Number Of Nestlings Research Articles

Revealing the key signals in nestling begging behavior perceived by parent birds during parent-offspring conflict.

The parent-offspring conflict in avian species encompasses resource allocation and a balance necessary for survival for both parties. Parental investment is modulated according to various factors, among which begging is important. Endogenous hormones, particularly corticosterone (CORT), play a role in modulating begging behavior. However, most studies on hormonal regulation of begging behavior induced elevated hormone levels in the offspring through feeding or injections, thus, limiting our knowledge of the evolution of the parent-offspring conflict under natural conditions. In this study, we aimed to identify the key signals that parents respond to during interactions with their nestlings in the wild, considering factors such as endogenous hormone CORT, nestling age, and brood size, which may affect nestling begging behavior. Begging performance was evaluated by measuring the begging frequency and score of the red-whiskered bulbul (Pycnonotus jocosus), along with assessing CORT levels in feathers. CORT levels were significantly correlated with both the begging frequency and score of nestlings, while variables such as body mass and tarsus length did not influence parental feeding frequency. Additionally, factors such as the number of nestlings (brood size), age, and begging frequency were predictors of parental feeding frequency. Our findings indicate that begging frequency, nestling age, and brood size are signals that help navigate the intricacies of the parent-offspring conflict and that parents may rely on these key signals from the range of begging cues exhibited by nestlings to adjust their feeding strategies.

Variation in parental investment preferences for nestlings of the Gray‐backed Shrike (Lanius tephronotus) in alpine environments

AbstractIn the northeastern edge of the Qinghai‐Tibet Plateau, the Gray‐backed Shrike, a shrubland bird species of the plateau, confronts harsh living conditions. The impact of such an environment on their reproductive strategies has long intrigued us. This study reveals significant environmental effects on the investment of the Gray‐backed Shrike during their nestling‐rearing and egg‐laying stages. (1) Based on measurements of 215 shrike eggs from 2017 to 2021, we found that under the cold alpine climate, Gray‐backed Shrikes opt for a strategy of larger clutches and bigger eggs as average rainfall decreases. Concurrently, parents display a decreasing hatching order strategy, resulting in significant weight differences among newly hatched nestlings. (2) Marginal and core offspring exhibited no significant differences in fledging conditions. Core offspring generally have a slightly larger physique than marginal ones. However, marginal offspring exhibit the highest growth rate, with similar survival rates across different offspring categories. Parental rearing adopts a nest survival strategy. (3) The food provisioning rate by parents correlates strongly with the number of nestlings, the age of the nestling, and the nest's sex ratio. Differences exist between female and male provisioning rates based on begging intensity and average temperature; higher average temperatures lead to more food, with males providing more food. (4) Factors like nest sex ratio, offspring category, nestling age, and nestling sex influence the feeding preferences of parents. When overall nestling ratios skew towards either male or female, parental feeding preferences align with the actual nest sex ratio. Male and female parental feeding preferences differ based on average temperature and nestling sex. Males consistently exhibit a stronger preference for feeding male nestlings, regardless of the nest's sex ratio. In contrast, females don't show a clear preference, leading to differences in survival rates for different nestling sex under male feeding preferences.

Reproductive Success of Tree Swallows at Abandoned Mine Drainage Treatment Ponds

Abandoned mine drainage treatment ponds could have contrasting effects on the reproductive success of birds living in the vicinity. The ponds and associated vegetation may, like any other body of freshwater, provide beneficial habitats for the insects that the birds use to feed their young; or instead, the ponds may act as an ecological trap, attracting the birds to a habitat that is poor in quality and negatively impacting their productivity. We monitored nests of an aerial insectivore, the Tree Swallow (Tachycineta bicolor), to determine whether the distance between the ponds and the nests affected various reproductive parameters including clutch size, hatch rate, number of nestlings, nestling size and mass, number of fledglings, fledging rate, and fledge date. Data were collected over two breeding seasons (2022 and 2023) from a swallow population in southwestern Pennsylvania, USA. We found that the nests closest to the treatment ponds had significantly more nestlings and fledglings, earlier fledge dates, and a better fledging rate when compared to nests that were more distant from the ponds. However, all these parameters were well below previously published values, which suggests that the mine drainage ponds provide good nesting habitats relative to what is available in the region but that they do not represent high-quality habitats for this species overall.

