Instream habitat use by blue duck (Hymenolaimus malacorhynchos) in a New Zealand river

1. The feeding habitat of a river specialist, blue duck (Hymenolaimus malacorhynchos (Gmelin 1789): Anatidae), was characterized in terms of water depth and velocity on eight occasions over a 13-month period in a river in the central North Island of New Zealand using video to record activity and relocate feeding sites. 2. Of the five feeding activities identified (‘pecking’, ‘grazing’, ‘head-dipping’, up-ending’ and ‘diving’), adult blue duck used mostly head-dipping (> 60% of feeding events on all dates), although diving or grazing from submerged surfaces of exposed boulders comprised major proportions of feeding behaviour (up to 33%) on occasions. Variations in feeding behaviour between dates partly reflected changes in antecedent flow conditions and the annual cycle of the birds. 3. Grazing and diving occurred in significantly faster water (mostly 0.3–0.45 m s^–1) and at significantly different depths (mean = 0.10 and 0.55 m, respectively) than head-dipping (0.20 m depth and 0.28 m s^–1 velocity). Adult feeding depths and velocities at four sites on different dates averaged 0.20 m and 0.31 m s^–1, respectively. Most feeding by 3–4-week-old ducklings occurred over a similar distribution of water velocities to adults but over a wider range of depths. 4. Adult birds fed in significantly shallower and lower velocity water than was available on the two dates that comparisons could be made. Ducklings also fed over a slower range of water velocities but were not selective in terms of water depth. 5. Energetically more expensive search methods were employed at times of high apparent energy demand to access flow microhabitats where larger bodied prey were more likely to be encountered. 6. These data indicate that, like other aquatic organisms, river birds can be influenced by basic hydraulic elements of river flow, but show at the same time that adult blue duck can accommodate variable lotic environments efficiently.     

Visual fields,foraging and collision vulnerability in Gyps vultures

The visual fields of vultures contain a small binocular region and large blind areas above, below and behind the head. Head positions typically adopted by foraging vultures suggest that these visual fields provide comprehensive visual coverage of the ground below, prohibit the eyes from imaging the sun and provide extensive visual coverage laterally. However, vultures will often be blind in the direction of travel. We conclude that by erecting structures such as wind turbines, which extend into open airspace, humans have provided a perceptual challenge that the vision of foraging vultures cannot overcome.     

Visual fields and foraging ecology of Blacksmith Lapwings Vanellus armatus

The visual fields of Blacksmith Lapwings Vanellus armatus show the characteristics of visual guided foragers that use precision pecking for prey capture – a binocular field of narrow width and limited vertical extent, with the projection of the bill close to its centre and a large blind area above and behind the head. The topography of the total field, particularly the binocular field, is similar to that of European Golden Plovers Pluvialis apricaria. We suggest that the ‘foot‐trembling’ behaviour associated with foraging in Plovers is not under visual guidance but forces the escape of hidden prey, which is detected when the prey item moves into the binocular field to enable its capture in the bill. Foot‐trembling thus functions to extend the effective foraging area of a bird beyond the limits of its visual field.     

Differences in foraging ecology determine variation in visual fields in ibises and spoonbills (Threskiornithidae)

Variations in visual field topography among birds have been interpreted as adaptations to the specific perceptual challenges posed by the species’ foraging ecology. To test this hypothesis we determined visual field topography in four bird species which have different foraging ecologies but are from the same family: Puna Ibis Plegadis ridgwayi (probes for prey in the soft substrates of marsh habitats), Northern Bald Ibis Geronticus eremita (surface pecks for prey in dry terrestrial habitats), African Spoonbill Platalea alba and Eurasian Spoonbill Platalea leucorodia (bill‐sweeps for prey in shallow turbid waters). All four species employ tactile cues provided by bill‐tip organs for prey detection. We predicted that the visual fields of these species would show general features similar to those found in other birds whose foraging is guided by tactile cues from the bill (i.e. bill falling outside the frontal binocular field and comprehensive visual coverage of the celestial hemisphere). However, the visual fields of all four species showed general features characteristic of birds that take food directly in the bill under visual guidance (i.e. a narrow and vertically long binocular field in which the projection of the bill tip is approximately central and with a blind area above and behind the head). Visual fields of the two spoonbills were very similar but differed from those of the ibises, which also differed between themselves. In the spoonbills, there was a blind area below the bill produced by the enlarged spatulate bill tip. We discuss how these differences in visual fields are related to the perceptual challenges of these birds’ different foraging ecologies, including the detection, identification and ingestion of prey. In particular we suggest that all species need to see binocularly around the bill and between the opened mandibles for the identification of caught prey items and its transport to the back of the mouth. Our findings support the hypothesis that sensory challenges associated with differences in foraging ecology, rather than shared ancestry or the control of locomotion, are the main determinants of variation in visual field topography in birds.     

