Influence of hatching order on growth rate and resting metabolism of kestrel nestlings

Hatching asynchrony in altricial birds may result in a competitive disadvantage for the youngest nestlings compared to older siblings. We studied the effects of a size hierarchy on the growth rate of Eurasian kestrels Falco tinnunculus chicks in nests with and without access to supplemented food in western Finland. Body mass stopped increasing on the 19th day after hatching while body size, estimated by a combination of bone and feather lengths continued to increase at least until fledging at 26 days. Body condition, reflecting muscle and fat, did not change markedly during the growth period from the 12th day to fledging. Body temperature and resting metabolism were usually lower in nestlings 12 days old than in nestlings at fledging. Growth of body mass, size and condition, and resting metabolism were delayed in last-hatched nestlings aged 19 days. Just before fledging, last-hatched nestlings attained a similar body mass and size, and had a similar resting metabolism to those of older siblings. At fledging, only in nests without access to supplemented food was the body condition of last-hatched chicks lower than that of its siblings, but in nests with access to supplemented food no such difference was detected. Our results highlight that the level of lipids in the last-hatched nestling can be affected by the food restriction imposed by hatching order.     

Post-fledging body mass increase in Common Terns Sterna hirundo: influence of age, sex and year

We studied the inter-year and inter-sex variation of the post-fledging body mass development of Common Terns Sterna hirundo in 2000 and 2001 at the Banter See colony, northern Germany. Here, post-fledglings can be identified and weighed remotely and automatically by a transponder system that makes use of automated balances installed at the colony. Individuals were sexed with PCR amplification methods. After fledging, young generally continued to increase their mass. However, in 2000, the young did not significantly increase their mass during the post-fledging period. In 2001, conditions were more favourable and body mass increased continuously. Further, in 2001, male post-fledglings were significantly heavier than female post-fledglings. Once having left the colony area (on average 18–23 days after fledging in 2000, and 14–16 days after fledging in 2001), post-fledgling body mass had still not reached adult body mass. The longer a juvenile stayed at the colony, the higher was its final body mass, which if acting as a threshold level may control departure time. Neither brood size nor hatching order affected post-fledging mass or period. In the unfavourable year 2000, when many individuals were found dead after fledging, fledging age but not fledging mass was found to be a predictor of post-fledging survival before departure: individuals fledging when older had a lower survival probability. Our results stress the importance of the post-fledging period for body mass increase and survival prior to departure. The variation in post-fledging mass growth between years and between the sexes is discussed with respect to parental effort and a possible selective provisioning of sons over daughters.     

Growth, fledging success and post-fledging survival of juvenile Oystercatchers Haematopus ostralegus

We studied the consequences of differences in growth rate on the subsequent survival of Oystercatcher Haematopus ostralegus chicks. Fledging success increased sharply with growth rate, from zero in chicks growing at less than 6 g per day to about 85% in chicks growing at more than 10 g per day. The age at which chicks fledged varied from 27 to 52 days. Chicks which fledged at an early age displayed a much faster growth rate than later fledging chicks. Although slow growth resulted in a considerable prolongation of the period before fledging, slow-growing chicks fledged at a smaller size and with a lower body-weight than fast-growing chicks. After fledging, all chicks remained almost completely dependent on their parents up to an age of 3 months and often longer.
Almost 40% of the fledglings eventually returned to the breeding area. This figure probably reflects post-fledging survival. Age and size at fledging had no effect on a chick's probability of return. Body-weight at fledging had a small positive correlation with the return probability, but this was not statistically significant. We conclude that although slow growth severely reduces a chick's chance of fledging, it probably does not result in irreversible damage causing an increased risk of mortality during the first years after fledging. Apparently, any possible disadvantage associated with small size or low body-weight could be compensated for after fledging.     