Sex ratio and sex-specific chick mortality in a species with moderate sexual size dimorphism and female brood desertion

An equal sex ratio at the population level is the usual, evolutionarily stable condition. However, at the individual level, it may be adaptive for parents to manipulate the sex of their offspring, especially in species with sexual size dimorphism (SSD) when the costs and benefits of producing sons and daughters can vary. In this study, we investigated the hatching sex ratio (HSR) and fledging sex ratio (FSR) in the Whiskered Tern (Chlidonias hybrida). Despite the fact that SSD exists in Whiskered Terns already at the chick stage, HSR and FSR did not deviate from parity at the population level. We tested the dependence of HSR, FSR and the survival probability of males and females on the individual hatching date, average egg volume (in a clutch) and the number of nestlings. None of these factors influenced HSR. Survival probability was negatively correlated with the number of hatchlings. The proportion of females among the fledglings was positively correlated with the average egg volume per clutch. To better explore the effect of egg volume on the sex ratio, we tested the relationship between exact egg volume and hatchling sex or hatching success at the individual level; but despite the quite large sample size, our analyses failed to reveal any relationship. The sex ratio was equal among chicks that were found dead in a nest, mostly due to starvation, but more female than male chicks disappeared from nests (mostly due to predation), primarily in the first week of life. This indicates that females may be easier to predate, very likely by frogs hunting small chicks.

Nestlings reared by males are in better body condition than those reared by females in uniparental European Penduline Tits

Conditions encountered during early development affect future survival and reproduction in many bird species. For parents, it is important what body condition the nestlings will achieve at fledging because the condition affects the offspring’s chances to survive and reproduce in the future. However, there is a trade-off between the number of nestlings and their condition. We studied parental behaviour and nestling body condition in uniparental Penduline Tits. In this small passerine, the parental care (incubation and food provisioning) is provided by the female only (49% of clutches in the study population) or the male only (15%). In addition, over a third of clutches are deserted by both parents before the start of incubation. We found that female-only cared clutches had more eggs and nestlings and produced more fledglings than male-only cared clutches. The incubation behaviour and incubation temperature in both types of clutches were similar. The provisioning rate per brood was positively, and the provisioning rate per nestling was negatively, correlated with brood size. Although males cared for smaller clutches, parent sex was not significant in both models of provisioning rates (per brood and per nestling). Moreover, the provisioning rate did not predict the brood’s average nestling condition. However, nestlings reared in broods with male care were in better condition than those reared by females. At the age of 13 days, they had a higher scaled mass index (describes the relative size of energy reserves) and higher haemoglobin levels. The results suggest that the lower productivity of male-only cared clutches, compared to those cared for only by females, may be compensated by the higher condition of nestlings. Information about the recruitment success of broods cared for by males and females will be necessary to test this prediction.

Variation in mesopredator abundance and nest predation rate of the endangered Strange‐tailed Tyrant (Alectrurus risora)

Nest predation is the main cause of nest failure in passerine birds and thus is a key determinant of breeding traits. Accordingly, nest predator community composition and abundance modulate nest predation rates. When top predators are absent, mesopredator populations may become unchecked, which in turn increases the predation pressure on their prey species. We evaluated whether nest predator abundance and breeding traits of an endangered grassland bird, the Strange‐tailed Tyrant Alectrurus risora, differed between two protected areas: Iberá National Park (INP), where top predators have been extinct for 50 years, and Reserva El Bagual (REB), where Pumas Puma concolor still have a stable population. We measured abundances of potential nest predator species and during the 2015–2018 breeding seasons we monitored Strange‐tailed Tyrant nests and set camera traps to identify nest predators. Mesopredator abundance was higher in INP, and foxes were identified as the main nest predators. Nest predation rate was also higher in INP, where the daily nest predation rate and cumulative probability of nest predation were 0.05 ± 0.006 and 0.81, whereas in REB they were 0.04 ± 0.004 and 0.70, respectively. The 10‐fold higher frequency of fox records in INP could explain the higher nest predation rate observed, suggesting that the extinction of top predators may increase nest predation rates of endangered grassland birds in protected areas through release of native mesopredator species. The lower nest predation observed in REB was compensated for by a higher nest abandonment rate, which resulted in a similar fledgling production in the two study sites. Clutch size, hatching success and number of nestlings did not differ between study sites. The low breeding success recorded for this endangered species despite its populations being in protected areas of high conservation value is alarming given the global decline that grassland bird populations are facing.

