Modern avian lineages evolved and radiated during the Cenozoic Era (66 Ma–present) following the end-Cretaceous extinction. Despite a wealth of isolated eggshells and nest structures, the global oological record remains unevenly studied. This review integrates the scattered literature on Cenozoic oological remains to produce the first comprehensive synthesis of their distribution, structure, palaeobiogeography, and palaeobiological significance. This record reconstructs temporal patterns in eggshell microstructure, nesting ecology, and biogeography. Methodological advances in microscopy, electron backscatter diffraction, isotopic geochemistry, and biomolecular preservation have enabled and refined taxonomic attributions and ecological interpretations of oological material. This synthesis highlights key gaps—particularly in Africa, Antarctica, and Oceania—and outlines research priorities aimed at linking palaeontology, molecular biology, conservation, de-extinction, and Earth-system sciences to better understand the evolutionary trajectory of avian reproduction. Furthermore, this evolving avian fossil record offers a critical foundation for reconstructing past ecosystems and informing efforts to conserve biodiversity into the future
Hematological parameters are widely used as integrative indicators of physiological condition in birds. The Cabanis’s Ground Sparrow ( Melozone cabanisi ), a Costa Rican endemic species commonly associated with coffee plantations and semi-modified landscapes, lacks baseline hematological information, limiting the interpretation of blood-based health assessments. In this study, we established descriptive hematologic intervals for M. cabanisi and evaluated the influence of intrinsic biological factors—pectoral muscle condition and molt stage—on hematological variation. Free-ranging individuals were captured using mist nets and processed following standardized protocols. We quantified erythrocyte, leukocyte, and thrombocyte parameters, plasma protein concentration, and erythrocyte indices. Mean corpuscular hemoglobin concentration (MCHC) was selected as a focal parameter to assess physiological condition. Effects of muscle condition and molt stage on MCHC were evaluated using ART ANOVA and complementary bootstrapped linear models. Hematological values for M. cabanisi were broadly consistent with those reported for other small passerines, indicating conserved erythrocytic and immunological profiles. Pectoral muscle condition emerged as the strongest predictor of MCHC, with individuals in better somatic condition exhibiting significantly higher values. In contrast, molt stage did not show a significant main effect on MCHC in conservative analyses, and no interaction between muscle condition and molt stage was detected. These results provide the first hematological reference intervals for M. cabanisi and highlight body condition as a key intrinsic driver of hematological variation. The reference values presented here offer a robust physiological baseline for future ecological, conservation, and wildlife health studies involving this endemic Neotropical passerine.
Corvids such as magpies can cause economic losses and management conflicts in urban and agricultural landscapes, and repeated exposure can reduce the effectiveness of non-lethal deterrents through habituation. This study evaluated short-term behavioral responses and habituation patterns in a flock of magpies (Pica serica) that repeatedly foraged at the same site. A drone-only stimulus and a combined stimulus consisting of a drone carrying a taxidermized magpie with conspecific mobbing-call playback were applied sequentially six and five times, respectively, at two-day intervals. Each trial consisted of 10 min of stimulus exposure followed by 50 min of post-stimulus observation. Magpie numbers were recorded at 5-min intervals, and behaviors were classified as predator-related or predator non-related based on field observations. Audio recordings were also collected to interpret mobbing calls and behavioral context. Under the drone-only stimulus, predator-related behavior increased immediately after stimulus onset, but this response declined over repeated trials, and predator non-related behavior recovered even during stimulus exposure, suggesting rapid habituation. Under the combined stimulus, no magpies remained in the experimental area during stimulus exposure in any trial, and in early trials they did not return before the end of observation. However, in later trials, individuals showing non-predator-related behavior re-entered the area 20-25 min after stimulus removal, indicating that habituation was delayed but not fully suppressed. These results suggest that a species-specific combined stimulus can induce stronger short-term avoidance and delay habituation compared with drone-only stimulus, but additional strategies are required to maintain deterrent effectiveness during repeated applications.
