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.

Sexual size dimorphism (SSD) commonly occurs in birds, with males typically larger than the females. One notable exception is the family Alcedinidae, which displays moderate reverse SSD. Using body mass data collected from birds hatched at Brookfield Zoo Chicago between 1989-2023, we confirm that the sihek (Guam kingfisher, Todiramphus cinnamominus ) exhibits moderate reverse SSD. Female chicks are significantly larger than males at fledging (t = 4.23, df = 23.33, p = 0.003). Adult birds 50 days and older display significantly different body masses, with females weighing on average 7% more than males (t = 3.20, df = 49.91, p = 0.00238). We assessed the growth patterns of male and female sihek chicks using logistic nonlinear mixed models and found that the null model was a better fit (lower AIC); therefore, there was no significant difference between the growth parameters for each sex from hatch through forty days. These results contribute to the body of work investigating the evolution of SSD in birds and provides data on the growth and development of an extinct-in-the-wild species.

A publicly available online webcam hosted by Reid Park Zoo (Tucson, AZ, USA) was utilized to study the ‘visitor effect’ in Chilean flamingos ( Phoenicopterus chilensis) to eliminate any potential influence that the presence of a researcher may have had on the behavior of the birds. Flamingos were found to be closer to one another in the webcam image on days when more humans were observed in the vicinity of the exhibit, successfully evidencing a ‘visitor effect.’ Higher temperatures, lower barometric pressures, and lower wind speeds were all found to be associated with increased flamingo activity. Higher temperatures and UV index, and lower humidity and wind speed were all associated with increased numbers of visitors seen near the flamingo exhibit.

In birds, sexual size dimorphism often becomes evident as early as chicks’ growth stage. A larger sex usually has an advantage in food competition among siblings. In the smaller sex, the lesser ultimate size can be compensated by faster growth or earlier fledging. As a consequence, sex differences can manifest themselves not only in body size but also in the body condition or the rate of weight gain. This phenomenon provides additional opportunities for sexing of chicks by discriminant analysis of growth parameters. Our work deals with the influence of sex on the growth of Black-headed Gull chicks. Using logistic models, we examined growth patterns of 80 males and 76 females from hatching to departure from breeding colonies during three seasons. In males, the total head length, tarsus length, and body mass were greater than those in females from the first days of life and reached large asymptotic values. Tarsus length was a better predictor of sex than head length or body mass was. The sex of chicks did not have a significant effect on global growth rates; however, compared to males, females had a lower body condition (the difference between observed and expected chick body mass) at age 8 days and gained less weight between 21 and 28 days. Using these differences, we developed a discriminant function that allowed to correctly predict the sex of 88.5% of Black-headed Gull chicks before fledging.

Resource mobilization and reallocation is a major endpoint of the physiological response to acute challenges. However, energy metabolites have not been the focus of most field studies. Here, we characterized the glycemic and free fatty acid (FFA) response to an acute-handling challenge in a breeding, free-living, population of Mountain Dark-eyed Juncos ( Junco hyemalis oreganus) in Mono County, CA. Juncos ( n = 12) were trapped in seed-baited potter traps at Tioga Pass Meadow, coinciding with territory establishment and early nesting period. Blood samples were collected at 0, 15, and 30 min post-capture, and analysis showed Juncos mobilized both glucose and FFA in response to an acute handling challenge. Blood glucose levels were significantly higher than baseline at 15 min (42.6% increase) and 30 min post-capture (66.7% increase). FFA levels were also significantly higher than baseline at 15 min (29.2% increase) and 30 min post-capture (22% increase). We also measured morphometrics (e.g., wing chord length, tarsus length, etc.), fat, and mass for each individual to investigate the effects of body size and fat storage on energy mobilization using linear models. We found no significant effects of body size or fat and mass on FFA mobilization. However, body size had a significant effect on glucose mobilization, with larger individuals displaying a higher percent increase in glucose from baseline to 15 min. Additionally, we found an effect of sex on glucose mobilization, with males showing a higher percent increase in glucose from baseline to 15 min. These results suggest that energy mobilization capacity is influenced by body size and male Juncos may increase energy mobilization relative to females during the breeding season.

Gene flow, the movement of genes between populations, profoundly influences genetic and phenotypic homogeneity among populations. This study investigates gene flow patterns in two migratory hummingbird species, Selasphorus platycercus and Calothorax lucifer, shedding light on the intricate interplay between migration, resource availability, and genetic diversity. Using previously published information on microsatellites, we examine the genetic makeup and the movement of genes within populations. Selasphorus platycercus displays distinct genetic groups which can be associated with its migratory behaviour. Gene flow analysis suggests a higher level of connectivity among populations sharing winter ranges. In contrast, Calothorax lucifer populations exhibit genetic divergence despite overlapping winter ranges, possibly due to environmental niche adaptation and limited reproductive opportunities for dispersing individuals. While geographical distance does not explain genetic differentiation in these species, environmental niche similarities appear to facilitate gene flow. This study underscores the significance of migratory routes, resource availability, and niche adaptation in shaping gene flow dynamics in hummingbirds. Understanding these dynamics is crucial for the conservation and management of these unique avian populations.