Parental food provisioning and nestling growth under Philornis downsi parasitism in the Galapagos Green Warbler-Finch, classified as ‘vulnerable’ by the IUCN

In the Galapagos Islands, many endemic landbird populations are declining due to habitat degradation, food availability, introduced species and other factors. Given nestlings typically lack efficient defense mechanisms against parasites, hematophagous ectoparasites such as the larvae of the introduced Avian Vampire Fly, Philornis downsi, can impose high brood mortality and cause threatening population declines in Darwin finches and other landbirds. Here, we assess whether the food compensation hypothesis (i.e., the parents’ potential to compensate for deleterious parasite effects via increased food provisioning) applies to the Green Warbler-Finch. We differentiated nests with low or high infestation levels by P. downsi and quantified food provisioning rates of male and female parents, time females spent brooding nestlings, and nestling growth. Male provisioning rates, total provisioning rates and female brooding time did not significantly vary in relation to infestation levels, nor by the number of nestlings. Opposed to the predictions of the food compensation hypothesis, females showed significantly reduced provisioning rates at high infestation levels. Nestling body mass was significantly lower and there was a reduction of skeletal growth, although not significantly, in highly infested nests. The females’ response to high infestation may be due to parasites directly attacking and weakening brooding females, or else that females actively reduce current reproductive effort in favor of future reproduction. This life-history trade-off may be typical for Darwin finches and many tropical birds with long lifespans and therefore high residual reproductive value. Conservation strategies may not build on the potential for parental food compensation by this species.

Мониторинг гнездовой группировки степного орла в Актюбинской области (Казахстан) в 2018–2023 годах

Мониторинг гнездовой группировки степного орла в Актюбинской области (Казахстан) в 2018–2023 годах

Гнездовые группировки орлов на ключевой орнитологической территории «Чинк Донызтау» в 2022 году

Гнездовые группировки орлов на ключевой орнитологической территории «Чинк Донызтау» в 2022 году

Современный статус степного орла в Казахстане

Современный статус степного орла в Казахстане

Сезонные аспекты питания Поволжской популяции солнечных орлов в гнездовой период

Сезонные аспекты питания Поволжской популяции солнечных орлов в гнездовой период

Rocky nests are better nesting sites than woodpecker cavities for the Eastern Rock Nuthatch Sitta Tephronota

The reproductive success of birds depends on many factors, including nest construction and placement. In the mountainous regions of southwestern Iran, broods of Eastern Rock Nuthatch Sitta tephronota were surveyed in 2016 and 2017. During the study, 11 broods in rocky cavities and 16 in abandoned Syrian woodpeckers’ Dendrocopos syriacus tree cavities were compared in terms of breeding performance (phenology, clutch size, hatching success, number of fledglings, breeding success). The Eastern Rock Nuthatch began egg-laying on March 24 and continued until April 15. The number of eggs in the clutch ranged from 3 and 7 (mean 5.6±1.19, median 6, N = 27). The two types of clutches compared usually contained 6 eggs, and the number of nestlings was statistically lower in tree cavities than in rocky nests. Hatching success was almost 30% higher in rocky nests than in tree cavities. In broods located in trees, 4 nestlings hatched most often (42%, N = 12), and in rock nests, 5 nestlings hatched (50%, N = 10). Rocky nests were also statistically greater (by over 40%) for breeding success. For all analysed broods and broods with success, roughly two extra fledglings left the rocky nests compared with tree cavities. 5 fledglings (50%, N = 10) most often left rocky nests, whereas, in general, 4 fledglings (50%, N = 10) left tree nests. Research results did not confirm that woodpecker cavities are safe nest sites for cavity dwellers.

