Radiographic anatomy of the cockatiel (Nymphicus hollandicus) axial and appendicular skeleton.

Cockatiels are popular pets. Still, despite medical and surgical relevance, the radiographic anatomy of the cockatiel (Nymphicus hollandicus) skeleton, like that of different wild and exotic bird species, has seldom been described. This study set out to describe the radiographic anatomy of the cockatiel skeleton. Twelve adult male and nine adult female specimens were radiographed using a digital X-ray system and different views. The radiographic anatomy of these birds was similar to that of other Psittacidae. However, some particularities inherent to the target species were detected, such as the presence of four flexion zones in the skull (craniofacial, nasal, jugal arch and palatine), complete bony orbit comprising a suborbital arch, 34-38 vertebrae (10 or 11 cervical, 8 or 9 thoracic, 9 or 10 lumbosacral, 5 or 6 caudal vertebrae and a pygostyle comprising 2 fused vertebrae), eight or nine pairs of ribs and a notarium made up of fused T2-T6 vertebrae. Poor radiopacity of the notarium, ribs and respective uncinate processes, and synsacral vertebrae made demarcation of these structures difficult. The appendicular skeleton of the cockatiel was very similar to that of other Psittacidae, and there were no gender-related differences.

The multifactorial nature of beak and skull shape evolution in parrots and cockatoos (Psittaciformes).

BACKGROUND: The Psittaciformes (parrots and cockatoos) are characterised by their large beaks, and are renowned for their ability to produce high bite forces. These birds also possess a suite of modifications to their cranial architecture interpreted to be adaptations for feeding on mechanically resistant foods, yet the relationship between cranial morphology and diet has never been explicitly tested. Here, we provide a three-dimensional geometric morphometric analysis of the developmental and biomechanical factors that may be influencing the evolution of psittaciformes' distinctive cranial morphologies. RESULTS: Contrary to our own predictions, we find that dietary preferences for more- or less- mechanically resistant foods have very little influence on beak and skull shape, and that diet predicts only 2.4% of the shape variation in psittaciform beaks and skulls. Conversely, evolutionary allometry and integration together predict almost half the observed shape variation, with phylogeny remaining an important factor in shape identity throughout our analyses, particularly in separating cockatoos (Cacatuoidea) from the true parrots (Psittacoidea). CONCLUSIONS: Our results are similar to recent findings about the evolutionary trajectories of skull and beak shape in other avian families. We therefore propose that allometry and integration are important factors causing canalization of the avian head, and while diet clearly has an influence on beak shape between families, this may not be as important at driving evolvability within families as is commonly assumed.

East or west: to which subspecies does the type specimen of the Galah, Eolophus roseicapilla (Vieillot, 1817) (Aves: Cacatuidae), belong?

The Galah (Eolophus roseicapilla) is a pink-and-grey cockatoo, widespread in and endemic to Australia, and now familiar as a cage bird world-wide. It has three currently recognised subspecies: roseicapilla Vieillot, 1817 in the Australian west, kuhli Mathews, 1912 in the far north, and albiceps Schodde, 1989 in the east (Schodde 1997; Higgins 1999; Dickinson & Remsen 2013; del Hoyo & Collar 2014; Engelhard et al. 2015). The northern subspecies, kuhli, is not involved in the issue of type identity of roseicapilla, and so is not considered further here. First to distinguish east and west subspecies was G.M. Mathews (1912). Without explanation then or later, Mathews arbitrarily applied the senior specific name, Cacatua roseicapilla Vieillot, 1817 and its two objective synonyms based on the same type-eos Kuhl, 1820 and rosea Vieillot, 1822-to the eastern subspecies, and introduced the new name assimilis for the then supposedly undescribed western form. Mathews' lead was followed unquestioningly until the late 1980s when Schodde (1989) and Rowley (1990: 3) concluded that the type of Vieillot's roseicapilla was of the western subspecies, collected by the Baudin expedition in the region of Shark Bay on the mid-western Australian coast. Rowley (l.c.), but not Schodde (l.c.) contrary to Rowley's reference, went further to claim that it had been taken by François Péron in 1803, presumably on the brief return visit of Baudin in Le Géographe to Shark Bay en route to France. This left the eastern subspecies un-named, which Schodde (l.c.) accordingly described as albiceps.

