Recent Publications about Birds
Past 'Recent Publications':
Journals with some bird-related papers:
(A) Spectrograms of call types played to Pied Babblers (i to iv) to determine whether mimicry of alarm calls increases target alarm response.
Drongo mimics of Glossy Starling and babbler alarm calls (mimic) are shown alongside these species’ alarm calls (true alarm).
(B) Response duration was longer to mimicked babbler (target species) or starling (other species) alarm calls than to drongo-specific alarm calls.
Deception by mimicry -- Deception is common in nature, but victims of deception discriminate against and ultimately ignore deceptive signals when they are produced too frequently. Flexible variation of signals could allow evasion of such constraints. Fork-tailed Drongos (Dicrurus adsimilis) use false alarm calls to scare other species away from food that they then steal. Flower et al. (2014) showed that drongos mimic the alarms of targeted species. Further, target species reduce their response to false alarm calls when they are repeated. However, the fear response is maintained when the call is varied. Drongos exploit this propensity by changing their alarm-call type when making repeated theft attempts on a particular species. These results show that drongos can evade the frequency-dependent constraints that typically limit deception payoffs through flexible variation of their alarm calls.
Flower, T. P., M. Gribble, and A. R. Ridley. 2014. Deception by flexible alarm mimicry in an African bird. Science 344: 513-516.
African bird 'cries wolf' to steal food
African bird shouts false alarms to deceive and steal
African bird uses sound effects to bamboozle other species
Mauritius Kestrels: speeding up their biological clock -- Recent work suggests that the environment experienced in early life can alter life histories in wild populations, but our understanding of the processes involved remains limited. Because anthropogenic environmental change is currently having a major impact on wild populations, this raises the possibility that life histories may be influenced by human activities that alter environmental conditions in early life. Whether this is the case and the processes involved remain unexplored in wild populations. Using 23 years of longitudinal data on the Mauritius Kestrel (Falco punctatus), a tropical forest specialist, Cartwright et al. (2014) found that females born in territories affected by anthropogenic habitat change shifted investment in reproduction to earlier in life at the expense of late life performance. They also had lower survival rates as young adults. This shift in life history strategy appears to be adaptive, because fitness was comparable to that of other females experiencing less anthropogenic modification in their natal environment. These results suggest that human activities can leave a legacy on wild birds through natal environmental effects. Whether these legacies have a detrimental effect on populations will depend on life history responses and the extent to which these reduce individual fitness.
Cartwright, S. J., M. A. C. Nicoll, C. G. Jones, V. Tatayah, and K. Norris. 2014. Anthropogenic natal environment effects on life histories in a wild bird population. Current Biology, in press.
How the resilient Mauritius Kestrel changed its life pattern to survive habitat loss
Mauritius Kestrels have to speed up their life histories
A phylogenetic tree illustrating evolutionary relationships and beak variation among 350 lineages of ovenbirds.
Credit: Joseph A. Tobias and D. Seddon.
Species coexistence and phenotypic evolution -- Interactions between species can promote evolutionary divergence of ecological traits and social signals, a process widely assumed to generate species differences in adaptive radiation. However, an alternative view is that lineages typically interact when relatively old, by which time selection for divergence is weak and potentially exceeded by convergent selection acting on traits mediating interspecific competition. Few studies have tested these contrasting predictions across large radiations, or by controlling for evolutionary time. Thus the role of species interactions in driving broad-scale patterns of trait divergence is unclear. Tobias et al. (2013) used phylogenetic estimates of divergence times to show that increased trait differences among coexisting lineages of ovenbirds (Furnariidae) are explained by their greater evolutionary age in relation to non-interacting lineages, and that—when these temporal biases are accounted for—the only significant effect of coexistence is convergence in a social signal (song). These results conflict with the conventional view that coexistence promotes trait divergence among co-occurring organisms at macroevolutionary scales, and instead provide evidence that species interactions can drive phenotypic convergence across entire radiations, a pattern generally concealed by biases in age.
Tobias, J. A., C. K. Cornwallis, E. P. Derryberry, S. Claramunt, R. T. Brumfield, and N. Seddon. 2013. Species coexistence and the dynamics of phenotypic evolution in adaptive radiation. Nature, online early.
