Development Of Nestlings Research Articles

The Role of Food Quantity and Prey Type in Nestling Development of American Kestrels

ABSTRACT Diet is an important component of life history that can vary with, and ultimately determine, individual variation in phenotypically plastic traits. American Kestrels (Falco sparverius) generally have low post-fledging survival rates, which suggests a need to better understand what ecological factors, such as diet, influence nestling maturity. The generalist diet of kestrels makes it unlikely that all nestlings in a population receive the same diet. We investigated how breeding phenology and nestling sex ratio interact with diet metrics (diet diversity, percentage of prey types, rate of prey biomass delivery) and relate to nestling maturity (mass, tarsus length, wing length, hematocrit, hemoglobin concentration). We hypothesized that: (1) phenology and nestling sex ratio would correlate with inter-nest diet variation; (2) diet metrics would be predictive of nestling development; and (3) the manipulation of food quantity through food supplementation would lead to nestlings with greater developmental maturity. We found that inter-nest variation in diet was correlated with breeding phenology and nestling sex ratio, independently. However, the variation in diet was unrelated to nestling maturity. In response to food supplementation, kestrel parents decreased their food-provisioning rate, indicating that food quantity regulates parental care. Male nestlings appeared to benefit from supplementation while females did not. Our data demonstrated high inter-brood variation in nestling diet, and suggested that diet variation interacts with sex to influence growth and development of nestlings, which could potentially be linked to population decline.

The effect of daylight exposure on the immune response and body condition of Great Tit nestlings

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.

Hungry or angry? Experimental evidence for the effects of food availability on two measures of stress in developing wild raptor nestlings.

Food shortage challenges the development of nestlings; yet, to cope with this stressor, nestlings can induce stress responses to adjust metabolism or behaviour. Food shortage also enhances the antagonism between siblings, but it remains unclear whether the stress response induced by food shortage operates via the individual nutritional state or via the social environment experienced. In addition, the understanding of these processes is hindered by the fact that effects of food availability often co-vary with other environmental factors. We used a food supplementation experiment to test the effect of food availability on two complementary stress measures, feather corticosterone (CORTf) and heterophil/lymphocyte ratio (H/L) in developing red kite (Milvus milvus) nestlings, a species with competitive brood hierarchy. By statistically controlling for the effect of food supplementation on the nestlings' body condition, we disentangled the effects of food and ambient temperature on nestlings during development. Experimental food supplementation increased body condition, and both CORTf and H/L were reduced in nestlings of high body condition. Additionally, CORTf decreased with age in non-supplemented nestlings. H/L decreased with age in all nestlings and was lower in supplemented last-hatched nestlings compared with non-supplemented ones. Ambient temperature showed a negative effect on H/L. Our results indicate that food shortage increases the nestlings' stress levels through a reduced food intake affecting both their nutritional state and their social environment. Thus, food availability in conjunction with ambient temperature shapes between- and within-nest differences in stress load, which may have carry-over effects on behaviour and performance in further life-history stages.

Growth and Development of Nestlings of White-Throated Kingfisher, Halcyon Smyrnensis (Linnaeus, 1758)

The growth and development of the nestlings of white-throated kingfisher (Halcyon smyrnensis) showed that at the hatching day, the mean body weight was 14.6±1.0 g which gained up to 69.9±3.0 g during fledging. The mean length of the body, wing, beak, head, tarsus and feet were 59.4±12.4, 19.4±5.7, 3.1±1.2, 11.7±1.4, 8.5±1.8 and 17.3±3.6 mm, respectively at the hatching day and 203.5±14.1, 105.7±5.8, 40.4±1.3, 29.1±1.1, 14.9±0.4 and 29.8±0.7 mm, respectively during fledging day. The primaries, rectrices and the claw was started to grow from 3rd day hatching and grew up to 67.8±5.6, 27.7±3.4 and 5.2±0.2 mm, respectively during fledging time.
 Asiat. Soc. Bangladesh, Sci. 46(1): 71-80, June 2020

