Unzipping bird feathers.

The bird feather vane can be separated into two parts by pulling the barbs apart. The original state can be re-established easily by lightly stroking through the feather. Hooklets responsible for holding vane barbs together are not damaged by multiple zipping and unzipping cycles. Because numerous microhooks keep the integrity of the feather, their properties are of great interest for understanding mechanics of the entire feather structure. This study was undertaken to estimate the separation force of single hooklets and their arrays using force measurement of an unzipping feather vane. The hooklets usually separate in some number synchronously (20 on average) with the highest observed separation force of 1.74 mN (average force 0.27 mN), whereas the single hooklet separation force was 14 µN. A simple numerical model was suggested for a better understanding of zipping and unzipping behaviour in feathers. The model demonstrates features similar to those observed in experiments.

Developmental basis of phallus reduction during bird evolution.

BACKGROUND: One of the most puzzling events in evolution is the reduction and loss of the phallus in birds. All birds reproduce by internal fertilization, but only ∼3% of birds have retained a phallus capable of intromission. A number of hypotheses have been proposed for the evolutionary mechanisms that drove phallus reduction; however, the underlying developmental mechanisms are unknown. RESULTS: We investigated genital development in two sister clades of birds, Galliformes (land fowl), most of which lack an intromittent phallus, and Anseriformes (waterfowl), which have well developed phalluses; and in two outgroups, Paleognathae (emus) and Crocodilia (alligators). Galliform embryos undergo cryptic development of a genital tubercle, the precursor of the phallus, but this later undergoes apoptosis, leading to regression of the tubercle. At the molecular level, a derived pattern of Bmp4 expression was identified in chick (a galliform) genital tubercles. Inhibition of Bmp signaling in chick genitalia rescues cells from apoptosis and prevents phallus regression, whereas activation of Bmp signaling in duck (an anseriform) genitalia induces a galliform-like pattern of apoptosis. Thus, distal Bmp activity is necessary and sufficient to induce apoptosis in Galloanserae genital tubercles. CONCLUSIONS: Our results indicate that evolutionary reduction of the intromittent phallus in galliform birds occurred not by disruption of outgrowth signals but by de novo activation of cell death by Bmp4 in the genital tubercle. These findings, together with discoveries implicating Bmps in evolution of beak shape, feathers, and toothlessness, suggest that modulation of Bmp gene regulation played a major role in the evolution of avian morphology.

Ecomorphology of eye shape and retinal topography in waterfowl (Aves: Anseriformes: Anatidae) with different foraging modes.

Despite the large body of literature on ecomorphological adaptations to foraging in waterfowl, little attention has been paid to their sensory systems, especially vision. Here, we compare eye shape and retinal topography across 12 species representing 4 different foraging modes. Eye shape was significantly different among foraging modes, with diving and pursuit-diving species having relatively smaller corneal diameters compared to non-diving species. This may be associated with differences in ambient light intensity while foraging or an ability to tightly constrict the pupil in divers in order to facilitate underwater vision. Retinal topography was similar across all species, consisting of an oblique visual streak, a central area of peak cell density, and no discernible fovea. Because the bill faces downwards when the head is held in the normal posture in waterfowl, the visual streak will be held horizontally, allowing the horizon to be sampled with higher visual acuity. Estimates of spatial resolving power were similar among species with only the Canada goose having a higher spatial resolution. Overall, we found no evidence of ecomorphological adaptations to different foraging modes in the retinal ganglion cell layer in waterfowl. Rather, retinal topography in these birds seems to reflect the 'openness' of their habitats.

Morphology of the quadrate in the Eocene anseriform Presbyornis and extant galloanserine birds.

