Cells from the inner ear of pigeons stained with a chemical that turns iron bright blue in colour.
Each ball of iron lies directly beneath the hairs, and there is just one per a cell.
Avian Biology
Recent Publications about Birds
Cells from the inner ear of pigeons stained with a chemical that turns iron bright blue in colour.
Each ball of iron lies directly beneath the hairs, and there is just one per a cell.
Mediator of magnetic detection in the inner ear? -- Hair cells reside in specialized epithelia in the inner ear of vertebrates, mediating the detection of sound, motion, and gravity. The transduction of these stimuli into a neuronal impulse requires the deflection of stereocilia, which are stabilized by the actin-rich cuticular plate. Recent electrophysiological studies have implicated the vestibular system in pigeon magnetosensation. Lauwers et al. (2013) report the discovery of a single iron-rich organelle that resides in the cuticular plate of cochlear and vestibular hair cells in the pigeon. Transmission electron microscopy, coupled with elemental analysis, has shown that this structure is composed of ferritin-like granules, is approximately 300–600 nm in diameter, is spherical, and in some instances is membrane-bound and/or organized in a paracrystalline array. This organelle is found in hair cells in a wide variety of avian species, but not in rodents or in humans. This structure may function as (1) a store of excess iron, (2) a stabilizer of stereocilia, or (3) a mediator of magnetic detection. Given the specific subcellular location, elemental composition, and evolutionary conservation, this structure may be an integral component of the sensory apparatus in birds.
Reference:
Lauwers, M., P. Pichler, N. B. Edelman, G. P. Resch, L. Ushakova, M. C. Salzer, D. Heyers, M. Saunders, J. Shaw, and D. A. Keays. 2013. An iron-rich organelle in the cuticular plate of avian hair cells. Current Biology, online early.
Link:
Bird navigation - great balls of iron
Iron could guide bird navigation
Bird extinctions in the Pacific -- The largest extinction event in the Holocene occurred on Pacific islands, where Late Quaternary fossils reveal the loss of thousands of bird populations following human colonization of the region. However, gaps in the fossil record mean that considerable uncertainty surrounds the magnitude and pattern of these extinctions. Duncan et al. (2013) used a Bayesian mark-recapture approach to model gaps in the fossil record and to quantify losses of nonpasserine landbirds on 41 Pacific islands. Two-thirds of the populations on these islands went extinct in the period between first human arrival and European contact, with extinction rates linked to island and species characteristics that increased susceptibility to hunting and habitat destruction. Thus, human colonization of remote Pacific islands caused the global extinction of close to 1,000 species of nonpasserine landbird alone; nonpasserine seabird and passerine extinctions will add to this total.
Reference:
Duncan, R. P., A. G. Boyer, and T. M. Blackburn. 2013. Magnitude and variation of prehistoric bird extinctions in the Pacific. Proceedings of the National Academy of Sciences USA, online early.
Links:
Scientists gauge ancient die-off of Pacific birds
How did early humans cause a massive die out of Pacific birds?
Ancient death toll of birds confirmed in new study
Humans wiped out Pacific island birds
Hind wings in basal birds -- Recent discoveries of large leg feathers in some theropods have implications for our understanding of the evolution of integumentary features on the avialan leg, and particularly of their relevance for the origin of avialan flight. Zheng et al. (2013) report 11 basal avialan specimens that improve our knowledge of leg integumentary features among early birds. In particular, they provide solid evidence for the existence of enlarged leg feathers on a variety of basal birds, suggest that extensively scaled feet might have appeared secondarily at an early stage in ornithuromorph evolution, and demonstrate a distal-to-proximal reduction pattern for leg feathers in avialan evolution. Such a transition may have accompanied a locomotory decoupling of the fore- and hindlimbs, which facilitated the development of the forelimbs into flight-capable wings.
Reference:
Zheng, X., Z. Zhou, X. Wang, F. Zhang, X. Zhang, Y. Wang, G. Wei, S. Wang, and X. Xu. 2013. Hind wings in basal birds and the evolution of leg feathers. Science 339: 1309-1312.
