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Foraging skills influence food intake and could therefore also play a role in mate choice decision. Previous empirical work has shown that individuals benefit from being in groups that include individuals with a variety of foraging skills as this increases foraging success. This idea, formalized in the skill-pool hypothesis, may extend to mate choice. Diverse foraging skills can expand the foraging niche of a pair and benefit offspring through enhanced parental provisioning, and exposure to a broader foraging skillset. To test this idea, we trained captive female and male budgerigars to solve one of two different novel foraging puzzle boxes. Then, females simultaneously observed two males that could solve either the same or the other box, and assessed female preferences in a binary mate choice apparatus. Females preferred males with foraging skills that differed from their own, independent of the skill type and the number of times males solved the foraging puzzle. These findings show that foraging skills can influence social preferences, including in a mate choice context, and support intraspecific diversity in foraging skills., Competing Interests: Declarations. Ethical approval: The study was approved by the Animal Care and Use Committee of the Institute of Zoology, Chinese Academy of Sciences (CAS). All experimental procedures complied with applicable governmental regulations concerning the ethical use of animals and biodiversity rights. Competing interests: The authors declare no competing interests., (© 2024. The Author(s).)

The ability to understand relational concepts, such as 'same' and 'different', is a critical feature of human cognition. To what extent non-human animals can acquire such concepts and which factors influence their learning are still unclear. We examined the acquisition and the breadth of understanding the 'same-different' concept in budgerigars ( Melopsittacus undulatus ). Budgerigars trained to discriminate stimulus pairs in which two identical figures were either the same or different size (Experiment 1) successfully generalized the discrimination to novel stimuli belonging to various categories (size, colour, shape, geometric type and number of dots). The results of Experiment 1 thus demonstrate that budgerigars can perceive and generalize the same-different concept across dimensions after training with a limited set of stimuli differing along a single dimension. In contrast, while most budgerigars trained to discriminate two pairs of discs that were either the same or different in colour (Experiment 2) could generalize the discrimination to novel stimuli within the training category (colour), only few generalized the discrimination to another category suggesting a generalization based on perceptual similarity. The results thus show that whether budgerigars generalize a relationship by conceptual or perceptual similarity depends on the nature of the training stimuli.

Complex behavioral sequences such as courtship displays are often multimodal, and coordination between modalities is critically important. In learned and variable behavioural sequences such as songs, individual variability may also extend to multimodal coordination and the associations between modalities. However, individual variability in complex multimodal sequences and in coordination between distinct behaviours remains underexplored. Here, we report that budgerigars, which continuously learn and modify their complex warble songs, exhibit associations between body movements and song notes during courtship. Some associations are unique to individuals, and others are universal across individuals. Additionally, some individuals exhibit more unique associations than others. We also find that birds warbling in the absence of body movements emit all notes with broadly similar odds ratios. Our data suggest a hierarchy of associations, some individual-specific and others common to all individuals, between body movements and songs. We propose that these associations may be learnt and modified through social interactions, resulting in individual variability., Competing Interests: Competing interests The authors declare no competing or financial interests., (© 2024. Published by The Company of Biologists Ltd.)

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., (© 2024. The Author(s).)

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., (© 2024. The Author(s).)

Recent psychophysical experiments have shown that zebra finches (Taeniopygia guttata-a songbird) are surprisingly insensitive to syllable sequence changes in their species-specific motifs while budgerigars (Melopsittacus undulatus-a psittacine) do much better when tested on exactly the same sounds. This is unexpected since zebra finch males learn the order of syllables in their songs when young and sing the same song throughout adulthood. Here we probe the limits of this species difference by testing birds on an order change involving just two syllables, hereafter called bi-syllable phrases. Results show budgerigars still perform better than zebra finches on an order change involving just two syllables. An analysis of response latencies shows that both species respond to an order change in a bi-syllable motif at the onset of the first syllable rather than listening to the entire sequence before responding. Additional tests with one syllable omitted or doubled, or with white noise bursts substituted for syllables, indicate that the first syllable in the sequence has a dominant effect on subsequent discrimination of changes in a bi-syllable pattern. These results are surprising in that zebra finch males sing their full motif syllable sequence with a high degree of stereotypy throughout life, suggesting that this consistency in production may not rely on perceptual mechanisms for processing syllable order in adulthood. Budgerigars, on the other hand, are quite sensitive to bi-syllable order changes, an ability that may be related to useful information being encoded in the sequence of syllables in their natural song. (PsycInfo Database Record (c) 2023 APA, all rights reserved).

Turn-taking is universally seen in humans during the completion of various tasks. Turn-taking is also reported in non-human animals in the wild; however, in these cases turn-taking is displayed during innate and stereotypic behaviors, so it may differ from turn-taking seen in humans. In the present study, budgerigars were trained to take turns between two individuals under operant control. Two cages were placed adjacent to one another and each cage contained one bird of a pair. Each bird pecked a response key in turn to produce a peck sequence for a reward. All pairs learned this task and one bird of the pairs often pecked the LED slightly before the signal onset, indicating that the peck was not a mere reaction to the LED signal. Furthermore, the preference examination suggested that a male bird pecked more rapidly while paired with a bird he preferred. Thus, they created a "pseudo" turn-taking sequence similar to humans. In addition, results from the male bird suggests a possibility that peck timing may be influenced by their preference. This study did not show whether birds collectively worked for a goal; however, the partner dependent behavior may be elements to form "true" turn-taking behavior., (Copyright © 2022 Elsevier B.V. All rights reserved.)

Currently, drug-induced stimulation of appetite is not commonly performed in hyporexic or anorexic companion psittacine birds. Instead, to prevent a catabolic state and weight loss, supplemental feedings are routinely performed by crop gavage. However, crop gavage is not without complications and is stressful to the patient and labor intensive. The objective of this study was to evaluate the effect of midazolam on food intake in healthy budgerigars. In a randomized, blinded, controlled study, change in food intake after intramuscular administration of midazolam (1 mg/kg) or a placebo-control treatment (0.9% saline) was evaluated in 12 healthy adult budgerigars ( Melopsittacus undulatus ). Food intake was quantified for 1 hour before and after drug administration. Birds were monitored for feeding behavior as well as signs of sedation. After midazolam administration, a median 6-fold (1.1-28) increase in food intake was recorded. In 3 of 6 (50%) birds, the food intake increase after midazolam administration was >10-fold (median 17-fold [10-28]), whereas in the remaining 3 birds, food intake increased by only 1.7-fold (1.1-1.8). The median amount of food ingested (16.7 g/kg [3.2-43.2 g/kg]) was significantly higher after midazolam administration compared with the control group (1.9 g/kg [0.0-19.7 g/kg], P = .015). The median time birds spent displaying feeding behavior after the midazolam injection was 18% (0-43%), compared with 1% (0-20%) in the control group after saline injection. Five of 6 (83%) birds showed signs consistent with mild sedation after midazolam administration. This study demonstrates that midazolam is an appetite stimulant in budgerigars. Future studies are needed to evaluate whether midazolam's effects on food intake are dose dependent and whether the duration of effect exceeds 1 hour.