Sex-specific differences in body condition indices and seasonal mass loss in Tufted Puffins

ABSTRACT.   Reduced prey availability can affect the growth and survival of nestling seabirds. However, few studies have demonstrated similar effects on indices of adult body condition. We examined body condition and seasonal mass loss of breeding adult male and female Tufted Puffins ( Fratercula cirrhata ) at Chiniak Bay, Kodiak Island, Alaska, in 2004–2005. We determined sex using genetic analysis, developed a discriminant function to determine sex using morphometric measurements, and examined the body condition of adult males and females relative to the growth rates of their offspring. We found that morphological measurements were only moderately useful for sexing Tufted Puffins, with 74% of adults ( N = 176) correctly classified. We also found that the relationship between adult body mass and size differed between sexes and conclude that body condition indices must be calculated separately for each sex to avoid inter- and intrasexual bias. Body condition of male and female Tufted Puffins declined during the chick-rearing period. However, body condition of females did not differ between years, whereas male condition declined to a greater degree during 2004 when the mass of young at fledging was significantly lower. Although these results suggest that adult male Tufted Puffins sacrifice their own body condition in years of diminished nestling growth and females do not, reasons for this apparent intersexual difference in reproductive strategies remain unclear.     

Influence of temperatures during the nestling period on post-fledging survival of great tit Parus major in a Mediterranean habitat

Survival during the first year is one of the most important factors determining fitness in birds. Birds have poor thermoregulatory abilities during the nestling period when the plumage is not fully developed, thus temperature during the nestling period is a serious candidate to affect post-fledging survival, although it has been usually ignored in previous studies. We analysed the relationship between temperatures and post-fledging survival in a great tit Parus major population in Sagunto (Spain) using capture-recapture data from 12 years. Hatching dates, mass at fledging and temperatures during the nestling period (maximum, minimum and mean ambient temperatures as an estimation of the mean and extreme weather conditions that chicks encountered at the nest) were used as individual covariates. Mean post-fledging survival was 0.13±0.01. Adult survival probability was 0.64±0.02. Multi-model inference suggested that post-fledging survival increased with fledging mass, and decreased as temperatures increased. Furthermore, the effect of mass on survival was less important as temperature was higher. We consider that high temperatures affect nestlings' health due to low thermoregulatory abilities of nestlings. Model selection did not support a relationship between hatching dates and survival once mass and temperatures were taken into account. The results suggest the possibility that the effect of date on post-fledging survival found in previous studies was, at least in part, a consequence of the seasonal pattern of temperature variation.     

Growth and energy expenditure of Wandering Albatross Diomedea exulans chicks

Wandering Albatross Diomedea exulans chicks require 9–10 months to achieve adult body size at fledging, at which time they are also sexually size dimorphic. Because the developmental period spans the winter season, chicks must endure severe winter conditions and variability in provisioning effort by their parents. Thus chicks may adjust their rate of energy utilization to accommodate variations in provisioning, but this has not previously been studied. We followed longitudinally the changes in growth, body composition and oxygen consumption of 10 chicks from the end of the brooding period until fledging on the Crozet Islands. Body mass, culmen length and wing length were measured every 10 days and total body water (TBW) and resting metabolic rate (RMR) were measured monthly. Overall growth followed a logistic curve for all chicks, and sexual dimorphism in body mass appeared as early as the second month of measurements (males being heavier than females). Absolute TBW followed a logistic increase like that of body mass and was significantly higher in males owing to the difference in body mass. Conversely, mass-specific TBW (i.e. the proportion of body mass made up of water) did not differ significantly between male and female chicks. Absolute RMR peaked at 1.5 × adult basal metabolism in midwinter when chicks achieved maximum body mass, but decreased to adult levels by the time chicks fledged. The decrease in absolute RMR following attainment of peak mass is atypical of most seabird chicks (Procellariiformes) and may be explained partly by a reduction in size of the gut when parents reduce provisioning effort. The changes in mass-specific RMR did not differ between sexes but male chicks, being heavier, had higher absolute oxygen consumption and therefore greater energy requirements.     

Effects of transmitters on the reproductive success of Tufted Puffins

ABSTRACT.   Although radiotelemetry is useful for monitoring nest attendance and the foraging ranges and distribution of breeding birds, attachment of transmitters may affect reproductive behavior. In 2003, we captured 25 adult Tufted Puffins ( Fratercula cirrhata ) at two colonies in Chiniak Bay, Kodiak Island, Alaska, and fitted them with subcutaneously anchored radiotransmitters (<1.2% of body mass). We determined the presence of radio-marked birds at each study site using automated, remote radiotelemetry systems, and compared rates of nestling growth, fledging mass, and fledging success for chicks with and without (control group) a radio-marked parent. Although most radio-marked adults continued to attend nests after capture and attachment of transmitters, nestlings with a radio-marked parent had lower mean growth rates (6.9 g/d vs. 14.4 g/d) and fledging success (33% vs. 84%) than control chicks. These results suggest that colony attendance by adult puffins fitted with transmitters declined sharply or completely and this led to high nestling mortality. Given the negative effects of transmitters on Tufted Puffins in our study and in other studies of alcids, we suggest delaying the attachment of transmitters until well after the brooding period. In addition, we recommend pilot studies be undertaken to distinguish the possible effects of capture and handling from those of actually carrying the device.     

