Chick Body Mass Research Articles

The impact of weather conditions on the competition and breeding success of three sympatric hornbill species in a semi-arid region

Recent studies have highlighted the vulnerability of hornbills breeding in hot, arid environments, raising concern about the species’ persistence with climate change. Hornbills are, however, a widespread avian family found in various climates in Africa and Asia. In this study, we investigated the factors impacting the breeding phenology of three sympatric African hornbill species in a semi-arid environment. We found that rainfall was associated with breeding initiation and breeding success in all three species (African grey hornbill Lophoceros nasutus, Southern yellow-billed hornbill Tockus leucomelas, and Southern red-billed hornbill Tockus rufirostris). Breeding success and chick body mass change of African grey hornbills and Southern yellow-billed hornbills, but not Southern red-billed hornbills, were negatively impacted by high air temperatures during the breeding season. This study shows that Southern red-billed hornbills were more successful at producing offspring compared to African grey hornbills and Southern yellow-billed hornbills, which was likely due to their later breeding initiation compared to the other two species. Future changes in rainfall patterns may cause the African grey hornbills and Southern yellow-billed hornbills to delay breeding activities. Delayed breeding could result in a greater overlap of the nesting period of the three species, which would, in turn, increase the competition for food and suitable nesting sites. This study confirms that also in semi-arid areas, climate change has the potential to affect the breeding success of hornbills.

Evaluation of methods used to improve grasslands as ring‐necked pheasant brood habitat

AbstractRing‐necked pheasant (Phasianus colchicus) demographic response is sensitive to chick survival and nest success. The establishment and management of grasslands within agricultural landscapes, often through cropland conversion programs (e.g., Conservation Reserve Program [CRP]), have positive impacts on survival and nest success. Newly established CRP and early successional habitat can provide vegetative structure selected by pheasant chicks. Ideal brood habitat provides an abundance of arthropods, an open understory promoting efficient chick movement, and a protective canopy cover. However, the natural succession of grasslands changes desired vegetative structure and challenges managers with providing adequate habitat for pheasant chicks. We investigated the efficacy of different methods of CRP management, including haying, burning, herbicide application, interseeding, and grazing, to provide adequate brood rearing habitat in cool‐ and warm‐season grasslands. We assessed chick body mass change using human‐imprinted ring‐necked pheasant chicks and investigated changes in vegetation composition and structure in relation to various habitat treatments in north‐central and north‐eastern South Dakota during mid‐June and mid‐July of 2013, 2014, and 2015. Generally, treatments that incorporated interseeding, herbicide application, or their combination had the greatest chick mass gain, reduced litter cover and depth, and increased bare ground and forb cover. Effective management for brood habitat may require more aggressive techniques than simple haying or prescribed fire techniques.

Environmental Drivers of Growth and Oxidative Status during Early Life in a Long-Lived Antarctic Seabird, the Adélie Penguin.

AbstractIn vertebrates, developmental conditions can have long-term effects on individual performance. It is increasingly recognized that oxidative stress could be one physiological mechanism connecting early-life experience to adult phenotype. Accordingly, markers of oxidative status could be useful for assessing the developmental constraints encountered by offspring. Although some studies have demonstrated that developmental constraints are associated with high levels of oxidative stress in offspring, it remains unclear how growth, parental behavior, and brood competition may altogether affect oxidative stress in long-lived species in the wild. Here, we investigated this question in a long-lived Antarctic bird species by testing the impact of brood competition (e.g., brood size and hatching order) on body mass and on two markers of oxidative damage in Adélie penguin chicks. We also examined the influence of parental effort (i.e., foraging trip duration) and parental body condition on chick body mass and oxidative damage. First, we found that brood competition and parental traits had significant impacts on chick body mass. Second, we found that chick age and, to a lesser extent, chick body mass were two strong determinants of the levels of oxidative damage in Adélie penguin chicks. Finally, and importantly, we also found that brood competition significantly increased the levels of one marker of oxidative damage and was associated with a lower survival probability. However, parental effort and parental condition were not significantly linked to chick levels of oxidative damage. Overall, our study demonstrates that sibling competition can generate an oxidative cost even for this long-lived Antarctic species with a limited brood size (maximum of two chicks).