Admission records from wildlife rescue centres can help identify causes of morbidity for species of conservation concern, and to assess the effectiveness of rehabilitation. This study documents the causes of admission and outcomes of treatment in 68 white-tailed eagles admitted to rescue centres in the Czech Republic. We determine the factors that contribute to the outcome of rehabilitation. Most admitted birds were juveniles (1 st calendar year [CY]; n = 25), followed by immatures (2 nd –4 th CY; n = 23) and adults (≥5 CY; n = 17). We categorised admission causes into (1) trauma-related cases (most often unknown trauma, followed by collision and intraspecific fights), (2) non-trauma cases (weakness, toxicosis and becoming stuck in mud or entangled in rope) and (3) orphaned young birds. Trauma-related admissions were most numerous totalling 59%, non-trauma admissions accounted for 35% with the remaining 6% comprising orphaned young birds. At least a third of eagle admissions were caused by anthropogenic factors. In total, 40% of admitted eagles were released back to the wild, 35% died or were euthanized and 25% remained permanently in captivity. Eagles admitted due to non-trauma-related causes had a significantly higher probability of being released into the wild than those admitted due to trauma. Immature eagles were less likely to be released than juvenile individuals. Admissions data are valuable for conservation research, allowing for trends in threats towards species of conservation concern to be quantified, over time, throughout human-dominated landscapes.

Few studies on bird migration address altitudinal migration in South America, a regional-scale movement currently known for only nine species within the threatened Atlantic Forest biome. The Yellow-legged Thrush Turdus flavipes (YLTH) is one of such migrants thus far studied within a narrow altitudinal gradient and for which only fruits are pointed as the likely triggers of its seasonal movements. Here, we expand this knowledge by testing the hypotheses that arthropod and fleshy fruit availabilities, and climatic variables may all play roles in the seasonal abundance of this species along a broader altitudinal gradient (10-1,100 m asl) in the Atlantic Forest. We estimated YLTH density and its food resource availability in sites at three different altitudes. Besides supporting previous findings on the YLTH migratory behaviour, our findings reveal a novel and complex seasonal density variation of the species across altitudes, consistent with a partial altitudinal migration from higher altitudes. Aside from fruit availability, rainfall also partially influenced such behaviour, a new perspective for this species. Besides providing a broader picture for the altitudinal migration of YLTHs, we conclude by stressing the need for further studies on the understudied altitudinal migration system of birds within South America, including the assessment of the general validity of current hypotheses on the mechanisms underlying this interesting behaviour and its evolution.

Egg recognition and rejection is a common and effective anti-parasitism adaptation in bird hosts. Hosts reject alien eggs using recognition signals such as egg ground color and maculation. Green-backed tits ( Parus monticolus) have a highly developed capability for recognizing parasite eggs, but the cues used for egg recognition are unclear. We combined avian visual perceptual modeling and field experiments to explore the effects of egg ground color and maculation on the recognition of parasite eggs. P. monticolus uses a multi-cue with possible hierarchical mechanism for egg recognition. The mechanism of egg recognition in P. monticolus appears to be a specific adaptation to the phenotypes of eggs laid by local brood parasites.

Owl diets undergo qualitative changes across the different regions of their area of distribution. During the four winters (from 2014–15 to 2017–18), Long-eared Owls’ pellets were collected at three winterroosts located at the southern part of Pannonian Plain, in the Serbian province of Vojvodina. In 8070 prey items from pellets, we identified 16 mammal and 32 bird species. The Common Vole was the dominant prey species with a proportion in a range from 27.4% to 71.6%. The Muridae family formed a supplementary part of the diet: Mus sp., wood mouse and harvest mouse, during all winters. Birds were also a major supplementary prey during winter 2014–15, comprising 10.6%. A comparison of our results with the diet of Long-eared Owls wintering at the northern Pannonian plain (southwestern Slovakia) indicated an increase the proportion of some species in the southern part. How different land uses in agriculture and environmental conditions may be reflected in the food supply are discussed in relation to the diet composition of Long-eared Owls and an environment whose is richer provides both growing diversity in the diet of these owls and an expansion of their food niche. Our study described the Long-eared Owl as opportunistic predators expanding their food niche in the presence of diversified prey.