Links:
Dramatic fossils suggest early birds were biplanes
Four-winged birds? First fossils identified
Four-winged birds? Feathery-legged fossils date back to dinosaur days
The rise and fall of four-winged birds
Gift-giving male jays know their females --State-attribution is the ability to ascribe to others an internal life like one’s own and to understand that internal, psychological states such as desire, hope, belief, and knowledge underlie others’ actions. Despite extensive research, comparative studies struggle to adequately integrate key factors of state-attribution that have been identified by evolutionary and developmental psychology as well as research on empathy. Ostojić et al. (2013) developed a behavioral paradigm to address these issues and investigate whether male Eurasian Jays respond to the changing desire-state of their female partners when sharing food. The authors demonstrated that males feed their mates flexibly according to the female’s current food preference. Critically, males need to see what the female has previously eaten to know what food she will currently want. Consequently, the males’ sharing pattern was not simply a response to their mate’s behavior indicating her preference as to what he should share, nor was it a response to the males’ own desire-state. These results raise the possibility that these birds may be capable of ascribing desire to their mates.
Reference:
Ostojić, L., R. C. Shaw, L. G. Cheke, and N. S. Clayton. 2013. Evidence suggesting that desire-state attribution may govern food sharing in Eurasian Jays. Proceedings of the National Academy of Sciences USA, online early
Link:
Gift-giving birds may think much like people
Some birds, like people, have awareness of mates' feelings
How owls rotate their heads 270 degrees without damaging arteries
Links:
Solving the mystery of owls' head-turning abilities
Study uncovers secret of the owl's amazing rotating head
Neural correlates of a magnetic sense -- Many animals rely on Earth’s magnetic field for spatial orientation and navigation. However, how the brain receives and interprets magnetic field information is unknown. Support for the existence of magnetic receptors in the vertebrate retina, beak, nose, and inner ear has been proposed, and immediate gene expression markers have identified several brain regions activated by magnetic stimulation, but the central neural mechanisms underlying magnetoreception remain unknown. Wu and Dickman (2012) described neuronal responses in the pigeon’s brainstem that show how single cells encode magnetic field direction, intensity, and polarity; qualities that are necessary to derive an internal model representing directional heading and geosurface location. These results demonstrate that there is a neural substrate for a vertebrate magnetic sense.
Reference:
Wu, L.-Q., and J. D. Dickman. 2012. Neural correlates of a magnetic sense. Science 336: 1054-1057.
Link:
Pigeons have GPS! Scientists find birds sense magnetic field
(a) Male Red-legged Partridge displaying its black bib (photo credit: Hans Hut). (b) Relationship between the fractal dimension (FD) and size (square millimeters of pigmented area) of the black bib.
Bibs of similar size but with high and low FDs
(above and below, respectively) are shown for a range of bib sizes. For a given bib size, bibs of higher FD consistently show a smooth transition between the
uniform
black
throat patch
and
the lower spots, whereas bibs with relatively smaller FD show
a sharper discontinuity between the solid and the spotted parts of the bib.
Complex plumage correlated with individual quality -- Animal coloration is key in natural and sexual selection, playing significant roles in intra- and interspecific communication because of its linkage to individual behavior, genetics and physiology. Simple animal traits such as the area or the colour intensity of homogeneous patches have been profusely studied. More complex patterns are widespread in nature, but they escape our understanding because their variation is difficult to capture effectively by standard, simple measures. Pérez-Rodríguez et al. (2013) used fractal geometry to quantify inter-individual variation in the expression of a complex plumage trait, the heterogeneous black bib of the Red-legged Partridge (Alectoris rufa). They found that a higher bib fractal dimension (FD) predicted better individual body condition, as well as immune responsiveness, which is condition-dependent in our study species. Moreover, when food intake was experimentally reduced during moult as a means to reduce body condition, the bib's FD significantly decreased. Fractal geometry therefore provides new opportunities for the study of complex animal color patterns and their roles in animal communication.
Reference:
Pérez-Rodríguez, L., R. Jovani, and F. Mougeot. 2013. Fractal geometry of a complex plumage trait reveals bird's quality. Proceedings of the Royal Society B, online early.
Links:
Puzzling plumage: fractals reveal birds' health
Fractal plumage indicates bird fitness
Female Japanese Quail know the patterning of their own eggs and choose laying spots to hide them best.
Quail camouflage eggs -- Camouflage is conferred by background matching and disruption, which are both affected by microhabitat. However, microhabitat selection that enhances camouflage has only been demonstrated in species with discrete phenotypic morphs. For most animals, phenotypic variation is continuous. To determine if such species can select microhabitats to best exploit camouflage, Lovell et al. (2013) examined substrate selection by ground-nesting Japanese Quail (Coturnix japonica). For such species, threat from visual predators is high and egg appearance shows strong between-female variation. In quail, variation in appearance is particularly obvious in the amount of dark maculation on the light-colored shell. When given a choice, birds consistently selected laying substrates that made visual detection of their egg outline most challenging. However, the strategy for maximizing camouflage varied with the degree of egg maculation. Females laying heavily maculated eggs selected the substrate that more closely matched egg maculation color properties, leading to camouflage through disruptive coloration. For lightly maculated eggs, females chose a substrate that best matched their egg background coloration, suggesting background matching. These results show that quail “know” their individual egg patterning and seek out a nest position that provides most effective camouflage for their individual phenotype.