'Be different or die' does not drive evolution
Creatures living together don't have to evolve differently after all
Oxford, LSU, Tulane research questions aspect of Darwin theory
Traffic noise and bird abundance -- Many authors have suggested that the negative effects of roads on animals are largely due to traffic noise. Although suggestive, most past studies of the effects of road noise on wildlife were conducted in the presence of the other confounding effects of roads, such as visual disturbance, collisions, and chemical pollution among others. McLure et al. (2013) examined the effect of traffic noise on birds in a roadless area at a landscape scale—thus avoiding the other confounding aspects of roads present in past studies. The sound of a roadway was replicated at intervals—alternating 4 days of noise on with 4 days off—during the autumn migratory period using a 0.5 km array of speakers within an established stopover site in southern Idaho. Daily bird surveys were conducted along the‘Phantom Road’ and in a nearby control site. There was over a one-quarter decline in bird abundance and almost complete avoidance by some species between noise-on and noise-off periods along the phantom road and no such effects at control sites—suggesting that traffic noise is a major driver of effects of roads on populations of animals.
McClure, C. J. W., H. E. Ware, J. Carlisle, G. Kaltenecker, and J. R. Barber. 2013. An experimental investigation into the effects of traffic noise on distributions of birds: avoiding the phantom road. Proceedings of the Royal Society B 280: no. 1773.
Negative effects of road noises on migratory birds
Study documents effects of road noises on migratory birds
Social complexity and avian intelligence -- A comparative approach is required to investigate the evolutionary origins of cognitive abilities. Krasheninnikova et al. (2013) compared the performance of four parrot species, Spectacled Parrotlets (Forpus conspicillatus), Rainbow Lorikeets (Trichoglossus haematodus), Green-winged Macaws (Ara chloroptera) and Sulphur-crested Cockatoos (Cacatua galerita triton), in standardized string-pulling and string-choice paradigms (Figure above; check Wired.com for an explanation).The spatial relationship between the strings, the presence of a reward, and the physical contact between the string and the reward were varied to test different cognitive skills requiring means–end comprehension. The species tested showed a high individual and inter-specific variation in their ability to solve the tasks. Spectacled Parrotlets performed best among the four species and solved the most complex choice tasks, namely crossed-string task and broken-string task, spontaneously. In contrast, macaws and cockatoos failed to identify the correct string in these two tasks. The rainbow lorikeets were outperformed by the parrotlets, but outperformed in turn the macaws and the cockatoos. These results can be best explained by the variation in social complexity among species, rather than in their ecology.
Krasheninnikova, A., S. Brager, and R. Wanker. 2013. Means-end comprehension in four parrot species: explained by social complexity. Animal Cognition 16: 755-764.
Problem-solving parrots understand cause and effect
Relationships between embryonic growth rate and the total quantity of three classes of antioxidant:
carotenoids (circles), vitamin E (triangles) and vitamin A (squares), allocated to egg yolk. Each data point
represents a species’ average, and least-square regression lines are shown.
Embryonic growth and antioxidants -- Avian embryos undergo extremely rapid development over a relatively short period of time, and so are likely to suffer high levels of oxidative damage unless this is mitigated by sufficient maternal allocation of appropriate antioxidants. At a species level, it is therefore predicted that antioxidants should be allocated to eggs according to the rate of embryonic growth, such that eggs containing embryos that grow faster are furnished with higher antioxidant levels, independent of egg size. Deeming and Pike (2013) tested this prediction for three potentially important classes of dietary-derived yolk antioxidants: carotenoids, vitamin E and vitamin A. Across species, positive relationships were found between embryonic growth rate and total yolk levels of each of the three antioxidant classes. Moreover, there were consistent differences in antioxidant provision between pairs of species that share a common initial egg mass yet have differing rates of embryonic growth, such that the eggs of the faster-developing species have higher levels of carotenoids and vitamin E. These results may explain the marked interspecific variation in antioxidant provision and provide evidence for the role that these antioxidants play during embryonic development.
Deeming, D. C., and T. W. Pike. 2013. Embryonic growth and antioxidant provision in avian eggs. Biology Letters 9: 20130757.
Antioxidants essential for bird embryo growth
Too risky to settle -- Predation risk is widely hypothesized as an important force structuring communities, but this potential force is rarely tested experimentally, particularly in terrestrial vertebrate communities. How animals respond to predation risk is generally considered predictable from species life-history and natural-history traits, but rigorous tests of these predictions remain scarce. Hua et al. (2013) report on a large-scale playback experiment with a forest bird community that addresses two questions: (i) does perceived predation risk shape the richness and composition of a breeding bird community? And (ii) can species life-history and natural-history traits predict prey community responses to different types of predation risk? On 9 ha plots, cues of three avian predators that preferentially prey on either adult birds or offspring, or both, were manipulated throughout the breeding season. Increased perception of predation risk led to generally negative responses in the abundance, occurrence and/or detection probability of most prey species, which in turn reduced the species richness and shifted the composition of the breeding bird community. Species-level responses were largely predicted from the key natural-history trait of body size, but there was no support for the life-history theory prediction of the relationship between species' slow/fast life-history strategy and their response to predation risk.
