Beak Opening Research Articles

How to see stress in chickens: On the way to a Stressed Chicken Scale

For many species, scales are used to classify discomfort and stress (e.g., facial expression/pain scales). Although a significant number of vertebrates used for scientific purposes are chickens, a corresponding scale for birds has not yet been established. We developed a Stressed Chicken Scale (SCS) to investigate whether it is possible to assess discomfort in a chicken by its body posture. A selective review with additional handsearch was conducted to find suitable parameters for visual stress assessment. Seven potential body signals were identified: Tail and head position, eye closure, beak opening, leg and wing position, and plumage fullness (ruffled or fluffed up feathers). The SCS was evaluated for interobserver reliability with veterinary students (n = 20), using randomized pictures of stressed and unstressed chickens in lateral view (n = 80). Observers were able to identify the body signals on the pictures after a brief training session. Agreement scores for interobserver agreement ranged from κ = 0.31 (fair agreement) for eye closure to κ = 0.78 (substantial agreement) for beak opening. We found that the number of body signals displayed in a stressed expression had an impact on observers' overall assessment of the chickens, for example, chickens were more likely to be rated as stressed if more than 4 signals indicative of stress were present. We conclude that the 7 individual body signals can be used to identify discomfort in chickens.

Structural design and mechanics research of a bionic pelican floating object fishing device

In order to meet the needs of surface floating objects fishing operations in small areas such as lakes and rivers, a fishing device is developed that can be used for high-intensity operations and is highly adaptable to the environment. In this paper, a water and land type bionic pelican surface floating object fishing device is developed based on the MeArm robotic arm combined with a three-degree-of-freedom linkage robotic arm using bionic principles. In order to meet the needs of the fishing function, the overall structure of the surface floating object fishing device was bionically designed by combining the large beak and flexible neck of the pelican, The innovative design of the mouth lower beak opening and closing mechanism, the lower beak gear rack lever slide mechanism, the mouth throat pouch bottom release mechanism and the neck structure are mainly carried out.The structural strength of the device under the most dangerous operating conditions was simulated using finite element analysis software for statics and dynamics simulation. The research results show that the structure of this design is reliable, and the experimental test of the prototype model verifies the validity and reliability of this design scheme, which provides the theoretical and experimental basis for the further development of the subsequent products.

Parent-offspring and inter-offspring responses to conspecific versus heterospecific distress calls in 2 sympatric birds.

Distress calls, as a type of alarm call, play important roles in expressing bodily condition and conveying information concerning predation threats. In this study, we examined the communication via distress calls in parent-offspring and inter-offspring interactions. First, we used playback of chick distress calls of 2 sympatric breeders, the vinous-throated parrotbill Sinosuthora webbiana and the oriental reed warbler Acrocephalus orientalis, to the adults/chicks of these 2 species, respectively, and measured the responses of conspecifics or heterospecifics. The playback-to-chicks experiment showed that both species of chicks reduced the number of begging calls and begging duration time as a response to conspecific/heterospecific distress calls compared with natural begging and background noise controls. However, reed warbler chicks also reduced beak opening frequency in the response to conspecific distress calls compared with other playback stimuli. Second, the results of the playback-to-adults experiment showed that reed warbler adults could eavesdrop on distress calls of conspecific neighbors and sympatric heterospecifics. Furthermore, the nest-leaving behavior of reed warblers did not differ significantly when they heard the distress calls of conspecifics or parrotbills. Finally, reed warbler adults responded to heterospecific distress calls more quickly than to conspecific distress calls, and parrotbill adults presented the same response. Our results supported the warn-kin hypothesis and show that chick distress calls play an important role in conveying risk and the condition of chicks to enhance individual fitness. In addition, we also found that eavesdropping on distress calls is a congenital behavior that begins in the chick stage.

Sound attenuation in the ear of domestic chickens (Gallus gallus domesticus) as a result of beak opening.