Long-term decline in fledging body condition of Flesh-footed Shearwaters (Ardenna carneipes)

Abstract Marine systems are under increasing pressure from anthropogenic activities. In recent decades, the deteriorating condition of the world’s seabird populations suggests these pressures have reached a tipping point. For young birds, body mass can significantly influence survival in the critical period between nest departure and recruitment to the breeding population. On Lord Howe Island, we measured Flesh-footed Shearwater (Ardenna carneipes) fledglings in the colony and adjacent beaches to determine how body condition changed during 2010–2022. Overall, we found chick body mass as well as wing, culmen, and head + bill length declined over time with larger declines observed in beach-washed birds. Culmen and head + bill length declined by 0.17 and 0.23 mm/year, respectively, and body mass by 16.1 g/year. The number of chicks fledging at <400 g has increased sharply in recent years, meaning significant numbers of birds are unlikely to survive after departing the island. Our results point to a deepening of the division in the shearwater population: adult birds who can successfully provision sufficient nutrient reserves so their chick fledges successfully, and those who cannot. In this latter group, failure at the fledging stage (beached birds) is resulting in birds in increasingly poor condition, the likes of which were seldom documented 13 years ago.

Initial evaluation of the care and rehabilitation success of Cape Cormorants Phalacrocorax capensis rescued from Robben and Jutten islands, South Africa, in January 2021

The population of the endangered Cape Cormorant Phalacrocorax capensis more than halved over the last three decades (BirdLife International 2018a). In January 2021, nearly 2 000 Cape Cormorant chicks were found abandoned, suffering from dehydration and heat stress, at two important nesting sites. The chicks were rescued and rehabilitated by the Southern African Foundation for the Conservation of Coastal Birds (SANCCOB, Cape Town, South Africa). About half (53.7%) of the cormorant chicks were successfully rehabilitated and released back into the breeding colonies. This study found a direct link between the initial body mass of cormorant chicks admitted to the rehabilitation centre and their probability of surviving during rehabilitation, with birds that were initially heavier having a greater probability of eventual release. Most cormorant chicks that died (80.7%) did so within the first 5 days of admission. This rescue required SANCCOB to care for and rehabilitate the largest number of Cape Cormorant chicks that has ever been admitted to its rehabilitation centre at one time, making it the first rescue of its kind. Despite the presumably limited positive impact on overall population numbers of Cape Cormorants, the rescue campaign improved SANCCOB’s preparedness to respond successfully to future disaster events and to deal with different species, both locally and globally.

Brood Sex Ratio in European Honey Buzzards Pernis apivorus is Related to Spring Phenology

In sexually size-dimorphic bird species, rearing costs of sons and daughters usually differ and may be important in the evolution of offspring sex ratio adjustment. Raptors have reversed sexual size dimorphism and the smaller males are sometimes found to be overrepresented in food-poor territories or years. As a raptor with small reversed sexual dimorphism (6% in body mass), the European Honey Buzzard Pernis apivorus is expected to show little or no brood sex ratio bias in relation to environmental conditions. We molecularly sexed 311 chicks of 195 broods in and around The Netherlands, during 1996–2014. We examined which environmental factors explained brood sex ratio variation best. Overall, sex ratio was not biased (all nests pooled: 50.8% females) but more females were produced in years when on average Honey Buzzards bred earlier (32% sex ratio change over a ten-day range in annual mean laying date). Within-year laying date variation, hatching order, abundance of wasp (Vespinae) nests (main food source) and summer weather did not explain sex ratio variation. In the Veluwe and Drenthe (1974–2014), Honey Buzzards laid eggs earlier when the spring was warmer, which resulted in a c. 9-day advance in laying date over 40 years. As warm spring weather was also a predictor of a higher density of wasp colonies, we expected female chicks to benefit more from growing up in wasp-rich years than males, if the sex ratio biases were adaptive. However, this differential growth benefit was not noticeable in chick body mass; chick body mass was best explained by negative effects of relative laying date (within a year) and hatching order. The potential benefit for female nestlings (compared to males) of growing up in years with warm springs, when egg laying occurs early and wasp colonies are more abundant, remains unknown.