Objective: To evaluate the sedative effects of IM administration of a high or low dose of dexmedetomidine in combination with midazolam in budgerigars (Melopsittacus undulatus)., Animals: 20 healthy adult budgerigars., Procedures: In a prospective, randomized, blinded study, birds were sedated with a high dose (HD; 0.04 mg/kg, IM; n = 10) or low dose (LD; 0.01 mg/kg, IM; 10) of dexmedetomidine in combination with midazolam (3 mg/kg, IM). Twenty minutes later, atipamezole (0.4 mg/kg [HD group] or 0.1 mg/kg [LD group], IM) and flumazenil (0.1 mg/kg, IM) were administered for reversal of sedation., Results: Times to first effect and to sternal recumbency after administration of the sedatives and times to standing and eating after administration of the antagonists did not differ between groups. Most birds (9/10 in the HD group and 7/10 in the LD group) lost the righting response by 10 minutes after sedative administration, and the peak effect for radiographic positioning was by 15 minutes. Although it was not clinically relevant, most birds showed mild resedation by 60 minutes after administration of the reversal agents. There was no significant cardiorespiratory compromise detected with either protocol., Clinical Relevance: Dexmedetomidine-midazolam can safely and effectively provide a dose-dependent level of sedation in healthy budgerigars. The HD protocol is recommended for radiographic positioning, as it allows for a more reliable, deeper plane of sedation.

A principle of choice in animal decision-making named probability matching (PM) has long been detected in animals, and can arise from different decision-making strategies. Little is known about how environmental stochasticity may influence the switching time of these different decision-making strategies. Here we address this problem using a combination of behavioral and theoretical approaches, and show, that although a simple Win-Stay-Loss-Shift (WSLS) strategy can generate PM in binary-choice tasks theoretically, budgerigars (Melopsittacus undulates) actually apply a range of sub-tactics more often when they are expected to make more accurate decisions. Surprisingly, budgerigars did not get more rewards than would be predicted when adopting a WSLS strategy, and their decisions also exhibited PM. Instead, budgerigars followed a learning strategy based on reward history, which potentially benefits individuals indirectly from paying lower switching costs. Furthermore, our data suggest that more stochastic environments may promote reward learning through significantly less switching. We suggest that switching costs driven by the stochasticity of an environmental niche can potentially represent an important selection pressure associated with decision-making that may play a key role in driving the evolution of complex cognition in animals., (© 2021. The Author(s).)

For a bird, it is often vital to visually detect food items, predators, or individuals from the same flock, i.e. moving stimuli of various shapes. Yet, behavioural tests of visual spatial acuity traditionally use stationary gratings as stimuli. We have behaviourally tested the ability of budgerigars (Melopsittacus undulatus) to detect a black circular target, moving semi-randomly at 1.69 degrees s-1 against a brighter background. We found a detection threshold of 0.107±0.007 degrees of the visual field for a target size corresponding to a resolution of a grating with a spatial frequency of 4.68 cycles degree-1. This detection threshold is lower than the resolution limit for gratings but similar to the threshold for stationary single objects of the same shape. We conclude that the target acuity of budgerigars for moving single targets, just as for stationary single targets, is lower than their acuity for gratings., Competing Interests: Competing interests The authors declare no competing or financial interests., (© 2021. Published by The Company of Biologists Ltd.)

Hearing in noise is a problem often assumed to depend on encoding of energy level by channels tuned to target frequencies, but few studies have tested this hypothesis. The present study examined neural correlates of behavioral tone-in-noise (TIN) detection in budgerigars ( Melopsittacus undulatus , either sex), a parakeet species with human-like behavioral sensitivity to many simple and complex sounds. Behavioral sensitivity to tones in band-limited noise was assessed using operant-conditioning procedures. Neural recordings were made in awake animals from midbrain-level neurons in the inferior colliculus, the first processing stage of the ascending auditory pathway with pronounced rate-based encoding of stimulus amplitude modulation. Budgerigar TIN detection thresholds were similar to human thresholds across the full range of frequencies (0.5-4 kHz) and noise levels (45-85 dB SPL) tested. Also as in humans, thresholds were minimally affected by a challenging roving-level condition with random variation in background-noise level. Many midbrain neurons showed a decreasing response rate as TIN signal-to-noise ratio (SNR) was increased by elevating the tone level, a pattern attributable to amplitude-modulation tuning in these cells and the fact that higher SNR tone-plus-noise stimuli have flatter amplitude envelopes. TIN thresholds of individual neurons were as sensitive as behavioral thresholds under most conditions, perhaps surprisingly even when the unit's characteristic frequency was tuned an octave or more away from the test frequency. A model that combined responses of two cell types enhanced TIN sensitivity in the roving-level condition. These results highlight the importance of midbrain-level envelope encoding and off-frequency neural channels for hearing in noise. SIGNIFICANCE STATEMENT Detection of target sounds in noise is often assumed to depend on energy-level encoding by neural processing channels tuned to the target frequency. In contrast, we found that tone-in-noise sensitivity in budgerigars was often greatest in midbrain neurons not tuned to the test frequency, underscoring the potential importance of off-frequency channels for perception. Furthermore, the results highlight the importance of envelope processing for hearing in noise, especially under challenging conditions with random variation in background noise level over time., (Copyright © 2021 the authors.)

Loss of auditory-nerve (AN) afferent cochlear innervation is a prevalent human condition that does not affect audiometric thresholds and therefore remains largely undetectable with standard clinical tests. AN loss is widely expected to cause hearing difficulties in noise, known as "hidden hearing loss," but support for this hypothesis is controversial. Here, we used operant conditioning procedures to examine the perceptual impact of AN loss on behavioral tone-in-noise (TIN) sensitivity in the budgerigar ( Melopsittacus undulatus ; of either sex), an avian animal model with complex hearing abilities similar to humans. Bilateral kainic acid (KA) infusions depressed compound AN responses by 40-70% without impacting otoacoustic emissions or behavioral tone sensitivity in quiet. Surprisingly, animals with AN damage showed normal thresholds for tone detection in noise (0.1 ± 1.0 dB compared to control animals; mean difference ± SE), even under a challenging roving-level condition with random stimulus variation across trials. Furthermore, decision-variable correlations (DVCs) showed no difference for AN-damaged animals in their use of energy and envelope cues to perform the task. These results show that AN damage has less impact on TIN detection than generally expected, even under a difficult roving-level condition known to impact TIN detection in individuals with sensorineural hearing loss (SNHL). Perceptual deficits could emerge for different perceptual tasks or with greater AN loss but are potentially minor compared with those caused by SNHL. SIGNIFICANCE STATEMENT Loss of auditory-nerve (AN) cochlear innervation is a common problem in humans that does not affect audiometric thresholds on a clinical hearing test. AN loss is widely expected to cause hearing problems in noise, known as "hidden hearing loss," but existing studies are controversial. Here, using an avian animal model with complex hearing abilities similar to humans, we examined for the first time the impact of an experimentally induced AN lesion on behavioral tone sensitivity in noise. Surprisingly, AN-lesioned animals showed no difference in hearing performance in noise or detection strategy compared with controls. These results show that perceptual deficits from AN damage are smaller than generally expected, and potentially minor compared with those caused by sensorineural hearing loss (SNHL)., (Copyright © 2021 the authors.)