Visual sensitivity and foraging in social wasps

Summary While there is a distinction between that intensity of illumination which permits social wasps to forage, and that to which a sessile worker can respond, nevertheless illumination is the most critical of the environmental factors which control the activity of wasps. Low temperatures, high winds, and heavy rain all reduce activity but unless exceptionally severe do not wholly stop it. At dawn, when the critical level of illumination is attained, workers leave the nest, but at dusk they will not leave should the same critical level be due in the course of the foraging flight, after which they could not return.The three species of wasp,Vespula vulgaris, V. rufa, andV. germanica have a common threshold of illumination, although the hornet,Vespa crabro can forage in moonlight at an altogether lower illumination. Honey-bees normally need a still higher illumination than do wasps.In all these species, the thresholds of illumination are related to the length of the compound eyes, so that species with large eyes need less light by which to forage. Moreover, there is a slight difference between the threshold at dawn when workers leave the nest, and that at dusk, when they must needs have sufficient light by which to return. This difference is almost constant for each species, when, as is customary, one measures it on a logarithmic scale.Lastly, the estimates, which these experiments provide, of the threshold illuminations depend stochastically on the number of workers foraging. A correction for this bias is given.

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Sommaire Parmi les facteurs du milieu qui contrôlent l'activité des guêpes, celui de l'intensité de lumière est le plus important; toutefois on note une différence entre l'intensité de lumière qui permet aux guêpes sociales de fourrager, et celle qui produit une réponse des ouvrières sessiles.En général, les basses températures, les vents forts, et les grandes pluies réduisent leur activité, mais ces facteurs ne l'arrêtent pas complètement, à moins qu'ils ne soient très marqués.A l'aube, quand le niveau critique de lumière est atteint, les ouvrières quittent le guêpier, mais, le soir, si elles s'attendent à ce que la lumière vienne à s'abaisser au cours de leur sortie au-dessous du niveau critique, elles ne sortent pas.Les trois espèces de guêpe,Vespula vulgaris, V. rufa, etV. germanica, réagissent au même seuil de lumière, mais le frelon,Vespa crabro, est capable de fourrager au clair de lune par une lumière moins intense. Normalement, les abeilles exigent une lumière plus intense que les guêpes.Dans toutes ces espèces, le seuil de lumière se rapporte à la hauteur des yeux composés, par conséquent les espèces pourvues de grands yeux sont à même de fourrager par une lumière moins intense. De plus, il y a une légère différence entre le seuil de lumière à l'aube, quand les ouvrières quittent le guêpier, et celui du soir lorsqu'elles ont besoin d'une lumière suffisante pour rentrer. Cette différence, quand elle est mesurée à l'échelle logarithmique, comme il est d'usage, est presque constante pour chaque espèce.Enfin, les évaluations du seuil de lumière dans ces expériences dépendent stochastiquement du nombre d'ouvrières en train de fourrager. On a tenu compte de ce fait.

     

Visual perception and social foraging in birds

Birds gather information about their environment mainly through vision by scanning their surroundings. Many prevalent models of social foraging assume that foraging and scanning are mutually exclusive. Although this assumption is valid for birds with narrow visual fields, these models have also been applied to species with wide fields. In fact, available models do not make precise predictions for birds with large visual fields, in which the head-up, head-down dichotomy is not accurate and, moreover, do not consider the effects of detection distance and limited attention. Studies of how different types of visual information are acquired as a function of body posture and of how information flows within flocks offer new insights into the costs and benefits of living in groups.     

Visual fields in hornbills: precision-grasping and sunshades

Retinal visual fields were determined in Southern Ground Hornbills Bucorvus leadbeateri and Southern Yellow-billed Hornbills Tockus leucomelas (Coraciiformes, Bucerotidae) using an ophthalmoscopic reflex technique. In both species the binocular field is relatively long and narrow with a maximum width of 30° occurring 40° above the bill. The bill tip projects into the lower half of the binocular field. This frontal visual field topography exhibits a number of key features that are also found in other terrestrial birds. This supports the hypothesis that avian visual fields are of three principal types that are correlated with the degree to which vision is employed when taking food items, rather than with phylogeny. However, unlike other species studied to date, in both hornbill species the bill intrudes into the binocular field. This intrusion of the bill restricts the width of the binocular field but allows the birds to view their own bill tips. It is suggested that this is associated with the precision-grasping feeding technique of hornbills. This involves forceps-like grasping and manipulation of items in the tips of the large decurved bill. The two hornbill species differ in the extent of the blind area perpendicularly above the head. Interspecific comparison shows that eye size and the width of the blind area above the head are significantly correlated. The limit of the upper visual field in hornbills is viewed through the long lash-like feathers of the upper lids and these appear to be used as a sunshade mechanism. In Ground Hornbills eye movements are non-conjugate and have sufficient amplitude (30–40°) to abolish the frontal binocular field and to produce markedly asymmetric visual field configurations.     