Growth model analysis of wild hyacinth macaw (Anodorhynchus hyacinthinus) nestlings based on long-term monitoring in the Brazilian Pantanal

Studies on the breeding of vulnerable and endangered bird species are hindered by low numbers of individuals, inaccessible location of nests, unfavourable environmental conditions, and complex behavioural patterns. In addition, intraspecific variation may emerge only following long-term, systematic observations of little-known patterns and processes. Here, data collected over 30 years were used to determine growth model of hyacinth macaw (Anodorhynchus hyacinthinus) chicks in the Pantanal biome of Brazil. During this period, the speed of growth and body mass of chicks varied widely. Four growth models were tested: logistic, Gompertz, Richards, and cubic polynomial. They were fitted using three biometric measurements: body mass, total length, and tail length. The best-fitting growth curves were identified using Akaike’s information criterion. The best models were the cubic polynomial for body mass, Richards for total length, and Gompertz for tail length. We confirmed the occurrence of dwarf individuals, whose body mass, total length, and tail length were 20%, 22%, and 70% smaller, respectively, than in the overall population. The dwarfs remain small in size after having fledged and are easily identified as adults. We discuss the importance of long-term studies to identify windows of opportunity for further research that will help in the conservation of endangered macaw species.

Differences in Rhinoceros Auklet diet and chick body mass at 4 breeding sites in Hokkaido

北海道周辺の異なる海洋環境に位置する4つのウトウCerorhinca monocerata繁殖地において，2016–2017年に雛に持ち帰った餌と雛の体重（成長段階で補正）を調べた．松前小島，天売島，トド島の3繁殖地はそれぞれ対馬暖流の南部，中北部，北部に位置しており，トド島はオホーツク海の東樺太海流に由来する冷水塊にも近い．また，大黒島は沿岸親潮および親潮が流入する太平洋側に位置する．主な餌種は繁殖地間で異なっており，天売島およびトド島ではホッケPleurogrammus azonus 0歳，松前小島ではスケトウダラGadus chalcogrammus 0歳，大黒島ではサケOncorhynchus keta 0歳だった．加えて，イカナゴ属Ammmodytes spp. 0歳もしくは1歳以上はすべての繁殖地である程度利用されていた．エネルギー密度が高いホッケ0歳をよく持ち帰ったトド島では，1給餌あたりの餌重量も大きく，結果として雛の成長段階補正体重も重かった．海水温の違いがトド島と天売島におけるホッケの利用割合の違いや，大黒島内におけるサケ0歳の利用割合の年変化を説明するかもしれない．また，サケ稚魚ふ化放流事業に由来した餌資源量の地域差も，繁殖地間のサケ0歳の利用割合を説明するかもしれない．さらに，イカナゴ属は，北海道周辺の沿岸に広く分布するのでいずれの繁殖地でも一定割合利用されたのかもしれない．本研究は，海流による海水温の差や人為的影響が餌資源量の海域間差をもたらし，それが各地域で繁殖するウトウの餌ひいては雛の体重に影響していることを示唆する．

An immune challenge of female great tits decreases offspring survival and has sex-specific effects on offspring body size

Investment in immunity is expected to decrease (costly immunity) or enhance (terminal investment) reproductive performance. Here, we tested the effects of activation of the immune system in female great tits (Parus major) on (1) their reproductive effort and (2) the survival and body condition of their offspring, controlling for chick sex. We injected females tending 3-day-old chicks with sheep red blood cells (SRBC) or saline (control) and recorded their provisioning rates 6 days later, during the expected peak of antibody production. We measured tarsus length and body mass in 11-day-old chicks and monitored changes in brood size. We found that female provisioning rates were unaffected by the SRBC challenge. An analysis without an outlier, however, showed a significant challenge-by-hatch date interaction. This interaction indicated that female provisioning rates decreased with hatch dates in the SRBC but not in the control nests, suggesting a stronger effect in later breeders. Chick body mass was not affected by female immunisation nor by its interaction with chick sex. However, we found a significant challenge-by-sex interaction on offspring tarsus. In SRBC nests, the difference in tarsus length between male and female chicks was lower than in controls, suggesting sex-dependent effects of the challenge on offspring structural growth. Finally, chick mortality was greater in SRBC nests compared with controls, but chick survival probability was not affected by sex. Overall, our results support the costly immunity but not the terminal investment hypothesis in the great tit.