Avian hybridization has been predominantly studied in natural contexts, such as hybrid zones or the identification of hybrid individuals. However, captive settings offer a complementary framework for understanding the ecological and evolutionary mechanisms underlying hybridization. Artificial conditions might relax premating isolation barriers that typically prevent interspecific breeding in the wild, although certain mate recognition mechanisms could remain effective in captivity. Here, I present a comparative analysis of wild and captive hybrids in owls (order Strigiformes; families Tytonidae and Strigidae) to test two predictions: (1) captivity facilitates hybridization between morphologically more divergent species than observed under natural conditions, and (2) certain premating isolation mechanisms are still effective in captivity, with a focus on iris coloration as a visual cue in species recognition. In total, I compiled an overview of 26 reported cases of owl hybridization. Of these cases, 11 (42%) were supported by reliable documentation, involving 19 species (8% of 244 assessed species). Seven additional cases (27%) remain provisional, and eight (31%) were deemed unreliable. Comparative analyses of morphological traits indicated that captive hybrid pairs showed a broader range of interspecific differences in body mass, tarsus length, and wing length than natural hybrid pairs. No consistent differences were found between captive and natural hybrid pairs in terms of iris coloration, activity pattern, or trophic niche. Overall, hybridization in owls appears rare. The tendency for captive hybrids to involve morphologically divergent species suggests that artificial conditions relax certain constraints on interbreeding. However, the similarity in iris coloration among most hybridizing species supports a potential role for this trait in premating isolation. Future studies integrating genomic data, experimental approaches, and broader comparative datasets will be needed to clarify the impact of captivity on reproductive barriers.
Both wild birds and commercial poultry species have the typical sex ratio at birth, which means that about half of the males are unable to produce eggs. Relationship between embryo sex and egg geometrical and physical properties is one of the most reexamined assumptions. The aim of this study was to identify the relationship between the geometric and physical parameters of Japanese quail ( Coturnix japonica ) eggs and the sex of the embryos contained within them. The various parameters tested included egg shape, asymmetry and conicity indices, volume, surface area, weight, densities of the whole egg and its contents, and several parameter combinations based on these variables. Of these, only heat transfer index showed significant differences between the groups of male and female eggs on Day 5 during incubation. It was hypothesized that the value of this coefficient is related to the stage of embryo development and the intensification of metabolic rate. This may differ significantly between male and female embryos. Differences in heat transfer values provided accurate information about the potential culling of approximately 18% of the total number of eggs containing male embryos. Suggestions were made for improving the conditions for similar studies aimed at increasing the efficiency of egg sexing.
Monitoring steroid hormone patterns via excreted metabolites is an effective, non-invasive method for assessing physiological states in wild animals. This method allows for the monitoring of individuals or social groups with minimal disturbance. Here we aimed at elucidating the measurable glucocorticoids and androgens in excreta, for monitoring stress and reproductive hormones in the common waxbill (Estrilda astrild), a small estrildid finch. We measured the excreted metabolites in response to physiologically induced stress and reproductive challenges, both in males and females. For this, we challenged 12 captive common waxbills with adrenocorticotropic hormone (ACTH) and another 12 with luteinizing hormone-releasing hormone (LHRH). Steroid concentrations in droppings were analyzed using liquid chromatography mass spectrometry (LC-MS) before and up to six hours after each challenge. We found that enzymatic hydrolysis prior to LC-MS increased the recovery of steroid metabolites from common waxbills excreta. The ACTH challenge resulted in a significant increase of excreted glucocorticoids with a cortisone standard within 2-3 hours, suggesting that metabolites with a cortisone-similar structure are a reliable measure for monitoring physiological stress in this species. Although the LHRH challenge was inconclusive for androgens, our results provide useful technical details for measuring glucocorticoid metabolites in common waxbill excreta. This enables future studies of behavior in this bird species with minimum disturbance or handling bias and ensuring animal welfare requirements.
This study aimed to examine and compare the breeding biology of two sympatric woodpecker species, Picus canus and Dendrocopos major, in the midwestern region of South Korea, with the goal of elucidating interspecific differences in breeding strategies among closely related taxa. From 2018 to 2021, a total of 106 breeding nests (57 belonging to P. canus and 49 to D. major) were identified within forested areas of Seocheon and Gunsan. Data were collected on the species of nest trees and their structural characteristics, alongside breeding parameters such as egg-laying date, clutch size, period of incubation and nestling, and rates of hatching and fledging success. Observations were conducted through external nest monitoring supplemented by internal inspections using an endoscopic camera. Both species primarily selected Paulownia coreana, Prunus sargentii, and Castanea crenata as nesting cavities; however, P. canus preferred nest trees with greater height and diameter at breast height compared to those chosen by D. major. The mean egg-laying date for D. major occurred approximately two weeks earlier than that of P. canus, while clutch size and incubation period were significantly larger and longer, respectively, in P. canus. In contrast, no significant interspecific differences were detected in nestling period or in hatching and fledging success rates. This suggests that a larger clutch size does not necessarily lead to higher breeding success under similar nesting conditions. These results indicate that sympatric woodpecker species may share overlapping nesting resources yet exhibit distinct species-specific differences in nest tree structural selection, and breeding traits. This study provides foundational insights into the breeding biology of woodpeckers inhabiting temperate East Asian forests and advances understanding of breeding strategies and coexistence mechanisms among cavity-nesting avian species.