The visual fields of Common Guillemots Uria aalge and Atlantic Puffins Fratercula arctica: foraging,vigilance and collision vulnerability

Significant differences in avian visual fields are found between closely related species that differ in their foraging technique. We report marked differences in the visual fields of two auk species. In air, Common Guillemots Uria aalge have relatively narrow binocular fields typical of those found in non‐passerine predatory birds. Atlantic Puffins Fratercula arctica have much broader binocular fields similar to those that have hitherto been recorded in passerines and in a penguin. In water, visual fields narrow considerably and binocularity in the direction of the bill is probably abolished in both auk species. Although perceptual challenges associated with foraging are similar in both species during the breeding season, when they are piscivorous, Puffins (but not Guillemots) face more exacting perceptual challenges when foraging at other times, when they take a high proportion of small invertebrate prey. Capturing this prey probably requires more accurate, visually guided bill placement and we argue that this is met by the Puffin's broader binocular field, which is retained upon immersion; its upward orientation may enable prey to be seen in silhouette. These visual field configurations have potentially important consequences that render these birds vulnerable to collision with human artefacts underwater, but not in air. They also have consequences for vigilance behaviour.     

Possible interactions between visual and tactile memories in octopus

Octopuses were trained first with a tactile and then a visual discrimination and the two sets of memories were then made to conflict. A negative visual memory (white) blocks the effect of a previously learned positive tactile memory (either rough or smooth) but only in the period immediately after seeing the colour. There is no longer‐term effect on the positive tactile memory. A positive visual memory (black) was not able to reverse a previously learned negative tactile memory (rough). A negative tactile memory (rough) had no effect on previously established positive visual memories (black or white).

The only interactions between the visual and tactile memories are a result of the sharing of final common paths to the arms. There is no good evidence of second order conditioning under these circumstances.     

Visual and tactile communication in Macaca arctoides and its ontogenetic development

This film is based on a 500-hour observational study of a laboratory social group of stump-tailed macaques. It demonstrates the visual and tactile adult communicative repertoire of the species and shows how the adult communication system develops in infants. The neonate produces only a small communicative repertoire of reflexive tactile behaviors that function primarily in clinging to the mother's fur (grasping) and nursing (rooting and sucking); their communicative function is secondary. As the infant develops, its repertoire becomes larger. The stereotyped, reflexive, tactile behaviors drop out of the repertoire; and more complex behaviors, which are mainly communicative in function and occur in response to complex environmental situations, appear. Most adult behaviors develop slowly. Behaviors present in one developmental stage often change gradually, both in form and in function as the infant matures; after modification, they appear as new behaviors in later stages. For example, the neonatal tactile sucking behavior gradually develops into the lipsmacking expression, a strictly communicative expression in the adult.     

The visual fields of two ground‐foraging birds,House Finches and House Sparrows,allow for simultaneous foraging and anti‐predator vigilance

In birds, differences in the extent and position of the binocular visual field reflect adaptations to varying foraging strategies, and the extent of the lateral portion of the field may reflect anti‐predator strategies. The goal of this study was to describe and compare the visual fields of two ground‐foraging passerines, House Finch Carpodacus mexicanus and House Sparrow Passer domesticus. We found that both species have a binocular field type that is associated with the accurate control of bill position when pecking. Both species have eye movements of relatively large amplitude, which can produce substantial variations in the configuration of the binocular fields. We propose that in these ground foragers, their relatively wide binocular fields could function to increase foraging efficiency by locating multiple rather than single food items prior to pecking events. The lateral fields of both species are wide enough to facilitate the detection of predators or conspecifics while head‐down foraging. This suggests that foraging and scanning are not mutually exclusive activities in these species, as previously assumed. Furthermore, we found some slight, but significant, differences between species: House Sparrow binocular fields are both wider and vertically taller, and the blind area is wider than in House Finches. These differences may be related to variations in the degree of eye movements and position of the orbits in the skull.     

Visual performance fields: frames of reference

Performance in most visual discrimination tasks is better along the horizontal than the vertical meridian (Horizontal-Vertical Anisotropy, HVA), and along the lower than the upper vertical meridian (Vertical Meridian Asymmetry, VMA), with intermediate performance at intercardinal locations. As these inhomogeneities are prevalent throughout visual tasks, it is important to understand the perceptual consequences of dissociating spatial reference frames. In all studies of performance fields so far, allocentric environmental references and egocentric observer reference frames were aligned. Here we quantified the effects of manipulating head-centric and retinotopic coordinates on the shape of visual performance fields. When observers viewed briefly presented radial arrays of Gabors and discriminated the tilt of a target relative to homogeneously oriented distractors, performance fields shifted with head tilt (Experiment 1), and fixation (Experiment 2). These results show that performance fields shift in-line with egocentric referents, corresponding to the retinal location of the stimulus.     

