Oriental Reed Warblers do not abandon Common Cuckoo chicks during prolonged nestling periods

The Oriental Reed Warbler(Acrocephalus orientalis)is one of the most commonly used hosts for the parasitic Common Cuckoo(Cuculus canorus).However,as hosts that feed unrelated parasitic nestlings may suffer extra reproductive costs,they may be less willing to care for nestlings that have prolonged nestling periods.To test this hypothesis,the duration of feeding by Oriental Reed Warblers under natural conditions for their own nestlings was compared with the duration of feeding under natural conditions for Common Cuckoo nestlings and for artificially prolonged cuckoo nestlings.The results showed that Oriental Reed Warblers did not starve,drive away,or desert any of the nestlings in the experiment,and neither parent was left alone.Our experimental study indicates that both Oriental Reed Warbler parents were willing to care for nestlings with a prolonged nestling period(up to 30 days,twice the average duration time that the Oriental Reed Warblers fed their own chicks in natural conditions).However,further experiments and observations are required in other host bird species to examine whether both parents or one of the parents may exhibit the behavior of abandoning nestlings with a prolonged nestling period.

Egg recognition and nestling discrimination in the Crested Myna(Acridotheres cristatellus):Size matters

Most studies exploring abilities of hosts to detect brood parasitism are based on detecting colour and/or pattern differences among parasitic and host eggs or nestlings,while only few were focused on size differences.True recognition and recognition by discordancy are used to explain cognitive mechanisms of host egg recognition;however,only a few studies have found that hosts use recognition by discordancy.This study investigated:1)whether egg and nestling recognitions in the Crested Myna(Acridotheres cristatellus) are based on size cues;2)whether the egg cognitive mechanism is recognition by discordancy based on size cues;and 3) whether the longer the experiment time,the higher the egg recognition rate.Our results showed that the Crested Myna uses egg or nestling size as a recognition cue while the egg and nestling colour and patterning are not associated with egg or nestling rejection,thus the cognitive mechanism of egg recognition in the Crested Myna is recognition by discordancy based on egg size cues.Furthermore,there is a rejection delay in time of egg rejection behaviour of the Crested Myna.Therefore,we suggest that the periodicity of egg rejection experiments could be appropriately extended,especially for species with relatively low egg recognition ability.

Artificial incubation and growth observation for the nestlings of Great Bustard (Otis tarda)

Growth indicators including weight, body length, wings length, tail length, tarsus, gape, the third toe and head width of 21 nestlings of Great Bustard (Otis tarda) were measured and investigated in Harbin Zoo, Harbin, China during 1999-2002, and methods on successfully fostering nestlings of the bird were also summarized in this article. The results showed: the Great Bustard is a kind of premature bird and its birth weight was 86.31?.56g (N=21); environmental temperature for the neonatal nestlings should be controlled at 36C; the feeding principle having many meals but little food at each for the nestlings should be followed; since six weeks after birth, nestlings of both gender began to show significant difference in body weight, the weight of male was 1.8 times of that of the female after fourteenth week, and by weight and body figure sexual identity could be easily discerned when 3 or 4 months old; There is no significant difference in growth and development of all organs between male and female nestlings and organ growth curves were fit into Logistic equation.

Species identification of sympatric cuckoo nestlings in a multiple-cuckoo system,China

Interaction between a parasite and its host could lead to a co-evolutionary arms race. Cuckoo-host system is among the most studied of all brood parasite systems, but the cuckoos of Asia, on the other hand, are much less well known. China has the most abundant cuckoo species in Asia. Many of these co-occur in sympatric areas, posing a potential risk of mis-identification of cuckoo nestlings, especially in Cuculus species. In this study we have provided a practical criterion to identify cuckoo nestlings species in the field and performed molecular phylogeny to confirm our empirical results. These results indicate that two distinct characteristics of cuckoo nestlings, i.e., the gape color pattern and feather traits can be considered as reliable species identification. To our knowledge, this is the first report for species identification of Cuculus nestlings through molecular analysis.