Birds and mammals share specialized forms of sleep including slow wave sleep (SWS) and rapid eye movement sleep (REM), raising the question of why and how specialized sleep evolved. Extensive prior studies concluded that avian sleep lacked many features characteristic of mammalian sleep, and therefore that specialized sleep must have evolved independently in birds and mammals. This has been challenged by evidence of more complex sleep in multiple songbird species. To extend this analysis beyond songbirds, we examined a species of parrot, the sister taxon to songbirds. We implanted adult budgerigars (Melopsittacus undulatus) with electroencephalogram (EEG) and electrooculogram (EOG) electrodes to evaluate sleep architecture, and video monitored birds during sleep. Sleep was scored with manual and automated techniques, including automated detection of slow waves and eye movements. This can help define a new standard for how to score sleep in birds. Budgerigars exhibited consolidated sleep, a pattern also observed in songbirds, and many mammalian species, including humans. We found that REM constituted 26.5% of total sleep, comparable to humans and an order of magnitude greater than previously reported. Although we observed no spindles, we found a clear state of intermediate sleep (IS) similar to non-REM (NREM) stage 2. Across the night, SWS decreased and REM increased, as observed in mammals and songbirds. Slow wave activity (SWA) fluctuated with a 29-min ultradian rhythm, indicating a tendency to move systematically through sleep states as observed in other species with consolidated sleep. These results are at variance with numerous older sleep studies, including for budgerigars. Here, we demonstrated that lighting conditions used in the prior budgerigar study-and commonly used in older bird studies-dramatically disrupted budgerigar sleep structure, explaining the prior results. Thus, it is likely that more complex sleep has been overlooked in a broad range of bird species. The similarities in sleep architecture observed in mammals, songbirds, and now budgerigars, alongside recent work in reptiles and basal birds, provide support for the hypothesis that a common amniote ancestor possessed the precursors that gave rise to REM and SWS at one or more loci in the parallel evolution of sleep in higher vertebrates. We discuss this hypothesis in terms of the common plan of forebrain organization shared by reptiles, birds, and mammals., Competing Interests: The authors have declared that no competing interests exist.

Numerous animal models have been used to investigate the neural mechanisms of auditory processing in complex acoustic environments, but it is unclear whether an animal's auditory attention is functionally similar to a human's in processing competing auditory scenes. Here we investigated the effects of attention capture in birds performing an objective auditory streaming paradigm. The classical ABAB… patterned pure tone sequences were modified and used for the task. We trained the birds to selectively attend to a target stream and only respond to the deviant appearing in the target stream, even though their attention may be captured by a deviant in the background stream. When no deviant appeared in the background stream, the birds experience the buildup of streaming process in a qualitatively similar way as they did in a subjective paradigm. Although the birds were trained to selectively attend to the target stream, they failed to avoid the involuntary attention switch caused by the background deviant, especially when the background deviant was sequentially unpredictable. Their global performance deteriorated more with increasingly salient background deviants, where the buildup process was reset by the background distractor. Moreover, sequential predictability of the background deviant facilitated the recovery of the buildup process after attention capture. This is the first study that addresses the perceptual consequences of the joint effects of top-down and bottom-up attention in behaving animals., Competing Interests: The authors have declared that no competing interests exist.

Alfaxalone is a neurosteroid anesthetic agent that has been extensively used in both human and veterinary medicine for more than 50 yr. Previous studies involving avian species demonstrated various dose ranges and multiple routes of administration. The aim of this study was to evaluate the short-term sedative, cardiorespiratory, and thermoregulatory effects of an intramuscular injection of alfaxalone on budgerigars ( Melopsittacus undulatus ). A crossover study was performed with a sample size of 10 male budgerigars, previously determined to be healthy based on physical examination. Alfaxalone was administered intramuscularly at two doses: 15 and 20 mg/kg. The lower dose resulted in mild to moderate sedation for 29 ± 5 min, whereas the higher dose resulted in moderate to profound sedation for 29 ± 7 min. A statistically significant decrease in heart rate was observed 2 min after administration of alfaxalone at 15 mg/kg; however, this finding was noted to be transient. A statistically significant decrease in respiratory rate was observed at 6 and 10 min after injection in both groups. Cloacal temperature measurement with a digital thermometer and eye temperature calculated from thermographic images demonstrated a decrease in body temperature over time but was not found to be statistically significant. Intramuscular use of alfaxalone proved to provide short-term sedation in budgerigars, with statistically significant but clinically mild cardiorespiratory effects. Due to a significant decrease in body temperature, active warming is recommended when using alfaxalone in budgerigars.

We have investigated the paths taken by Budgerigars while flying in a tunnel. The flight trajectories of nine Budgerigars (Melopsittacus undulatus) were reconstructed in 3D from high speed stereo videography of their flights in an obstacle-free tunnel. Individual birds displayed highly idiosyncratic flight trajectories that were consistent from flight to flight over the course of several months. We then investigated the robustness of each bird's trajectory by interposing a disk-shaped obstacle in its preferred flight path. We found that each bird continued to fly along its preferred trajectory up to a point very close to the obstacle before veering over the obstacle rapidly, making a minimal deviation to avoid a collision, and subsequently returning to its original path. Thus, Budgerigars show a high propensity to stick to their individual, preferred flight paths even when confronted with a clearly visible obstacle, and do not adopt a substantially different, unobstructed route. The robust preference for idiosyncratic flight paths, and the tendency to pass obstacles by flying above them, provide new insights into the strategies that underpin obstacle avoidance in birds. We believe that this is the first carefully controlled study of the behaviour of birds in response to a newly introduced obstacle in their flight path. The insights from the study could also have implications for conservation efforts to mitigate collisions of birds with man-made obstacles.

The complex and melodic nature of many birds' songs has raised interest in potential parallels between avian vocal sequences and human speech. The similarities between birdsong and speech in production and learning are well established, but surprisingly little is known about how birds perceive song sequences. One popular laboratory songbird, the zebra finch ( Taeniopygia guttata ), has recently attracted attention as an avian model for human speech, in part because the male learns to produce the individual elements in its song motif in a fixed sequence. But psychoacoustic evidence shows that adult zebra finches are relatively insensitive to the sequential features of song syllables. Instead, zebra finches and other birds seem to be exquisitely sensitive to the acoustic details of individual syllables to a degree that is beyond human hearing capacity. Based on these findings, we present a finite-state model of zebra finch perception of song syllable sequences and discuss the rich informational capacity of their vocal system. Furthermore, we highlight the abilities of budgerigars ( Melopsittacus undulatus ), a parrot species, to hear sequential features better than zebra finches and suggest that neurophysiological investigations comparing these species could prove fruitful for uncovering neural mechanisms for auditory sequence perception in human speech. This article is part of the theme issue 'What can animal communication teach us about human language?'