Reference:
Lovell, P. G., G. D. Ruxton, K. V. Langridge, and K. S. Spencer. 2013. Egg-laying substrate selection for optimal camouflage by quail. Current Biology, online early.
Link:
Quails demonstrate mastery of camouflage to protect their colorful eggs
Japanese Quails camouflage eggs from predators
Quail really know their camouflage
Condors drive cougars to kill more -- Predation risk describes the energetic cost an animal suffers when making a trade off between maximizing energy intake and minimizing threats to its survival. Elbroch and Wittmer (2013) tested whether Andean Condors (Vultur gryphus) influenced the foraging behaviors of a top predator in Patagonia, the puma (Puma concolor), in ways comparable to direct risks of predation for prey to address three questions: 1) Do condors exact a foraging cost on pumas?; 2) If so, do pumas exhibit behaviors indicative of these risks?; and 3) Do pumas display predictable behaviors associated with prey species foraging in risky environments? Using GPS location data, 433 kill sites of 9 pumas were located and kill rates quantified. Based upon time pumas spent at a carcass, handling time was also quantified. Pumas abandoned >10% of edible meat at 133 of 266 large carcasses after a single night, and did so most often in open grasslands where their carcasses were easily detected by condors. These data suggest that condors exacted foraging costs on pumas by significantly decreasing puma handling times at carcasses, and that pumas increased their kill rates by 50% relative to those reported for North America to compensate for these losses. Finally, the relative risks of detection and associated harassment by condors, rather than prey densities, explained puma “giving up times” (GUTs) across structurally variable risk classes in the study area and, like many prey species, pumas disproportionately hunted in high-risk, high-resource reward areas.
Reference:
Elbroch, L. M., and H. U. Wittmer. 2013. Nuisance ecology: do scavenging condors exact foraging costs on pumas in Patagonia? PLoS ONE 8: e53595.
Link:
Condors drive cougars to kill more
Primitive wing feather arrangement in Archaeopteryx -- In modern birds (Neornithes), the wing is composed of a layer of long, asymmetrical flight feathers overlain by short covert feathers. It has generally been assumed that wing feathers in the Jurassic bird Archaeopteryx, and Cretaceous feathered dinosaurs and had the same arrangement. Longrich et al. (2012) redescribed the wings of the archaic bird Archaeopteryx lithographica and the dinosaur Anchiornis huxleyi and show that their wings differ from those of Neornithes in being composed of multiple layers of feathers. In Archaeopteryx, primaries are overlapped by long dorsal and ventral coverts. Anchiornis has a similar configuration but is more primitive in having short, slender, symmetrical remiges. Archaeopteryx and Anchiornis therefore appear to represent early experiments in the evolution of the wing. This primitive configuration has important functional implications: although the slender feather shafts of Archaeopteryx and Anchiornis make individual feathers weak, layering of the wing feathers may have produced a strong airfoil. Furthermore, the layered arrangement may have prevented the feathers from forming a slotted tip or separating to reduce drag on the upstroke. The wings of early birds therefore may have lacked the range of functions seen in Neornithes, limiting their flight ability.
Reference:
Longrich, N. R., J. Vinther, Q. Meng, Q. Li, and A. P. Russell. 2012. Primitive Wing Feather Arrangement in Archaeopteryx lithographica and Anchiornis huxleyi. Current Biology, online early.
Links:
More evidence shows evolution of birds from dinosaurs
Feather by feather, scientists reconstruct primitive wing of prehistoric bird
For ancient birds, wing feathers were a serious drag
Video showing capillary suction along a hummingbird's tongue at high magnification.
The hummingbird tongue can be a capillary siphon and a fluid trap -- Observations of a hummingbird drinking by Kim et al. (2012) indicate both elastocapillary deformation of the hummingbird's tongue and capillary suction along its length. The hummingbird's tongue may thus be best described as a self-assembling capillary syphon. These observations clearly indicate that fluid trapping and capillary suction are complementary rather than mutually exclusive mechanisms. Although both are viable mechanisms for nectar uptake, Kim et al. (2012) concluded that capillary suction is important in many natural settings. Nectar reservoirs are often shallow, relative to the tongue's groove length, thus precluding tongue submergence, in which case capillary suction is predominantly used.