Endocrine response of early-hatching Asian Short-toed Lark nestlings exposed to cold temperature in a high-latitude grassland habitat

Background:In high latitude grassland habitats,altricial nestlings hatching in open-cup nests early in the breeding season must cope with cold temperature challenges.Thyroid hormones(triiodothyronine,T_(3)and thyroxine,T_(4))and corticosterone play a crucial role in avian thermoregulation response to cold.Investigating the endocrine response of altricial nestlings to temperature variation is important for understanding the adaptive mechanisms of individual variation in the timing of breeding in birds.Methods:We compared nest temperature,ambient temperature,body temperature,plasma T_(3),T_(4)and corticosterone levels in Asian Short-toed Lark(Alaudala cheleensis)nestlings hatching in the early-,middle-,and late-stages of the breeding season in Hulunbuir grassland,northeast China.Results:Mean nest temperature in the early-,middle-and late-stage groups was-1.85,3.81 and 10.23℃,respectively,for the 3-day-old nestlings,and 6.83,10.41 and 11.81℃,respectively,for the 6-day-old nestlings.The nest temperature significantly correlated with body temperature,plasma T_(3),T_(4)and corticosterone concentrations of nestlings.Body temperature of 3-day-old nestlings in the early and middle groups was significantly lower than that of the late group,but there was no significant difference between the nestlings in the early and middle groups.The T_(4)and T_(3)concentrations and the ratio of T_(3)/T_(4)of both 3-and 6-day-old nestlings in the early-stage group were significantly higher compared to the middle and late groups.The corticosterone levels of 3-day-old nestlings were significantly higher in the early-stage group compared to the middle-and late-stage groups.Conclusion:Nestlings hatching early responded to cold temperature by increasing thyroid hormones and corticosterone levels even in the early days of post hatching development when the endothermy has not been established.These hormones may play a physiological role in neonatal nestlings coping with cold temperature challenges.

A field guide for aging passerine nestlings using growth data and predictive modeling

Background:Accurate nestling age is valuable for studies on nesting strategies,productivity,and impacts on repro-ductive success.Most aging guides consist of descriptions and photographs that are time consuming to read and subjective to interpret.The Western Bluebird(Sialia mexicana)is a secondary cavity-nesting passerine that nests in coniferous and open deciduous forests.Nest box programs for cavity-nesting species have provided suitable nesting locations and opportunities for data collection on nestling growth and development.Methods:We developed models for predicting the age of Western Bluebird nestlings from morphometric meas-urements using model training and validation.These were developed for mass,tarsus,and two different culmen measurements.Results:Our models were accurate to within less than a day,and each model worked best for a specific age range.The mass and tarsus models can be used to estimate the ages of Western Bluebird nestlings 0-10 days old and were accurate to within 0.5 days for mass and 0.7 days for tarsus.The culmen models can be used to estimate ages of nest-lings 0-15 days old and were also accurate to within less than a day.The daily mean,minimum,and maximum values of each morphometric measurement are provided and can be used in the field for accurate nestling age estimations in real time.Conclusions:The model training and validation procedures used here demonstrate that this method can create aging models that are highly accurate.The methods can be applied to any passerine species provided sufficient nest-ling morphometric data are available.

Differential cell stress responses to food availability by the nestlings of Asian Short-toed Lark(Calandrella cheleensis)

Background:Timing of breeding season of temperate passerines has been considered to be adjusted to their food availability.There is little work to reveal the cell stress responses of the nestlings hatched asynchronized with the food abundance peak,which is important for understanding the physiological link between the timing of breeding and the fitness of offspring.Methods:Using gene expression level of blood HSP70 and HSP90 as indicators,we compared the cell stress response of Asian Short-toed Lark(Calandrella cheleensis)nestlings hatched under conditions of low,mid or high food(grasshopper nymph)availability in 2017.Results:Nymph biomass,sample time and interaction of these two factors significantly influenced the blood gene expression level of HSP70 and HSP90 of Asian Short-toed Lark nestlings.HSP70 and HSP90 gene expression levels of the nestlings at 14:00 were significantly higher than those at 5:00.At either 5:00 or 14:00,the gene expression levels of HSP70 and HSP90 increase with the decrease of nymph biomass.Conclusions:These results indicate that food availability is an important environment factor inducing cellular stress of Asian Short-toed Lark nestlings.The interactive effect of the nymph abundance and sample time on the HSPs response may be related with the daily temperature variation of the grassland.Over cell stress response may be one of physiological factor mediating the effect of food availability and the nestling’s fitness.

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.