[Pathologic-anatomic and morphometric examinations on the heart in feral cockatoos]. / Pathologisch-anatomische und morphometrische Untersuchungen am Herzen von wildlebenden Kakadus.

OBJECTIVE: To evaluate the heart of free-living psittacine birds macroscopically and morphologically, and to compare the results to findings published for psittacine birds living in captivity to obtain information on the influence of bird keeping in a human environment on the psittacine heart. MATERIAL AND METHODS: In total, 84 wild-living cockatoos were examined, including 50 sulphur-crested cockatoos (Cacatua galerita), 31 galahs (Eolophus roseicapilla) and three long-billed corellas (Cacatua tenuirostris). The birds were euthanized because of a local cockatoo control program in Australia, and were examined pathologically within 8 hours of euthanasia. A macroscopic necropsy was performed, and the heart was assessed morphologically. Furthermore, a histological organ screening was conducted. RESULTS: The birds demonstrated good body condition and excellent muscle condition. Except for some paleness of the heart muscle, none of the animals showed any pathological alteration of the heart or large vessels. The mean heart mass was 8.7 g for the sulphur-crested cockatoos, 5.3 g for the galahs and 8.6 g for the long-billed corellas. Independent of the species examined, a highly significant correlation was found between the heart and body masses (r = 0.91; p < 0.001), which was also confirmed as significant within the sulphur-crested cockatoo (r = 0.59; p < 0.001) and galah groups (r = 0.52; p = 0.003). This correlation can be used to calculate the expected heart mass based on the body mass, using the formula: heart mass (g) = 2.9 + 0.01 x body mass (g). In comparison to reports on Australian parakeets, the relative thickness of the heart muscle wall of the left ventricle found in this study was greater. CONCLUSION: In comparison to psittacine birds kept in captivity, wild-living cockatoos have good body condition and rarely suffer from macroscopically detectable diseases of the heart or large vessels. The cardiac fitness level is superior in comparison to that found in healthy appearing psittacine birds kept in captivity. CLINICAL RELEVANCE: The results can serve as a basis for the assessment of the heart in psittacine birds, because in contrast to earlier reports, the heart of healthy psittacine birds not previously exposed to any human influence could be assessed.

Topographic specializations in the retinal ganglion cell layer correlate with lateralized visual behavior, ecology, and evolution in cockatoos.

Cockatoos are a unique avian group inhabiting a diversity of arboreal and terrestrial microhabitats. Most species display strong lateralized visual behaviors using their left eye/foot to assist with food manipulation during foraging. In this study, we used retinal wholemounts and stereological methods to investigate whether the topographic distribution of retinal ganglion cells in cockatoos reflects their lateralized behaviors and microhabitat diversity. We found that all species studied possess a horizontal visual streak and a shallow central fovea that afford increased spatial resolution in the lateral visual field. Arboreal cockatoos have a well-defined dorsotemporal area, in contrast to terrestrial cockatoos, in which this specialization is inconspicuous or absent. Terrestrial cockatoos also have a triangular extension of increased ganglion cell density directed toward the dorsotemporal retinal periphery. Both the dorsotemporal area and the triangular extension enhance spatial resolution in the frontal and inferior visual fields, which potentially assists with binocular coordination during foraging. We found significantly higher ganglion cell densities in the left (52,000-72,000 cells/mm2) compared with the right (42,500-50,000 cells/mm2) perifoveal region of species that have strong left eye-left foot lateralized behaviors. In contrast, cockatoo species that show no lateralized behaviors have equivalent retinal ganglion cell densities in both left and right perifoveal regions (42,500-52,500 cells/mm2). Retinal ganglion cell peak densities in the dorsotemporal area showed no significant difference between left and right eyes for any species, suggesting that cockatoos use both eyes to extract information in the binocular visual field, independent of the degree of lateralization.