Metabolic and Hematological Responses to Endotoxin-Induced Inflammation in Chicks Experiencing Embryonic 2,3,7,8-Tetrachlorodibenzodioxin Exposure.

Dioxin exposure during bird embryonic development disrupts immunity as well as mechanisms involved in energy metabolism, potentially affecting negatively acute-phase responses to pathogens. Thus, we hypothesized that embryonic exposure to 2,3,7,8-tetrachlorodibenzodioxin (TCDD) changes the metabolism and blood physiology of domestic chicks, affecting their physiological competence for responding to immune challenges. To test this hypothesis, we injected doses of 0, 1.5, and 3 ng TCDD/egg (based on survival experiments) on embryonic day 4 and then measured O2 consumption and CO2 production for metabolic rate, ventilation, and body temperature (TB ) in 5-d-old chicks. Then, chicks were injected with lipopolysaccharide (LPS, endotoxin) or saline prior to repeating the physiological measurements. A second chick group exposed to identical TCDD and LPS treatments had blood partial pressure of oxygen, partial pressure of carbon dioxide, pH, bicarbonate concentration, lactate concentration, osmolality, hemoglobin concentration, red blood cell concentration, and hematocrit, as well as TB , analyzed at 1 and 5 h after LPS injection. Metabolism in chicks embryonically exposed to 1.5 and 3 ng TCDD/egg was up to 37% higher, whereas body mass of chicks exposed to 3 ng TCDD/egg was approximately 6% lower. Chicks embryonically exposed to 3 ng TCDD/egg challenged with LPS showed a relative persistent hypometabolism accompanied by elimination of the normal hematological and osmotic responses to LPS. We conclude that embryonic exposure to TCDD affects posthatching metabolism as well as impairs metabolic, hematological, and osmotic responses to LPS. Environ Toxicol Chem 2020;39:2208-2220. © 2020 SETAC.

Lead concentrations in blood from incubating common eiders (Somateria mollissima) in the Baltic Sea

Here we investigate if lead may be a contributing factor to the observed population decline in a Baltic colony of incubating eiders (Somateria mollissima). Body mass and blood samples were obtained from 50 incubating female eiders at the Baltic breeding colony on Christiansø during spring 2017 (n = 27) and 2018 (n = 23). All the females were sampled twice during early (day 4) and late (day 24) incubation. The full blood was analysed for lead to investigate if the concentrations exceeded toxic thresholds or changed over the incubation period due to remobilisation from bones and liver tissue. Body mass, hatch date and number of chicks were also analysed with respect to lead concentrations. The body mass (mean ± SD g) increased significantly in the order: day 24 in 2018 (1561 ± 154 g) < day 24 in 2017 (1618 ± 156 g) < day 4 in 2018 (2183 ± 140 g) < day 4 in 2017 (2359 ± 167 g) (all p < 0.001). The lead concentrations increased significantly in the opposite order i.e. day 4 in 2017 (41.7 ± 67.1 μg/L) < day 24 in 2017 (55.4 ± 66.8 μg/L) < day 4 in 2018 (177 ± 196 μg/L) < day 24 in 2018 (258 ± 243) (all p < 0.001). From day 4 to 24, the eider females had a 1.33-fold increase in blood lead concentrations in 2017 and a 1.46-fold increase in 2018. Three of the birds (13%) sampled in 2018 had lead concentrations that exceeded concentrations of clinical poisoning (500 μg/L) and eleven (48%) had concentrations that exceeded the threshold for subclinical poisoning (200 μg/L). In 2017, none of the birds exceeded the high toxic threshold of clinical poisoning while only one (4%) exceeded the lower threshold for subclinical poisoning. Three of the birds (6%) sampled in 2018 had lead concentrations that exceeded those of clinical poisoning while 12 birds (24%) resampled in both years exceeded the threshold for subclinical poisoning. In addition, lead concentrations and body mass on day 4 affected hatch date positively in 2018 (both p < 0.03) but not in 2017. These results show that bioavailable lead in bone and liver tissue pose a threat to the health of about 25% of the incubating eiders sampled. This is particularly critical because eiders are largely capital breeding which means that incubating eiders are in an energetically stressed state. The origin of lead in incubating eiders in the Christiansø colony is unknown and it remains an urgent priority to establish the source, prevalence and mechanism for uptake. The increase in lead from day 4 to day 24 is due to bone and liver remobilization; however, the additional lead source(s) on the breeding grounds needs to be identified. Continued investigations should determine the origin, uptake mechanisms and degree of exposure to lead for individual birds. Such research should include necropsies, x-ray, lead isotope and stable C and N isotope analyses to find the lead sources(s) in the course of the annual cycle and how it may affect the population dynamics of the Christiansø colony which reflects the ecology of the Baltic eiders being suitable for biomonitoring the overall flyway.

