Simultaneous Discrimination Learning in Chicks: Spatial Representations and Object Characteristics

Chicks were trained to discriminate (1) between two boxes of the same colour on the basis of their positions; (2) between two boxes of different colours on the basis of their positions or on the basis of their colours. No significant differences between these tasks appeared. Addition of colour and position improved learning when the boxes were entirely coloured but not when differently coloured discs were placed over the lids of two identical boxes. It is argued that in simultaneous discrimination learning chicks rely primarily on the “relative” position of the goal objects (i. e. in relation to each other) and utilize featural information (colour) to segregate the goal objects as distinct perceptual units. Results also stressed the role of “object characteristics” as opposed to the traditional notion of “cues”.     

Learning of colour and position cues in domestic chicks: Males are better at position,females at colour

Male and female chicks were trained to discriminate between two boxes for food reinforcement. The correct box was indicated by a colour cue (red or brown) and a position cue (right or left). After learning, the colour and the position cues were dissociated: the right-left location of the two boxes was alternated between trials according to a semi-random sequence.The chicks were thus retrained to discriminate either on the basis of colour (irrespective of position) or on the basis of position (irrespective of colour). There were no sex differences, during training, with both position and colour cues. However, during re-training females performed better on the colour learning task and males performed better on the position learning task.     

Spatial reorientation by geometry with freestanding objects and extended surfaces: a unifying view

The macroscopic, three-dimensional surface layout geometry of an enclosure apparently provides a different contribution for spatial reorientation than the geometric cues associated with freestanding objects arranged in arrays with similar geometric shape. Here, we showed that a unitary spatial representation can account for the capability of animals to reorient both by extended surfaces and discrete objects in a small-scale spatial task. We trained domestic chicks to locate a food-reward from an opening on isolated cylinders arranged either in a geometrically uninformative (square-shaped) or informative (rectangular-shaped) arrays. The arrays were located centrally within a rectangular-shaped enclosure. Chicks trained to access the reward from a fixed position of openings proved able to reorient according to the geometric cues specified by the shape of the enclosure in all conditions. Chicks trained in a fixed position of opening with geometric cues provided both by the arena and the array proved able to reorient according to each shape separately. However, chicks trained to access the reward from a variable position of openings failed to reorient. The results suggest that the physical constrains associated with the presence of obstacles in a scene, rather than their apparent visual extension, are crucial for spatial reorientation.     

Visual memory of shapes in quail chicks: discrimination among 2-dimensional objects

Newly hatched chicks spontaneously peck at conspicuous objects, and soon learn to discriminate between edible food particles and inedible objects. To examine whether this discrimination is based on a chick's ability to memorize objects by shape cues, we analyzed the pecking behavior. One- to 3-day old quail chicks (Coturnix japonica) were presented with dry objects of different shapes (ball, disk, triangle and T-shape) of similar size (4 mm) and color (green). Habituation occurred after repeated presentation of any one of these objects (duration: 30 sec; interval: 4 min). When chicks showed significantly more pecks at a novel object (dishabituation), we assumed that chicks had memorized the habituated shapes and distinguished the novel object. Chicks did not show dishabituation between a ball and a disk. On the other hand, chicks discriminated a triangle or T-shape from the memorized image of disk, but did not memorize either triangle or T-shape by its shape. Similarly, chicks did not memorize the size of disks as a reference for subsequent pecking behavior. Chicks proved to have a limited ability to memorize shape and size cues for selective pecking behavior, in strong contrast to their accurate memorization of colors.     

Predisposed visual memory of shapes in quail chicks

Newly hatched chicks will spontaneously peck at conspicuous objects in their field of view, and soon learn to distinguish between edible food particles and unpleasant tasting objects. To examine whether the selective pecking is based on the ability to memorize shapes, we analyzed pecking behavior of 1- to 2-days-old quail chicks (Coturnix japonica) by using ball- and triangle-shaped beads both painted in green. Repeated presentation of dry bead (either ball or triangle) resulted in a progressively fewer number of pecks (habituation). When chicks were tested by triangle after repeated presentation of ball, chicks showed a significant increase in the number of pecks at the triangle (dishabituation). On the other hand, when tested by ball after a series of triangle presentations, pecking frequency did not increase (no dishabituation). Chicks thus distinguished the triangle as a novel object after being habituated to ball, but did not respond to the ball after triangle. A similar asymmetry was found in one-trial passive avoidance task. Chicks were pre-trained by water-coated (neutral) triangle and then trained by methylanthranilate-coated (aversive) ball. In this case, most chicks learned to avoid the ball, and half of these successful learners pecked at the triangle; they distinguished triangle from ball. When chicks were pre-trained by neutral ball and trained by aversive triangle, on the other hand, most chicks did not distinguish the ball from triangle, and showed a generalized avoidance for both beads. Chicks may be innately predisposed to memorize a limited category of shapes such as ball, and associate them with selective avoidance.     