Despite the notoriety, phylogenetic significance, and large number of available specimens of Presbyornis, its cranial anatomy has never been studied in detail, and its quadrate has been partly misinterpreted. We studied five quadrates of Presbyornis that reveal features hitherto unknown in the anseriforms but otherwise present in galliforms. As a result, we analyzed the variable quadrate characters among all extant galloanserine families and identified synapomorphies and other morphological variation among the major galloanserine clades. In terms of quadrate morphology, Presbyornis is more plesiomorphic than any extant anseriform (including the Anhimidae) and shares ancestral galloanserine characters with the Megapodiidae, the earliest branch of extant galliforms. The quadrate's morphology is inconsistent with the currently accepted anseriform phylogeny that nests Presbyornis within the crown-group as a close relative of the Anatidae. The presbyornithid quadrates exhibit an unusual variation in the presence of a caudomedial pneumatic foramen, which we interpret as a result of a discontinuous change in the growth path of the pneumatic diverticulum. Another episode of morphogenetic imbalance in the growth path of the pneumatic diverticulum may have accompanied the disappearance of the basiorbital pneumatic foramen (along with the pneumatization of the pterygoid) at the origin of the crown-group anseriforms. This episode is marked by the striking individual variation in the presence and location of pneumatic foramina in the mandibular part of the quadrate in the Anhimidae.

Longer guts and higher food quality increase energy intake in migratory swans.

1. Within the broad field of optimal foraging, it is increasingly acknowledged that animals often face digestive constraints rather than constraints on rates of food collection. This therefore calls for a formalization of how animals could optimize food absorption rates. 2. Here we generate predictions from a simple graphical optimal digestion model for foragers that aim to maximize their (true) metabolizable food intake over total time (i.e. including nonforaging bouts) under a digestive constraint. 3. The model predicts that such foragers should maintain a constant food retention time, even if gut length or food quality changes. For phenotypically flexible foragers, which are able to change the size of their digestive machinery, this means that an increase in gut length should go hand in hand with an increase in gross intake rate. It also means that better quality food should be digested more efficiently. 4. These latter two predictions are tested in a large avian long-distance migrant, the Bewick's swan (Cygnus columbianus bewickii), feeding on grasslands in its Dutch wintering quarters. 5. Throughout winter, free-ranging Bewick's swans, growing a longer gut and experiencing improved food quality, increased their gross intake rate (i.e. bite rate) and showed a higher digestive efficiency. These responses were in accordance with the model and suggest maintenance of a constant food retention time. 6. These changes doubled the birds' absorption rate. Had only food quality changed (and not gut length), then absorption rate would have increased by only 67%; absorption rate would have increased by only 17% had only gut length changed (and not food quality). 7. The prediction that gross intake rate should go up with gut length parallels the mechanism included in some proximate models of foraging that feeding motivation scales inversely to gut fullness. We plea for a tighter integration between ultimate and proximate foraging models.

Adaptaciones musculares relacionadas a áreas corporales que participan activamente en el vuelo de Anhima cornuta (Aves: Anseriformes, Anhimidae) / Related muscular adaptations to corporal regions that actively participate in the flight of Anhima cornuta (Aves: Anseriformes, Anhimidae)

La forma y correspondencia entre la anatomía muscular y ósea revela en gran medida el hábito locomotor de cualquier ave. Las especies pertenecientes a la Familia Anhimidae son relevantes dentro de las Aves, debido a las adaptaciones óseas (y por lo tanto, musculares) que presentan, como la pérdida de procesos uncinados, el desarrollo de espolones metarcapales, la extrema neumatización y el notable desarrollo de forámenes. Se analizaron anatómicamente y numéricamente (superficie de origen e inserción, longitud en reposo y masa) los componentes musculares relacionados a las zonas de la columna vertebral, tronco, miembros y cinturas de tres ejemplares de Anhima cornuta de distintos sexos y se compararon con lo estudiado en 4 ejemplares de especies relacionadas (Dendrocygna bicolor y Dendrocygna viduata, Anatidae). El estudio reveló que en Anhima existe un gran desarrollo de los músculos intercostales e intervertebrales (torácicos y lumbares), evidenciando una adaptación a la ausencia de procesos uncinados. En Anhima existen fascículos proporcionalmente menos pesados y de menor tamaño que en Dendrocygna, indicando morfológicamente la ocurrencia de un vuelo menos desarrollado en el primero. Algunos tendones y fibras musculares metacarpales cuya inserción ocurre en el primer dígito en Dendrocygna, en Anhima se insertan en la base de los espolones proximal y distal, demostrando el poco control del vuelo en Anhima. La musculatura de los miembros posteriores en Anhima es mucho más desarrollada, tanto en tamaño, como en masa proporcional, evidenciando una gran actividad en esta zona en la propulsión del vuelo y en hábitos terrestres.