Physiological impacts of pollution exposure in seabird's progeny nesting in a Mediterranean contaminated area

Aquatic wildlife is exposed through trophic transfer of hazardous substances to several threats inducing physiological impairments. We aimed at assessing the impact of contamination in one of the hot spots of pollution along Mediterranean coasts, the gulf of Gabes in Tunisia, on Common tern Sterna hirundo, a piscivorous top predator bird. Firstly, we compared the reproductive effort of breeding adults through clutch size distribution in three sites with different levels of pollution. Then, a battery of genotoxicity and oxidative stress biomarkers was carried out to assess physiological impairments in chicks. While defense mechanisms showed a depletion, lipid peroxidation and genotoxicity increased significantly according to pollution level. The multi-biomarker approach used here, discriminated chicks according to contamination degree of their nesting sites. Increases in genotoxicity and oxidative stress were correlated to a decrease in chick body mass known to lead to long-term impacts on juvenile survival and recruitment in birds.

Effect of Brood Size on Food Provisioning Rate in Common KingfishersAlcedo atthis

We measured food provisioning to broods of Common Kingfishers Alcedo atthis. We collected regurgitated undigested fish remains from artificial nests. Using artificial nests ensured that fish remains originated from the current nesting period and were not a result of multiple use of a nest within one breeding season or between seasons. In total, 4722 specimens of 24 fish species were identified in six nests; the remains were used to estimate the mass of individual fish prey. Chicks were fed with fish weighing between 0.01 and 16.2 g (average: 3.0 g, median: 2.6 g). Provisioning rate significantly increased with increasing brood size from 1498 g (505 fishes for four nestlings) to 2968 g (894 fishes for eight nestlings). During the fledging period each chick consumed on average 334 g of fish, which resulted in an estimated daily food intake of 37% of the chick's body mass (average over the entire nestling period). The average daily energy intake was 73.5 kJ per chick, which was lower than expected for birds ...

Growth heterogeneity in broiler breeder pullets is settled before the onset of feed restriction but is not predicted by size at hatch.

