suggest that risk to adults themselves influences territory location, especially relative to raptor nests. An almost completely unexplored area concerns the sorts of social protection from predators that might exist during the breeding season. Flocking typical of the non-breeding season appears unusual while breeding, but a mated pair may sometimes act as a “flock of two”. Opportunistic heterospecific sociality may exist, with heterospecific protector species associations more prevalent than currently appreciated. The dynamics of singing during the breeding season may also respond to variation in predation risk, but empirical research on this subject is limited. Furthermore, a few theoretical and empirical studies suggest that changes in predation risk also influence the behaviour of lekking males.
The major influence of predators on avian life histories is undoubtedly expressed at a broad phylogenetic scale, but several studies hint at much flexibility on an ecological time scale. Some species may forgo breeding completely if the risk of nest predation is too high, and a few studies document smaller clutch sizes in response to an increase in nest predation. Recent evidence suggests that a female may produce smaller eggs rather than smaller clutches following an increase in nest predation risk. Such an increase may also influence decisions about intraspecific brood parasitism. There are no clear examples of changes in clutch/egg size with changes in risk experienced by adults, but parental responses to predators have clear consequences for offspring fitness. Changes in risk to adults may also influence body mass changes across the breeding season, although research here is sparse. The topics highlighted herein are all in need more empirical attention, and more experimental field work whenever feasible.
This paper presents an antithesis to the view that gregarious behaviour is evolved through benefits to the population or species. Following Galton (1871) and Williams (1964) gregarious behaviour is considered as a form of cover-seeking in which each animal tries to reduce its chance of being caught by a predator.It is easy to see how pruning of marginal individuals can maintain centripetal instincts in already gregarious species; some evidence that marginal pruning actually occurs is summarized. Besides this, simply defined models are used to show that even in non-gregarious species selection is likely to favour individuals who stay close to others.Although not universal or unipotent, cover-seeking is a widespread and important element in animal aggregation, as the literature shows. Neglect of the idea has probably followed from a general disbelief that evolution can be dysgenic for a species. Nevertheless, selection theory provides no support for such disbelief in the case of species with outbreeding or unsubdivided populations.The model for two dimensions involves a complex problem in geometrical probability which has relevance also in metallurgy and communication science. Some empirical data on this, gathered from random number plots, is presented as of possible heuristic value.
Amphibian metamorphosis has long intrigued ecologists and developmental biologists, yet the two research programs have progressed separately and toward different goals. Plasticity in metamorphic timing has profound effects on fitness, which has prompted ecologists to develop and test models for predicting how environmental factors affect the size and age of metamorphosis. These models rely upon untested assumptions about the mechanisms for regulating growth and development. Whereas developmental biologists explicitly investigate these mechanisms at the hormonal and genetic levels, they largely ignore the role of environmental input. Recent developments in our understanding of the molecular biology of frog metamorphosis are revealing how these two research programs could be integrated. Here, I review these developments to test ecologists' assumptions about frog metamorphosis, and to present strategies for both research fields to investigate the mechanistic basis of metamorphic plasticity.
Parental benefits and offspring costs reflect parenteoffspring conflict over the age of fledging among songbirds
- T M Jones
- J D Brawn
- I J Ausprey
- A C Vitz
- A D Rodewald
- D W Raybuck
- T J Boves
- C J Fiss
- D J Mcneil
- S H Stoleson
- J L Larkin
- W A Cox
- A C Schwarzer
- N P Horsley
- E M Trumbo
- M P Ward
Jones, T. M., Brawn, J. D., Ausprey, I. J., Vitz, A. C., Rodewald, A. D., Raybuck, D. W.,
Boves, T. J., Fiss, C. J., McNeil, D. J., Stoleson, S. H., Larkin, J. L., Cox, W. A.,
Schwarzer, A. C., Horsley, N. P., Trumbo, E. M., & Ward, M. P. (2020). Parental
benefits and offspring costs reflect parenteoffspring conflict over the age of
fledging among songbirds. Proceedings of the National Academy of Sciences,
202008955.
Intraspecific fledging mass variation in the Alcidae, with special reference to the seasonal fledging mass decline
- R C Ydenberg
- C W Clark
- A Harenfenist
Ydenberg, R. C., Clark, C. W., & Harenfenist, A. (1995). Intraspecific fledging mass
variation in the Alcidae, with special reference to the seasonal fledging mass
decline. American Naturalist, 145, 412e433.