Artificial light at night (ALAN) can cause circadian disruption and result in adverse behavioral and ecological effects in free-living birds, but studies on captive pet birds as companion animals have been infrequent. We studied the effects of exposure to bright ALAN on body mass, melatonin sulfate levels, reproduction and disease severity in Australian budgerigars (Melopsittacus undulatus) kept in captivity. During the experiment, birds were kept under outdoor temperature, humidity and natural photoperiod from September to December. A total of 48 birds were equally split into 4 groups (6 mating pairs each) and concurrently exposed to ALAN of 200 lux with different duration (0, 30, 60 and 90 min). Monthly observations were recorded for all dependent parameters. ALAN exposure increased mass gain and suppressed melatonin levels in a dose-dependent manner, especially during December. In addition, ALAN exposure in all duration groups decreased egg production and reduced hatchability from 61% ± 14% in the ALAN-unexposed control group to 0% in the ALAN-exposed birds. Disease severity was also found to increase in line with the duration of ALAN exposure. In captive M. undulatus, ALAN exposure was demonstrated to affect photoperiodic regulation with subsequent excess mass gain and reproduction impairment, and increased susceptibility to infections plausibly through duration dose-dependent suppression of melatonin. To the best of our knowledge, this is the first study to demonstrate a possible association between acute bright ALAN of increasing duration and both natural development of infections as well as reproductive cessation in captive birds. Our findings could be used to improve breeding conditions of captive birds., (© 2019 International Society of Zoological Sciences, Institute of Zoology/Chinese Academy of Sciences and John Wiley & Sons Australia, Ltd.)

OBJECTIVE To evaluate the anesthetic and cardiorespiratory effects of IM alfaxalone and isoflurane administration in budgerigars ( Melopsittacus undulatus ) and compare use of these agents with use of manual restraint. ANIMALS 42 healthy budgerigars. PROCEDURES For dose comparison, birds received alfaxalone (5 or 10 mg/kg [2.27 or 4.54 mg/lb], IM; groups A5 and A10, respectively; n = 6/group). For treatment comparison, birds received alfaxalone (10 mg/kg, IM) or isoflurane (via face mask) or were manually restrained (groups A, I, and M, respectively; n = 10/group). Data were obtained on onset, degree, and duration of sedation or anesthesia; heart and respiratory rates; and recovery times. Birds in the treatment comparison underwent physical examination and blood gas analysis. RESULTS All group A5 birds became sedate, but not recumbent. In group A10, 5 of 6 birds lost the righting reflex; however, none lost the noxious stimulus response. Median time to initial effects was significantly shorter and mean time to complete recovery was significantly longer in group A10 than in group A5. Heart and respiratory rates in group A10 remained clinically acceptable; however, some birds had signs of excitement during induction and recovery. Times to initial effects, recumbency, and complete recovery were significantly longer, yet clinically practical, in group A than in group I. Plasma lactate concentrations were significantly higher in group M than in groups A and I. CONCLUSIONS AND CLINICAL RELEVANCE Alfaxalone administered IM at 10 mg/kg produced effective sedation in healthy budgerigars and may be a viable alternative to isoflurane and manual restraint for brief, minimally invasive procedures. Brief manual restraint resulted in a significant increase in plasma lactate concentration.

Auditory-nerve fibers are lost steadily with age and as a possible consequence of noise-induced glutamate excitotoxicity. Auditory-nerve loss in the absence of other cochlear pathologies is thought to be undetectable with a pure-tone audiogram while degrading real-world speech perception (hidden hearing loss). Perceptual deficits remain unclear, however, due in part to the limited behavioral capacity of existing rodent models to discriminate complex sounds. The budgerigar is an avian vocal learner with human-like behavioral sensitivity to many simple and complex sounds and the capacity to mimic speech. Previous studies in this species show that intracochlear kainic-acid infusion reduces wave 1 of the auditory brainstem response by 40-70%, consistent with substantial excitotoxic auditory-nerve damage. The present study used operant-conditioning procedures in trained budgerigars to quantify kainic-acid effects on tone detection across frequency (0.25-8 kHz; the audiogram) and as a function of duration (20-160 ms; temporal integration). Tone thresholds in control animals were lowest from 1 to 4 kHz and decreased with increasing duration as in previous studies of the budgerigar. Behavioral results in kainic-acid-exposed animals were as sensitive as in controls, suggesting preservation of the audiogram and temporal integration despite auditory-nerve loss associated with up to 70% wave 1 reduction. Distortion-product otoacoustic emissions were also preserved in kainic-acid exposed animals, consistent with normal hair-cell function. These results highlight considerable perceptual resistance of tone-detection performance with selective auditory-nerve loss. Future behavioral studies in budgerigars with auditory-nerve damage can use complex speech-like stimuli to help clarify aspects of auditory perception impacted by this common cochlear pathology., (Copyright © 2019 Elsevier B.V. All rights reserved.)

Darwin proposed that mate choice might contribute to the evolution of cognitive abilities. An open question is whether observing the cognitive skills of an individual makes it more attractive as a mate. In this study, we demonstrated that initially less-preferred budgerigar males became preferred after females observed that these males, but not the initially preferred ones, were able to solve extractive foraging problems. This preference shift did not occur in control experiments in which females observed males with free access to food or in which females observed female demonstrators solving these extractive foraging problems. Our results suggest that direct observation of problem-solving skills increases male attractiveness and that this could contribute to the evolution of the cognitive abilities underlying such skills., (Copyright © 2019 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works.)

Intramuscular (IM) administration of either alfaxalone or butorphanol with midazolam was evaluated for sedation and effects on heart and respiratory rates in budgerigars ( Melopsittacus undulatus ). Twenty adult budgerigars were randomly assigned to receive 1 of 2 treatments: alfaxalone at 15 mg/kg IM or butorphanol and midazolam at 2.5 mg/kg IM and 1.25 mg/kg IM, respectively. Baseline heart and respiratory rates and sedation score were collected and, after injection, time to initial effects and initial recumbency were recorded. Five minutes after injection, birds were assessed for a righting reflex, and, if absent, response to noxious stimulus was assessed by hemostat clamp on the first digit. Birds then underwent a standardized diagnostic evaluation of radiographs, jugular venipuncture, and physical examination. At the end of the physical examination, a sedation score was assigned, and birds were placed in dorsal recumbency for recovery. Times from injection to initial arousal, final recumbency, standing, and full recovery were recorded. Although time to onset of sedation was the same between groups, alfaxalone produced a shorter ( P = .04) and more consistent duration of sedation (mean ± SD: 27.5 ± 5.9 minutes) compared with butorphanol-midazolam (72.0 ± 56.9 minutes). Only 3 of 10 birds receiving butorphanol-midazolam were recumbent by 5 minutes compared with 10 of 10 birds receiving alfaxalone. Radiographs were successfully obtained in 9 of 10 and 7 of 10 birds administered alfaxalone and butorphanol-midazolam, respectively. No adverse effects were observed in any bird. Intramuscular alfaxalone produces safe, effective, and reliable sedation in budgerigars and is a more consistent and shorter duration alternative to intramuscular butorphanol-midazolam., (© 2018 by the Association of Avian Veterinarians.)