Uniform growth is a desirable trait in all large-scale animal production systems because it simplifies animal management and increases profitability. In parental broiler flocks, so-called broiler breeders, low growth uniformity is largely attributed to the feed competition that arises from quantitatively restricted feeding. As feed restriction is crucial to maintaining healthy and fertile breeders, several practices for reducing feed competition and the associated growth heterogeneity have been suggested and range from nutrient dilution by increasing fiber content in feed to intermittent fasting with increased portion size ("skip a day"), but no practice appears to be entirely effective. The fact that a large part of the heterogeneity remains even when feed competition is minimized suggests that some growth variation is caused by other factors. We investigated whether this variation arises during embryonic development (as measured by size at hatch) or during posthatch development by following the growth and body composition of birds of varying hatch sizes. Our results support the posthatch alternative, with animals that later grow to be small or large (here defined as >1 SD lighter or heavier than mean BW of the flock) being significantly different in size as early as 1 d after gaining access to feed ( < 0.05). We then investigated 2 possible causes for different postnatal growth: that high growth performance is linked 1) to interindividual variations in metabolism (as measured by cloacal temperature and verified by respirometry) or 2) to higher levels of social motivation (as measured in a social reinstatement T-maze), which should reduce the stress of being reared in large-scale commercial flocks. Neither of these follow-up hypotheses could account for the observed heterogeneity in growth. We suggest that the basis of growth heterogeneity in broiler breeder pullets may already be determined at the time of hatch in the form of qualitatively different maternal investments or immediately thereafter as an indirect result of differences in incubation conditions, hatching time, and resulting fasting time. Although this potential difference in maternal investment is not seen in body mass, tarsometatarsal length, or full body length of day-old chicks arriving at the farm, it may influence the development of differential feed and water intake during the first day of feeding, which in turn has direct effects on growth heterogeneity.

Contrasting effects of climate on juvenile body size in a Southern Hemisphere passerine bird.

Despite extensive research on the topic, it has been difficult to reach general conclusions as to the effects of climate change on morphology in wild animals: in particular, the effects of warming temperatures have been associated with increases, decreases or stasis in body size in different populations. Here, we use a fine-scale analysis of associations between weather and offspring body size in a long-term study of a wild passerine bird, the cooperatively breeding superb fairy-wren, in south-eastern Australia to show that such variation in the direction of associations occurs even within a population. Over the past 26years, our study population has experienced increased temperatures, increased frequency of heatwaves and reduced rainfall - but the mean body mass of chicks has not changed. Despite the apparent stasis, mass was associated with weather across the previous year, but in multiple counteracting ways. Firstly, (i) chick mass was negatively associated with extremely recent heatwaves, but there also positive associations with (ii) higher maximum temperatures and (iii) higher rainfall, both occurring in a period prior to and during the nesting period, and finally (iv) a longer-term negative association with higher maximum temperatures following the previous breeding season. Our results illustrate how a morphological trait may be affected by both short- and long-term effects of the same weather variable at multiple times of the year and that these effects may act in different directions. We also show that climate within the relevant time windows may not be changing in the same way, such that overall long-term temporal trends in body size may be minimal. Such complexity means that analytical approaches that search for a single 'best' window for one particular weather variable may miss other relevant information, and is also likely to make analyses of phenotypic plasticity and prediction of longer-term population dynamics difficult.

Artificial polychromatic light affects growth and physiology in chicks.

Despite the overwhelming use of artificial light on captive animals, its effect on those animals has rarely been studied experimentally. Housing animals in controlled light conditions is useful for assessing the effects of light. The chicken is one of the best-studied animals in artificial light experiments, and here, we evaluate the effect of polychromatic light with various green and blue components on the growth and physiology in chicks. The results indicate that green-blue dual light has two side-effects on chick body mass, depending on the various green to blue ratios. Green-blue dual light with depleted and medium blue component decreased body mass, whereas enriched blue component promoted body mass in chicks compared with monochromatic green- or blue spectra-treated chicks. Moreover, progressive changes in the green to blue ratios of green-blue dual light could give rise to consistent progressive changes in body mass, as suggested by polychromatic light with higher blue component resulting in higher body mass. Correlation analysis confirmed that food intake was positively correlated with final body mass in chicks (R2 = 0.7664, P = 0.0001), suggesting that increased food intake contributed to the increased body mass in chicks exposed to higher blue component. We also found that chicks exposed to higher blue component exhibited higher blood glucose levels. Furthermore, the glucose level was positively related to the final body mass (R2 = 0.6406, P = 0.0001) and food intake (R2 = 0.784, P = 0.0001). These results demonstrate that spectral composition plays a crucial role in affecting growth and physiology in chicks. Moreover, consistent changes in spectral components might cause the synchronous response of growth and physiology.