Because the quadrate and the eardrum are connected, the hypothesis was tested that birds attenuate the transmission of sound through their ears by opening the bill, which potentially serves as an additional protective mechanism for self-generated vocalizations. In domestic chickens, it was examined if a difference exists between hens and roosters, given the difference in vocalization capacity between the sexes. To test the hypothesis, vibrations of the columellar footplate were measured ex vivo with laser Doppler vibrometry (LDV) for closed and maximally opened beak conditions, with sounds introduced at the ear canal. The average attenuation was 3.5 dB in roosters and only 0.5 dB in hens. To demonstrate the importance of a putative protective mechanism, audio recordings were performed of a crowing rooster. Sound pressures levels of 133.5 dB were recorded near the ears. The frequency content of the vocalizations was in accordance with the range of highest hearing sensitivity in chickens. The results indicate a small but significant difference in sound attenuation between hens and roosters. However, the amount of attenuation as measured in the experiments on both hens and roosters is small and will provide little effective protection in addition to other mechanisms such as stapedius muscle activity.

Effect of bandwidth modifications on the quality of speech imitated by Alexandrine and Indian Ringneck parrots

Alexandrine and Indian Ringneck parrots are known for imitating the voice of other animals. The objective of this paper is to estimate the spectral limits of the imitated sounds produced by parrots and quantify the quality. The investigations showed that 500–3000 Hz spectral band is adequate for retaining the important perceptual information in the phrases uttered by human speakers and imitated by parrots. Investigations confirmed that the Indian Ringneck parrots are capable of following the formant structure and pitch contour of the phrases uttered by the human subjects. The dynamic range of the pitch of Indian Ringneck parrots was observed as higher than that of the human subjects. A rise of about 1000 Hz in the formant F1 of the parrots was observed, indicating the tongue height small and beak opening, relatively large, as compared to that of human subjects. The quality of some of the synthesized and processed phrases was found slightly better as compared to that of the original phrases because of the inherent enhancement capability of the Harmonic plus noise model (HNM). The average Mean opinion score (MOS) score of the Indian Ringnech parrots for the original, synthesized, and processed phrases was observed as 2.65, 2.59, and 2.77, respectively. The investigations may be beneficial for studying the behavior of endangered birds, defense related activities, safeguarding the crashes with aero planes, and safeguard of the birds from wind power generator etc.

The effect of craniokinesis on the middle ear of domestic chickens (Gallus gallus domesticus).

The avian middle ear differs from that of mammalians and contains a tympanic membrane, one ossicle (bony columella and cartilaginous extra-columella), some ligaments and one muscle. The rim of the eardrum (closing the middle ear cavity) is connected to the neurocranium and, by means of a broad ligament, to the otic process of the quadrate. Due to the limited number of components in the avian middle ear, the possibilities of attenuating the conduction of sound seem to be limited to activity of the stapedius muscle. We investigate to what extent craniokinesis may impact the components of the middle ear because of the connection of the eardrum to the movable quadrate. The quadrate is a part of the beak suspension and plays an important role in craniokinesis. Micro-computed tomography was used to visualize morphology and the effect of craniokinesis on the middle ear in the domestic chicken (Gallus gallus domesticus). Both hens and roosters are considered because of their difference in vocalization capacity. It is hypothesized that effects, if present, of craniokinesis on the middle ear will be greater in roosters because of their louder vocalization. Maximal lower jaw depression was comparable for hens and roosters (respectively 34.1±2.6° and 32.7±2.5°). There is no overlap in ranges of maximal upper jaw elevation between the sexes (respectively 12.7±2.5° and 18.5±3.8°). Frontal rotation about the transversal quadrato-squamosal, and inward rotation about the squamosal-mandibular axes of the quadrate were both considered to be greater in roosters (respectively 15.4±2.8° and 11.1±2.5°). These quadrate rotations did not affect the columellar position or orientation. In hens, an influence of the quadrate movements on the shape of the eardrum could not be detected either; however, craniokinesis caused slight stretching of the eardrum towards the caudal rim of the otic process of the quadrate. In roosters, an inward displacement of the conical tip of the tympanic membrane of 0.378±0.21mm, as a result of craniokinesis, was observed. This is linked to a flattening and slackening of the eardrum. These changes most likely go along with a deformation of the extra-columella. Generally, in birds, larger beak opening is related to the intensity of vocalization. The coupling between larger maximal upper jaw lifting in roosters and the slackening of the eardrum suggest the presence of a passive sound attenuation mechanism during self-vocalization.