The form and correspondence between the muscular and bony anatomy shows, principally, the locomotive habit of the birds. The screamers are a peculiar group in the Aves Class, because their bony adaptations (and therefore, muscular adaptations), the absence of uncinate processes, two long and sharp metacarpal spurs, their bones are far more pneumatic than in others birds and the bony foramens development. Four specimens of Anhima cornuta and four specimens of linked species (two of Dendrocygna bicolor and two of Dendrocygna viduata) were studied and compared, and their muscular components of the spine, trunk, forelimbs, hind limbs, tail and waists were analyzed, anatomically and quantitatively (origin and insertion surface, long, mass). The study revealed that Anhima has a great development of the intercostals and intervertebrals muscles (thoracic and lumbar regions), evidencing an adaptation to the absence of uncinate processes. Anhima has muscular fascicles, proportionally less heavy and smaller that Dendrocygna, indicating a less capacity of the flight. Some metacarpal tendons and muscular fibers whose inserts in the first digit in Dendrocygna, in Anhima are inserted in the spurs base, showing the few flight control. The hind limbs musculature in Anhima is much more developed, in size and proportional mass, evidencing a great activity in this area, specifically in the flight propulsion and in terrestrial habits.

Associations between persistent organic pollutants and vitamin status in Brünnich's guillemot and common eider hatchlings.

The aim of the study was to examine associations between persistent organic pollutants and vitamin A (retinol), retinyl palmitate and vitamin E status (alpha-tocopherol) in two species occupying different trophic positions in the Arctic food web. Levels of polychlorinated biphenyls (PCBs), some selected organochlorine pesticides (OCPs), polybrominated diphenyl ethers (PBDEs) and hexabromocyclododecane (HBCD) were analyzed in yolk sac of newly hatched chicks of Brünnich's guillemot (Uria lomvia) and common eider (Somateria mollissima) from Kongsfjorden, Svalbard (Norwegian Arctic) (79 degrees N). Morphological variables were measured, and levels of retinol, retinyl palmitate and alpha-tocopherol were analyzed in plasma and liver. Brünnich's guillemot had significantly higher levels of POPs than common eider, as expected from its higher trophic position. Morphological traits seemed to be negatively related to POPs in Brünnich's guillemots, but not in common eiders. In Brünnich's guillemot, negative relationships were found between some OCPs (hexachlorobenzene, oxychlordane, p,p'-DDE) and liver alpha-tocopherol levels. The negative relationships between these OCPs and liver alpha-tocopherol levels in Brünnich's guillemot hatchlings became less evident when the confounding effect of liver mass was corrected for. In common eider positive relationships were found between summed PCB (SigmaPCBs) and some OCPs (beta-hexachlorocyclohexane, oxychlordane) and liver alpha-tocopherol levels. Differences in relationships between POPs and vitamin status in the two species may be related to differences in POP exposure levels linked to their trophic position in the Arctic marine food web, or to intrinsic physiological differences between the species.

Allobilharzia visceralis gen. nov., sp. nov. (Schistosomatidae-Trematoda) from Cygnus cygnus (L.) (Anatidae).

In Iceland, the examination of whooper swans (Cygnus cygnus L.) viscera resulted in the detection of adult digenean flukes of the family Schistosomatidae. The mature worms occurring in the blood vessels of the large intestine and mesenterium caused vascular lesions, around the eggs deposited in the intestinal mucosa and liver granulomatous reactions developed. The morphology of the isolated schistosomes shows certain similarity with the flukes of the genus Trichobilharzia; in males reduced gynecophoral canal, and on both sexes both suckers and spatulate ends are present. However, the Icelandic flukes possess other morphological features which are distinct from the genus: the point of caecal reunion in males takes place posterior to gynecophoral canal and the genital pore is behind acetabulum and anterior to caecal reunion. In order to evaluate the identity of Icelandic schistosomes, sequencing of ITS region of DNA was performed, and the obtained sequence was deposited in GenBank under the accession no. DQ067561. Following phylogenetic analysis of relationship between the sequence of Icelandic flukes and database sequences of other bird schistosome genera (Trichobilharzia, Gigantobilharzia and Dendritobilharzia) showed different position of Icelandic worms in the phylogenetic tree. In conclusion, our study revealed new genus and species of schistosome flukes--Allobilharzia visceralis gen. et sp. n.

Anseriform brain and its parts versus taxonomic and ecological categories.