Accurate visual memory of colors in controlling the pecking behavior of quail chicks

Animals are predisposed to memorize specific features of objects they encounter, and to link them with behavioral outputs in a selective manner. In this study, we examined whether chicks memorize objects by colors, and how they exploit the memorized color cues for selective pecking in 1- to 2-days-old quail chicks (Coturnix japonica). Ball-shaped beads painted in green (G), yellowish green (YG) and the intermediate color (YGG) were used. Repetitive presentation of a bead (interval: 4.5 min) resulted in gradually fewer pecks (habituation). Subsequent presentation of a different color caused proportionately more pecks (dishabituation); e.g., after habituation to the G bead, the YG bead caused a stronger dishabituation than the YGG bead did. The dishabituation appeared symmetric; e.g., the YG bead caused as strong dishabituation after the G-habituation, as was caused by the G bead after the YG-habituation. Number of pecks could thus reveal the memory-based color perception in chicks. Similar discrimination of beads by memorized color cues was found after one-trial passive avoidance training, where chicks learned to avoid a bitter-tasting object without any differential pre-training experiences. However, proportion of the chicks that discriminated between different colors became progressively smaller at test 15 min, 1 hr, and 24 hr post-training. On the other hand, proportion of chicks that distinguished beads by non-color cues remained unchanged. Chicks may primarily form an accurate memory of colors, but gradually change the link between the color memory and the pecking behavior.     

Arithmetic in newborn chicks

Newly hatched domestic chicks were reared with five identical objects. On days 3 or 4, chicks underwent free-choice tests in which sets of three and two of the five original objects disappeared (either simultaneously or one by one), each behind one of two opaque identical screens. Chicks spontaneously inspected the screen occluding the larger set (experiment 1). Results were confirmed under conditions controlling for continuous variables (total surface area or contour length; experiment 2). In the third experiment, after the initial disappearance of the two sets (first event, FE), some of the objects were visibly transferred, one by one, from one screen to the other (second event, SE). Thus, computation of a series of subsequent additions or subtractions of elements that appeared and disappeared, one by one, was needed in order to perform the task successfully. Chicks spontaneously chose the screen, hiding the larger number of elements at the end of the SE, irrespective of the directional cues provided by the initial (FE) and final (SE) displacements. Results suggest impressive proto-arithmetic capacities in the young and relatively inexperienced chicks of this precocial species.     

Navigational ability in the domestic fowl (Gallus gallus domesticus)

Little is known about the navigational abilities of domestic fowl. The question of how chickens represent and orient in space becomes relevant when they are kept in non-cage systems. Since the sun is known to be the dominant spatial organiser in other diurnal bird species, we started our investigation of the chicken’s spatial abilities by subjecting them to a food-searching task with the sun as the only consistent visual cue. In an additional experiment we tried to rule out the use of auditory cues in finding a food reward.

Eight ISA Brown chicks were housed in outdoor pens. A separate test arena comprised an open-topped, opaque-sided wooden octagon (2 m wide and 1.5 m high). Eight goal boxes with food pots were attached to each of the arena sides; a wooden barrier inside each goal box prevented the birds from seeing the food pot before entering. After habituation we tested during five daily 5 min trials whether the chicks were able to find food in a systematically allocated goal direction. Food residue in every foot pot controlled for the use of olfactory cues and no external landmark cues were visible. Every day each box was unpredictably moved to a randomly assigned side of the arena and the side to face north was also randomly allocated, to prevent the chicks from using cues other than the sun’s position. Circular statistics were used to determine whether birds moved in a non-random direction and if so, if they significantly oriented goalwards. The results showed that seven of the eight birds moved significantly in the goal direction. It seems likely that the chicks used the sun to orient. Due to weather constraints only four chicks received the same treatment on a new location, to rule out the use of auditory cues. Two of these four chicks significantly moved in the goal direction.

The results from our experiments show that domestic chicks use spatial memory to orient towards a hidden goal. Moreover, their orientation is most likely to be based on sun cues opening up the possibility that the sun compass may dominate even in this ancestrally predominantly ground-living forest bird.     

Orientation of attention in the visual space]

The display was composed of four boxes, horizontally aligned above the fixation point. In Experiment I, each box was cued by a digit shown at fixation. In Experiment II there were only two numeric cues, signalling the inner or the outer boxes, depending on the experimental condition. The subject was instructed to orient attention to the cued box, and to respond to the imperative stimulus as fast as possible, wherever it appeared. By using four time interval (SOAs), we tried to determine the route covered by attention movements. In Experiment I, with the shortest SOA (100 msec), it was shown that attention does not reach the cued box through a direct path. Rather it moves first on the inner boxes, thereafter focusing on the cued location. The same results were obtained in Experiment II, where the cue directed attention to the inner boxes. When the external boxes were cued, however, this trend was not observed.     