WELFARE OF BROILERS INGESTING A PRE-SLAUGHTER HYDRIC DIET OF LEMON GRASS

The pre-slaughter period is considered critical in broiler production. Several factors contribute to increase the birds' stress, such as handling, harvesting, and transportation, negatively affecting their welfare. This study aimed at evaluating the addition of lemon grass (Cymbopogon citratusStapf) to the drinking water of broilers during the pre-slaughter period on their behavior, blood cortisol, and surface temperature. The study was carried out at the experimental farm of the Federal University of Grande Dourados (UFGD), Dourados, MS, Brazil. In total, 2594 broilers were distributed according to a completely randomized experimental design, in a 3x2x2 factorial arrangement, with four replicates per treatment. Treatments consisted of three different lemon grass levels (Cymbopogon citratus Stapf) used in the form of an infusion (0, 0.1, and 5 g per L of water), sex (male or female), and genetic strain (Ross(r) 308 or Cobb(r) 500). The infusion was offered when birds were 42 days old. On that day, blood was collected for blood cortisol level determination, broiler surface temperature was recorded, and an ethogram was applied to register broiler behavior. Blood cortisol level and broiler surface temperature were not affected by treatments (p>0.05). The behavior of beak opening was different between the genetic strains (p<0.05), being more frequent in Ross(r) 308 broilers. Lemon grass water content did not affect broilers' surface temperature when consumed during the pre-slaughter period.

Image analysis method to evaluate beak and head motion of broiler chickens during feeding

While feeding broiler chickens may exhibit different biomechanical movements in relation to the physical properties of feed such as size, shape and hardness. Furthermore, the chicken’s anatomical features at various ages, genders and breeds in conjunction with feed type and feeder design parameters may also have an influence on biomechanical movement. To determine the significance of these parameters during feeding, kinematic measurements related to the biomechanical motions are required. However, determining this information manually from video by a human operator is tedious and prone to errors. The aim of this study was to develop a machine vision technique which visually identifies the relevant biomechanical variables attributed to broiler feeding behaviour from high-speed video footages. A total of 369 frames from three broiler chicks of 5days old were manually measured and compared to the automatic measurement. For each bird six mandibulations (i.e. a cycle of opening and closing the beak) were manually selected, which were two different sequences of three consecutive mandibulations starting right after a feed grasping. The kinematics variables considered were: (i) head displacement (eye centre position; x- and y-axis); (ii) beak opening speed (given in mmms−1); (iii) beak closing speed (measured in mmms−1); (iv) beak opening acceleration (given in mmms−2); and (v) beak closing acceleration (given in mmms−2). Results indicated that the highest error for eye position detection was 1.05mm for x-axis and 0.67 for the y-axis. The difference between manual and automatic (algorithm output) measurements for the beak gape was 0.22±0.009mm, in which the maximum difference was 0.76mm. Regression analysis indicated that both measures are highly correlated (R2=99.2%). Statistical tests suggested that the primary probably causes of error are the speed and acceleration of the beak motion (i.e. blurred image), as well as the presence of feed particles in the first and second mandibulations right after the feed grasping (i.e. occluded beak tips by feed particles). The presented method calculated automatically the position of the eye centre (x- and y-axis) and both upper and lower beak tips distance in a high level of accuracy, but the model can be improved by using a camera with higher resolution, a higher acquisition rate, and infrared-reflective markers. The method has the potential to facilitate efficient and repeatable acquisition of biomechanical data of broiler chickens during feeding, and be used to benchmark the feed physical properties and its processing methods, likewise evolving knowledge for futures studies in feeders’ design.

Individual differences in learning a novel discrete motor task.