Reference:
Kim, W., F. Peaudecerf, M. W. Baldwin, and J. W. M. Bush. 2012. The hummingbird's tongue: a self-assembling capillary siphon. Proceedings of the Royal Society B, online early.
Links:
The hummingbird and the nectar collector
Tricks of the hummingbird tongue
Migration routes and wintering grounds of three Northern Wheatears breeding in Alaskan (AK) and one in the eastern Canadian Arctic (CN; grey dot, breeding area, blue, autumn migration, orange, spring migration, dashed lines indicate uncertainty in migration routes close to equinoxes). Fifty per cent kernel densities of winter fixes (beginning of December 2009–end of February; purple, bird AK-1; green, bird AK-2; orange, bird AK-3; blue, bird CN-1) are given). Pie charts indicate the proportion of individuals (AK: n = 9, CN: n = 4) originating from one of the three pre-defined wintering regions (red, western; orange, central; yellow, eastern) [8] based on stable-hydrogen isotope (δD) values in winter grown feathers and the δD values within each wintering region (mean ± s.d. shown).
Cross-hemisphere migration -- The Northern Wheatear (Oenanthe oenanthe) is a small (~ 25 g), insectivorous migrant with one of the largest ranges of any songbird in the world, breeding from the eastern Canadian Arctic across Greenland, Eurasia and into Alaska. However, there is no evidence that breeding populations in the New World have established overwintering sites in the Western Hemisphere. Using light-level geolocators, Barlein et al. (2012) demonstrated that individuals from these New World regions overwinter in northern sub-Sahara Africa, with Alaskan birds travelling approximately 14,500 km each way and an eastern Canadian Arctic bird crossing a wide stretch of the North Atlantic (approx. 3500 km). These remarkable journeys, particularly for a bird of this size, last between one to three months depending on breeding location and season (autumn/spring) and result in mean overall migration speeds of up to 290 km d−1. Stable-hydrogen isotope analysis of winter-grown feathers sampled from breeding birds generally support the notion that Alaskan birds overwinter primarily in eastern Africa and eastern Canadian Arctic birds overwinter mainly in western Africa. These results provide the first evidence of a migratory songbird capable of linking African ecosystems of the Old World with Arctic regions of the New World.
Reference:
Barlein, F., D. R. Norris, R. Nagel, M. Bulte, C. C. Voigt, J. W. Fox, D. J. T. Hussell, and H. Schmaljohann. 2012. Cross-hemisphere migration of a 25 g songbird. Biology Letters, online early.
Link:
A songbird's epic migration across hemispheres
Male Northern Wheatear
Adaptive sleep loss in Pectoral Sandpipers -- The functions of sleep remain elusive. Extensive evidence suggests that sleep performs restorative processes that sustain waking brain performance. An alternative view proposes that sleep simply enforces adaptive inactivity to conserve energy when activity is unproductive. Under this hypothesis, animals may evolve the ability to dispense with sleep when ecological demands favor wakefulness. Lesku et al. (2012) found that male Pectoral Sandpipers (Calidris melanotos), polygynous Arctic-breeding shorebirds, are able to maintain high neurobehavioral performance despite greatly reducing their time spent sleeping during a 3-week period of intense male-male competition for access to fertile females. Males that slept the least sired the most offspring. These results challenge the view that decreased performance is an inescapable outcome of sleep loss.
Reference:
Lesku, J. A., N. C. Rattenborg, M. Valcu, A. L. Vyssotski, S. Kuhn, F. Kuemmeth, W. Heidrich, and B. Kempenaers. 2012. Adaptive sleep loss in polygynous Pectoral Sandpipers. Science, online early.