The perception of the build-up of auditory streaming has been widely investigated in humans, while it is unknown whether animals experience a similar perception when hearing high (H) and low (L) tonal pattern sequences. The paradigm previously used in European starlings ( Sturnus vulgaris ) was adopted in two experiments to address the build-up of auditory streaming in budgerigars ( Melopsittacus undulatus ). In experiment 1, different numbers of repetitions of low-high-low triplets were used in five conditions to study the build-up process. In experiment 2, 5 and 15 repetitions of high-low-high triplets were used to investigate the effects of repetition rate, frequency separation, and frequency range of the two tones on the birds' streaming perception. Similar to humans, budgerigars subjectively experienced the build-up process in auditory streaming; faster repetition rates and larger frequency separations enhanced the streaming perception, and these results were consistent across the two frequency ranges. Response latency analysis indicated that the budgerigars needed a longer amount of time to respond to stimuli that elicited a salient streaming perception. These results indicate, for the first time using a behavioral paradigm, that budgerigars experience a build-up of auditory streaming in a manner similar to humans.

Hemispheric laterality and its provision of potential fitness advantages to aves is a widespread topic of research in budgerigars and other parrot species [e.g., Magat, M. & Brown, C. (2009). Laterality enhances cognition in Australian parrots. Proceedings of the Royal Society B: Biological Sciences, 276, 4155-4162]. In the current study, lateral preferences were tracked for 11 captive-reared budgerigars that subsequently underwent 2 cognitive problem-solving tests: a tool-use problem and a dig-discrimination task. Two significant individual-level lateral preferences (a leftward unipedal support preference and a rightward preening side preference) and 1 significant population-level preference (a right-side preening preference) were obtained. Lateral preening side preference indices for individual subjects correlated with various measures of performance on the dig task, such that right-side preening preferences and stronger lateral preferences irrespective of direction were associated with enhanced dig task performance. The data generally support the idea that laterality in aves serves as a good predictor of increased cognitive capability, while also offering new evidence for population-level lateral preferences in the species.

Birds have many physiological characteristics that are convergent with mammals. In the light of recent evidence that mammals can maintain a constant insensible evaporative water loss (EWL) over a range of perturbing environmental conditions, we hypothesized that birds might also regulate insensible EWL, reflecting this convergence. We found that budgerigars ( Melopsittacus undulatus ) maintain EWL constant over a range of relative humidities at three ambient temperatures. EWL, expressed as a function of water vapour pressure deficit, differed from a physical model where the water vapour pressure deficit between the animal and the ambient air is the driver of evaporation, indicating physiological control of EWL. Regulating EWL avoids thermoregulatory impacts of varied evaporative heat loss; changes in relative humidity had no effect on body temperature, metabolic rate or thermal conductance. Our findings that a small bird can regulate EWL are evidence that this is a common feature of convergently endothermic birds and mammals, and may therefore be a fundamental characteristic of endothermy., (© 2017 The Author(s).)

Parrot feathers contain red, orange, and yellow polyene pigments called psittacofulvins. Budgerigars are parrots that have been extensively bred for plumage traits during the last century, but the underlying genes are unknown. Here we use genome-wide association mapping and gene-expression analysis to map the Mendelian blue locus, which abolishes yellow pigmentation in the budgerigar. We find that the blue trait maps to a single amino acid substitution (R644W) in an uncharacterized polyketide synthase (MuPKS). When we expressed MuPKS heterologously in yeast, yellow pigments accumulated. Mass spectrometry confirmed that these yellow pigments match those found in feathers. The R644W substitution abolished MuPKS activity. Furthermore, gene-expression data from feathers of different bird species suggest that parrots acquired their colors through regulatory changes that drive high expression of MuPKS in feather epithelia. Our data also help formulate biochemical models that may explain natural color variation in parrots. VIDEO ABSTRACT., (Copyright © 2017 Elsevier Inc. All rights reserved.)

Melopsittacus undulatus is largely used as a potential model for assisted reproduction in other endangered parrot species. Semen was collected from nineteen healthy adult males, by massage technique, during the breeding season. After preliminary evaluations through CASA analysis, eight birds were selected as semen donors and five ejaculates of each bird were utilized to evaluate the effect of 10% ethylene glycol (EG) addition, in two times, during 40min of equilibration time at 4°C, and to compare two programmable freezing curves (a rapid and a slow temperature descent rate) and freezing on nitrogen vapors. Diluted semen (modified TALP, pH 8.4) was divided into two aliquots, the first for freezing individual samples, the second to be mixed in a semen pool from the eight birds. Potential inseminating doses of 10μl, containing 1×10 6 spermatozoa, were frozen. The effect of EG addition on semen motility and kinetic parameters was analyzed and the three freezing methods were compared. EG addition caused a significant decline of semen motility in individual samples, not in semen pools. The three freezing curves resulted in significant differences in thawed-semen parameters, with nitrogen vapors showing the worst results, while the higher total and progressive motility values were obtained with the 'fast' protocol. Thawed-semen pools motility and kinetic parameters appeared lower than those of the individual ejaculates. The differences found between single ejaculates and semen pools emphasize the importance of performing artificial insemination tests in order to assess the in vivo performance of single ejaculates in the parrot species., (Copyright © 2017 Elsevier B.V. All rights reserved.)

The influence of experience with human speech sounds on speech perception in budgerigars, vocal mimics whose speech exposure can be tightly controlled in a laboratory setting, was measured. Budgerigars were divided into groups that differed in auditory exposure and then tested on a cue-trading identification paradigm with synthetic speech. Phonetic cue trading is a perceptual phenomenon observed when changes on one cue dimension are offset by changes in another cue dimension while still maintaining the same phonetic percept. The current study examined whether budgerigars would trade the cues of voice onset time (VOT) and the first formant onset frequency when identifying syllable initial stop consonants and if this would be influenced by exposure to speech sounds. There were a total of four different exposure groups: No speech exposure (completely isolated), Passive speech exposure (regular exposure to human speech), and two Speech-trained groups. After the exposure period, all budgerigars were tested for phonetic cue trading using operant conditioning procedures. Birds were trained to peck keys in response to different synthetic speech sounds that began with "d" or "t" and varied in VOT and frequency of the first formant at voicing onset. Once training performance criteria were met, budgerigars were presented with the entire intermediate series, including ambiguous sounds. Responses on these trials were used to determine which speech cues were used, if a trading relation between VOT and the onset frequency of the first formant was present, and whether speech exposure had an influence on perception. Cue trading was found in all birds and these results were largely similar to those of a group of humans. Results indicated that prior speech experience was not a requirement for cue trading by budgerigars. The results are consistent with theories that explain phonetic cue trading in terms of a rich auditory encoding of the speech signal.