Many motor learning studies focus on average performance while it is known from everyday life experience that humans differ in their way of learning new motor tasks. This study emphasises the importance of recognizing individual differences in motor learning. We studied individual tool grasping profiles of individuals who learned to pick up objects with a novel tool, a pair of pliers. The pair of pliers was attached to the thumb and the index finger so that the tip of the thumb and the tip of the index finger were displaced to the beaks of the pair of pliers. The grasp component was manipulated by varying the location of the hinge of the pair of pliers, which resulted in different relations between beak opening and closing and finger opening and closing. The Wider Beak group had the hinge at 7 cm, the Same Beak group had the hinge at 10 cm (i.e., in the middle), and the Smaller Beak group had the hinge at 13 cm from the digits. Each group consisted of ten right-handed participants who picked up an object with one of the pairs of pliers 200 times on two subsequent days. Hand opening, plateau phase, hand closing, grasping time and maximum aperture were analyzed. To characterize individual changes over practice time, a log function was fitted on these dependent variables and the ratio of improvement was determined. Results showed that at the beginning stage of tool use learning the characteristic grasping profile consisted of three phases; hand opening, plateau phase and hand closing. Over practicing individual participants differed in the number of phases that changed, the amount of change in a phase and/or the direction of change. Moreover, with different pliers different learning paths were found. The importance of recognizing individual differences in motor learning is discussed.

Trigeminal and telencephalic projections to jaw and other upper vocal tract premotor neurons in songbirds: Sensorimotor circuitry for beak movements during singing

During singing in songbirds, the extent of beak opening, like the extent of mouth opening in human singers, is partially correlated with the fundamental frequency of the sounds emitted. Since song in songbirds is under the control of "the song system" (a collection of interconnected forebrain nuclei dedicated to the learning and production of song), it might be expected that beak movements during singing would also be controlled by this system. However, direct neural connections between the telencephalic output of the song system and beak muscle motor neurons in the brainstem are conspicuous by their absence, leaving unresolved the question of how beak movements are affected during singing. By using standard tract tracing methods, we sought to answer this question by defining beak premotor neurons and examining their afferent projections. In the caudal medulla, jaw premotor cell bodies were located adjacent to the terminal field of the output of the song system, into which many premotor neurons extended their dendrites. The premotor neurons also received a novel input from the trigeminal ganglion and an overlapping input from a lateral arcopallial component of a trigeminal sensorimotor circuit that traverses the forebrain. The ganglionic input in songbirds, which is not present in doves and pigeons that vocalize with a closed beak, may modulate the activity of beak premotor neurons in concert with the output of the song system. These inputs to jaw premotor neurons could, together, affect beak movements as a means of modulating filter properties of the upper vocal tract during singing.

PARAKEETS ARTICULATE SOUNDS WITH TONGUE

Speech almost defines the human race. But we are not the only animals with a versatile vocal repertoire; birds are also renowned for learning and producing intricate trains of sound. Verena Ohms and her colleagues from The Netherlands, Germany and USA explain that speech scientists are particularly interested in bird sound production because of the parallels between bird and human vocal learning. However, there are significant differences too. For example, humans use the tongue extensively to articulate sounds while most birds do not use the tongue; instead, they expand the oesophagus and adjust how wide they open their beaks. Yet, there are several groups of birds that may buck this trend. Ohms explains that speech-imitating parrots have a prominent tongue that they may use to modulate sounds produced by their simple syrinxes. But, there was no direct evidence that parrots use their tongues while calling, so Ohms and her colleagues, Gabriel Beckers, Carel ten Cate and Roderick Suthers, decided to make X-ray movies of four squawking monk parakeets to find out whether or not they articulate sounds with their tongues (p. 85).Placing minute metal markers in the birds' tongues and at two locations on the tracheae near the top of the throat, the team filmed the parakeets with 10 ms bursts of X-rays as they chattered and made contact and greeting calls. Analysing the markers' movements, the team saw that the birds use their tongues extensively as they squawk and chatter. Having lowered the tongue and opened their beaks before initiating a call, the parakeets then further lowered their tongues by as much as 6.7 mm as they began calling. They also varied the strength of their calls using two strategies: opening the beak wider and varying the height of the tongue to alter the distance between it and the beak's upper mandible.Analysing the birds' throat, beak and tongue movements during contact and greeting calls, the team found that the parrots prepared for a call by lowering the larynx, opening the beak and lowering the tongue before uttering a sound. They also shortened the distance between the two markers on the tracheae by as much as 44%. Then, as the birds began squawking, they continued depressing their tongues and pulling their larynxes down. Comparing the greeting and contact calls, Ohms and her colleagues found that the throat structure movements were slower in the longer greeting calls. However, when the birds were chattering – rattling out a train of alternating notes – the team noticed that the birds produced two distinct tones by changing the relative timing of their beak, tongue and tracheal movements.So monk parakeets modulate their calls by adjusting their tongue height, beak opening and tracheal length and the team points out that this is the first observation that a bird contracts the trachea to articulate distinct sounds. However, the parakeets did not perform one tongue movement that is particularly important in human speech. Explaining that humans extend the tongue back and forth, the team noticed that the parakeets appeared not to move the tongue horizontally. However, knowing that the parakeets produce a repertoire of nine calls when communicating naturally, they say, ‘It cannot be ruled out that in some of the other call types these birds use the front–back dimension more heavily.’ They are also keen to analyse the beak, tongue and throat movements of birds mimicking human speech to discover more about the mechanisms of speech production.