The mechanical power output of the pectoralis muscle of cockatiel (Nymphicus hollandicus): the in vivo muscle length trajectory and activity patterns and their implications for power modulation.

In order to meet the varying demands of flight, pectoralis muscle power output must be modulated. In birds with pectoralis muscles with a homogeneous fibre type composition, power output can be modulated at the level of the motor unit (via changes in muscle length trajectory and the pattern of activation), at the level of the muscle (via changes in the number of motor units recruited), and at the level of the whole animal (through the use of intermittent flight). Pectoralis muscle length trajectory and activity patterns were measured in vivo in the cockatiel (Nymphicus hollandicus) at a range of flight speeds (0-16 m s(-1)) using sonomicrometry and electromyography. The work loop technique was used to measure the mechanical power output of a bundle of fascicles isolated from the pectoralis muscle during simulated in vivo length change and activity patterns. The mechanical power-speed relationship was U-shaped, with a 2.97-fold variation in power output (40-120 W kg(-1)). In this species, modulation of neuromuscular activation is the primary strategy utilised to modulate pectoralis muscle power output. Maximum in vivo power output was 22% of the maximum isotonic power output (533 W kg(-1)) and was generated at a lower relative shortening velocity (0.28 V(max)) than the maximum power output during isotonic contractions (0.34 V(max)). It seems probable that the large pectoralis muscle strains result in a shift in the optimal relative shortening velocity in comparison with the optimum during isotonic contractions as a result of length-force effects.

Comparison between mechanical power requirements of flight estimated using an aerodynamic model and in vitro muscle performance in the cockatiel (Nymphicus hollandicus).

There have been few comparisons between the relationship between the mechanical power requirements of flight and flight speed obtained using different approaches. It is unclear whether differences in the power-speed relationships reported in the literature are due to the use of different techniques for determining flight power or due to inter-specific differences. Here we compare the power-speed relationships in cockatiels (Nymphicus hollandicus) determined using both an aerodynamic model and measurements of in vitro performance of bundles of pectoralis muscle fibres under simulated in vivo strain and activity patterns. Aerodynamic power was calculated using different ranges of values for the coefficients in the equations: induced power factor (k 1.0-1.4), the profile (C(D, pro) 0.01-0.03) and parasite drag (C(D, par) 0.05-0.195) coefficients. We found that the aerodynamic power-speed relationship was highly sensitive to the values assumed for these coefficients and best fit the power calculated from in vitro muscle performance when k=1.2, C(D, pro)=0.02 and C(D, par)=0.13.

The metabolic power requirements of flight and estimations of flight muscle efficiency in the cockatiel (Nymphicus hollandicus).

Little is known about how in vivo muscle efficiency, that is the ratio of mechanical and metabolic power, is affected by changes in locomotory tasks. One of the main problems with determining in vivo muscle efficiency is the large number of muscles generally used to produce mechanical power. Animal flight provides a unique model for determining muscle efficiency because only one muscle, the pectoralis muscle, produces nearly all of the mechanical power required for flight. In order to estimate in vivo flight muscle efficiency, we measured the metabolic cost of flight across a range of flight speeds (6-13 m s(-1)) using masked respirometry in the cockatiel (Nymphicus hollandicus) and compared it with measurements of mechanical power determined in the same wind tunnel. Similar to measurements of the mechanical power-speed relationship, the metabolic power-speed relationship had a U-shape, with a minimum at 10 m s(-1). Although the mechanical and metabolic power-speed relationships had similar minimum power speeds, the metabolic power requirements are not a simple multiple of the mechanical power requirements across a range of flight speeds. The pectoralis muscle efficiency (estimated from mechanical and metabolic power, basal metabolism and an assumed value for the 'postural costs' of flight) increased with flight speed and ranged from 6.9% to 11.2%. However, it is probable that previous estimates of the postural costs of flight have been too low and that the pectoralis muscle efficiency is higher.