Post-fledging body mass as a determinant of subadult survival in Common Terns Sterna hirundo

Once a bird has fledged it becomes hardly accessible for researchers and consequently knowledge about post-fledging ontogeny is scarce. In this study on juvenile Common Terns (Sterna hirundo) we used an automated transponder-based detection and weighing system at Banter See colony, Northern Germany, which enabled us to investigate body mass growth of post-fledglings and its consequences for their survival until first return to the natal colony when 2 years old. We analysed data from two contrasting breeding seasons, 2000 and 2001, in order to determine inter-year and inter-sex variation of post-fledging parameters assumed to potentially affect subadult survival, such as the period a juvenile is still present at colony surroundings (departure age), its fledging mass and last recorded post-fledging body mass, and hatch date. Using an information-theoretic model selection approach, neither the date of hatching nor the departure age was found to affect survival. The only predictor of survival was last post-fledging body mass whereas fledging mass itself was of minor importance. Although there was weak evidence for an interaction with year, individuals of the cohort 2000, which left the colony area on average 5 g lighter than those reared under the more favourable conditions in 2001, did not exhibit lower return probability. We suggest that under unfavourable conditions selection had eliminated weak individuals prior to fledging or during the post-fledging period. This study underlines the importance of the post-fledging period and its consequences for survival, especially in species with prolonged parental care post-fledging.     

Nestling feeding strategy of the British storm-petrel Hydrobates pelagicus in a Mediterranean colony

The pattern of chick feeding of the British storm-petrel Hydrobates pelagicus in a Mediterranean colony was examined by weighing chicks at 24-h intervals on different days during the nestling period. In order to calibrate daily mass increments (NET) against number of feedings, daily mass changes of chicks were regressed upon the sum of positive mass increments recorded overnight (SUM) during four nights. The average meal size delivered to chicks per night by one parent was 3.5 ß 1.3 g or 12% of adult weight. This was insufficient for sustaining constant chick mass during a day. On average 85% of chicks were fed each night, and the mean interval between feeds was 1.2 ß 0.5 nights. Nightly feeding frequencies differed among days, but this night-to-night variation was not related to meteorological conditions. Both food requirements necessary for chick body maintenance (zero-growth) and meal size were relatively constant for ages up to 59 days. However, feeding frequency decreased throughout the fledging period, accounting for agespecific variation in growth rates until fledging. Food requirement and feeding patterns at Benidorm were different from North Atlantic colonies. None the less, growth patterns were almost identical, suggesting adjustment to maintain chick body mass at a determined level, as food delivery to nestling appears to be regulated to chicks'nutritional requirements.     

Juvenile survival and recruitment of wood thrushes Hylocichla mustelina in a forest fragment

We tested if juvenile survival and recruitment (returning to breed) of wood thrushes Hylocichla mustelina into their natal population was dependent on several measures of nestling condition, growth, and site fidelity. Overall, nestling mass, wing chord, condition, and rank within the brood did not affect the probability of survival to the post-fledging stage, independence, or recruitment. We did not identify any morphometric differences among nestlings that remained in the study area after fledging and those that did not (or those that did not survive). Time of season and the number of days nestlings were present in the study area after hatching, or site fidelity, were the only variables measured that positively influenced juvenile survival and recruitment. Based on a restricted sample, fledglings that eventually recruited did not differ in size during post-fledging or post-independence from fledglings that did not return to breed. Independent, immigrant hatching-year (HY) birds are briefly described. Overall, immigrant HY birds had a higher probability of recruitment than all local fledglings. There was no difference in the probability of recruitment between immigrant HY birds and independent local fledglings (those present ≥35 days after hatching), however. Similar to local young, the number of days present in the study area increased the likelihood of recruitment for immigrant HY birds, although these effects could not be distinguished from those of emigration or survival.     