Nestling discrimination and feeding habits during brooding of Chestnut Thrushes

Background:Nestling discrimination and feeding habits during brooding are important factors affecting host selec-tion of parasitic birds.Some host birds can avoid being parasitized by discriminating their nestlings or feeding food not suitable for parasitic nestlings.Thrushes are common medium-sized birds with widespread distribution and an open nesting habit,but they are rarely parasitized.It remains controversial whether this is due to feeding habits and/or nestling discrimination.Methods:In this study,we tested the nestling discrimination ability and feeding habits of Chestnut Thrushes(Turdus rubrocanus)which is distributed in China’s multi-cuckoo parasitism system.Their nestling discriminability and feeding habits during brooding were studied by cross-fostering experiments and video recording to examine evolutionary restrictions on nestling discrimination and whether feeding habits are consistent with the growth of cuckoo nestlings.Results:Our results indicate that Chestnut Thrushes using earthworms as the main brooding food can feed and maintain cuckoo nestlings and show no nestling discrimination.Conclusions:The present study confirms that feeding habits cannot be regarded as the main factor affecting Chestnut Thrushes being rarely parasitized by cuckoos but suggests that egg rejection is likely to limit the evolution of nestling discrimination in thrushes.

Nestling sex ratio is unaffected by individual and population traits in the griffon vulture

Variation in offspring sex ratios is a central topic in animal demography and population dynamics.Most studies have focused on bird species with marked sexual dimorphism and multiple-nestling broods,where the offspring sex ratio is often biased due to different individual or environmental variables.However,biases in offspring sex ratios have been far less investigated in monomorphic and single-egg laying species,and few studies have evaluated long-term and large-scale variations in the sex ratio of nestling vultures.Here,we explore individual and environmental factors potentially affecting the secondary sex ratio of the monomorphic griffon vulture Gyps fulvus.We used information collected at three breeding nuclei from central Spain over a 30-year period(1990–2020)to analyse the effects of nestling age,parental age,breeding phenology,conspecific density,population reproductive parameters,and spatial and temporal variability on nestling sex.Sex ratio did not differ from parity either at the population or the nuclei level.No significant between-year differences were detected,even under highly changing conditions of food availability associated with the mad-cow crisis.We found that tree nesting breeders tend to have more sons than daughters,but as this nesting behavior is rare and we consequently have a small sample size,this issue would require additional examination.Whereas further research is needed to assess the potential effect of breeder identity on nestling sex ratio,this study contributes to understanding the basic ecology and population dynamics of Griffon Vultures,a long-lived species with deferred maturity and low fecundity,whose minor deviations in the offspring sex ratio might imply major changes at the population level.

Hard life for sons in the nest?Sex-dependent offspring mortality in Great Tits in urban and forest areas

Sex-biased mortality can occur in birds during development,for example due to sexual differences in energy requirement and/or environmental sensitivity,or the effects of sex hormones or sex differences in the expression of mutations linked to sex chromosomes.The extent of sex-bias in mortality may also be related to environmental conditions that influence offspring development and survival.Urban areas often provide poorer conditions for nestling development resulting in higher offspring mortality compared to natural areas,which may accelerate sex differences in offspring mortality in cities.To test this hypothesis,we examined the sex ratio of dead offspring in Great Tits(Parus major),using 427 samples of unhatched eggs and dead nestlings collected in two urban and two forest sites between 2013 and 2019.The ratio of males in the whole sample of dead offspring(56.9%)was significantly higher than expected by an 1:1 ratio,and the strongest sex biases were detected in urban areas(57.6%males)and in young nestlings(<14 days old,59.0%males).However,the sex ratios of dead offspring did not differ significantly among study sites and between offspring developmental stages.29.3%of unhatched eggs contained a visible embryo,and the proportion of embryo-containing unhatched eggs did not differ significantly between urban and forest study sites.These results suggest male-biased offspring mortality in Great Tits,and highlight the need of large datasets to detect subtle differences between habitats and developmental stages.

Discrimination and ejection of eggs and nestlings by the fan-tailed gerygone from New Caledonia

Nestling rejection is a rare type of host defense against brood parasitism compared with egg rejection.Theoretically,host defenses at both egg and nestling stages could be based on similar underlying discrimination mechanisms but,due to the rarity of nestling rejector hosts,few studies have actually tested this hypothesis.We investigated egg and nestling discrimination by the fan-tailed gerygone Gerygone flavolateralis,a host that seemingly accepts nonmimetic eggs of its parasite,the shining bronze-cuckoo Chalcites lucidus,but ejects mimetic parasite nestlings.We introduced artificial eggs or nestlings and foreign gerygone nestlings in gerygone nests and compared begging calls of parasite and host nestlings.We found that the gerygone ejected artificial eggs only if their size was smaller than the parasite or host eggs.Ejection of artificial nestlings did not depend on whether their color matched that of the brood.The frequency of ejection increased during the course of the breeding season mirroring the increase in ejection frequency of parasite nestlings by the host.Cross-fostered gerygone nestlings were frequently ejected when lacking natal down and when introduced in the nest before hatching of the foster brood,but only occasionally when they did not match the color of the foster brood.Begging calls differed significantly between parasite and host nestlings throughout the nestling period.Our results suggest that the fan-tailed gerygone accepts eggs within the size range of gerygone and cuckoo eggs and that nestling discrimination is based on auditory and visual cues other than skin color.This highlights the importance of using a combined approach to study discrimination mechanisms of hosts.