Radiographic evaluation of perching-joint angles in cockatiels (Nymphicus hollandicus), Hispaniolan Amazon parrots (Amazona ventralis), and barred owls (Strix varia).

Information on perching-joint angles in birds is limited. Joint immobilization in a physiologic perching angle has the potential to result more often in complete restoration of limb function. We evaluated perching-joint angles in 10 healthy cockatiels (Nymphicus hollandicus), 10 Hispaniolan Amazons (Amazona ventralis), and 9 barred owls (Strix varia) and determined intra- and interobserver variability for goniometric measurements in 2 different radiographic projections. Intra- and interobserver variation was less than 7% for all stifle and intertarsal joint measurements but frequently exceeded 10% for the hip-joint measurements. Hip, stifle, and intertarsal perching angles differed significantly among cockatiels, Hispaniolan Amazon parrots, and barred owls. The accuracy of measurements performed on straight lateral radiographic projections with superimposed limbs was not consistently superior to measurements on oblique projections with a slightly rotated pelvis. Stifle and intertarsal joint angles can be measured on radiographs by different observers with acceptable variability, but intra- and interobserver variability for hip-joint-angle measurements is higher.

Genome size is inversely correlated with relative brain size in parrots and cockatoos.

Genome size (haploid nuclear DNA content) has been found to correlate positively with cell size and negatively with cell division rate in a variety of taxa. These cytological relationships manifest in various ways at the organism level, for example, in terms of body size, metabolic rate, or developmental rate, depending on the biology of the organisms. In birds, it has been suggested that high metabolic rate and strong flight ability are linked to small genome size. However, it was also hypothesized that the exceptional cognitive abilities of birds may impose additional constraints on genome size through effects on neuron size and differentiation, as has been observed in amphibians. To test this hypothesis, a comparative analysis was made between genome size, cell (erythrocyte) size, and brain size in 54 species of parrots and cockatoos (order Psittaciformes, family Psittacidae). Relative brain volume, which is taken as an indicator of investment in brain tissue and is widely correlated with behavioural and ecological traits, was found to correlate inversely with genome size. Several possible and mutually compatible explanations for this relationship are described.

Morphoregulation of avian beaks: comparative mapping of growth zone activities and morphological evolution.

Avian beak diversity is a classic example of morphological evolution. Recently, we showed that localized cell proliferation mediated by bone morphogenetic protein 4 (BMP4) can explain the different shapes of chicken and duck beaks (Wu et al. [2004] Science 305:1465). Here, we compare further growth activities among chicken (conical and slightly curved), duck (straight and long), and cockatiel (highly curved) developing beak primordia. We found differential growth activities among different facial prominences and within one prominence. The duck has a wider frontal nasal mass (FNM), and more sustained fibroblast growth factor 8 activity. The cockatiel has a thicker FNM that grows more vertically and a relatively reduced mandibular prominence. In each prominence the number, size, and position of localized growth zones can vary: it is positioned more rostrally in the duck and more posteriorly in the cockatiel FNM, correlating with beak curvature. BMP4 is enriched in these localized growth zones. When BMP activity is experimentally altered in all prominences, beak size was enlarged or reduced proportionally. When only specific prominences were altered, the prototypic conical shaped chicken beaks were converted into an array of beak shapes mimicking those in nature. These results suggest that the size of beaks can be modulated by the overall activity of the BMP pathway, which mediates the growth. The shape of the beaks can be fine-tuned by localized BMP activity, which mediates the range, level, and duration of locally enhanced growth. Implications of topobiology vs. molecular blueprint concepts in the Evo-Devo of avian beak forms are discussed.