The enigmatic Rothschild's Swift (Cypseloides rothschildi): Natural history, distribution, and seasonality

Rothschild's Swift (Cypseloides rothschildi) is among the least known South American swifts. Here we clarify its distribution and seasonality, and provide detailed natural history data and breeding information. We compiled 197 records of Rothschild's Swifts (museum specimens, citizen science initiatives, literature, and field observations) from Argentina and Bolivia; most from the breeding season (Oct–Mar, 177 records; 44 documented), a few thought to be on migration (Apr and Sep, 15 records; 3 documented), and fewer during the nonbreeding period (May–Aug, 5 records; 1 documented) with no records from July/August. Rothschild's Swifts are migratory, but the wintering quarters remain unknown. The distribution during the breeding season is broadly overlapping with the Austral Yungas of Argentina and Bolivia, with sparse records in Andean and extra-Andean ranges with forested and non-forested waterfalls. Our breeding distribution model indicated high presence probabilities in the Austral Yungas of Bolivia and Argentina. The breeding season during the austral spring and summer (late Oct/mid-Nov to mid-Mar/early Apr in northwest Argentina) began roughly with the early rains as in other Neotropical swifts. Our data from 8 breeding sites and from 8 nests that we studied in northwest Argentina regarding nest placement (near waterfalls), nest features (moss or moss and mud cups), eggs (single and white), and on the protracted development of Rothschild's Swift nestlings (∼55–60 d) and the sequence of plumage acquisition and behavior were coincidental with what is known from other Cypseloides. We provide behavioral information from a temporarily captive individual, which provided the first sound recordings of nestling/fledgling vocalizations of Rothschild's Swift—presumably the first available for any Cypseloides. It is unclear whether these vocalizations, recorded in captivity, represent developmental precursors of adult sounds or begging calls.

Association of Success in Interspecific Rearing of Nestlings with the Width of Trophic Niche of the Recipient Species in Hollow-Nesting Birds

The structure of the diet of passerine bird nestlings was analyzed in order to identify possible ways to reduce food competition between these species during the breeding period. We assumed that analysis of the effects of obtaining diets of heterospecific birds by nestlings in nature can help better understand their species-specific adaptations to living conditions, and we considered the case of joint nesting of the coal tit (Periparus ater (L. 1758)) (CT) and pied flycatcher (Ficedula hypoleuca (Pallas 1764)) (PF) in Moscow oblast as a key link. A PF male attracted a female to an artificial nest box, which has been already occupied by a CT pair. The females of both species incubated a mixed clutch sitting side by side. The CT nestlings hatched earlier than the PF nestlings, and the parents of both species began to feed them. The CT nestlings started to die one by one on the 4th day of joint feeding, and the last nestling died on the 11th day. This case encouraged us to compare the diets of nestlings from 22 broods of CTs and PFs in the same region. To compare the ratios of nestlings, we collected the portions of food that were delivered to nestlings by their parents and analyzed video recordings from the nests. The diet of PF nestlings was significantly more diverse than in CT nestlings (Berger–Parker reverse indices (1/d) were 3.01 and 2.11, respectively). Caterpillars and spiders (objects with a high content of carotenoids and taurine important for the development of nestlings) dominated in the CT diet. In PF feed, these objects occupied a much smaller portion. In addition to the above, compared with coal tits, PFs brought the following to nestlings: a significant number of objects with rough, highly chitinized covers (Coleoptera, Homoptera, etc.); objects with a sharp taste, such as true bugs (Heteroptera), ladybirds (Coleoptera, Coccinellidae), and millipedes (Diplopoda, Julidae); insects containing cantharidin toxin (soldier beetles, Coleoptera, Cantharidae). The nestlings developed successfully in PF nests to which parents brought such feed objects. The dimensional ranges of objects in the CT and PF diets completely overlapped. According to our opinion, the rougher, highly chitinized food and some poisonous insects (Cantharidae) in the PF diet make fundamentally important differences in the nutrition of PFs and CTs. Most likely, PFs have resistance to cantharidin and some other toxins that are contained in insects and therefore have a wider trophic niche.