The present study explored the cloacal temperature, respiratory rate, and behavior of ostrich chicks aged 0 to 1 months during the cool (February to April) and hot (June to August) seasons in Taiwan to evaluate their environmental adaptability under subtropical climatic conditions. Ambient temperature, humidity, and temperature-humidity index (THI) values differed considerably between the cool and hot seasons. However, the cloacal temperature and respiratory rate of the ostrich chicks reared on raised beds inside a shelter did not substantially differ between seasons. Behavioral analysis revealed that the chicks spent 64% and 30.9% of their daytime hours resting during the cool and hot seasons, respectively. Overall, these findings indicate that using heating or ventilation equipment during seasonal transitions can enhance the rearing environment of ostrich chicks and increase their adaptability to subtropical environmental conditions.
Management and conservation efforts for shorebirds are generally conducted with a focus on habitat quality (e.g., forage availability) but often lack detail on the thermal conditions that can directly influence migratory success. Much of this discrepancy is due to a dearth of empirical data or modeled predictions of microclimate exposure along migration routes (i.e., stopover sites). Our objectives were to, 1) quantify thermal environments at interior mid-continental stopover mudflats during autumn migration and 2) compare the ability of modeled outputs (T-model) from mechanistic models and local weather station data (T-weather) to predict field measurements (T-mudflat). T-mudflat was collected at shorebird height (10 cm) on three mudflats routinely used by shorebirds during late summer and autumn 2024 in Kentucky, United States. Temporal variation in mudflat microclimate was substantial across diel and seasonal periods (range; 1.71 - 48.13 degrees C), yet notably, spatial variation was low for any given hour. Consequently, shorebirds experienced limited thermal options on mudflats that routinely exceeded thermal stress thresholds for shorebirds (i.e., 74.25% and 20.61% of temperatures >= 25 degrees C and >= 35 degrees C). Thermal extremes were most pronounced for diurnal periods (0700 - 1900 hour) in late summer when early long-distance migrants are using mudflat stopover sites. T-weather (F-1,F- 7,F-687 = 40,820, R-2 = 0.84, p < 0.05; RMSE = 3.41) outperformed T-model (F-1,F- 7,F-687 = 18,020, R-2 = 0.70, p < 0.05; RMSE = 6.15) at predicting T-mudflat, suggesting that T-weather may offer managers and researchers a relatively simple and often publicly accessible proxy for thermal exposure on shorebirds (albeit not necessarily a substitute for in situ microclimate measurements). Our findings 1) should encourage researchers and managers to add a thermal context to their current assessments of habitat quality for shorebirds, and 2) offer a framework for studying thermal patterns across different habitat types, latitudinal gradients, and sampling methods.
The objective of this study was to estimate the population density of five dove species: Rock pigeon (Columba livia), Red-billed pigeon (Patagioenas flavirostris), Eurasian collared-dove (Streptopelia decaocto), White-winged dove (Zenaida asiatica), and Mourning dove (Zenaida macroura) within the riparian corridor of the Sinaloa River, located in the municipality of Guasave, Sinaloa. The perpendicular distance sampling method was applied using line transects, with a total survey effort of 58.5 km conducted between March and November 2024. Data were analyzed using Distance software, and species-specific detection models were constructed. Parametric (Welch ANOVA and Tukey HSD) and non-parametric (Kruskal-Wallis and Mann-Whitney U with Bonferroni correction) statistical analyses were performed to assess differences in density among species and across seasons of the year. Results indicated that White-winged dove was the most abundant and widely distributed species, with a mean density of 744.03 individuals/km2, significantly higher than that of the other species. Seasonal variation was observed in White-winged dove, with the highest density during the breeding season in spring and the lowest in autumn, reflecting changes in resource availability and local movements rather than long-term population trends. The remaining species exhibited lower densities and more restricted distributions, with Rock pigeon showing localized presence along the waterfront promenade in the urban area of Guasave, and Red-billed pigeon being sparsely represented throughout the riparian corridor. These findings underscore the ecological importance of riparian corridors as key habitats for generalist species such as White-winged dove, and highlight the need for long-term monitoring of less abundant dove populations. The information generated is relevant for the design of conservation and management strategies for avifauna in agricultural and urban landscapes of northwestern Mexico.