Vocal tract articulation revisited: the case of the monk parakeet

Birdsong and human speech share many features with respect to vocal learning and development. However, the vocal production mechanisms have long been considered to be distinct. The vocal organ of songbirds is more complex than the human larynx, leading to the hypothesis that vocal variation in birdsong originates mainly at the sound source, while in humans it is primarily due to vocal tract filtering. However, several recent studies have indicated the importance of vocal tract articulators such as the beak and oropharyngeal-esophageal cavity. In contrast to most other bird groups, parrots have a prominent tongue, raising the possibility that tongue movements may also be of significant importance in vocal production in parrots, but evidence is rare and observations often anecdotal. In the current study we used X-ray cinematographic imaging of naturally vocalizing monk parakeets (Myiopsitta monachus) to assess which articulators are possibly involved in vocal tract filtering in this species. We observed prominent tongue height changes, beak opening movements and tracheal length changes, which suggests that all of these components play an important role in modulating vocal tract resonance. Moreover, the observation of tracheal shortening as a vocal articulator in live birds has to our knowledge not been described before. We also found strong positive correlations between beak opening and amplitude as well as changes in tongue height and amplitude in several types of vocalization. Our results suggest considerable differences between parrot and songbird vocal production while at the same time the parrot's vocal articulation might more closely resemble human speech production in the sense that both make extensive use of the tongue as a vocal articulator.

Behavioural responses, traumatic injuries and live weight losses in ostrich (&amp;lt;i&amp;gt;Struthio camelus&amp;lt;/i&amp;gt;) chicks transported by road during hot-dry conditions

Abstract. The aim of this study was to evaluate the effect of six-hour road transportation on behavioural activities, live weight and traumatic injuries of 40 (20 males and 20 females) ostrich chicks age 3.5 months. The average weight of the birds was 27.7 kg. Four separate journeys were conducted and each vehicle was loaded with 10 ostriches. The behavioural events, environmental data, live weights and traumatic injuries were recorded before, during and after transportation. The result showed that the most stressful behaviours exhibited by the chicks during transportation were hyperventilation (66.7±21.2 %), wing fluffing (65±12.0 %), and prolonged standing (60±15.3 %). The most frequent behaviours per hour of the journey were beak opening (5.9±1.8 bouts), elimination (5.3±2.3 bouts) and pecking (5.6±2.8 bouts). The chicks spent 27.0±11.8, 18.2±1.0, and 17.5±0.1 min per hour of the journey, standing, restless and lying down, respectively. 15.0±2.3 % of the chicks sustained mild injuries during handling and loading. The birds lost 6.5±1.4 % of their live weight after transportation. The relationships between the journey period, temperature humidity index (THI) and stressful behaviours of wing fluffing, pecking, hyperventilation (beak opening) and lying down recorded during the transportation was positive and significant (P&lt;0.01), while behaviours of standing, elimination and restlessness were negatively and significantly (P&lt;0.01) correlated. Student's t-test and Pearson’s correlation test were employed in the statistical analysis. The results suggest that THI of 33–40 °C constitutes moderate risk, while that of 47 °C and above may result in severe stressful behaviours, and this may be considered as recommended ranges and limits of thermal load values in transported chicks. In conclusion, six hours road transportation during hot-dry conditions and the introduction of ostrich chicks into a new environment post-transportation induce behavioural stress.