Links:
Sandpipers forgo sleep for days because there's too much sex to be had
Sleep deprived birds have more chicks
Condors still at risk from lead poisoning -- Endangered species recovery programs seek to restore populations to self-sustaining levels. Nonetheless, many recovering species require continuing management to compensate for persistent threats in their environment. Judging true recovery in the face of this management is often difficult, impeding thorough analysis of the success of conservation programs. California Condors (Gymnogyps californianus) were brought to the brink of extinction, in part, because of lead poisoning, and lead poisoning remains a significant threat today. Finkelstein et al. (2012) evaluated individual lead-related health effects, the efficacy of current efforts to prevent lead-caused deaths, and the consequences of any reduction in currently intensive management actions. Analysis revealed that condors in California remain chronically exposed to harmful levels of lead; 30% of the annual blood samples collected from condors indicate lead exposure (blood lead ≥ 200 ng/mL) that causes significant subclinical health effects, measured as >60% inhibition of the heme biosynthetic enzyme δ-aminolevulinic acid dehydratase. Furthermore, each year, about 20% of free-flying birds have blood lead levels (≥450 ng/mL) that indicate the need for clinical intervention to avert morbidity and mortality. Lead isotopic analysis shows that lead-based ammunition is the principle source of lead poisoning in condors. Finally, population models based on condor demographic data show that the condor’s apparent recovery is solely because of intensive ongoing management, with the only hope of achieving true recovery dependent on the elimination or substantial reduction of lead poisoning rates.
Reference:
Finkelstein, M. E., D. F. Doak, D. George, J. Burnett, J. Brandt, M. Church, J. Grantham, and D. R. Smith. 2012. Lead poisoning and the deceptive recovery of the critically endangered California Condor. Proceedings of the National Academy of Sciences USA, online early.
Links:
Lead poisoning blocks recovery of California Condor population
Scavenging bullets dooming condors
Avian predators and insect size -- Giant insects, with wingspans as large as 70 cm, ruled the Carboniferous and Permian skies. Gigantism has been linked to hyperoxic conditions because oxygen concentration is a key physiological control on body size, particularly in groups like flying insects that have high metabolic oxygen demands. Clapham and Karr (2012) showed, using a dataset of more than 10,500 fossil insect wing lengths, that size tracked atmospheric oxygen concentrations only for the first 150 Myr of insect evolution. The data are best explained by a model relating maximum size to atmospheric environmental oxygen concentration (pO2) until the end of the Jurassic, and then at constant sizes, independent of oxygen fluctuations, during the Cretaceous and, at a smaller size, the Cenozoic. Maximum insect size decreased even as atmospheric pO2 rose in the Early Cretaceous following the evolution and radiation of early birds, particularly as birds acquired adaptations that allowed more agile flight. A further decrease in maximum size during the Cenozoic may relate to the evolution of bats, the Cretaceous mass extinction, or further specialization of flying birds. The decoupling of insect size and atmospheric pO2 coincident with the radiation of birds suggests that biotic interactions, such as predation and competition, superseded oxygen as the most important constraint on maximum body size of the largest insects.
Reference:
Clapham, M. E., and J. A. Karr. 2012. Environmental and biotic controls on the evolutionary history of insect body size. Proceedings of the National Academy of Sciences USA, online early.
Links:
Giant bugs eaten out of existence by first birds?
Did early birds exterminate giant insects?
Evolution of the avian skull -- The interplay of evolution and development has been at the heart of evolutionary theory for more than a century. Heterochrony—change in the timing or rate of developmental events—has been implicated in the evolution of major vertebrate lineages such as mammals, including humans. Birds are the most speciose land vertebrates, with more than 10,000 living species representing a bewildering array of ecologies. Their anatomy is radically different from that of other vertebrates. The unique bird skull houses two highly specialized systems: the sophisticated visual and neuromuscular coordination system allows flight coordination and exploitation of diverse visual landscapes, and the astonishing variations of the beak enable a wide range of avian lifestyles. Bhullar et al. (2012) used a geometric morphometric approach integrating developmental, neontological and palaeontological data to show that the heterochronic process of paedomorphosis, by which descendants resemble the juveniles of their ancestors, is responsible for several major evolutionary transitions in the origin of birds. We analysed the variability of a series of landmarks on all known theropod dinosaur skull ontogenies as well as outgroups and birds. The first dimension of variability captured ontogeny, indicating a conserved ontogenetic trajectory. The second dimension accounted for phylogenetic change towards more bird-like dinosaurs. Basally branching eumaniraptorans and avialans clustered with embryos of other archosaurs, indicating paedomorphosis. These results reveal at least four paedomorphic episodes in the history of birds combined with localized peramorphosis (development beyond the adult state of ancestors) in the beak. Paedomorphic enlargement of the eyes and associated brain regions parallels the enlargement of the nasal cavity and olfactory brain in mammals. This study can be a model for investigations of heterochrony in evolutionary transitions, illuminating the origin of adaptive features and inspiring studies of developmental mechanisms.