Biología reproductiva de <i>Porphyriops melanops bogotensis</i> (Gruiformes, Rallidae) subespecie endémica y amenazada del norte de los Andes

La familia Rallidae, ampliamente distribuida, tiene una alta proporción de especies amenazadas e información limitada sobre su biología reproductiva. La subespecie endémica y amenazada de la tingua moteada, Porphyriops melanops bogotensis, constituye un grupo aislado de Colombia con poca información sobre su reproducción y desarrollo. Describimos la biología reproductiva y el desarrollo de los pollos de P. m. bogotensis, aportando información novedosa y útil para su conservación. El estudio se hizo en la sabana de Bogotá, Colombia entre 2016 y 2019. Semanalmente hicimos recorridos en busca de nidos para su descripción y seguimiento. Se incubaron artificialmente catorce huevos; los polluelos fueron criados en cautiverio, haciendo seguimiento de su crecimiento y cambio de plumaje hasta terminar su desarrollo. Las aves anidaron durante todo el año; el número de huevos varió entre tres y seis, con un período de incubación de 18-20 días. Se alcanzó el tamaño definitivo alrededor de los 55 días, con diferencias significativas entre sexos. El color definitivo del pico se adquiere a los 75 días mientras que el color del iris y plumaje adulto se alcanza entre los días 150 y 165. En términos generales la reproducción y desarrollo de P. m. bogotensis concuerda con lo descrito para otros miembros de la familia Rallidae. Los detalles del cambio en coloración de la subespecie durante su desarrollo permiten determinar la edad de individuos silvestres.

Maternal care of platypus nestlings (Ornithorhynchus anatinus)

Maternal care in platypuses has never been rigorously studied due to the difficulty in locating and accessing nesting burrows. Here we describe the maternal behaviour of a captive female platypus and the growth and development of her offspring over 11 breeding seasons. We located a nesting burrow and inserted a camera to record the activity and behaviour of the female and her offspring. We also measured the female’s food intake during lactation. The ages of the offspring were assigned to developmental milestones including opening of the eyes and development of pelage. Twins (n=4) were left alone for periods longer than 24h by the mother at an earlier age than single nestlings (n=2). The dietary energy intake of the breeding female was more than double that of non-lactating females in the last month of lactation, indicating the large energy requirements of milk production. The mean age of young at emergence from the burrow was 128±1 days and in 60% of nestlings emergence occurred after weaning. This suggests a rapid transition from a completely milk-based diet to a diet of aquatic macroinvertebrates. The techniques we developed have allowed us to study maternal care in platypuses and the development of nestlings, both of which were previously only poorly understood.

Genome Resequencing Reveals Congenital Causes of Embryo and Nestling Death in Crested Ibis (Nipponia nippon).

The crested ibis (Nipponia nippon) is endangered worldwide. Although a series of conservation measures have markedly increased the population size and distribution area of these birds, the high mortality of embryos and nestlings considerably decreases the survival potential of this bird species. High-throughput sequencing technology was utilized to compare whole genomes between ten samples from dead crested ibises (including six dead embryos and four dead nestlings aged 0–45 days) and 32 samples from living birds. The results indicated that the dead samples all shared the genetic background of a specific ancestral subpopulation. Furthermore, the dead individuals were less genetically diverse and suffered higher degrees of inbreeding compared with these measures in live birds. Several candidate genes (KLHL3, SETDB2, TNNT2, PKP1, AK1, and EXOSC3) associated with detrimental diseases were identified in the genomic regions that differed between the alive and dead samples, which are likely responsible for the death of embryos and nestlings. In addition, in these regions, we also found several genes involved in the protein catabolic process (UBE4A and LONP1), lipid metabolism (ACOT1), glycan biosynthesis and metabolism (HYAL1 and HYAL4), and the immune system (JAM2) that are likely to promote the normal development of embryos and nestlings. The aberrant conditions of these genes and biological processes may contribute to the death of embryos and nestlings. Our data identify congenital factors underlying the death of embryos and nestlings at the whole genome level, which may be useful toward informing more effective conservation efforts for this bird species.