Hua, F., R. J. Fletcher, Jr., K. E. Sieving, and R. M. Dorazio. 2013. Too risky to settle: avian community structure changes in response to perceived predation risk on adults and offspring. Proceedings of the Royal Society B 280: 1764.
Boomboxes amplify predatory bird sounds and are used as cues
Body temperature (Tb) increases for no-flight birds between the first hypothermic flight attempt and a normothermic flight test conducted 20 min later.
Each line on the graph represents an individual bird that could not fly during the first flight attempt of the night. Birds that were unable to fly while hypothermic
were able to fly after warming up to near-normal daytime Tb, with several birds exceeding their normal daytime Tb (indicated by values that fall above ‘0’ on the y-axis).
Different line types indicate the duration of food deprivation experienced by a given bird (1–3 days).
Nocturnal hypothermia: a cost of being cool -- Many birds use regulated drops in night-time body temperature (Tb) to conserve energy critical to winter survival. However, a significant degree of hypothermia may limit a bird's ability to respond to predatory attack. Despite this likely energy–predation trade-off, the behavioral costs of avian hypothermia have yet to be examined. Carr and Lima (2013) monitored the nocturnal hypothermia of Mourning Doves (Zenaida macroura) in a laboratory setting in response to food deprivation. Nocturnal flight tests were used to quantify the flight ability of hypothermic doves. Many hypothermic doves (39% of tests) could not fly while carrying a small weight, but could do so after quickly warming up to typical daytime Tb. Doves that were unable to fly during their first test were more hypothermic than those that could fly, with average Tb reductions of 5.3°C and 3.3°C, respectively, but there was no overall indication of a threshold Tb reduction beyond which doves were consistently incapable of flight. These results suggest that energy-saving hypothermia interferes with avian antipredator behavior via a reduction in flight ability, likely leading to a trade-off between energy-saving hypothermia and the risk of predation.
Carr, J. M., and S. L. Lima. 2013. Nocturnal hypothermia impairs flight ability in birds: a cost of being cool. Proceedings of the Royal Society B 280: 1772.
Alpine Swifts are native to mountains from souther Europe to the Himalayas (Wikipedia Commons).
200-day non-stop flight -- Being airborne is considered to be energetically more costly as compared with being on the ground or in water. Birds migrating or foraging while airborne are thought to spend some time resting on the ground or water to recover from these energetically demanding activities. However, for several decades ornithologists have claimed that some swifts may stay airborne for almost their whole lifetime. Liechti et al. (2013) provided the first unequivocal evidence that an individual bird of the Alpine Swift (Tachymarptis melba) can stay airborne for migration, foraging and roosting over a period of more than 6 months. To date, such long-lasting locomotive activities had been reported only for animals living in the sea. Even for an aerodynamically optimized bird, like the Alpine Swift, flying requires a considerable amount of energy for continuous locomotive control. These data imply that all vital physiological processes, including sleep, can be perpetuated during flight.
Liechti, F., W. Witvliet, R. Weber, and E. Bächler. 2013. First evidence of a 200-day non-stop flight in a bird. Nature Communications 4: 2554.
Alpine Swfit fly nonstop for 200 days
Migrating birds fly nonstop for more than six months
(a) Monthly distribution of observed deaths among adult raptors.
(b) Daily mortality rates during four main periods of the year for adult raptors.
(c) Total mortality during four main periods of the year for adult raptors.
Geographical distribution of cases of (probable) mortality of adult raptors during (a) autumn and (b) spring migration. Symbols show positions where birds have died according to satellite tracking information. Blue = Osprey, green = Marsh Harrier, and orange = Montagu's Harrier.