A long-term study indicates that tree clearance negatively affects fledgling recruitment to the Blue-fronted Amazon (Amazona aestiva) population.

The Blue-fronted Amazon (Amazona aestiva) is a Neotropical parrot with a large distribution in South America, including areas in Brazil, Bolivia, Argentina and Paraguay. A substantial part of the population of this parrot is concentrated in the Pantanal, a large wetland located in the center of South America. There, the clearing of forest and savannas has occurred through the years to accommodate beef-cattle pasture, and crops. Our objective was to understand the direct and indirect effects of time, availability of forest and savannas, and rainfall over the number of nestlings and fledged young of Blue-fronted Amazons inhabiting the southern Pantanal. We surveyed their nests from 1997 to 2018 and counted the number of nestlings produced and the number of fledglings capable to leave the nest in each year. Additionally, we used available data on the area covered by arboreal vegetation, and rainfall data collected at a Meteorological Station located in a central area of the study, as predictors of the numbers of nestlings and fledglings produced every year. Then, we applied structural equation modeling to examine both the direct and indirect effects of time, arboreal habitat availability, and annual cumulative rainfall on the number of nestlings and fledgling per nest. Finally, we estimated the long-term trend of the number of fledglings per nest as a surrogate to the populational trend of Blue-fronted Amazon. We found that none of the variables in our model explained the number of nestlings in nests, but the number of nestlings and the arboreal habitat availability directly and positively affected the number of fledglings. Time indirectly and negatively affected the number of fledglings per nest, whereas rainfall affected it indirectly positively. Additionally, we detected a concerning decrease of about 30% of the fledglings during the 22-years study, which could lead to a change in the species conservational status.

Impacts on Hazel Dormice (Muscardinus avellanarius) of twenty years of incremental conifer removal

Within a Planted Ancient Woodland Site (PAWS) of Corsican Pine, planted in 1970, Hazel Dormice (Muscardinus avellanarius) in nestboxes were individually marked by PIT tags from 2000 onwards. In adjacent experimental study plots of 3 ha each, different patterns of forest restoration were used. In early winter 2003 c.33 % of conifers were removed: [a] in very small groups; [b] larger felling coupes similar to hazel coppicing; [c] traditional ‘rack-and-thin’ regime. In 2009 and 2015 a third of remaining pines were removed and in 2020 almost all remaining conifers were removed. The effects on three dormouse abundance indices were recorded through routine monitoring of nest boxes. The overall number of captures varied from year to year, increasing the year following forestry operations in 2003 and 2009, 2015. This was possibly because nestboxes temporarily became more attractive except in 2021 which was a very poor dormouse year. In the rack-and-thin treatment little regeneration occurred and dormouse numbers slowly declined to almost zero. The numbers of individually marked adults in the other plots showed a rising trend. The numbers of nestlings and juveniles recorded initially increased, but have oscillated recently. This study demonstrates that during regular forestry operations in conifers, maintaining a population of this species is possible. This has important implications for managers. A regime of patchwork conifer removal over 4 phases appears to be pragmatic for an economic forestry business and also ensures that dormice remain. The rack-and-thin area lost its dormice but may recover in the next few years.