Early Life Conditions and Immune Defense in Nestling Swainson's Hawks.

The quality of perinatal conditions directly influences the physical and immunological development of nestlings, yet it is inherently variable across space and time. Long-term breeding data for a population of Swainson's hawks (Buteo swainsoni) in northern California show a continuum of territory occupancy and productivity values of individual territories and nests. Here we explore effects of variation among territories on immune system development. We hypothesize that nestlings benefitting from favorable conditions will invest in stronger immune systems, a trait with long-term benefits. We used two immunological assays, a bactericidal assay and a hemolytic-complement activity assay, with leukocyte differentials (heterophil∶lymphocyte ratio) to evaluate the constitutive innate immune system. We examined whether early brood-rearing conditions (i.e., number of siblings, hatch date, endoparasite prevalence) were associated with immunological development. Linear mixed-effects models indicated a positive relationship between extended territory occupancy history-an index of habitat quality-and nestling immune function during years with poorer reproduction. There was no association during an exceptionally good reproductive year. Hence, at least under some circumstances, nestling environments or territory characteristics may affect immune function of nestlings. Our study contributes to the growing body of evidence highlighting the importance of facultative allocation to immune traits using long-term demographic data of a top avian predator.

Variation in offspring development is driven more by weather and maternal condition than predation risk

Abstract Variation in offspring development is expected to be driven by constraints on resource allocation between growth and maintenance (e.g. thermoregulation). Rapid post‐natal development decreases predation risk to offspring, while inclement weather likely prolongs development. For taxa with parental care, parental behaviour may partially buffer offspring against extrinsic drivers like predation risk and severe weather. Using a 7‐year dataset from an alpine population of horned lark Eremophila alpestris, a ground‐nesting songbird in northern British Columbia, Canada, we investigated multiple potential drivers of variation in the duration of incubation and nestling development. Using path analysis, we evaluated the direct effects of weather, predation risk and parental care on offspring development, as well as indirect developmental “carry‐over” effects of conditions during incubation on the nestling period. Nestling period duration varied by nearly 100% (7–13 days) and incubation duration by 40% (10–14 days). Cold ambient temperatures late in the nestling period prolonged development by 1 day for every 2 days below 10°C, particularly when combined with heavy precipitation. Rapid nestling development was associated with high predation risk, and prolonging development incurred a nest survival cost (–2.3% per day). Females in good condition created nest environments that promoted rapid nestling development periods (average = 8–9 days) compared to poor condition females during harsh, early‐season conditions (10–11 days), indicating parental buffering capabilities against environmental constraints. Fledging age was weakly correlated with incubation duration (r = –0.21) suggesting minimal developmental carry‐over effects. Given high nest predation risk, immediate fitness benefits can be derived by overcoming environmental constraints and reducing development time. While predation risk was influential, inclement weather and maternal condition had stronger effects on variation in offspring development. Addressing multiple drivers of variation in key life‐history traits can provide important context for understanding life‐history theory under changing environmental conditions. A plain language summary is available for this article.

Activation of Auditory Centers during Freezing Response Depends on Visual Afferentation in Course of the Development of Pied Flycatcher Nestlings