Despite their prevalent use amongst avian species, particularly in Budgerigars, the relationship between mirror use and social behaviors is in need of elucidation. After establishing social behavior measures (e.g., agonistic and pair-bond data) in a colony of Budgerigars, mirrors were introduced and subsequent use was documented. Results illustrated a significant relationship between mirror use and pair-bonds, such that mirror use increased with increasing pair-bond strength. The authors posit that individual differences in gregariousness may best account for the obtained results, with certain birds seeking more social stimulation than others, whether it be from a pair-bond or from its own reflected mirror image. Additionally, the trends observed within agonistic behaviors were consistent with previous avian literature such that those who initiated more encounters also won more encounters and that there was a preference to be closer to birds that win more encounters., (Copyright © 2016 Elsevier B.V. All rights reserved.)

Previous observational research suggests that stretching is contagious in budgerigars (Melopsittacus undulatus). Here we report the first experimental evidence of this response through a reanalysis of a previous experiment testing for contagious yawning in this species. Using a repeated measures design, 16 birds were tested as pairs alongside familiar and unfamiliar conspecifics with and without visual barriers. Our results show that stretching behavior was temporally clustered only when the birds could see one another, corroborating previous observational findings supporting contagion. Additionally, for the first time, we show an ingroup bias in this response. That is, while the overall frequency of stretching did not significantly differ as a function of conspecific familiarity, contagious stretching was only present when cage mates were paired together. These findings are discussed in relation to recent research studying social cognition in this species. (PsycINFO Database Record, ((c) 2017 APA, all rights reserved).)

While color vision and spatial resolution have been studied in many bird species, less is known about the temporal aspects of bird vision. High temporal resolution has been described in three species of passerines but it is unknown whether this is specific to passerines, to small actively flying birds, to insectivores or to birds living in bright habitats. Temporal resolution of vision is commonly tested by determining the flicker fusion frequency (FFF), at which the eye can no longer distinguish a flickering light from a constant light of equal intensity at different luminances. Using a food reward, we trained the birds to discriminate a constant light from a flickering light, at four different luminances between 750 and 7500 cd/m 2 . The highest FFF found in one bird at 3500 cd/m 2 was 93 Hz. Three birds had higher FFF (82 Hz) at 7500 cd/m 2 than at 3500 cd/m 2 . Six human subjects had lower FFF than the birds at 1500 but similar FFF at 750 cd/m 2 . These results indicate that high temporal resolution is not a common trait for all small and active birds living in bright light habitats. Whether it is typical for passerines or for insectivorous birds remains to be tested.

The pure-tone thresholds of three budgerigars were determined from 8 Hz to 10 kHz. At a level of 60 dB sound pressure level (re 20 μN/m 2 ), their hearing range extends 6.6 octaves from 77 Hz to 7.6 kHz, with a best sensitivity of 1.1 dB at 3 kHz. Unlike pigeons and chickens, budgerigars do not have better low-frequency hearing than humans. This difference implies anatomical, physiological, and ecological differences between birds that hear infrasound (so far, pigeons and chickens) and those that do not (budgerigars).

It is essential for birds to be agile and aware of their immediate environment, especially when flying through dense foliage. To investigate the type of visual signals and strategies used by birds while negotiating cluttered environments, we presented budgerigars with vertically oriented apertures of different widths. We find that, when flying through narrow apertures, birds execute their maneuvers in an anticipatory fashion, with wing closures, if necessary, occurring well in advance of the aperture. When passing through an aperture that is narrower than the wingspan, the birds close their wings at a specific, constant distance before the aperture, which is independent of aperture width. In these cases, the birds also fly significantly higher, possibly pre-compensating for the drop in altitude. The speed of approach is largely constant, and independent of the width of the aperture. The constancy of the approach speed suggests a simple means by which optic flow can be used to gauge the distance and width of the aperture, and guide wing closure.

How do flying birds respond to changing environments? The behaviour of budgerigars, Melopsittacus undulatus, was filmed as they flew through a tapered tunnel. Unlike flying insects-which vary their speed progressively and continuously by holding constant the optic flow induced by the walls-the birds showed a tendency to fly at only two distinct, fixed speeds. They switched between a high speed in the wider section of the tunnel, and a low speed in the narrower section. The transition between the two speeds was abrupt, and anticipatory. The high speed was close to the energy-efficient, outdoor cruising speed for these birds, while the low speed was approximately half this value. This is the first observation of the existence of two distinct, preferred flight speeds in birds. A dual-speed flight strategy may be beneficial for birds that fly in varying environments, with the high speed set at an energy-efficient value for flight through open spaces, and the low speed suited to safe manoeuvring in a cluttered environment. The constancy of flight speed within each regime enables the distances of obstacles and landmarks to be directly calibrated in terms of optic flow, thus facilitating simple and efficient guidance of flight through changing environments., (© 2016 The Author(s).)

Metrical phonology is the perceptual "strength" in language of some syllables relative to others. The ability to perceive lexical stress is important, as it can help a listener segment speech and distinguish the meaning of words and sentences. Despite this importance, there has been little comparative work on the perception of lexical stress across species. We used a go/no-go operant paradigm to train human participants and budgerigars (Melopsittacus undulatus) to distinguish trochaic (stress-initial) from iambic (stress-final) two-syllable nonsense words. Once participants learned the task, we presented both novel nonsense words, and familiar nonsense words that had certain cues removed (e.g., pitch, duration, loudness, or vowel quality) to determine which cues were most important in stress perception. Members of both species learned the task and were then able to generalize to novel exemplars, showing categorical learning rather than rote memorization. Tests using reduced stimuli showed that humans could identify stress patterns with amplitude and pitch alone, but not with only duration or vowel quality. Budgerigars required more than one cue to be present and had trouble if vowel quality or amplitude were missing as cues. The results suggest that stress patterns in human speech can be decoded by other species. Further comparative stress-perception research with more species could help to determine what species characteristics predict this ability. In addition, tests with a variety of stimuli could help to determine how much this ability depends on general pattern learning processes versus vocalization-specific cues.