Are microbes and metabolites influencing the parental consumption of nestlings’feces in gray-backed shrikes?

The behavioral video recordings of the gray-backed shrike Lanius tephronotus revealed that parent birds eat the feces produced by their nestlings.“Parental nutrition hypothesis”attributes the origin of this behavior to nutrition-recovery and cost-saving,respectively.However,the presence of usable nutrients in the nestlings’feces is unknown because of traditional technology.In this study,we analyzed all the metabolites and the variations in the diversity and content of microbes in the feces of gray-backed shrike nestlings.We aimed to report the changes in microbes and metabolites with the age of nestlings and point out that the parent birds that eat the feces may gain potential nutrition benefits.The results showed that the relative abundances of Proteobacteria,Firmicutes,and Bacteroidota,changed significantly when the nestlings were 6 days old.The relative abundances of 6 probiotics,which are involved in digestion,metabolism,and immunity-related physiological functions,decreased in the nestlings’feces gradually with age;therefore,these probiotics may be obtained by parent birds upon ingestion of the feces of young nestlings.Among the metabolites that were detected,20 were lipids and some had a role in anti-parasitic functions and wound healing;however,their relative contents decreased with age.These beneficial substances in the nestlings’feces may stimulate the parents to swallow the feces.Moreover,there were many aromatic metabolites in the newly hatched nestlings’feces,but the content of bitter metabolites increased as they grew up.Therefore,our results are in accordance with the nutritional hypothesis.

Selecting the best:Interspecific and age-related diet differences among sympatric steppe passerines

Parental food provisioning is crucial for the growth and survival of offspring.Growth rate depends on food quality and food supplied to offspring may differ from what adults use for their own.In the case of steppe passerine birds,detailed characterization on nestling dietary composition,as well as prey choice and resource partitioning among species,is a pending subject.Dietary differences between nestlings and adults remain also largely unexplored.By using faecal DNA metabarcoding,we described the diet of nestlings and adults of five shrub-steppe passerine species over the 2017–2019 breeding seasons in central Spain.We also monitored arthropod availability in the field to assess dietary selection.We expected interspecific dietary differences to limit competition for food resources among sympatric species,as well as parental selection of high quality prey for nestlings.We also predicted age-related differences,with nestlings being fed nutrient-rich prey more frequently than adults.The main arthropod orders provisioned to nestlings were Orthoptera,Julida,Araneae and Lepidoptera.Nestlings of the different species showed high interspecific diet overlap,indicating both a coincidence in growth needs among bird species and no or little limitation of the most profitable resources during the breeding season.Adults of all species showed higher diet richness than nestlings,and age-related differences in prey composition were mainly driven by the selection of the most easily digestible,larger protein-and calcium-rich prey for nestlings,which may favour their rapid growth,and avoiding highly sclerotized and less nutritional prey such as ants.Our study sheds light on the basic ecology and conservation of these declining steppe birds,indicating that interspecific competition may not be a major factor during the breeding season.Given the current global decline of arthropods,further long-term research would be necessary,along with the implementation of effective conservation measures that ensure a sufficient availability of resources identified as key prey in the diet of steppe bird nestlings.

The breeding biology of Red-Whiskered Bulbul(Pycnonotus jocosus) in Xishuangbanna, southwest China

To fill the gap in breeding biology information about the Red-Whiskered Bulbul （Pycnonotus jocosus）, in 2013, we studied the breeding biology of this species in Xishuangbanna, southwest China. The breeding began from February and continued until early August. The breeding strategy of P. jocosus was more flexible and their nests were only built in cultivated landscapes, whereas, no nest building in native tropical rain forest was found. Small open cup nests were built on 50 different plant species, and at heights ranging from 2.1±0.6 m above the ground （n=102）. The mean clutch size was 2.53±0.51 eggs （n=40） and the mean egg mass was 2.81±0.25 g （n=60）. The average incubation period was 11.1±0.5 days （n=14）, and the average nestling period was 11.0±0.8 days （n=31）. The overall nest success was 34.22%.The hatching and fledging showed either asynchrony or synchrony. Invertebrate food decreased with nestling age, whereas, plant food increased with nestling age. Moreover, distinct parental roles of the parents in nestling period were found. Compared with other passerine species, P. jocosus spent less time in incubating （58%）. The clutch size, incubation and nestling period of the P. jocosus in southwest China were different from those of the R jocosus in India.