Quantifying density dependence in a bird population using human disturbance

Although density dependence has long been recognised as vital to population regulation, there have been relatively few studies demonstrating it spatially in wildlife populations, often due to the confounding effects of variation in habitat quality. We report on a study of woodlarks Lullula arborea, a species of European conservation concern, breeding on lowland heath in Dorset, England. We take the novel approach of utilising the birds’ response to human disturbance, which resulted in much of the variation in density but had no direct impact on demographic rates. Within years, in sites with greater density there were smaller mean chick masses, lower post-fledging survival, and higher rates of nestling mortality attributed to starvation. The effects on clutch size and fledging success were confounded by the area of grassland within a site. There was no effect on brood size. Density dependence also operated within sites between years: as density increased there were reductions in mean chick mass and post-fledging survival, while nestling mortality attributed to starvation increased. Density-dependent effects on clutch size were only weakly regulatory, whereas density-dependent starvation and post-fledging mortality rates contributed strongly to differences in overall breeding output. Heavier chicks (when 7 days old) were significantly more likely to fledge and less likely to starve. Broods with heavier chicks were more likely to supply recruits to the breeding population. Nestling mass was not a factor in survival in the immediate post-fledging period, suggesting that density-dependent processes act independently on this stage. We conclude that the number of birds per hectare of suitable habitat is a valid means of expressing density, and that habitat acts as a surrogate for food abundance through which density dependence operates on the woodlark population.     

Post‐fledging survival of Little Owls Athene noctua in relation to nestling food supply

Among the range of determinants of post‐fledging survival in altricial birds, the energy supply to the growing juveniles is likely to play a central role. However, the exact mechanisms shaping post‐fledging survival are poorly understood. Using a food supplementation experiment, we determined the effect of variation in food supply on the survival of juvenile Little Owls Athene noctua from hatching to 2 months post‐fledging. Experimental broods were food‐supplemented for 36 days during the nestling and the early post‐fledging period. The fate of 307 juveniles (95 of them provided with extra food) was determined by nest monitoring and radiotelemetry. In unsupplemented birds, the rates of survival measured at 5‐day intervals were lowest during the nestling stage, remained low during the early post‐fledging stage and steadily increased after about 2 weeks post‐fledging. Food supplementation substantially increased nestling survival, but we detected no direct treatment effect on post‐fledging survival. Instead, we found a strong indirect effect of food supplementation, in that fledglings of good physical condition had markedly higher chances of surviving the post‐fledging period compared with those in poor condition. Experimental food supplementation increased survival over the first 3 months from 45% to 64.6%. This suggests that energy reserves built up during the nestling stage influence post‐fledging survival and ultimately parental reproductive output. The low nestling and post‐fledging survival shows that the early life‐history stages constitute a crucial bottleneck of reproductive ecology in Little Owls. The strong treatment effects on the number of independent offspring indicate that natural variation in food supply is an important determinant of spatio‐temporal patterns in Little Owl demography.     

Post-fledging survival of individual great tits: the effect of hatching date and fledging mass

Pre-breeeding survival is one of the major sources of individual variation in lifetime reproductive success. However, very little is known about the reasons for differences in survival among individuals during this important phase of the life cycle. Some studies, using local return rates as indices of survival, have shown a relationship between post-fledging survival and fledging date and mass in birds, most of them suggesting directional selection towards heavy masses and early fledging dates. Recent development of capture-recapture models allows the separate estimate of survival and recapture probabilities, as well as the inclusion of individual covariates into the modelling process. We used here these models to explore the relative effects of fledging date and fledging mass on local recruitment of individual great tit Parus major fledglings. Individual capture-recapture histories of 2051 fledglings (cohorts 1992–1999), 184 of which were recaptured as breeding birds during 1993–2000, were used in the analyses. Hatching date, offspring mass at day 15, their squared terms, and interactions between mass and date, were included as covariates into the modelling process. Models with age (fledglings and adults) and time (year) dependence were used. The probability of local recruitment increased with fledging mass in each of the years studied. Fledging date also affected recruitment but, against what is commonly thought, fledgling early is not the best option every year. Either early, intermediate or late fledglings were favoured in different years. This between-year variation in the optimum fledging date offers an alternative explanation to the lack of evolution towards earlier breeding dates, in spite of the advantages of early breeding some years.     