Deciphering the auditory scene is a problem faced by many organisms. However, when faced with numerous overlapping sounds from multiple locations, listeners are still able to attribute the individual sound objects to their individual sound-producing sources. Here, the characteristics of sounds important for integrating versus segregating in birds were determined. Budgerigars and zebra finches were trained using operant conditioning procedures on an identification task to peck one key when they heard a whole zebra finch song and to peck another when they heard a zebra finch song missing a middle syllable. Once the birds were trained to a criterion performance level on those stimuli, probe trials were introduced on a small proportion of trials. The probe songs contained modifications of the incomplete training song's missing syllable. When the bird responded as if the probe was a whole song, it suggests they streamed together the altered syllable and the rest of the song. When the bird responded as if the probe was a non-whole song, it suggests they segregated the altered probe from the rest of the song. Results show that some features, such as location and intensity, are more important for segregating than other features, such as timing and frequency.

The budgerigar (Melopsittacus undulatus) is a highly social species and serves as an excellent model of vocal learning and production. This species can be trained to vocalize as a conditioned response using an operant conditioning paradigm. In addition, the birds can be trained to produce different vocalizations in response to different visual signals. Budgerigars may be fairly unique in the capability for vocal production under operant control. Whether acoustic features of the bird's natural social milieu can influence this conditioned vocal output is uncertain. The present study asked whether conditioned vocal behavior in budgerigars can be influenced by hearing vocalizations of other birds. The results show that birds vocalizing under operant control produced louder calls in the presence of vocalizations from other birds, than in pure tones or in quiet. The acoustic variation of the conditioned vocalization also increased when it is in the context of hearing other . These results reveal a functional connection between the vocal production under operant control and the perceptual mechanisms subserving vocal production in the budgerigars' natural social milieu., (Copyright © 2015 Elsevier B.V. All rights reserved.)

Experimental evidence of contagious yawning has only been documented in four mammalian species. Here, we report the results from two separate experimental studies designed to investigate the presence of contagious yawning in a social parrot, the budgerigar (Melopsittacus undulatus). In Study 1, birds were paired in adjacent cages with and without visual barriers, and the temporal association of yawning was assessed between visual conditions. In Study 2, the same birds were exposed to video stimuli of both conspecific yawns and control behavior, and yawning frequency was compared between conditions. Results from both studies demonstrate that yawning is contagious. To date, this is the first experimental evidence of contagious yawning in a non-mammalian species. We propose that future research could use budgerigars to explore questions related to basic forms of empathic processing.

We have investigated whether, and, if so, how birds use vision to regulate the speed of their flight. Budgerigars, Melopsittacus undulatus, were filmed in 3-D using high-speed video cameras as they flew along a 25 m tunnel in which stationary or moving vertically oriented black and white stripes were projected on the side walls. We found that the birds increased their flight speed when the stripes were moved in the birds' flight direction, but decreased it only marginally when the stripes were moved in the opposite direction. The results provide the first direct evidence that Budgerigars use cues based on optic flow, to regulate their flight speed. However, unlike the situation in flying insects, it appears that the control of flight speed in Budgerigars is direction-specific. It does not rely solely on cues derived from optic flow, but may also be determined by energy constraints.

It is well established that in many avian species, prenatal maternal resource allocation varies both between and within clutches and may affect offspring fitness. Differential allocation of maternal resources, in terms of egg weight and yolk composition, may therefore allow the female to adjust brood reduction and to fine-tune reproductive investment in accordance with the expected fitness returns. The adaptive value of such maternal resource allocation is thought to be context-dependent as well as species-specific. We investigated the effects of female preference for her mate on the allocation of prenatal maternal resources in the budgerigar, Melopsittacus undulatus, a monogamous species of parrot that shows an extreme hatching asynchrony. We assessed mate preferences in a two-way preference test and allowed females two breeding rounds: one with the preferred and one with the non-preferred partner. We found no effect of preference on either latency to lay or clutch size, but females mated with the preferred partner laid eggs that contained significantly more yolk. Their eggs also contained significantly more androstenedione but not testosterone. Our results suggest that in this species, female preference may influence maternal resource allocation, and that the functional roles of each androgen in the yolk should be considered separately. In addition, we found a significant effect of laying order on egg and yolk weight as well as on yolk testosterone and androstenedione levels. These measures, however, did not change linearly with the laying order and render it unlikely that female budgerigars compensate for the extreme hatching asynchrony by adjusting within-clutch allocation of prenatal maternal resources., (Copyright © 2015 Elsevier Inc. All rights reserved.)

The auditory scene is filled with an array of overlapping acoustic signals, yet relatively little work has focused on how animals are able to perceptually isolate different sound sources necessary for survival. Much of the previous work on auditory scene analysis has investigated how sequential pure tone stimuli are perceived, but how temporally overlapping complex communication signals are segregated has been largely ignored. In this study, budgerigars and humans were tested using psychophysical procedures to measure their perception of synchronous, asynchronous, and partially overlapping complex signals, including bird calls and human vowels. Segregation thresholds for complex stimuli were significantly lower than those for pure tone stimuli in both humans and birds. Additionally, a species effect was discovered such that relative to humans, budgerigars required significantly less temporal separation between 2 sounds in order to segregate them. Overall, and similar to previous behavioral results investigating temporal coherence, the results from this experiment illustrate that temporal cues are particularly important for auditory scene analysis across multiple species and for both simple and complex acoustic signals., ((c) 2015 APA, all rights reserved).)

Auditory scene analysis has been suggested as a universal process that exists across all animals. Relative to humans, however, little work has been devoted to how animals perceptually isolate different sound sources. Frequency separation of sounds is arguably the most common parameter studied in auditory streaming, but it is not the only factor contributing to how the auditory scene is perceived. Researchers have found that in humans, even at large frequency separations, synchronous tones are heard as a single auditory stream, whereas asynchronous tones with the same frequency separations are perceived as 2 distinct sounds. These findings demonstrate how both the timing and frequency separation of sounds are important for auditory scene analysis. It is unclear how animals, such as budgerigars (Melopsittacus undulatus), perceive synchronous and asynchronous sounds. In this study, budgerigars and humans (Homo sapiens) were tested on their perception of synchronous, asynchronous, and partially overlapping pure tones using the same psychophysical procedures. Species differences were found between budgerigars and humans in how partially overlapping sounds were perceived, with budgerigars more likely to segregate overlapping sounds and humans more apt to fuse the 2 sounds together. The results also illustrated that temporal cues are particularly important for stream segregation of overlapping sounds. Lastly, budgerigars were found to segregate partially overlapping sounds in a manner predicted by computational models of streaming, whereas humans were not., (PsycINFO Database Record (c) 2015 APA, all rights reserved.)

Photoreceptor adaptation ensures appropriate visual responses during changing light conditions and contributes to colour constancy. We used behavioural tests to compare UV-sensitivity of budgerigars after adaptation to UV-rich and UV-poor backgrounds. In the latter case, we found lower UV-sensitivity than expected, which could be the result of photon-shot noise corrupting cone signal robustness or nonlinear background adaptation. We suggest that nonlinear adaptation may be necessary for allowing cones to discriminate UV-rich signals, such as bird plumage colours, against UV-poor natural backgrounds.

