BACKGROUND: Most vocal learning species exhibit an early critical period during which their vocal control neural circuitry facilitates the acquisition of new vocalizations. Some taxa, most notably humans and parrots, retain some degree of neurobehavioral plasticity throughout adulthood, but both the extent of this plasticity and the neurogenetic mechanisms underlying it remain unclear. Differential expression of the transcription factor FoxP2 in both songbird and parrot vocal control nuclei has been identified previously as a key pattern facilitating vocal learning. We hypothesize that the resilience of vocal learning to cognitive decline in open-ended learners will be reflected in an absence of age-related changes in neural FoxP2 expression. We tested this hypothesis in the budgerigar (Melopsittacus undulatus), a small gregarious parrot in which adults converge on shared call types in response to shifts in group membership. We formed novel flocks of 4 previously unfamiliar males belonging to the same age class, either \"young adult\" (6 mo - 1 year) or \"older adult\" (≥ 3 year), and then collected audio-recordings over a 20-day learning period to assess vocal learning ability. Following behavioral recording, immunohistochemistry was performed on collected neural tissue to measure FoxP2 protein expression in a parrot vocal learning center, the magnocellular nucleus of the medial striatum (MMSt), and its adjacent striatum.
RESULTS: Although older adults show lower vocal diversity (i.e. repertoire size) and higher absolute levels of FoxP2 in the MMSt than young adults, we find similarly persistent downregulation of FoxP2 and equivalent vocal plasticity and vocal convergence in the two age cohorts. No relationship between individual variation in vocal learning measures and FoxP2 expression was detected.
CONCLUSIONS: We find neural evidence to support persistent vocal learning in the budgerigar, suggesting resilience to aging in the open-ended learning program of this species. The lack of a significant relationship between FoxP2 expression and individual variability in vocal learning performance suggests that other neurogenetic mechanisms could also regulate this complex behavior.

Regulation of neuroimmune interactions varies across avian species. Little is presently known about the interplay between periphery and central nervous system (CNS) in parrots, birds sensitive to neuroinflammation. Here we investigated the systemic and CNS responses to dextran sulphate sodium (DSS)- and lipopolysaccharide (LPS)-induced subclinical acute peripheral inflammation in budgerigar (Melopsittacus undulatus). Three experimental treatment groups differing in DSS and LPS stimulation were compared to controls. Individuals treated with DSS showed significant histological intestinal damage. Through quantitative proteomics we described changes in plasma (PL) and cerebrospinal fluid (CSF) composition. In total, we identified 180 proteins in PL and 978 proteins in CSF, with moderate co-structure between the proteomes. Between treatments we detected differences in immune, coagulation and metabolic pathways. Proteomic variation was associated with the levels of pro-inflammatory cytokine mRNA expression in intestine and brain. Our findings shed light on systemic impacts of peripheral low-grade inflammation in birds.

Psittacine beak and feather disease virus (PBFDV) and budgerigar fledgling disease virus (BFDV) are significant avian pathogens that threaten both captive and wild birds, particularly parrots, which are common hosts. This study involved sampling and testing of 516 captive birds from households, pet shops, and an animal clinic in Hong Kong for PBFDV and BFDV. The results showed that PBFDV and BFDV were present in 7.17% and 0.58% of the samples, respectively. These rates were lower than those reported in most parts of Asia. Notably, the infection rates of PBFDV in pet shops were significantly higher compared to other sources, while no BFDV-positive samples were found in pet shops. Most of the positive samples came from parrots, but PBFDV was also detected in two non-parrot species, including Swinhoe\'s white-eyes (Zosterops simplex), which had not been reported previously. The ability of PBFDV to infect both psittacine and passerine birds is concerning, especially in densely populated urban areas such as Hong Kong, where captive flocks come into close contact with wildlife. Phylogenetic analysis of the Cap and Rep genes of PBFDV revealed that the strains found in Hong Kong were closely related to those in Europe and other parts of Asia, including mainland China, Thailand, Taiwan, and Saudi Arabia. These findings indicate the presence of both viruses among captive birds in Hong Kong. We recommend implementing regular surveillance for both viruses and adopting measures to prevent contact between captive and wild birds, thereby reducing the transmission of introduced diseases to native species.