Microfilariae are blood parasites transmitted by hematophagous vectors, yet short-term, within-morning dynamics of the infection in wild passerines are poorly understood. This study aimed to (i) assess within-morning fluctuations in microfilariae prevalence and intensity in breeding adult village weavers (Ploceus cucullatus), and (ii) evaluate the influence of infection on host body condition (reflected in their body mass). A total of 124 birds (72 males, 52 females) were trapped in the Amurum Forest Reserve, Nigeria, using mist nets during early, mid-, and late-morning intervals. Microfilariae were detected via the buffy coat method, and body condition was estimated from body mass. Overall, 94.4% of males and 30.8% of females were infected. Contrary to our hypothesis that early-morning captures would predominantly sample filaria-free birds, prevalence and intensity peaked in mid-morning, especially in males (P < 0.05). Infected males were consistently in better condition than uninfected males, indicating trade-offs favoring reproductive investment over immune defense, whereas infected females exhibited a mid-morning reduction in body mass, likely reflecting the energetic costs of infection. These results reveal pronounced sex-biased infection patterns and highlight temporal variation in host activity and condition, with implications for sampling and understanding host-parasite interactions in wild passerines.
This study investigated the foraging behaviour and diet composition of grey francolin (Ortygornis pondicerianus) in different seasons (breeding and non-breeding) and habitats (agricultural land, tree-covered land, shrubland, and barren land). Focal sampling and faecal analysis methods were employed to examine the foraging behaviour and diet composition of the grey francolin, respectively. Foraging techniques showed non-significant (p=0.829) variation across different habitat types; however, walk-halt-peck (WHP) was the most commonly utilized foraging technique across all habitats. Additionally, foraging success varied significantly across seasons (p<0.05) and habitats (p<0.05). We recorded significantly higher feeding rates in the shrubland during the breeding season. The percentage of successful attempts was significantly higher (p<0.05) in the breeding season compared to the non-breeding season. Furthermore, faecal analysis results showed a significant (p<0.05) difference in composition between plant and animal matter, especially during the breeding season. However, the grit content showed non-significant variation (p>0.05) across seasons.
Most cavity-nesting birds are considered limited by the availability of nesting sites, either in terms of obtaining suitable cavities for nesting or the time or energy to excavate new cavities. We investigated the rate of nest cavity reuse in a cold, multispecies forest for cavity-nesting birds in southwestern Iran. We measured 80 Syrian Woodpecker (Dendrocopos syriacus) nest trees for 9 years and their cavity reuse by 6 cavity-nesting bird and mammal species. Analysis examined the relationship between nest cavity reuse and the characteristics of the cavities and nest trees. In all cases, cavities that were abandoned after a year of re-occupancy remained unoccupied for the subsequent years thereafter. Once a species had adopted a cavity then it was used by the same species thereafter, with only seven (2.5% of 282) exceptions - in one nest, the occupying species changes in three successive years. Over the entire study period, for all the cavities and occupancies, the average number of years a cavity was reused was highest for the Eastern rock nuthatches and lowest for the Syrian woodpecker, but this was unaffected by species. The Mount Atlas Mastic was used by Syrian woodpeckers most frequently followed by Narrow-laved Ash trees and then Wild Pear trees (n = 54, 22, and 4, respectively). Almost all of the physical characteristics of the tree or cavity did not correlate with the proportion of nest re-occupied, except for circumference at breast height and diameter at breast height, which exhibited significant positive relationships. Vertical depth of the nest cavity was significantly affected by species reusing the cavity, largely because the Eastern rock nuthatches (Sitta tephronota) reused swallower nest cavities. As agriculture increases, logging and the removal of older trees decrease the availability of suitable nesting cavities for birds.