Степной орёл в Республике Калмыкия (Россия): результаты исследования 2021 года

The article presents the results of the Steppe Eagle (Aquila nipalensis) study in the Republic of Kalmykia. 135 breeding territories of eagles were examined and 155 birds were observed during summer registrations and counts. The average distribution density of the occupied breeding territories in 2021 in the main part of the area was 2.15 (1.54–2.99)/100 km², in the zone of the large number of food resources – 5.72 (4.45–7.35)/100 km². The percentage of occupied breeding territories was 71%, and 43% of the occupied territories were successful. The number of nestlings in broods ranged from 1 to 3, averaging 1.81±0.69 per successful nest (n=43) and 0.73±0.95 per occupied nest (n=105). The percentage of nests with dead clutches and nestlings was high at all surveyed plots. The main diet of eagles during the breeding period included the Little Ground Squirrel (Spermophilus pygmaeus) (44%) and several additional prey items. A preliminary assessment of habitat suitability for the Steppe Eagle in terms of food conditions was carried out using GIS methods. Based on the registration data and clarification of the breeding range borders (47086.7 km²), the number of the Steppe Eagle in Kalmykia was re-estimated at 789 (587–1059) pairs. The signs indicating a negative trend in the population intensified: the percentage of immature birds in breeding pairs was 27%, the percentage of abandoned breeding territories was 19%. There is a consolidation of breeding groups in the population nucleus with a simultaneous decrease in breeding density at the periphery. Among the negative anthropogenic factors in 2021 there were the following: mass mortality on power lines, destruction of the food potential by the locals, disturbance during breeding, probable taking away of nestlings from nests.

Spatial and temporal variation in breeding performance in the increasing White-tailed Eagle Haliaeetus albicilla population to the east of the Baltic Sea

ABSTRACT Capsule We found no evidence of decreased reproductive performance of the White-tailed Eagle Haliaeetus albicilla, despite ongoing population increases in an environment characterized by different types of utilized habitats. Aim To characterize temporal and spatial variations in several components of breeding performance in an increasing White-tailed Eagle population. Methods The breeding performance and number of pairs located in the region east of the Baltic Sea was monitored between 2005 and 2020. We analysed the trends in the numbers of pairs and several reproduction parameters for 16 years, and compared variation in breeding performance in four different habitats through application of generalized linear (mixed) models. Results The number of White-tailed Eagle pairs increased three-fold locally between 2005 and 2020, but we found no evidence for a deterioration in breeding performance parameters (nesting success, brood size, proportion of females among nestlings, body condition of nestlings). The probability of successful nesting, nestling sex and number of nestlings in a brood were found to be similar between pairs associated with different habitats, ranging from coastal lagoons to natural waterbodies within an inland landscape. The body condition of the nestlings, however, was habitat-dependent, with the best body condition evident in nestlings reared near the Curonian Lagoon. Conclusion Results indicate that the abundance of this predator population will continue to grow in the region east of the Baltic Sea.

Endemic Cyprus Scops Owl Otus cyprius Readily Breeds in Artificial Nest Boxes.

Simple SummaryNest boxes are considered a valid conservation tool in order to sustain wild populations of birds. The Cyprus Scops Owl was recently defined as a new species. However, the extant information on the species is sporadic and the population level is not confirmed. In order to evaluate the ability of the species to use nest boxes, and to understand its habitat preferences, we placed boxes in rural areas, at the forest edge, and in the Paphos Forest. We found that the Cyprus Scops Owl displayed a preference for the forest edge and rural areas; although we also had, several pairs occupy nest boxes in the forest. We show that the nest box strategy can be implemented if in the future the species is threatened.As is well-known, endemic island bird species are especially vulnerable to extinction from anthropogenic environmental change and reduced fitness compared with mainland taxa. The Cyprus Scops Owl, Otus cyprius, is a recently recognized island endemic species whose ecology and breeding biology have not been studied. It nests mainly in holes in trees and buildings, so the felling of old trees, modern architectural practices, and the renovation of old houses in villages may reduce nest site availability. Its population trend is also unknown. Therefore, to better determine its ecological requirements and habitat preferences we placed nest boxes in rural areas adjacent to the forest, in the forest, and in the ecotone between them, and used breeding success as our indicator of habitat suitability. We found that breeding parameters like laying date, clutch size, length of the incubation period, hatching day, hatching success, and number of nestlings did not differ between the three habitats. Despite the low level of nest box occupancy rate (5–11%) the endemic Cyprus Scops Owl readily breeds in artificial nests. Therefore, although we are unaware of any current threats to the Cyprus Scops Owl, we recommend that its conservation be prioritized, including studies, monitoring, habitat conservation, and the provision of nest boxes.