Measuring foraging activity in a deep-diving bird: comparing wiggles, oesophageal temperatures and beak-opening angles as proxies of feeding

Quantification of prey consumption by marine predators is key to understanding the organisation of ecosystems. This especially concerns penguins, which are major consumers of southern food webs. As direct observation of their feeding activity is not possible, several indirect methods have been developed that take advantage of miniaturised data logging technology, most commonly: detection of (i) anomalies in diving profiles (wiggles), (ii) drops in oesophageal temperature and (iii) the opening of mouth parts (recorded with a Hall sensor). In the present study, we used these three techniques to compare their validity and obtain information about the feeding activity of two free-ranging king penguins (Aptenodytes patagonicus). Crucially, and for the first time, two types of beak-opening events were identified. Type A was believed to correspond to failed prey-capture attempts and type B to successful attempts, because, in nearly all cases, only type B was followed by a drop in oesophageal temperature. The number of beak-opening events, oesophageal temperature drops and wiggles per dive were all correlated. However, for a given dive, the number of wiggles and oesophageal temperature drops were lower than the number of beak-opening events. Our results suggest that recording beak opening is a very accurate method for detecting prey ingestions by diving seabirds at a fine scale. However, these advantages are counterbalanced by the difficulty, and hence potential adverse effects, of instrumenting birds with the necessary sensor/magnet, which is in contrast to the less accurate but more practicable methods of measuring dive profiles or, to a lesser extent, oesophageal temperature.

Birdsong: The role of the vocal tract

The avian vocal organ, the syrinx, is unique among vertebrates in its morphology and location at or near the base of the trachea. In oscine songbirds, two independent sound sources share the same vocal tract. Despite a growing knowledge of the neural and syringeal mechanisms underlying song, the acoustic role of the suprasyringeal vocal tract in modulating birdsong is still poorly understood. During song, the beak opening, or gape, is typically positively correlated with the dominant frequency of the vocalization, but the mechanism by which beak gape influences vocal tract acoustics is controversial. X-ray cinematography of singing birds reveals song-related movements of the hyoid apparatus and larynx that cause the volume of the upper vocal tract to vary inversely with the songs fundamental frequency. At low fundamental frequencies, the oropharynx and cranial end of the esophagus expand to form a single large chamber, the volume of which is reduced at higher frequencies by collapse of the esophagus and reduction of the oropharyngeal cavity. A computational acoustic model indicates that birds actively tune the volume of their oropharyngeal-esophageal cavity so that its major resonance tracks the fundamental frequency of the song. [Work supported by NIH.]

Songbirds tune their vocal tract to the fundamental frequency of their song.

In human speech, the sound generated by the larynx is modified by articulatory movements of the upper vocal tract, which acts as a variable resonant filter concentrating energy near particular frequencies, or formants, essential in speech recognition. Despite its potential importance in vocal communication, little is known about the presence of tunable vocal tract filters in other vertebrates. The tonal quality of much birdsong, in which upper harmonics have relatively little energy, depends on filtering of the vocal source, but the nature of this filter is controversial. Current hypotheses treat the songbird vocal tract as a rigid tube with a resonance that is modulated by the end-correction of a variable beak opening. Through x-ray cinematography of singing birds, we show that birdsong is accompanied by cyclical movements of the hyoid skeleton and changes in the diameter of the cranial end of the esophagus that maintain an inverse relationship between the volume of the oropharyngeal cavity and esophagus and the song's fundamental frequency. A computational acoustic model indicates that this song-related motor pattern tunes the major resonance of the oropharyngeal-esophageal cavity to actively track the song's fundamental frequency.