The study of defense behavior development in pied flycatcher altricial nestlings has shown that preceding visual deprivation decreased the capability to freeze in the young. At the same time, auditory thresholds of deprived nestlings were lower than those of the nestlings developing in unaltered visual environment. Our goal in the present work was to study effects of visual input on the functional development of neural circuitry for flycatcher’s acoustically-guided defensive behavior. We compared the immunohistochemical response of transcription factors ZENK and c-Fos in the nestlings’ auditory telencephalic structures in visually deprived and non-deprived flycatcher nestlings to alarm calls emitted by adult birds. We have demonstrated that the development of flycatcher nestlings under the conditions of limited visual afferentation results in the decrease of induction of the immediate-early genes c-Fos and ZENK in auditory structures of 9-day-old nestlings performing auditory-guided defense behavior. The most marked decrease of induction of both genes is observed in Field L. Our data suggest that visual afferentation affects neuronal activations in higher auditory structures of nestlings’ brain that, in turn, may increase the efficiency of species-typical alarm call. Thus, the work demonstrated for the first time that visual affererntation facilitates the growth of efficiency of alarm call affecting the activity of neurons in auditory integrative structures.

Prevailing weather conditions and diet composition affect chick growth and survival in the black-legged kittiwake

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 604:237-249 (2018) - DOI: https://doi.org/10.3354/meps12744 Prevailing weather conditions and diet composition affect chick growth and survival in the black-legged kittiwake Signe Christensen-Dalsgaard1,2,*, Roel F. May1, Robert T. Barrett3, Magdalene Langset1, Brett K. Sandercock1, Svein-Håkon Lorentsen1 1Norwegian Institute for Nature Research (NINA), PO Box 5685 Torgard, 7034 Trondheim, Norway 2Department of Biology, Norwegian University of Science and Technology (NTNU), Realfagbygget, 7491 Trondheim, Norway 3Department of Natural Sciences, Tromsø University Museum, PO Box 6050 Langnes, 9037 Tromsø, Norway *Corresponding author: signe.dalsgaard@nina.no ABSTRACT: To identify priorities for management of seabirds during the breeding season, it is important to understand the ecological mechanisms driving chick growth and survival. In this study, we examined the effects of diet and prevailing weather on the growth and survival of chicks of black-legged kittiwakes Rissa tridactyla over a 10 yr period at Anda, a seabird colony in northern Norway. We show that across all years, there was a significant effect of diet composition delivered to chicks on their growth and survival. A higher proportion of sandeel Ammodytes spp. in the chick diet was associated with an increase in daily growth rates, a pattern that was especially pronounced for the youngest chick in 2-chick broods. A high proportion of mesopelagic fish in the chick diet was associated with a decrease in survival, again, especially for the youngest chick in 2-chick broods. Periods of strong southerly winds also led to reduced survival, probably linked to nests being washed down from the colony. Growth rates of kittiwake chicks were negatively affected by wind speed, likely due to adults having to work more in the exposed habitats in strong winds, causing a reduction in the amount of food supplied to the chicks. Our results emphasise the importance of conservation of specific marine habitats shown to be important foraging areas in ensuring the reproductive success of seabirds. This might prove increasingly important if future climate regimes make ecological conditions more challenging for seabirds. KEY WORDS: Foraging effort · Mesopelagic fish · Nestling development · Prey availability · Rissa tridactyla · Sandeel · Wind conditions Full text in pdf format Supplementary material PreviousNextCite this article as: Christensen-Dalsgaard S, May RF, Barrett RT, Langset M, Sandercock BK, Lorentsen SH (2018) Prevailing weather conditions and diet composition affect chick growth and survival in the black-legged kittiwake. Mar Ecol Prog Ser 604:237-249. https://doi.org/10.3354/meps12744 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 604. Online publication date: October 04, 2018 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2018 Inter-Research.

The ecological consequences of solitary breeding in a species with bi-parental care

A higher rate of nestling development reduces their exposure time to predators, which is advantageous but simultaneously it involves an increased parental investment in incubation, brooding and feeding, which may be difficult to obtain by a single parent. An interesting question is whether, and to what degree, a single parent in a typical bi-parental species is able to compensate the lack of its mate’s contribution in species with fast developing nestlings. Our study species is the Blackcap Sylvia atricapilla, a small passerine that experiences high levels of nest predation and rapid development of nestlings. We test the hypotheses that (i) single parents are not able to fully compensate for the lack of mate in rearing a brood and (ii) parents pay cost for breeding alone by increasing the time that the offspring is exposed to predators in the nest. We also inquire in potential trade-off between brooding and feeding and its consequences for nestling growth in nests reared by single parents. Our results show that single parents were able to compensate for the lack of the mate in terms of feeding rate, but this was at the cost of time spent brooding. Nestlings in uni-parental nests grew more slowly and lagged about two days behind their bi-parental counterparts, which may extend nestling exposure time to a predator by about 20%.