Post-fledging interactions between the Common Cuckoo Cuculus canorus and its cavity-nesting Common Redstart Phoenicurus phoenicurus host

Brood parasite–host interactions during the incubation and nestling stages have been well studied, but the post-fledging period remains virtually unknown. Using radiotracking, we provide the first detailed data on post-fledging interactions between the Common Cuckoo Cuculus canorus and its only regular cavity-nesting host, the Common Redstart Phoenicurus phoenicurus. Cuckoos raised alone (‘solitary’) fledged at higher mass, with higher wing and tarsus length and started to fly at a younger age than Cuckoos raised alongside young Redstarts (‘mixed’). However, a further 23 fledging and post-fledging parameters measured at five pre-determined times (fledging, first-flight, predation, starvation, independence) did not differ between solitary and mixed Cuckoos. In addition, none of the parameters measured during the post-fledging period (growth, dispersal distances, number of flights) differed between solitary and mixed Cuckoos. Redstart fledglings from non-parasitized broods (‘solitary’) showed generally similar fledging and post-fledging parameters to fledglings reared alongside a Cuckoo (‘mixed’). Surprisingly, there were no significant differences in post-fledging predation rate, starvation or overall survival rates between mixed and solitary Cuckoos or mixed and solitary Redstarts. Thus, during the post-fledging period, mixed Cuckoo fledglings successfully compensated for the poorer performance experienced during the nestling stage whereas mixed and solitary Redstarts did not differ in any measured parameters. This suggests that the regular occurrence of mixed broods in this host–parasite system – which is unique among the many Cuckoo hosts – is evolutionarily stable for both hosts and parasites.     

Timing of fledging is influenced by glucocorticoid physiology in Laysan Albatross chicks

Fledging is a major life transition for birds, when juveniles move from the safety of a nest into an environment where they must find food and avoid predators. The timing of fledging within a season can have significant effects on future survival and breeding success. Proximate triggers of fledging are unknown: though wing development is likely a primary factor, other physiological changes, such as elevated plasma corticosterone (CORT), may affect fledging behavior. Laysan Albatross (Phoebastria immutabilis) chicks have an extended post−hatching period during which they reach 150% of adult mass. However, approaching fledging, chicks fast for days to weeks and lose mass while still putting energy into feather growth. We evaluated chick morphology and physiology to elucidate proximate triggers of fledging. As in some other species, CORT increased as chicks fasted and lost body mass. At the same time, corticosteroid binding globulin (CBG) declined, thus amplifying free CORT prior to fledging. Once chicks reached a morphological threshold, free CORT levels predicted how long they stayed at the colony: chicks with higher free CORT fledged sooner. To perturb the relationship between body condition, endocrine physiology, and fledging behavior, we supplementally fed chicks for the month before fledging. Fed birds had a slower decrease in body mass, slower decrease in CBG, slower increase in free CORT, and stayed at the colony longer after reaching a morphological threshold. Our study suggests that as chicks lose mass, free CORT acts as a signal of energetic or nutritional state to adjust the timing of fledging.     

Variation in the growth and survival of Golden Plover Pluvialis apricaria chicks

The growth of Golden Plover Pluvialis apricaria chicks is modelled in detail for the first time. The pattern of growth is typical of postnatal development in waders, although the mean fledging time of 37 days is slower than would be expected from adult body weight. Bill length and weight at hatching had significant effects on the rate of weight gain shown by 2-day-old chicks, although this effect was not noticeable at 4 days of age. Chick survival was significantly affected by bill length, as a result of the variation in weight gain. The growth of older chicks was positively correlated with mean minimum temperature. The slow rate of growth exhibited by Golden Plover chicks is discussed in relation to breeding habitat and the effects of weather and hatchling biometrics.     