Reference:
Bhullar, B.-A. S., et al. 2012. Birds have paedomorphic dinosaur skulls. Nature, online early.
Links:
Evolution of birds is result of a drastic change in how dinosaurs developed
Baby boom: did retained juvenile traits help birds outlive dinosaurs?
Modern birds are really baby dinosaurs
Birds may be dinosaurs that never grew up
Lifetime reproductive success of extra-pair young -- The forces driving extra-pair reproduction by socially monogamous females, and the resulting genetic polyandry, remain unclear. A testable prediction of the hypothesis that extra-pair reproduction partly reflects indirect selection on females is that extra-pair young (EPY) will be fitter than their within-pair young (WPY) maternal half-siblings. This prediction has not been comprehensively tested in a wild population, requiring data on the lifetime reproductive success (LRS) of maternal half-sib EPY and WPY. Sardell et al. (2012) used 17 years of genetic parentage data from Song Sparrows, Melospiza melodia, to compare the LRS of hatched EPY and WPY maternal half-siblings measured as their lifetime number of hatched offspring, recruited offspring, and hatched grandoffspring. EPY hatchlings were not significantly fitter than WPY hatchlings for any of three measures of LRS. Furthermore, opposite to prediction, EPY hatchlings tended to have lower LRS than their maternal half-sibling WPY hatchlings on average. EPY also tended to be less likely to survive to hatch than their maternal half-sibling WPY. Taken together, these results fail to support one key hypothesis explaining the evolution of genetic polyandry by socially monogamous females and suggest there may be weak indirect selection against female extra-pair reproduction in Song Sparrows.
Reference:
Sardell, R. J., P. Arcese, L. F. Keller, and J. M. Reid. 2012. Are their indirect benefits of female extra-pair reproduction? Lifetime reproductive success of within-pair and extra-pair offspring. American Naturalist 179: 779-793.
Link:
For monogamous sparrows, it doesn't pay to stray (but they do it anyway)
Benefits of monogamy in Song Sparrows revealed
Accelerated speciation in color-polymorphic birds -- Color polymorphism exemplifies extreme morphological diversity within populations. It is taxonomically widespread but generally rare. Theory suggests that where color polymorphism does occur, processes generating and maintaining it can promote speciation but the generality of this claim is unclear. Hugall and Fox (2012) confirmed, using species-level molecular phylogenies for five families of non-passerine birds, that color polymorphism is associated with accelerated speciation rates in the three groups in which polymorphism is most prevalent. In all five groups, colour polymorphism is lost at a significantly greater rate than it is gained. Thus, the general rarity and phylogenetic dispersion of color polymorphism is accounted for by a combination of higher speciation rate and higher transition rate from polymorphism to monomorphism, consistent with theoretical models where speciation is driven by fixation of one or more morphs. This is corroborated by evidence from a species-level molecular phylogeny of passerines, incorporating 4,128 (66.5%) extant species, that polymorphic species tend to be younger than monomorphic species. Our results provide empirical support for the general proposition, dating from classical evolutionary theory, that color polymorphism can increase speciation rates.
Reference:
Hugall, A. F., and D. Stuart-Fox. 2012. Accelerated speciation in colour-polymorphic birds. Nature, online early.
Link:
Bird color variations speed up evolution
Color of an Archaeopteryx feather -- Archaeopteryx has been regarded as an icon of evolution ever since its discovery from the Late Jurassic limestone deposits of Solnhofen, Germany in 1861. Carney et al. (2012) report the first evidence of color from Archaeopteryx based on fossilized colour-imparting melanosomes discovered in this isolated feather specimen. Using a phylogenetically diverse database of extant bird feathers, statistical analysis of melanosome morphology predicts that the original colour of this Archaeopteryx feather was black, with 95% probability. Furthermore, reexamination of the feather's morphology indicates it was an upper major primary covert, contrary to previous interpretations. Additional findings reveal that the specimen is preserved as an organosulphur residue, and that barbule microstructure identical to that of modern bird feathers had evolved as early as the Jurassic. As in extant birds, the extensive melanization would have provided structural advantages to the Archaeopteryx wing feather during this early evolutionary stage of dinosaur flight.
Reference:
Carney, R. M., J. Vinther, M. D. Shawkey, L. D'Alba, and J. Ackermann. 2012. New evidence on the colour and nature of the isolated Archaeopteryx feather. Nature Communications 3:637.
Links:
Feathered dinosaur had black wings?