Movements and foraging effort of Steller's Eiders and Harlequin Ducks wintering near Dutch Harbor, Alaska

ABSTRACT.   We studied the movements and foraging effort of radio-marked Steller's Eiders ( Polysticta stelleri ) and Harlequin Ducks ( Histrionicus histrionicus ) to evaluate habitat quality in an area impacted by industrial activity near Dutch Harbor, Alaska. Foraging effort was relatively low, with Steller's Eiders foraging only 2.7 ± 0.6 (SE) hours per day and Harlequin Ducks 4.1 ± 0.5 hours per day. Low-foraging effort during periods of high-energetic demand generally suggests high food availability, and high food availability frequently corresponds with reductions in home range size. However, the winter ranges of Harlequin Ducks did not appear to be smaller than usual, with the mean range size in our study (5.5 ± 1.1 km²) similar to that reported by previous investigators. The mean size of the winter ranges of Steller's Eiders was similar (5.1 ± 1.3 km²), but no comparable estimates are available. Eutrophication of the waters near Dutch Harbor caused by seafood processing and municipal sewage effluent may have increased populations of the invertebrate prey of these sea ducks and contributed to their low-foraging effort. The threat of predation by Bald Eagles ( Haliaeetus leucocephalus ) that winter near Dutch Harbor may cause Steller's Eiders and Harlequin Ducks to move further offshore when not foraging, contributing to an increase in range sizes. Thus, the movement patterns and foraging behavior of these ducks likely represent a balance between the cost and benefits of wintering in a human-influenced environment.     

Ubiquitous crossmodal Stochastic Resonance in humans: auditory noise facilitates tactile, visual and proprioceptive sensations

Background

Stochastic resonance is a nonlinear phenomenon whereby the addition of noise can improve the detection of weak stimuli. An optimal amount of added noise results in the maximum enhancement, whereas further increases in noise intensity only degrade detection or information content. The phenomenon does not occur in linear systems, where the addition of noise to either the system or the stimulus only degrades the signal quality. Stochastic Resonance (SR) has been extensively studied in different physical systems. It has been extended to human sensory systems where it can be classified as unimodal, central, behavioral and recently crossmodal. However what has not been explored is the extension of this crossmodal SR in humans. For instance, if under the same auditory noise conditions the crossmodal SR persists among different sensory systems.

Methodology/Principal Findings

Using physiological and psychophysical techniques we demonstrate that the same auditory noise can enhance the sensitivity of tactile, visual and propioceptive system responses to weak signals. Specifically, we show that the effective auditory noise significantly increased tactile sensations of the finger, decreased luminance and contrast visual thresholds and significantly changed EMG recordings of the leg muscles during posture maintenance.

Conclusions/Significance

We conclude that crossmodal SR is a ubiquitous phenomenon in humans that can be interpreted within an energy and frequency model of multisensory neurons spontaneous activity. Initially the energy and frequency content of the multisensory neurons'' activity (supplied by the weak signals) is not enough to be detected but when the auditory noise enters the brain, it generates a general activation among multisensory neurons of different regions, modifying their original activity. The result is an integrated activation that promotes sensitivity transitions and the signals are then perceived. A physiologically plausible model for crossmodal stochastic resonance is presented.     

Visual perception: understanding visual cues to depth

A new study shows that, in vision, object blur can be a more accurate depth cue than stereo disparity.     

Disentangling olfactory and visual information used by field foraging birds

Foraging strategies of birds can influence trophic plant–insect networks with impacts on primary plant production. Recent experiments show that some forest insectivorous birds can use herbivore‐induced plant volatiles (HIPVs) to locate herbivore‐infested trees, but it is unclear how birds combine or prioritize visual and olfactory information when making foraging decisions. Here, we investigated attraction of ground‐foraging birds to HIPVs and visible prey in short vegetation on farmland in a series of foraging choice experiments. Birds showed an initial preference for HIPVs when visual information was the same for all choice options (i.e., one experimental setup had all options with visible prey, another setup with hidden prey). However, if the alternatives within an experimental setup included visible prey (without HIPV) in competition with HIPV‐only, then birds preferred the visual option over HIPVs. Our results show that olfactory cues can play an important role in birds’ foraging choices when visual information contains little variation; however, visual cues are preferred when variation is present. This suggests certain aspects of bird foraging decisions in agricultural habitats are mediated by olfactory interaction mechanisms between birds and plants. We also found that birds from variety of dietary food guilds were attracted to HIPVs; hence, the ability of birds to use plant cues is probably more general than previously thought, and may influence the biological pest control potential of birds on farmland.