Incubation is a fundamental component of avian reproductive biology. One element of avian incubation, egg turning, is nearly universal among avian taxa and is vital for optimal embryonic development, hatch success, and chick quality. Despite its importance, egg turning behaviors are poorly understood. Egg turn parameters, such as rate and angle, are subject to wide variation among and within taxa and may vary over the incubation period. In this study, we used data loggers in artificial eggs to measure the rate and angle of egg turns from wild Scarlet Macaw (Ara macao macao) hens nesting within artificial cavities in southeast Peru. Our results from four of these hens indicate that egg turn rates averaged 11.5 turns h-1, turn angles averaged 42.2 degrees turn-1, and these parameters varied significantly among hens. Egg turn rates were dynamic over the incubation period, peaking during the middle third of incubation, whereas egg turn angles increased linearly over the incubation period. Comparison with the literature suggests that the highly altricial Scarlet Macaws turned their eggs at a higher rate than the more precocial taxa studied with similar methods. Our study is the first to characterize the egg turn parameters of any wild parrot using data loggers and may prove useful for discerning larger taxonomic patterns in incubation. We found wild Scarlet Macaw egg turn rates to be much higher than published recommendations for the artificial incubation of parrot eggs, suggesting this work could be used to inform captive breeding and other conservation techniques.
Urbanization modifies bird and plant communities, affecting ecological processes such as fruit consumption and the structure of interaction networks. Our study evaluated how the abundances of synanthropic and non-synanthropic birds, along with native and non-native plants, influence fruit consumption and bird-plant feeding networks in 12 urban green areas in M & eacute;rida, Yucat & aacute;n, Mexico. Over a year, we recorded bird-plant interactions, measured species abundances, and analyzed feeding networks using metrics of specialization, nestedness, and evenness. We found that, in M & eacute;rida, urban green areas are dominated by synanthropic birds and non-native plants, promoting feeding networks that are more resilient but less specialized. We found that non-native fruit consumption was significantly associated with the abundances of synanthropic birds and non- native plants, while native fruit consumption depended primarily on the abundance of native plants and showed no significant relationships with birds. Feeding networks in areas with higher synanthropic bird abundance were less specialized, more nested, and more even, indicating a homogenization of interactions in urbanized sites. In contrast, non-synanthropic birds and native plants abundances showed weak or non-significant relationships with network structure. While synanthropic birds play an important role in feeding networks in urban environments and may stabilize certain interactions, it poses risks to the conservation of native biodiversity and ecological processes. Therefore, it is essential to implement management strategies that prioritize native species to maintain the ecological functionality of urban green areas.
Global bird populations are declining due to habitat loss, climate change, and hunting, among other factors, potentially leading to species extinction and loss of ecosystem services. Also, protected areas are increasingly threatened by human activities, thus affecting their effectiveness as cornerstones for biodiversity conservation. Their effectiveness is further exacerbated by logistical and other resource constraints, which call for prioritising conservation areas to ensure the efficient use of limited resources in developing nations like Ghana. Thus, this study was conducted to identify and prioritise conservation areas based on vulnerability by analysing bird inventory data of national parks in Ghana. Our findings revealed that some smaller protected areas hosted a higher diversity of species, including imperilled species, despite the positive correlation between national park size (i.e., area) and species richness and vulnerability indices. In addition, we found that Mole National Park, located in the savanna, was the most vulnerable protected area because it hosted the highest proportion of imperilled bird species in the country. Although vulnerability indices did not differ statistically between parks in the savanna and forest ecozones, they did differ based on their assemblages, highlighting their potential in differentially hosting varied species with different habitat requirements (and probably varying species and habitat vulnerabilities). We advocate that vulnerability indices can be cautiously applied to prioritise conservation efforts or areas while considering other site-specific factors influencing biodiversity.
Breeding endangered species in captivity for reintroduction into their natural environment does not always yield the desired results. Despite significant financial and human resource input, adult birds and their offspring often die of disease. This research compared the breeding success of capercaillies kept in breeding centre in relatively natural conditions and under strictly controlled, highly sanitary conditions between 1993 and 2020. The results showed that breeding under controlled conditions was more successful, with the females laying, on average, more eggs (+3.4 eggs), hatching more chicks (+20.5%) and raising more offspring (+3.1 individuals). Furthermore, hatching success was higher (+13.18%) under capercaillie females than under foster parents (domestic hens). The percentage of chicks lost was higher (+14.8%) when incubated by domestic hens and reared without the involvement of capercaillie females. Controlled maintenance conditions thus led to significantly better breeding results (number of reared birds intended for release or sale to other facilities) and ensured the profitability of the breeding center.