Archaeopteryx feather colour and structure revealed
Flying dinosaur had black feathers
Parrots are the closest living relatives of passerines -- The relationships of passerines with non-passerine birds is one of the great enigmas of avian phylogenetic research because decades of extensive morphological and molecular studies have yielded highly inconsistent results between and within data sets. Suh et al. (2011) examined ~200,000 retroposon-containing loci from various avian genomes and retrieved 51 markers resolving early bird phylogeny. Among these, they obtained statistically significant evidence that parrots are the closest and falcons the second-closest relatives of passerines, together constituting the Psittacopasserae and the Eufalconimorphae, respectively. This new and robust phylogenetic framework has substantial implications for the interpretation of various conclusions drawn from passerines as model organisms. This includes insights of relevance to human neuroscience, as vocal learning (that is, birdsong) probably evolved in the psittacopasseran ancestor, >30 million years earlier than previously assumed.
Reference:
Suh, A., M. Paus, M. Kiefmann, G. Churakov, F. A. Franke, J. Brosius, J. O. Kriegs, and J. Schmitz. 2011. Meszoic retroposons reveal parrots as the closest living relatives of passerine birds. Nature Communications 2: 443.
Links:
New research reveals the parrot-passerine link
Observed clutch sizes can affect offspring investment decisions -- Optimal investment in offspring is important in maximizing lifetime reproductive success. Yet, very little is known how animals gather and integrate information about environmental factors to fine tune investment. Observing the decisions and success of other individuals, particularly when those individuals initiate breeding earlier, may provide a way for animals to quickly arrive at better breeding investment decisions. Forsman et al. (2012) showed, with a field experiment using artificial nests appearing similar to resident tit nests with completed clutches, that Pied Flycatchers can use the observed high and low clutch size of a resident competing bird species to increase and decrease clutch size and egg mass, accordingly. These results demonstrate that songbirds can discriminate between high and low quantity of heterospecific eggs, and that social information can have long-term physiological consequences affecting reproductive strategies. Such behavior may help animals to better adapt to changing environments and lead to convergent traits with competitors.
Reference:
Forsman, J. T., J.-T. Seppänen, and I. L. Nykänen. 2012. Observed heterospecific clutch size can affect offspring investment decisions. Biology Letters, online early.
Natal effects on a carotenoid-based color -- The information content of signals such as animal coloration depends on the extent to which variation reflects underlying biological processes. Although animal coloration has received considerable attention, little work has addressed the quantitative genetics of color variation in natural populations. Evans and Sheldon (2012) investigated the quantitative genetics of a carotenoid-based color patch, the ventral plumage of mature Great Tits (Parus major), in a wild population. Carotenoid-based colors are often suggested to reflect environmental variation in carotenoid availability, but numerous mechanisms could also lead to genetic variation in coloration. Analyses of individuals of known origin showed that, although plumage chromaticity (i.e., color) was moderately heritable, there was no significant heritability to achromaticity (i.e., brightness). Multiple long-lasting effects of natal environment were detected, with hatching date and brood size both negatively related to plumage chromaticity at maturity. Reflectance measures contrasted in their spatiotemporal sensitivity, with plumage chromaticity exhibiting significant spatial variation and achromatic variation exhibiting marked annual variation. Hence, color variation in this species reflects both genetic and environmental influences on different scales. These results demonstrate the context dependence of components of color variation and suggest that color patches may convey multiple aspects of individual state.
Reference:
Evans, S. R., and B. C. Sheldon. 2012. Quantitative genetics of a carotenoid-based color: heritability and persistent natal environmental effects in the Great Tit. American Naturalist 179: 79-94.
Distribution of seabird and prey species considered in Cury et al.'s analysis
Seabird responses to fish depletion -- Determining the form of key predator-prey relationships is critical for understanding marine ecosystem dynamics. Using a comprehensive global database, Cury et al. (2011) quantified the effect of fluctuations in food abundance on seabird breeding success, and identified a threshold in prey (fish and krill, termed “forage fish”) abundance below which seabirds experience consistently reduced and more variable productivity. This response was common to all seven ecosystems and 14 bird species examined within the Atlantic, Pacific, and Southern Oceans. The threshold approximated one-third of the maximum prey biomass observed in long-term studies. This provides an indicator of the minimal forage fish biomass needed to sustain seabird productivity over the long term.
Reference:
Cury, P. M., I. L. Boyd, S. Bonhommeau, T. Anker-Nilssen, R. J. M. Crawford, R. W. Furness, J. A. Mills, E. J. Murphy, H. Osterblom, M. Paleczny, J. F. Piatt, J.-P. Roux, L. Shannon, and W. J. Sydeman. 2011. Global seabird response to forage fish depletion - one-third for the birds. Science 334: 1703-1706.