Basal metabolic rate (BMR) is one of the most widely used metabolic variables in endotherm ecological and evolutionary physiology. Surprisingly few studies have investigated how BMR is influenced by experimental and analytical variables over and above the standardized conditions required for minimum normothermic resting metabolism. We tested whether avian BMR is affected by habituation to the conditions experienced during laboratory gas exchange measurements by measuring BMR five times in succession in budgerigars (Melopsittacus undulatus) housed under constant temperature and photoperiod. Both the magnitude and the variability of BMR decreased significantly with repeated measurements, from 0.410 ± 0.092 W (n = 9) during the first measurement to 0.285 ± 0.042 W (n = 9) during the fifth measurement. Thus, estimated BMR decreased by ∼30% within individuals solely on account of the number of times they had previously experienced the experimental conditions. The most likely explanation for these results is an attenuation with repeated exposure of the acute stress response induced by birds being handled and placed in respirometry chambers. Our data suggest that habituation to experimental conditions is potentially an important determinant of observed BMR, and this source of variation needs to be taken into account in future studies of metabolic variation among individuals, populations, and species.

Birds are generally thought to have excellent vision with high spatial resolution. However, spatial contrast sensitivity of birds for stationary targets is low compared to other animals with similar acuity, such as mammals. For fast flying animals body stability and coordination are highly important, and visual motion cues are known to be relevant for flight control. We have tested five budgerigars (Melopsittacus undulatus) in behavioural discrimination experiments to determine whether or not stimulus motion improves contrast sensitivity. The birds were trained to distinguish between a homogenous grey field and sine-wave gratings of spatial frequencies between 0.48 and 6.5 cyc/deg, and Michelson contrasts between 0.7% and 99%. The gratings were either stationary or drifting with velocities between 0.9 and 13 deg/s. Budgerigars were able to discriminate patterns of lower contrast from grey when the gratings were drifting, and the improvement in sensitivity was strongest at lower spatial frequencies and higher drift velocities. Our findings indicate that motion cues can have positive effects on visual perception of birds. This is similar to earlier results on human vision. Contrast sensitivity, tested solely with stationary stimuli, underestimates the sensory capacity of budgerigars flying through their natural environments., (Copyright © 2014 The Authors. Published by Elsevier Ltd.. All rights reserved.)

There is currently no suitable system available for the assessment of budgerigar body condition. A tool has been developed that uses an algorithmic decision tree of yes-no answers based on physical examination to objectively guide the assessor to a body condition score. The aim of this work was to evaluate the guide. Repeatability and reproducibility were measured by four assessors on three sequential days, using 38 budgerigars of mixed sex, age and weight. Data were analysed using a 3-factor anova, with Person and Bird as variable factors and occasion as a fixed factor. The association between body condition score and body fat was measured using three assessors and 63 dead budgerigars, which were chemically analysed for fat content after assessment. Data were statistically analysed to determine correlation using Spearman's Rank Coefficient. Occasion and person had no significant effect on body condition score (p = 0.988 and 0.347 respectively). Body condition score and percentage body fat were highly significantly correlated (R(2) = 0.768): percentage fat increased with increasing body condition score. The guide would appear to be a repeatable measure of body condition in budgerigars, suitable for use during physical examinations., (Journal of Animal Physiology and Animal Nutrition © 2013 Blackwell Verlag GmbH.)

Birds flying through a cluttered environment require the ability to choose routes that will take them through the environment safely and quickly. We have investigated some of the strategies by which they achieve this. We trained budgerigars to fly through a tunnel in which they encountered a barrier that offered two passages, positioned side by side, at the halfway point. When one of the passages was substantially wider than the other, the birds tended to fly through the wider passage to continue their transit to the end of the tunnel, regardless of whether this passage was on the right or the left. Evidently, the birds were selecting the safest and quickest route. However, when the two passages were of equal or nearly equal width, some individuals consistently preferred the left-hand passage, while others consistently preferred the passage on the right. Thus, the birds displayed idiosyncratic biases when choosing between alternative routes. Surprisingly--and unlike most of the instances in which behavioral lateralization has previously been discovered--the bias was found to vary from individual to individual, in its direction as well as its magnitude. This is very different from handedness in humans, where the majority of humans are right-handed, giving rise to a so-called 'population' bias. Our experimental results and mathematical model of this behavior suggest that individually varying lateralization, working in concert with a tendency to choose the wider aperture, can expedite the passage of a flock of birds through a cluttered environment.

Bird colour vision is mediated by single cones, while double cones and rods mediate luminance vision in bright and dim light, respectively. In daylight conditions, birds use colour vision to discriminate large objects such as fruit and plumage patches, and luminance vision to detect fine spatial detail and motion. However, decreasing light intensity favours achromatic mechanisms and eventually, in dim light, luminance vision outperforms colour vision in all visual tasks. We have used behavioural tests in budgerigars (Melopsittacus undulatus) to investigate how single cones, double cones and rods contribute to spectral sensitivity for large (3.4°) static monochromatic stimuli at light intensities ranging from 0.08 to 63.5 cd/m². We found no influences of rods at any intensity level. Single cones dominate the spectral sensitivity function at intensities above 1.1 cd/m², as predicted by a receptor noise-limited colour discrimination model. Below 1.1 cd/m², spectral sensitivity is lower than expected at all wavelengths except 575 nm, which corresponds to double cone function. We suggest that luminance vision mediated by double cones restores visual sensitivity when single cone sensitivity quickly decreases at light intensities close to the absolute threshold of colour vision.

Whereas several studies have shown that experimentally increased levels of the androgenic steroid testosterone can affect female behavior, fewer studies have focused on the activational effects of exogenous testosterone on female morphology. With respect to colorful displays in birds, almost exclusively the effects of testosterone manipulation on female carotenoid-based colorations have been studied. Other color types such as structural colors (i.e. UV, blue and violet colors that result from differential light reflection in the nanostructures of the tissue) remain largely unstudied. Here, we investigated the short- and long-term effects of exogenous testosterone on the expression of structural bare-part coloration in female budgerigars, Melopsittacus undulatus. In this parrot species, bare-part coloration is expressed in the cere, a structure over the beak which is brown in females and structural blue in males. We experimentally increased plasma testosterone levels in testosterone-treated females (T-females) compared to controls (C-females) and we performed weekly spectrophotometric measurements of the cere for five weeks after implantation and one measurement after ten weeks. We also estimated the extent to which testosterone masculinized female cere color by comparing the experimental females with untreated males. We found significant effects of testosterone on cere color from week four after implantation onwards. T-females expressed significantly bluer ceres than C-females with higher values for brightness and UV reflectance. T-female cere color, however, remained significantly less blue than in males, while values for brightness and UV reflectance were significantly higher in T-females than in males. Our quantitative results show that exogenous testosterone induces the expression of structural blue color in females but does not strongly masculinize female cere coloration. We provide several potential pathways for the action of testosterone on structural color.