Effect of natural brood size variability on growth and survival of thornbird nestlings

AbstractFor many bird species, brood size is a highly variable trait. Several aspects of the development and survival of nestlings are affected by brood size. Most scientific evidence comes from brood manipulation experiments, and the complementary information offered by studies of natural variability has received little attention in tropical and subtropical species. Here, we provide data on the effect of brood size on the development and survival of two furnariid species under natural conditions. Weekly during two breeding seasons, two forest patches (40 ha. each) from central Argentina, were exhaustively examined for active nests. Nestlings were monitored repeatedly from hatching to fledging. Factors that were considered potential confounders or effect modifiers were also recorded and included in the statistical analysis. We found a positive effect of brood size on growth, and a negative effect on survival. The first effect was only observed when preceding weeks were not rainy, and the latter was present in only one breeding season, so both effects appeared to depend on environmental conditions. Our results suggest that the benefit of a large or small brood size is dependent on context. In the studied populations, plasticity in or within‐population genetic diversity in brood size may be advantageous in the light of the unpredictable circumstances that will prevail during the breeding season.

Local weather conditions have complex effects on the growth of blue tit nestlings

Adverse weather conditions are expected to result in impaired nestling development in birds, but empirical studies have provided equivocal support for such a relationship. This may be because the negative effects of adverse weather conditions are masked by parental effects. Globally, ambient temperatures, rainfall levels and wind speeds are all expected to increase in a changing climate and so there is a need for a better understanding of the relationship between weather conditions and nestling growth. Here, we describe a correlative study that examined the relationships between local temperatures, rainfall levels and wind speeds and the growth of individual blue tit (Cyanistes caeruleus) nestlings in relation to their hatching order and sex. We found that changes in a range of morphological characters were negatively related to both temperature and wind speed, but positively related to rainfall. These patterns were further influenced by the hatching order of the nestlings but not by nestling sex. This suggests that the predicted changes in local weather conditions may have complex effects on nestling growth, but that parents may be able to mitigate the adverse effects via adaptive parental effects. We therefore conclude that local weather conditions have complex effects on avian growth and the implications for patterns of avian growth in a changing climate are discussed.

Diurnal brooding behavior of long-tailed tits (Aegithalos caudatus glaucogularis).

Brooding is a major breeding investment of parental birds during the early nestling stage, and has important effects on the development and survival of nestlings. Investigating brooding behavior can help to understand avian breeding investment strategies. From January to June in 2013 and 2014, we studied the brooding behaviors of long-tailed tits (Aegithalos caudatus glaucogularis) in Dongzhai National Nature Reserve, Henan Province, China. We analyzed the relationships between parental diurnal brooding duration and nestling age, brood size, temperature, relative breeding season, time of day and nestling frequencies during brooding duration. Results showed that female and male long-tailed tit parents had different breeding investment strategies during the early nestling stage. Female parents bore most of the brooding investment, while male parents performed most of the nestling feedings. In addition, helpers were not found to brood nestlings at the two cooperative breeding nests. Parental brooding duration was significantly associated with the food delivered to nestlings (F=86.10, df=1, 193.94, P<0.001), and was longer when the nestlings received more food. We found that parental brooding duration declined significantly as nestlings aged (F=5.99, df=1, 50.13, P=0.018). When nestlings were six days old, daytime parental brooding almost ceased, implying that longtailed tit nestlings might be able to maintain their own body temperature by this age. In addition, brooding duration was affected by both brood size (F=12.74, df=1, 32.08, P=0.001) and temperature (F=5.83, df=1, 39.59, P=0.021), with it being shorter in larger broods and when ambient temperature was higher.