Avian gastric yeast (Macrorhabdus ornithogaster) is a microorganism that infects aviary birds worldwide, both captive and wild. A total number of 352 birds, belonging to 18 avian species, were examined from 2019 to 2022 for M. ornithogaster, using fecal smears of live birds or cytological samples of the proventriculus taken at necropsy. These cytological samples were taken from birds that died from different causes. Some of the birds exhibited symptoms such as lethargy, regurgitation, weight loss and anorexia. Faecal samples were collected from all the birds and analysed for gastric yeast using a direct smear and Gram-staining method. The microorganism was diagnosed most frequently in budgerigars (55.5%), the African gray parrot (33.3%), and nymphs (34.3%). The prevalence of M. ornithogaster in canaries was 10%. The infection was detected in 31% of the examined birds, which shows that the occurrence of M. ornithogaster in exotic birds is common. No clinical signs were observed in the vast majority of birds that tested positive for gastric yeast.

This randomized, crossover study evaluated three sedation protocols administered subcutaneously in nine budgerigars (Melopsittacus undulatus) and nine black-cheeked lovebirds (Agapornis nigrigenis). All protocols included midazolam (5 mg/kg), combined with butorphanol (5 mg/kg) (BM), medetomidine (20 lg/kg) (MM), or alfaxalone (13 mg/kg) (AM). Mortalities from suspected cardiorespiratory arrest were observed when AM was used in lovebirds, even after reduction of alfaxalone dosage to 3 mg/kg, and therefore this protocol was excluded from further use in this species. Induction and recovery times were recorded and their quality assessed. Sedation depth and heart and respiratory rates were measured every 5 min and radiographic positioning was attempted at 10 and 20 min. At 30 min, midazolam and medetomidine were reversed with flumazenil (0.05 mg/kg, SC), and atipamezole (0.2 mg/kg, SC), respectively. MM consistently provided deep sedation in both species, with successful radiographic positioning at every attempt. As expected, heart rate was often lower with MM than with other protocols, but no associated complications were noted. In budgerigars, BM had the lowest radiographic positioning success rate (10 min: 5/9, 20 min: 3/9), whereas in lovebirds it provided significantly deeper sedation (P < 0.001), allowing radiographic positioning in all subjects. In both species, BM provided the shortest recovery times. AM resulted in reliable radiographic positioning of all budgerigars at 10 min, but not at 20 min (5/ 9), and provided consistently poor recoveries. This study highlights how differently two psittacine species of similar size may react to the same sedation protocols. AM sedation cannot be fully reversed and produced significant undesirable effects, several of which have been previously reported with alfaxalone administration to avian species. The authors therefore caution against using alfaxalone-midazolam combinations in budgerigars and black-cheeked lovebirds. Both BM and MM provided reliable sedation in these species, and appear to be suitable alternatives to AM.

Predation risk may affect the foraging behavior of birds. However, there has been little research on the ability of domestic birds to perceive predation risk and thus adjust their feeding behavior. In this study, we tested whether domestic budgerigars (Melopsittacus undulatus) perceived predation risk after the presentation of specimens and sounds of sparrowhawks (Accipiter nisus), domestic cats (Felis catus), and humans, and whether this in turn influenced their feeding behavior. When exposed to visual or acoustic stimuli, budgerigars showed significantly longer latency to feed under sparrowhawk, domestic cat, and human treatments than with controls. Budgerigars responded more strongly to acoustic stimuli than visual stimuli, and they showed the longest latency to feed and the least number of feeding times in response to sparrowhawk calls. Moreover, budgerigars showed shorter latency to feed and greater numbers of feeding times in response to human voices than to sparrowhawk or domestic cat calls. Our results suggest that domestic budgerigars may identify predation risk through visual or acoustic signals and adjust their feeding behavior accordingly.

The purpose of this study was to assess the pelvimetric values obtained from radiographic pelvis images of budgerigars in terms of sexual dimorphism. The objectives included determining linear osteometric and angle measurements of the pelvis, as well as calculating the length-to-width ratios among different pelvimetric measurements. Additionally, the study aimed to reveal the correlations between age and body weight with both the pelvimetric measurements and ratio measurements in these animals.
In this study, measurements of linear distance, angle and length-to-width ratios were obtained from ventrodorsal images of the pelvis in a sample of 60 budgerigars, consisting of 30 males and 30 females. Subsequently, the statistical analysis of the obtained measurement values was performed.
When analysing the morphometric measurement values based on sex, it was observed that all linear measurements (L1, L2, L3, L4, L5, L6, L7, L8, L9, L10 and L11) were higher in males, whereas the angle measurements (A1, LA2 and RA2) were found to be significantly greater in females (p < 0.05). Additionally, both male and female budgerigars exhibited a greater pre-acetabular length of the ilium compared to the post-acetabular length. Moreover, there were mostly positive significant correlations between age and body weight with the pelvic measurement values in both sexes (p < 0.05).
The obtained biometric measurement values from pelvimetric X-ray images in budgerigars were analysed to assess sexual dimorphism. Furthermore, this study presents fundamental morphometric data that can be valuable for clinical, taxonomic, phylogenetic, ornithological, allometric and characterization studies of budgerigars.