Studies on the impact of microfilariae does not only contribute to ecological conservation but bird-human-environmental interaction. As such, breeding and survival in the face of infections are among the ultimate goals of all species; however, this may also incur a cost of physiological or oxidative stress response when infected breeding birds must invest additional nutrients to suppress the activities of infections during breeding. We aimed to investigate how adult male breeding and non-breeding village weavers ( Ploceus cucullatus ) body condition, corticosterone (CORT) and superoxide dismutase (SOD) varied with microfilariae-infections during breeding period. Body condition was measured as body mass corrected for the size of adult male breeding and non-breeding birds during their breeding period. About 106 adult male village weavers were trapped at breeding, and our results suggests more 56% (33 out of 59) breeding birds were found to be infected, while 44% (26 out of 59) were not infected. In a general linear model (GLM), body mass correlated ( P < 0.05) to microfilariae infection status and the interaction between infection and body size. Whereas, SOD only correlated to the infections status, and CORT concentration correlated with the breeding status of the birds during the breeding season. Based on the direction of relationship, CORT concentration was significantly higher in the breeding adult male birds during breeding, while microfilariae caused a reduction in body mass and a rise in SOD activity of the infected birds. Suggesting a poor body condition in the infected birds, and a stress-mediated antioxidant defense response that may have a long-term future implication in the breeding village weavers.
Bird feathers serve many purposes, ranging from flight and thermoregulation to camouflage and communication. Considerable attention has been paid to the insulative and heat-dissipation functions of feathers, which can depend on many factors, including the local environment and feather pigmentation. However, more studies are needed to understand the heating and cooling properties of different feathers, including in situations where certain color ornaments (e.g. melanin, carotenoid) are favored for signaling and where hot environments (e.g. urban heat-islands) may exert particularly strong and novel thermal selection pressures. We investigated heating and cooling responses of different contour feathers in male house finches ( Haemorhous mexicanus ) – an urban-adapted passerine bird species where males exhibit sexually selected carotenoid-pigmented plumage – in a controlled laboratory setting (i.e. standard illuminant exposure from a close distance). We used samples of carotenoid- and melanin-colored contour feathers from males captured from urban and non-urban habitats to understand the impacts of urbanization and feather pigment type on plumage thermal properties. We experimentally heated feathers for 1 min and tracked surface temperatures over this time as well as during a 1 min. cooling phase immediately after removal of the heat source. We found that, at the end of the heating phase and beginning of the cooling phase, urban feathers were cooler than non-urban feathers, and that, in non-urban areas, carotenoid-containing feathers had higher temperatures than melanized feathers. We discuss the possible morphological adaptations and implications of these thermal differences, specifically in this desert- and urban-adapted species in which males have carotenoid-based plumage color signals.
Psittacides are birds characterized by a curved beak, zygodactyl feet and colorful feathers, with species varying in size and without apparent sexual dimorphism. They are among the birds most threatened with extinction, with around 31% of species in the Neotropical region in this condition. Reproduction of these birds in captivity is crucial for the maintenance and recovery of populations, with sex identification being essential in this process. Given the difficulty of differentiating between males and females, it is proposed to use external morphometry to determine sex in a population of parrots, correlating it with the measurement of five parameters: length of the culmen, tomium, depth of the beak, length of the head and cloaca opening. Sex was determined by DNA testing, where females presented two copies of genes amplified by PCR (one from each chromosome, W and Z) and males presented only one copy (Z chromosome). 40 parrot specimens of different species were used: 7 Amazona amazonica , 8 Amazona aestiva , 9 Ara chloropterus , 5 Anodorhynchus hyacinthinus , 11 Ara ararauna . Of the total, 55% (22/40) were males and 45% (18/40) were females. Among the parameters evaluated, there were no significant variances between the sexes of the species studied, with the exception of one variable vent opening of one species Ara ararauna . Additionally, the lack of information about the age range of the animals meant that some individuals showed similarities, as in the case of A. amazonica , possibly linked to the stage of development. Thus, in addition to verifying that not all species can be subjected to the morphometric technique, the development phase also interferes with its use. It is concluded that among the species studied, only Ara ararauna is possible to determine the sex by measuring the cloaca opening, which showed significant differences, with no divergence from other biometric parameters.