Links:
A surprising threshold for seabird survival
Save a third of fish for birds, scientists urge
Relative to non-predator playbacks, playbacks of predator calls and sounds broadcast throughout the 130-day breeding season reduced the numbers of eggs,
hatchlings, and fledglings in successive nests of female song sparrows. All females produced two broods; and several (2 predator, 3 non-predator) attempted a
third (not shown). Asterisks indicate significant differences. Values are means ± SE.
Perceived predation risk and breeding success -- Predator effects on prey demography have traditionally been ascribed solely to direct killing in studies of population ecology and wildlife management. Predators also affect the prey’s perception of predation risk, but this has not been thought to meaningfully affect prey demography. Zanette et al. (2011) isolated the effects of perceived predation risk in a free-living population of song sparrows by actively eliminating direct predation and used playbacks of predator calls and sounds to manipulate perceived risk. The perception of predation risk alone reduced the number of offspring produced per year by 40%. These results suggest that the perception of predation risk is itself powerful enough to affect wildlife population dynamics, and should thus be given greater consideration in vertebrate conservation and management.
Reference:
Zanette, L., A. F. White, M. C. Allen, and M. Clinchy. 2011. Perceived predation risk reduces the number of offspring songbirds produce per year. Science 334: 1398-1401.
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Mear fear shrinks bird families
Changes in elevational ranges of tropical montane birds -- Species may respond to a warming climate by moving to higher latitudes or elevations. Shifts in geographic ranges are common responses in temperate regions. For the tropics, latitudinal temperature gradients are shallow; the only escape for species may be to move to higher elevations. There are few data to suggest that they do. Yet, the greatest loss of species from climate disruption may be for tropical montane species. Forero-Medina (2011) repeated a historical transect in Peru and found an average upward shift of 49 m for 55 bird species over a 41 year interval. This shift is significantly upward, but also significantly smaller than the 152 m one expects from warming in the region. To estimate the expected shift in elevation we first determined the magnitude of warming in the locality from historical data. The temperature lapse rate was then used to infer the required shift in altitude to compensate for warming. The range shifts in elevation were similar across different trophic guilds. Endothermy may provide birds with some flexibility to temperature changes and allow them to move less than expected. Instead of being directly dependent on temperature, birds may be responding to gradual changes in the nature of the habitat or availability of food resources, and presence of competitors. If so, this has important implications for estimates of mountaintop extinctions from climate change.
Reference:
Forero-Medina, G., J. Terborgh, S. J. Socolar, and S. L. Pimm. 2011. Elevational ranges of birds on a tropical montane gradient lag behind warming temperatures. PLoS ONE 6: e28535.
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Climate change driving tropical birds to higher elevations
Rapid ascent of Emperor Penguins -- To jump out of water onto sea ice, Emperor Penguins must achieve sufficient underwater speed to overcome the influence of gravity when they leave the water. The relevant combination of density and kinematic viscosity of air is much lower than for water. Injection of air into boundary layers (air lubrication, i.e., an air film separates the water from the surface of a structure or a bird thus reducing friction) has been used by engineers to speed movement of vehicles (ships, torpedoes) through sea water. Based on analysis of published and unpublished underwater film, Davenport et al. (2011) hypothesized that free-ranging Emperor Penguins employ air lubrication in achieving high, probably maximal, underwater speeds (mean = 5.3 meters/sec), prior to jumps. Penguins dive to 15 to 20 meters with air in their plumage and that compressed air is released as the birds subsequently ascend while maintaining depressed feathers. Fine bubbles emerge continuously from the entire plumage, forming a smooth layer over the body and generating bubbly wakes behind the penguins. In several hours of film of hundreds of penguins, none were seen to swim rapidly upwards without bubbly wakes. Penguins descend and swim horizontally at about 2 meters/sec. Davenport et al. (2011) hypothesized that a significant proportion of the enhanced ascent speed is due to air lubrication reducing frictional and form drag and that buoyancy forces alone cannot explain the observed speeds.
Emperor Penguins create bubble trails (image: Blue Planet, BBC)
Reference:
Davenport, J., R. N. Hughes, M. Shorten, and P. S. Larsen. 2011. Drag reduction by air release promotes fast ascent in jumping Emperor Penguins - a novel hypothesis. Marine Ecology Progress Series 430: 171-182.
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