The size of the brain and its macro-anatomical parts in 206 birds representing 19 anseriform species and 4 tribes (Anserini, Anatini, Aythyini and Mergini) was the subject of a comparative analysis. The comparisons involved two aspects: taxonomic (differences among species within tribes and differences among tribes) and ecological (diet composition: vegetation, invertebrates, or fish and the foraging mode: browsing, dabbling, shallow diving, and deep diving). The relative size of the encephalon (E) and its parts (optic tectum, OT; cerebellum, C; brain stem, BS; hemispheres, H) were described using appropriate indices. Five of them, called the cerebral-body indices (E/BW, OT/BW, C/BW, BS/BW, H/BW), involved a ratio between the weight of E or its parts and that of the body (BW). Four intracerebral indices (OT/E, C/E, BS/E, H/E) and allometric equations were used as well. Almost all the indices showed a high intraspecific variability within the Anserini and Mergini; on the other hand, the intracerebral indices did not differ between the species of the Anatini and Aythyini (except for OT/E in the Aythyini). Between-tribe differences were reflected in all 9 indices. The birds feeding on different diets were found to differ in their OT/E and H/E. The herbivorous anserifom OT/E was clearly lower than that of those birds feeding on invertebrates and fish. The highest OT/E was that of the piscivorous birds. In terms of foraging mode, significant differences were revealed in 7 out of the 9 indices used (differences in OT/BW and C/BW proved non-significant). OT/E of the browsing birds was clearly lower than that of the deep diving ducks; BS/E of the browsers was much lower than that of the dabbling and shallow diving ducks. Geese and swans (browsers) showed much higher H/E compared to the deep diving sea ducks. The latter revealed the highest C/E, but significant differences were detected only in comparison with C/E of the shallow diving ducks. The taxonomic (among tribes) and ecological comparisons showed more differences in the intracerebral indices than in the cerebral-body indices.

Assimilation efficiency of Rhinoceros Auklet (Cerorhinca monocerata) chicks fed Japanese anchovy (Engraulis japonicus) and Japanese sand lance (Ammodytes personatus).

We investigated the assimilation efficiency (AE) of a piscivorous alcid, Rhinoceros Auklet (Cerorhinca monocerata), chicks when fed Japanese anchovy (Engraulis japonicus) and Japanese sand lance (Ammodytes personatus), which are their main prey species. The assimilation efficiency corrected for nitrogen retention (NR) of the chicks fed sand lance (81.6%) was significantly higher than those fed anchovy (78.0%). The values of assimilation efficiencies for both fish species are similar to those of fish-fed seabird adults and fledglings.

Pulmonary pneumaticity in the postcranial skeleton of extant aves: a case study examining Anseriformes.

Anseriform birds were surveyed to examine how the degree of postcranial pneumaticity varies in a behaviorally and size-diverse clade of living birds. This study attempts to extricate the relative effects of phylogeny, body size, and behavioral specializations (e.g., diving, soaring) that have been postulated to influence the extent of postcranial skeletal pneumaticity. One hundred anseriform species were examined as the focal study group. Methods included latex injection of the pulmonary apparatus followed by gross dissection or direct examination of osteological specimens. The Pneumaticity Index (PI) is introduced as a means of quantifying and comparing postcranial pneumaticity in a number of species simultaneously. Phylogenetically independent contrasts (PICs) were used to examine the relationship between body size and the degree of postcranial pneumaticity throughout the clade. There is a high degree of similarity (i.e., clade-specificity) within most anseriform subgroups. As a whole, Anseriformes demonstrate no significant relationship between relative pneumaticity and body size, as indicated by regression analysis of body mass on PI. It is apparent, however, that many clades of diving ducks do exhibit lower PIs than their nondiving relatives. By exclusion of diving taxa from analyses, a significant positive slope is observed and the hypothesis of relatively higher pneumaticity in larger-bodied birds is only weakly supported. However, low correlations indicate that factors other than body size account for much of the variation observed in relative pneumaticity. Pneumaticity profiles were mapped onto existing phylogenetic hypotheses. A reduction in the degree of postcranial pneumaticity occurred independently in at least three anseriform subclades specialized for diving. Finally, enigmatic pneumatic features located in distal forelimb elements of screamers (Anhimidae) result from invasion of bone by a network of subcutaneous air sac diverticula spreading distally along the wings.