When and where does mortality occur during migration? -- Information about when and where animals die is important to understand population regulation. In migratory animals, mortality might occur not only during the stationary periods (e.g. breeding and wintering) but also during the migration seasons. However, the relative importance of population limiting factors during different periods of the year remains poorly understood, and previous studies mainly relied on indirect evidence. Here, we provide direct evidence about when and where migrants die by identifying cases of confirmed and probable deaths in three species of long-distance migratory raptors tracked by satellite telemetry. Klaassen et al. (2013) found that mortality rate was about six times higher during migration seasons than during stationary periods. However, total mortality was surprisingly similar between periods, which can be explained by the fact that risky migration periods are shorter than safer stationary periods. Nevertheless, more than half of the annual mortality occurred during migration. In addition, spring mortality occurred mainly in Africa in association with the crossing of the Sahara desert, while most mortality during autumn took place in Europe. These results strongly suggest that events during the migration seasons have an important impact on the population dynamics of long-distance migrants. Mortality during spring migration may account for short-term annual variation in survival and population sizes, while mortality during autumn migration may be more important for long-term population regulation (through density-dependent effects).
Klaassen, R. H. G., M. Hake, R. Strandberg, B. J. Koks, C. Tierweiler, K.-M. Exo, F. Bairlein, and T. Alerstam. 2013. When and where does mortality occur in migratory birds? Direct evidence from long-term satellite tracking of raptors. Journal of Animal Ecology, early view.
Competitive ability of soaring birds -- The ability of many animals to access and exploit food is dependent on the ability to move. In the case of scavenging birds, which use soaring flight to locate and exploit ephemeral resources, the cost and speed of movement vary with meteorological factors. These factors are likely to modify the nature of interspecific interactions, as well as individual movement capacity, although the former are less well understood. Shepard and Lambertucci (2013) used aeronautical models to examine how soaring performance varies with weather within a guild of scavenging birds and the consequences this has for access to a common resource. Birds could be divided broadly into those with low wing loading that are more competitive in conditions with weak updraughts and low winds (black vultures and caracaras), and those with high wing loading that are well adapted for soaring in strong updraughts and moderate to high winds (Andean condors). Spatial trends in meteorological factors seem to confine scavengers with high wing loading to the mountains where they out-compete other birds; a trend that is borne out in worldwide distributions of the largest species. However, model predictions and carcass observations suggest that the competitive ability of these and other birds varies with meteorological conditions in areas where distributions overlap. This challenges the view that scavenging guilds are structured by fixed patterns of dominance and suggests that competitive ability varies across spatial and temporal scales, which may ultimately be a mechanism promoting diversity among aerial scavengers.
Shepard, E. L. C., and S. A. Lambertucci. 2013. From daily movements to population distributions: weather affects competitive ability in a guild of soaring birds. Journal of the Royal Society Interface 10: no. 88.
Relationship between residual brain size and levels of baseline and peak corticosterone. Residual brain mass was calculated
as residuals from a linear regression between log body mass (independent variable) and log brain mass (response variable). Lines
are linear regression fits to the raw data in each life-history stage.
Smart birds = less stress -- Vertebrates respond to unpredictable noxious environmental stimuli by increasing secretion of glucocorticoids (CORT). Although this hormonal stress response is adaptive, high levels of CORT may induce significant costs if stressful situations are frequent. Thus, alternative coping mechanisms that help buffer individuals against environmental stressors may be selected for when the costs of CORT levels are elevated. By allowing individuals to identify, anticipate and cope with the stressful circumstances, cognition may enable stress-specific behavioural coping. Although there is evidence that behavioural responses allow animals to cope with stressful situations, it is unclear whether or not cognition reduces investment in the neuroendocrine stress response. Lendvai et al. (2013) found that species of birds with larger brains relative to their body size show lower baseline and peak CORT levels than species with smaller brains. This relationship is consistent across life-history stages, and cannot be accounted for by differences in life history and geographical latitude. Because a large brain is a major feature of birds that base their lifetime in learning new things, these results support the hypothesis that enhanced cognition represents a general alternative to the neuroendocrine stress response.
Lendvai, Á. Z., V. Bókony, F. Angelier, O. Chastel, and D. Sol. 2013. Do smart birds stress less? An interspecfic relationship between brain size and corticosterone levels. Proceedings of the Royal Society B 280: no. 1770.