Nest-site selection and breeding ecology of Streaked Wren-Babbler(Napothera brevicaudata)in a tropical limestone forest of southern China

Background: The breeding information of most birds in Asian tropical areas,especially in limestone forests,is still poorly known.The Streaked Wren-Babbler(Napothera brevicaudata) is an uncommon tropical limestone bird with a small range.We studied its nest-site selection and breeding ecology,in order to understand the adaptations of birds to the conditions of tropical limestone forest in southern China.Methods: We used methods of systematical searching and parent-following to locate the nests of the Streaked Wren-Babbler.We measured characteristics of nest sites and rock cavities.Data loggers and video cameras were used to monitor the breeding behavior.Results: All the observed nests of the Streaked Wren-Babbler were placed in natural shallow cavities or deep holes in large boulders or limestone cliffs.The great majority(96.6%) of Streaked Wren-Babbler nests had three eggs with an average fresh weight of 3.46-± 0.43 g(n = 36,range 2.52-4.20 g).Most(80.4%) females laid their first eggs between March and April(n = 46).The average incubation and nestling period of the Streaked Wren-Babbler was 10.2 range 9-11 days),respectively.Most(87.9%) nests h± 0.4 days(n = 5,range 1011 days) and 10.5 ± 0.8 days(n = 6,ad at least one nestling fledge between 2011 and 2013(n = 33).Conclusions: Our study suggests that several features of the breeding ecology of the Streaked Wren-Babbler,including building nests in rocky cavities,commencing breeding earlier than most species,and reducing foraging times during the incubation period,are well-adapted to the unique habitat of tropical limestone forest.

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, dr=l, 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, dr=-1, 50.13, P=0.018）. When nestlings were six days old, daytime parental brooding almost ceased, implying that long- tailed 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, dr=-1,32.08, P=0.001） and temperature （F=5.83, df=-l, 39.59, P=-0.021）, with it being shorter in larger broods and when ambient temperature was higher.

Breeding ecology of the Yellow-bellied Warbler (Abroscopus superciliaris)

The life history of birds dictates their activities and is crucial to population success.However,the life history traits of only one-third of the world’s bird species have been described;the rest are poorly understood.We studied the breeding ecology of the Yellow-bellied Warbler(Abroscopus superciliaris)and documented reproductive information throughout the egg and nestling periods.The data included natural nest sites,nest components,nest size,egg laying dates and time,egg morph,egg size,clutch size,egg incubation,nestling brooding and feeding,nestling morph and growth,and reproductive outcome.This study provided particular information of breeding ecology that has not been reported before in the Yellow-bellied Warbler.

Breeding biology of the Green-backed Tit(Parus monticolus)in southwest China

Studies on breeding biology enable us to broaden our understanding of the evolution of life history strategies.We studied the breeding biology of the Green-backed Tit(Parus monticolus)to provide comprehensive data on nest and egg characteristics,parental behavior throughout egg laying and nestling periods,and reproductive outcome.Our study reveals adaptive behavioral patterns and reproductive strategies for P.monticolus.

Cowbirds, conservation, and coevolution: potential misconceptions and directions for future research

Avian brood parasitism is a model system for studies of coevolution and ecological interactions between parasites and their hosts. However, recent work may have led to misconceptions concerning the Brown-headed Cowbird (Molothrus ater), the most widely studied brood parasitic bird in the world, and its effects on host species. Potential misconceptions about this species that could affect management issues are as follows: cowbird populations are increasing; cowbirds are relatively new to North America; recently exposed hosts are defenseless against parasitism; cowbirds have caused widespread declines of songbirds; and cowbird control is always effective in increasing the size of endangered host populations. Potential coevolutionary misconceptions are that cowbirds are typically 'host tolerant'; cowbirds evict host nestmates; and the mafia effect is widespread. It is important to clarify these issues because such misconceptions could hinder our understanding of parasite-host interactions, and thus obscure the direction of basic research and of management efforts taken to limit cowbird impacts on endangered species. We discuss these issues and suggest future research directions to enhance our understanding of this fascinating species.