Does the interaction between glucocorticoids and insulin-like growth factor 1 predict nestling fitness in a wild passerine?

The crucial question in evolutionary ecology is to find out how physiological traits have coevolved so animals fit their stochastic environments. The plasticity of these different physiological mechanisms is largely mediated by hormones, like glucocorticoids and insulin-like growth factor 1 (IGF-1). Brood size manipulation with nestlings of free-living great tits (Parus major) was carried out to see the way in which plasma IGF-1 and feather corticosterone, a predictor of long-term sustained plasma corticosterone level, are associated across different nutritional conditions and how this association predicts survival during the nestling phase. We showed that the association between levels of IGF-1 and corticosterone depended on physiological condition of nestlings. Namely, there was a positive association between the hormones in nestlings from the decreased broods and a negative association in nestlings from the enlarged broods. Furthermore, we showed that the interaction between levels of IGF-1 and corticosterone was also related with the survival of the nestlings. Our results suggest that signalling pathways of IGF-1 and corticosterone most likely interact with each other in a nutrition-dependent way to maximize the rate of development and survival of nestlings in their stochastic environment.

Context-dependent effects of yolk androgens on nestling growth and immune function in a multibrooded passerine.

Female birds may adjust their offspring phenotype to the specific requirements of the environment by differential allocation of physiologically active substances into yolks, such as androgens. Yolk androgens have been shown to accelerate embryonic development, growth rate and competitive ability of nestlings, but they can also entail immunological costs. The balance between costs and benefits of androgen allocation is expected to depend on nestling environment. We tested this hypothesis in a multibrooded passerine, the spotless starling, Sturnus unicolor. We experimentally manipulated yolk androgen levels using a between-brood design and evaluated its effects on nestling development, survival and immune function. Both in first and replacement broods, the embryonic development period was shorter for androgen-treated chicks than controls, but there were no differences in second broods. In replacement broods, androgen-treated chicks were heavier and larger than those hatched from control eggs, but this effect was not observed in the other breeding attempts. Androgen exposure reduced survival with respect to controls only in second broods. Regarding immune function, we detected nonsignificant trends for androgen treatment to activate two important components of innate and adaptive immunity (IL-6 and Ig-A levels, respectively). Similarly, androgen-treated chicks showed greater lymphocyte proliferation than controls in the first brood and an opposite trend in the second brood. Our results indicate that yolk androgen effects on nestling development and immunity depend on the environmental conditions of each breeding attempt. Variation in maternal androgen allocation to eggs could be explained as the result of context-dependent optimal strategies to maximize offspring fitness.

Nest-dwelling ectoparasites influence the start and duration of the first pre-basic moult in the European starling Sturnus vulgaris

Nest-dwelling ectoparasites represent an early stressor for birds as they impair the development of nestlings, which can adaptively respond by adjusting their growth rate to current conditions. While nest ectoparasites have long-term effects on nesting adults, no study has examined if they also have an impact on the moult patterns of juveniles. Herein, we investigated whether the presence of ectoparasites in the nest influences the start and duration of the first pre-basic moult in the European starling. To do so, we experimentally removed nest-dwelling ectoparasites from a group of nests and used another group of unmanipulated (i.e. naturally infested) nests as the control. The moult began at an earlier age and lasted longer in birds from the ectoparasite-free nests compared to their control counterparts. The timing of the moult was also affected by the hatching date (i.e. birds that fledged later had shorter moults) and the brood size (i.e. birds in larger broods started their moult at an older age). We also found evidence that the removal of nest ectoparasites influenced the condition of individuals during the course of the moult. In the control birds, we observed a decrease in hematocrit levels, but these were unaltered in the birds fledged from the ectoparasite-free nests. Our study shows that nest-dwelling ectoparasites adversely affected the timing of the moult and the individual condition of juvenile starlings, with possible major consequences for their subsequent life-history events.