Big-brained birds keep their cool
Evolution of the avian brain -- Features that were once considered exclusive to modern birds, such as feathers and a furcula, are now known to have first appeared in non-avian dinosaurs. However, relatively little is known of the early evolutionary history of the hyperinflated brain that distinguishes birds from other living reptiles and provides the important neurological capablities required by flight. Balanoff et al. (2013) used high-resolution computed tomography to estimate and compare cranial volumes of extant birds, the early avialan Archaeopteryx lithographica, and a number of non-avian maniraptoran dinosaurs that are phylogenetically close to the origins of both Avialae and avian flight. Previous work established that avian cerebral expansion began early in theropod history and that the cranial cavity of Archaeopteryx was volumetrically intermediate between these early forms and modern birds. Data obtained by Balanoff et al. (2013) indicate that the relative size of the cranial cavity of Archaeopteryx is reflective of a more generalized maniraptoran volumetric signature and in several instances is actually smaller than that of other non-avian dinosaurs. Thus, bird-like encephalization indices evolved multiple times, supporting the conclusion that if Archaeopteryx had the neurological capabilities required of flight, so did at least some other non-avian maniraptorans. This is congruent with recent findings that avialans were not unique among maniraptorans in their ability to fly in some form.
Balanoff, A. M., G. S. Bever, T. B. Rowe, and M. A. Norell. 2013. Evolutionary origins of the avian brain. Nature 501: 93-96.
Archaeopteryx was no birdbrain, but neither was it bird brained
Studying flight capability in dinosaur brains
(A) Migration map for the eastern migratory population of Whooping Cranes (2002–2009). Each bird’s summer and winter ranges were identified in each year using the mean
coordinates of all locations for that individual during summer and winter times when birds were not migrating. The straight-line path for each migration event linking consecutive summer and winter (or
winter and summer) ranges was identified for each bird. The deviation of each migratory relocation from the straight-line path was calculated and used as a simple proxy for migratory performance. Variation
in data availability over the 8 years of the study precluded application of more complex measures of deviation, such as those based on full trajectories that might take into account heterogeneity in wind
strength and direction, topography, and the availability of suitable stopover sites. (B) Typical migratory pattern for two 1-year-old individuals migrating in spring 2005 traveling without (red) and with (blue) older birds.
Social learning of migratory performance -- Successful bird migration can depend on individual learning, social learning, and innate navigation programs. Using 8 years of data on migrating whooping cranes, Mueller et al. (2013) were able to partition genetic and socially learned aspects of migration. Specifically, data from a reintroduced population where all birds were captive bred and artificially trained by ultralight aircraft on their first lifetime migration were analyzed. For subsequent migrations, in which birds fly individually or in groups but without ultralight escort, evidence for long-term social learning was found, but no effect of genetic relatedness on migratory performance. Social learning from older birds reduced deviations from a straight-line path, with 7 years of experience yielding a 38% improvement in migratory accuracy.
Mueller, T., R. B. O'Hara, S. J. Converse, R. P. Urbanek, and W. F. Fagan. 2013. Social learning of migratory performance. Science 341: 999-1002.
Practice makes perfect: endangered Whooping Cranes rely on social learning for migration
Nurture, not nature: Whooping Cranes learn to migrate from their elders
Old Whooping Cranes keep the young ones on course
Learning how to migrate: young Whoopers stay the course when they follow a wise old bird
Functional extinction of birds drives changes in seed size -- Local extinctions have cascading effects on ecosystem functions, yet little is known about the potential for the rapid evolutionary change of species in human-modified scenarios. Galetti et al. (2013) found that the functional extinction of large-gape seed dispersers in the Brazilian Atlantic forest is associated with the consistent reduction of the seed size of a keystone palm species. Among 22 palm populations, areas deprived of large avian frugivores for several decades present smaller seeds than nondefaunated forests, with negative consequences for palm regeneration. Coalescence and phenotypic selection models indicate that seed size reduction most likely occurred within the past 100 years, associated with human-driven fragmentation. The fast-paced defaunation of large vertebrates is most likely causing unprecedented changes in the evolutionary trajectories and community composition of tropical forests.
Galetti, M. et al. 2013. Functional extinction of birds drives rapid evolutionary changes in seed size. Science 340: 1086-1090.
How human activity - and extinctions - are driving evolution
Big-mouthed toucans key to forest evolution
Brazil rainforest deforestation leads to seed shrinkage
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.
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.
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.
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.
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.
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.
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.
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
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
How owls swivel their heads
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.
Wu, L.-Q., and J. D. Dickman. 2012. Neural correlates of a magnetic sense. Science 336: 1054-1057.
An avian magnetometer
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.
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.
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.
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.
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.
Elbroch, L. M., and H. U. Wittmer. 2013. Nuisance ecology: do scavenging condors exact foraging costs on pumas in Patagonia? PLoS ONE 8: e53595.
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.
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.
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.
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.
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)  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.
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.
A songbird's epic migration across hemispheres
Male Northern Wheatear