Male skin color signals direct and indirect benefits in a species with biparental care

Particularly in species with biparental care and low levels of extrapair paternity, sexual traits that honestly indicate phenotypic and genetic quality are expected. We investigated in the brown booby, Sula leucogaster, whether gular color displayed by males during courtship is related to direct or indirect benefits to females. We performed a cross-fostering experiment in order to identify the relative contribution of parental care and genetic effects on offspring condition. We found that rearing father gular color was positively related to parental care (offspring attendance and provisioning) and chick body mass increase, whereas the genetic father gular color was related to chick structural growth. Contrary to expectations, females paired to more colorful males laid smaller eggs and did not increase parental care. Interestingly, chicks from genetic mothers with more colorful gulars and chicks that hatched from larger eggs “begged” at higher rates to mothers than to fathers. Overall, the results suggest that male gular color may provide females with reliable information on mate genetic quality and parenting abilities.

Consequences of experimental clutch enlargement in a High Arctic single-egg layer, the Little Auk (Alle alle)

Initial reproductive investments in birds are energy-demanding. Amount of energy allocated to egg production and incubation may have an important role in determining parental fitness and evolution of clutch size. Here, we investigated whether the Little Auk (Alle alle (L., 1758)), a small alcid with one-egg clutch but two brood patches (probably remnant of the original two-egg clutch), is capable of incubating two eggs and rearing two chicks. We performed an experiment with removing the egg from 20 nests and transferring it to 20 experimental nests (EN). In 25% of EN, both eggs failed to hatch; in 75% of EN, only one egg hatched successfully. Hatching success in EN was 2.5 times lower than in control nests (CN). In EN, chicks hatched only from eggs warmed during &gt;90% of inspections. Owing to the prolonged incubation, the chicks in EN hatched 2 days later than in CN. However, due to the shorter period spent in the nest in EN, fledging dates in both types of nests were similar. The similar body mass and survival of chicks from EN and CN suggest that these traits were influenced mainly by the rearing conditions. Our study emphasize the importance of the incubation phase as a constraint on clutch size.

Predicting chick body mass by artificial intelligence-based models

The objective of this work was to develop, validate, and compare 190 artificial intelligence-based models for predicting the body mass of chicks from 2 to 21 days of age subjected to different duration and intensities of thermal challenge. The experiment was conducted inside four climate-controlled wind tunnels using 210 chicks. A database containing 840 datasets (from 2 to 21-day-old chicks) - with the variables dry-bulb air temperature, duration of thermal stress (days), chick age (days), and the daily body mass of chicks - was used for network training, validation, and tests of models based on artificial neural networks (ANNs) and neuro-fuzzy networks (NFNs). The ANNs were most accurate in predicting the body mass of chicks from 2 to 21 days of age after they were subjected to the input variables, and they showed an R² of 0.9993 and a standard error of 4.62 g. The ANNs enable the simulation of different scenarios, which can assist in managerial decision-making, and they can be embedded in the heating control systems.

Vocal development and voice breaking in Demoiselle Cranes (Anthropoides virgo)

The vocal development of cranes (Gruidae) has attracted scientific interest due to a special stage, so-called voice breaking. During voice breaking, chicks produce both adult low-frequency and juvenile high-frequency vocalizations. The triggers that affect voice breaking are unknown. For the first time, we study the vocal development of the Demoiselle Crane (Anthropoides virgo). We describe the age and possible drivers of the onset of voice breaking. We analyse the calls of 21 Demoiselle Crane chicks, and compare them with the calls of six adult birds, noting the day when adult low-frequency calls are first recorded as the day when voice breaking begins. The age of voice breaking onset does not depend on hatching date, clutch order or chick body mass. Thus, there is no correlation between body growth and the onset of voice breaking for individual Demoiselle Crane chicks. However, there is a strong relationship between body mass and voice breaking among different crane species. Demoiselle Cranes stop intense body growth at the age of 2 months and start voice breaking at 70 ± 46 days. By way of comparison, Red-crowned Cranes finish the period of intense body growth at the age of 7 months and start voice breaking at 211 ± 60 days. Thus, we show that the Demoiselle Crane has a sudden vocal development, similar to other crane species, and we suggest that the end of intense body growth is the trigger for the onset of voice breaking in cranes.