Functional morphology of the cephalopod buccal mass: A novel joint type

The arrangement of the musculature and connective tissues of the buccal mass of the coleoid cephalopods Octopus bimaculoides, Sepia officinalis, and Loliguncula brevis was examined using dissection and histology. Serial sections in three mutually perpendicular planes were used to identify the muscles and connective tissues responsible for beak movements and stability and to describe their morphology and fiber trajectories. Four major beak muscles were identified: the anterior, posterior, superior, and lateral mandibular muscles. The anterior, posterior, and superior mandibular muscles connect the upper beak and the lower beak. Although the lateral mandibular muscles originate on the upper beak, they do not connect to the lower beak and instead insert on a connective tissue sheath surrounding the buccal mass. Examination of the fibers of the lateral mandibular muscles reveals that they have the organization of a muscular hydrostat, with muscle fibers oriented in three mutually perpendicular orientations. Although the beaks are capable of complex opening, closing, and shearing movements, they do not contact one another and are instead connected only by the musculature of the buccal mass. Based on the morphological analysis and observations of freshly dissected beaks undergoing the stereotyped bite cycle, the functional role of the beak muscles is hypothesized. The anterior and superior mandibular muscles are likely responsible for beak closing and shearing movements. The posterior mandibular muscle is likely also involved in beak closing, but may act synergistically with the lateral mandibular muscles to open the beaks. The lateral mandibular muscles may use a muscular-hydrostatic mechanism to control the location of the pivot between the beaks and to generate the force required for beak opening. The lack of contact between the beaks and the morphology of the lateral mandibular muscles suggests that the buccal mass of coleoid cephalopods may represent a previously unexamined flexible joint mechanism. The term "muscle articulation" is proposed here to denote the importance of the musculature in the function of such a joint.

In-depth studies of Magellanic penguin ( Spheniscus magellanicus ) foraging: can we estimate prey consumption by perturbations in the dive profile?

A new concept based on analysis of dive depth data was developed to help estimate prey consumption in ten free-ranging Magellanic penguins (Spheniscus magellanicus) that were brooding chicks. By simultaneously analysing the undulations in the dive depth profile (measured by time-depth recorders, TDRs) and beak opening (obtained from the recently developed intra-mandibular angle sensors, IMASEN), it was possible to determine the proportions of the undulations in the dive profile that resulted (or not) in prey capture. This methodology allowed the number of prey consumed to be estimated with a mean error of 10±6% using TDR data alone. If the mean mass of prey is known, then the overall mass of prey consumed per unit time can be determined. Additionally, the method allows estimation of the depth at which prey is taken and thus indicates how penguins exploit the water column. Due to its simplicity, the proposed methodology has applications for other Spheniscus penguin species and should be considered for other marine endotherm divers that show undulations in the dive depth profile.

Mechanisms of American English Vowel Production in a Grey Parrot (Psittacus erithacus)

Parrots are known for their capacity to reproduce the sounds of human speech, but few studies have investigated their mechanisms for producing such vocalizations. Using three methods of noninvasive video imaging (Super VHS video, infrared, X-ray radiography), we examined correlations between several elements of a Grey Parrot's (Psittacus erithacus) vocal-tract configuration and the bird's production of two vowels, /i/ ("eat") and /a/ ("rock"). This parrot uses mechanisms that both resemble and differ from those used by: (a) humans to produce English speech; and (b) some avian species to produce conspecific vocalizations. This Grey Parrot, for example, uses its vocal apparatus in some but not all of the ways used by humans to produce vowels. Although our Grey Parrot, like some oscines, appears to use beak opening to modify the characteristics of sound, the specific sound-modification properties of beak opening may or may not be similar to those of nonpsittacids. We describe a first-order model that, although simplistic, may aid our understanding of the mechanisms that enable a parrot to reproduce human speech.

Effects of food-pellet size on rate, latency, and topography of autoshaped key pecks and gapes in pigeons.

Four pigeons responded under autoshaping contingencies in which different conditional stimuli (red or green keylights) were associated with unconditional stimuli of different magnitudes (large or small food pellets) over successive trials within a session. Both topography (beak opening or gape) and strength (rates and latencies of key pecks and gapes) of responding during the conditional stimuli depended on the magnitude of the correlated unconditional stimulus. Key-peck and gape rates were higher and latencies were shorter in large-pellet trials than in small-pellet trials. Gape amplitudes varied directly with pellet size, although conditional and unconditional gapes were larger than either pellet. These findings were replicated when the key colors were presented either on one or two keys and after reversals of the color-size correlations. Because the unconditional stimulus was varied through pellet size, magnitude was not confounded with food-access duration or quality. These results demonstrate the effects of the magnitude of the unconditional stimulus, in that rates and latencies of both key pecks (which are directed movements toward the key) and gapes (which are independent of the bird's position and key properties) varied with pellet size. Gape measures were unique in that two dimensions (response strength and topography) of a single response class varied simultaneously with magnitude.