Yolk carotenoids increase fledging success in great tit nestlings

Avian mothers can influence offspring phenotype through the deposition of different compounds into eggs, such as antibodies, hormones and antioxidants. The concentration of carotenoids in yolk is larger than in maternal plasma, suggesting an important role of these compounds for offspring development. Since carotenoids have to be acquired from the diet, they may be available in limiting amounts to the mothers. Here, we investigated the role of egg carotenoids for offspring growth by experimentally increasing the concentration of yolk lutein, the main carotenoid in great tit (Parus major) yolk. We subsequently measured body condition, oxidative stress, immune response, plumage colouration and fledging success. Lutein increased body mass soon after hatching and fledging success, but did not affect tarsus length, oxidative stress, immune response and plumage colouration. The higher content of yolk lutein could have increased body mass by reducing oxidative stress caused by high metabolic rates of rapidly growing embryos or by promoting cell differentiation and proliferation. The positive effect of lutein on fledging success seems to be mediated by its influence on body mass 3 days post-hatch, since these two traits were correlated. The finding that our treatment did not affect traits measured later in the nestling period, except for fledging success, suggests that yolk lutein has short-term effects that are essential to increase survival until fledging. Our study shows the positive effect of yolk lutein on offspring survival in the great tit, and therefore suggests an important role of carotenoid-mediated maternal effects.     

High blowfly parasitic loads affect breeding success in a Mediterranean population of blue tits

The detrimental effects of ectoparasites on the breeding success of birds have been especially well demonstrated in the case of ectoparasites that affect both chicks and their parents. Since blowfly larvae of the genus Protocalliphora attack only nestling birds, they represent a good model for testing the consequences of parasitism on nestlings. A Corsican population of blue tit suffers extremely high rates of infestation by blowflies, which are suspected to negatively affect young birds. Comparing experimentally deparasitized (treated) and naturally infested (control) broods, we showed that the attack by Protocalliphora causes anaemia and an important disturbance to the chicks. Therefore, we expected that these effects would have a negative impact on body condition and survival in the infested broods. Although we did not find any effect of treatment on fledging success, our predictions were confirmed by lower growth rate, body mass at fledging and tarsus length at fledging in the control compared with the treated group. This suggests that in this population, blowflies decrease the probability of recruitment of young blue tits. Received: 6 May 1997 / Accepted: 14 July 1997     

Lipid reserves,fasting capability and the evolution of nestling obesity in procellariiform seabirds

Several alternative explanations have been proposed to account for the evolution of nestling obesity in a variety of avian groups. These predict quite different patterns of fat accumulation, storage and use by chicks of different ages. Yet surprisingly few studies have measured changes in body composition during chick development. We tested the applicability of these hypotheses for fulmars, Fulmarus glacialis, by direct measurement of changes in water, lipid and lean dry mass in growing chicks. Lipid and lean dry mass increased until ca. 70% of the way through chick rearing, but then levelled off. Total body water also increased until the same stage, but gradually declined thereafter, and it was this change rather than fat metabolism that resulted in mass recession. The observed pattern of a continued increase in stored lipid, and most importantly, its maintenance all the way through the mass-recession phase until chicks reach fledging, is incompatible with many of the proposed hypotheses. We suggest that the most likely ultimate explanation for large fat deposits is to fuel chicks during the initial critical period away from the nest site while they learn to forage     

Physiological ecology of Mediterranean blue tits (Parus caeruleus L.): effects of ectoparasites (Protocalliphora spp.) and food abundance on metabolic capacity of nestlings

The consequences of nest ectoparasites, such as Protocalliphora larvae, on nestling birds have been the subject of numerous studies. Despite observed reductions in mass and hematocrit of chicks from parasitized nests, no studies have found any effect of Protocalliphora on nestling survival, suggesting that fitness consequences of Protocalliphora are either weak or occur after fledging. From experiments on the metabolic performance of chicks, we found that parasitized chicks suffer from reduced thermogenic and metabolic capacities as a result of decreased mass and hematocrit. Hence, Protocalliphora may potentially affect nestling survival after fledging, when energetically costly activities such as flight and moult are undertaken. Previous studies have demonstrated an increase in parental feeding rate to compensate for the detrimental consequences of parasite infestation. We tested whether parasite effects on nestling aerobic capacity were dependent on food availability during the feeding period. Measures of caterpillar densities and experimental manipulations of parasite loads allowed us to investigate relationships among host, parasite, and environment. A positive relationship between chick aerobic and thermogenic performances and caterpillar density suggests that negative effects of parasitism may be offset by increased food availability. This study provides the first measurement of the effects of an ectoparasite on metabolic competence in wild birds and documentation of the effect of food availability on ectoparasite virulence using a quantitative measure of food abundance.