Cochlear synaptopathy is a common pathology in humans associated with aging and potentially sound overexposure. Synaptopathy is widely expected to cause \"hidden hearing loss,\" including difficulty perceiving speech in noise, but support for this hypothesis is controversial. Here in budgerigars (Melopsittacus undulatus), we evaluated the impact of long-term cochlear synaptopathy on behavioral discrimination of Gaussian noise (GN) and low-noise noise (LNN) signals processed to have a flatter envelope. Stimuli had center frequencies of 1-3kHz, 100-Hz bandwidth, and were presented at sensation levels (SLs) from 10 to 30dB. We reasoned that narrowband, low-SL stimuli of this type should minimize spread of excitation across auditory-nerve fibers, and hence might reveal synaptopathy-related defects if they exist. Cochlear synaptopathy was induced without hair-cell injury using kainic acid (KA). Behavioral threshold tracking experiments characterized the minimum stimulus duration above which animals could reliably discriminate between LNN and GN. Budgerigar thresholds for LNN-GN discrimination ranged from 40 to 60ms at 30dB SL, were similar across frequencies, and increased for lower SLs. Notably, animals with long-term 39-77% estimated synaptopathy performed similarly to controls, requiring on average a ∼7.5% shorter stimulus duration (-0.7±1.0dB; mean difference ±SE) for LNN-GN discrimination. Decision-variable correlation analyses of detailed behavioral response patterns showed that individual animals relied on envelope cues to discriminate LNN and GN, with lesser roles of FM and energy cues; no difference was found between KA-exposed and control groups. These results suggest that long-term cochlear synaptopathy does not impair discrimination of low-level signals with different envelope statistics.

OBJECTIVE: Loss of auditory nerve afferent synapses with cochlear hair cells, called cochlear synaptopathy, is a common pathology in humans caused by aging and noise overexposure. The perceptual consequences of synaptopathy in isolation from other cochlear pathologies are still unclear. Animal models provide an effective approach to resolve uncertainty regarding the physiological and perceptual consequences of auditory nerve loss, because neural lesions can be induced and readily quantified. The budgerigar, a parakeet species, has recently emerged as an animal model for synaptopathy studies based on its capacity for vocal learning and ability to behaviorally discriminate simple and complex sounds with acuity similar to humans. Kainic acid infusions in the budgerigar produce a profound reduction of compound auditory nerve responses, including wave I of the auditory brainstem response, without impacting physiological hair cell measures. These results suggest selective auditory nerve damage. However, histological correlates of neural injury from kainic acid are still lacking.
METHODS: We quantified the histological effects caused by intracochlear infusion of kainic acid (1 mM; 2.5 µL), and evaluated correlations between the histological and physiological assessments of auditory nerve status.
RESULTS: Kainic acid infusion in budgerigars produced pronounced loss of neural auditory nerve soma (60% on average) in the cochlear ganglion, and of peripheral axons, at time points 2 or more months following injury. The hair cell epithelium was unaffected by kainic acid. Neural loss was significantly correlated with reduction of compound auditory nerve responses and auditory brainstem response wave I.
CONCLUSIONS: Compound auditory nerve responses and wave I provide a useful index of cochlear synaptopathy in this animal model.

Dialectic signatures in animal acoustic signals are key in the identification of and association with group members. Complex vocal sequences may also convey information about behavioral state, and may thus vary according to social environment. Some bird species, such as psittaciforms, learn and modify their complex acoustic signals throughout their lives. However, the structure and function of vocal sequences in open-ended vocal learners remains understudied. Here, we examined vocal sequence variation in the warble song of budgerigars, and how these change upon contact between social groups. Budgerigars are open-ended vocal learners which exhibit fission-fusion flock dynamics in the wild. We found that two captive colonies of budgerigars exhibited colony-specific differences in the syntactic structure of their vocal sequences. Individuals from the two colonies differed in the propensity to repeat certain note types, forming repetitive motifs which served as higher-order signatures of colony identity. When the two groups were brought into contact, their vocal sequences converged, and these colony-specific repetitive patterns disappeared, with males from both erstwhile colonies now producing similar sequences with similar syntactic structure. We present data suggesting that the higher-order temporal arrangement of notes/vocal units is modified throughout life by social learning as groups of birds continually associate and dissociate. Our study sheds light on the importance of examining signal structure at multiple levels of organization, and the potential for psittaciform birds as model systems to examine the influence of learning and social environment on acoustic signals.