Environmental conditions but not nest composition affect reproductive success in an urban bird.

Adjusting the composition of their nests, breeding birds can influence the environmental conditions that eggs and offspring experience. Birds often use feathers to build nests, presumably due to their insulating properties. The amount of feathers in nests is often associated with increased nestling survival and body condition. However, it is unclear whether these putative beneficial effects of adding feathers to nests are relevant in a wide range of environmental conditions. Here, we combine data on weather conditions and feathers in nests (i.e., nest composition) to investigate their relative contribution to reproductive success in the Eurasian tree sparrow (Passer montanus). Specifically, we investigate whether the effect of weather conditions on breeding success is modulated by the amount of feathers added to the nest. We found a strong negative effect of rainfall on the number of nestlings that successfully fledged per breeding attempt, but this negative effect was not mitigated by the amount of feathers in nests. We also found that the amount of feathers in nests varied along the breeding season, with nests containing more feathers early in the breeding season, when temperatures were lower. Despite considerable variation in nest composition, our results do not suggest an important role of feathers in nests protecting eggs or nestling tree sparrows against fluctuations in environmental conditions.

Snake slough in nests of crested mynas: effect on breeding success and nestling growth

The choice of suitable nest materials is a key to nest-building process in birds. During the breeding season (March-August) in 2018 and 2019, we discovered that crested mynas (Acridotheres cristatellus) added snake slough (2–18.3 cm in length) to their nests. The addition of snake slough continued throughout the breeding period, with a proportion of 38.9% being during the nest-building period. The use of snake slough in 2018 (38.5%) was significantly less than in 2019 (71.4%). No significant differences were found in clutch size, egg mass, and egg size between nests with snake slough (the slough group) and nests without snake slough (the non-slough group). There were also no significant differences in the number of nestlings hatched for each nest, nestling growing and breeding success between the snake slough and the non-snake slough group. This is the first study to report that crested mynas add snake slough to their nests throughout their breeding period, but snake slough had little impact on most of the breeding parameters of crested mynas. We speculate that snake slough in crested myna nests may serve to reduce nest predation, improve the immunity of nestlings or serve as a post-mating sexual signal eliciting differential reproductive investment in mates; however, these speculations require further investigation.

Parental investment does not directly affect reproductive success in the saffron finch

In tropical species, the study of parental care and the description of the intraspecific variation of parental care remain relatively understudied, especially when compared to the vast works dedicated to species from the Northern Hemisphere. In Colombia, the saffron finch Sicalis flaveola, is a species with a wide geographical distribution, and despite its abundance in open habitats and urban environments, little is known about its reproductive ecology. As a small‐bodied, short‐lived passerine, we postulated that the saffron finch should behave according to the ‘reproductive value hypothesis', investing in the current brood at the expense of future survival. Consequently, we predicted: 1) that parental investment would be associated with brood size and 2) parental investment would be positively associated with nestling growth rate and reproductive success (defined as the number of nestlings which reached fledging age). In 2018, two reproductive peaks of S. flaveola flaveola were documented in the Meléndez campus of Universidad del Valle, Cali. Direct observations and video cameras (> 1700 h of recording) were used to monitor the nests from 38 different breeding pairs. We found that feeding visits and the number of regurgitation events were positively related to brood size. In an experiment of simulated nest predation, 85% of breeding pairs responded to the stimulus and parents who exhibited highly responsive behaviours (50%) raised nestlings with a higher growth rate. We also found that egg surface area positively affected the number of incubation bouts per hour. Whilst no relationship was found between overall parental investment and reproductive success, our results appear to show that the intensity of parental investment during reproduction was modulated by brood size. Our findings suggest that there are multiple ecological factors that influence reproductive success in the saffron finch, and reinforce the need for longer term studies of tropical passerines.