The effects of the visual environment on responses to colour by domestic chicks

It is well known that development of vision is affected by experience, but there are few studies of environmental effects on colour vision. Natural scenes contain predominantly a restricted range of reflectance spectra, so such effects might be important, perhaps biasing visual mechanisms towards common colours. We investigated how the visual environment affects colour preferences of domestic chicks ( Gallus gallus), by training week-old birds to select small food containers distinguished from an achromatic alternative either by an orange or by a greenish-blue colour. Chicks that had been raised in control conditions, with long-wavelength-dominated reflectance spectra, responded more readily to orange than to blue. This was not due to avoidance of blue, as increasing saturation enhanced the chicks' preference for the same hue. The advantage of orange was, however, reduced or abolished for chicks raised in an environment dominated by blue objects. This indicates that responses to coloured food are affected by experience of non-food objects. If colours of ordinary objects in the environment do influence responses to specialised visual signals this might help explain why biological signals directed at birds are often coloured yellow, orange or red; long-wavelength-dominated spectra being more prevalent than short-wavelength-dominated spectra.     

Changes in learning ability and mechanism during development of grasshopper nymphs, Melanoplus bivittatus

Abstract. In an experimental arena, Melanoplus bivittatus (Say) (Orthoptera: Acrididae) nymphs of four stadia were observed to determine whether they learn to associate food with positional or light-related cues. Nymphs were observed for 4 h in the arena containing one yellow box and one green box, then they were trained by placing food in the green box overnight. Following training, the responses of nymphs to green and yellow boxes were observed for a second 4 h period.
Before training, nymphs of all stadia visited the yellow box more frequently than the green box. Training did not affect the behaviour of second-stadium nymphs, but training increased the relative frequency of visits to the green box by third, fourth and fifth instars. Effects of training on duration of visits to boxes were not evident. Investigations of the mechanism of learning showed that positional cues were used by third-stadium nymphs, but that fourth and fifth instars responded to light-related cues. The progression from no learning in second instars, through use of positional cues by third instars, to use of light-related cues by fourth and fifth instars is probably associated with the greater mobility, greater food consumption, and more varied diet of older nymphs.     

Interaction between acquired preferences and developing predispositions during imprinting

Preferences of domestic chicks were studied either at approximately 2 h or approximately 24 h after exposure to a red box or a stuffed jungle fowl. Preferences of the chicks were measured in a simultaneous choice test involving these two stimuli. When tested at about 2 h, chicks preferred the object to which they had previously been exposed. Chicks tested at about 24 h showed a significantly greater preference for the jungle folw than those tested at about 2 h, regardless of the training stimulus. Birds that had been placed in a running wheel and exposed to diffuse light also showed an increasing preference for the fowl over time when tested in the same manner. These results may be accounted for in terms of an interaction between two processes, a developing predisposition for the fowl on the one hand and a preference acquired through learning on the other.     

Owl Monkeys (Aotus nigriceps and A. infulatus) Follow Routes Instead of Food-Related Cues during Foraging in Captivity

Foraging at night imposes different challenges from those faced during daylight, including the reliability of sensory cues. Owl monkeys (Aotus spp.) are ideal models among anthropoids to study the information used during foraging at low light levels because they are unique by having a nocturnal lifestyle. Six Aotus nigriceps and four A. infulatus individuals distributed into five enclosures were studied for testing their ability to rely on olfactory, visual, auditory, or spatial and quantitative information for locating food rewards and for evaluating the use of routes to navigate among five visually similar artificial feeding boxes mounted in each enclosure. During most experiments only a single box was baited with a food reward in each session. The baited box changed randomly throughout the experiment. In the spatial and quantitative information experiment there were two baited boxes varying in the amount of food provided. These baited boxes remained the same throughout the experiment. A total of 45 sessions (three sessions per night during 15 consecutive nights) per enclosure was conducted in each experiment. Only one female showed a performance suggestive of learning of the usefulness of sight to locate the food reward in the visual information experiment. Subjects showed a chance performance in the remaining experiments. All owl monkeys showed a preference for one box or a subset of boxes to inspect upon the beginning of each experimental session and consistently followed individual routes among feeding boxes.     

Spontaneous discrimination of possible and impossible objects by newly hatched chicks

Four-month-old infants can integrate local cues provided by two-dimensional pictures and interpret global inconsistencies in structural information to discriminate between possible and impossible objects. This leaves unanswered the issue of the relative contribution of maturation of biologically predisposed mechanisms and of experience with real objects, to the development of this capability. Here we show that, after exposure to objects in which junctions providing cues to global structure were occluded, day-old chicks selectively approach the two-dimensional image that depicted the possible rather than the impossible version of a three-dimensional object, after restoration of the junctions. Even more impressively, completely naive newly hatched chicks showed spontaneous preferences towards approaching two-dimensional depictions of structurally possible rather than impossible objects. These findings suggest that the vertebrate brain can be biologically predisposed towards approaching a two-dimensional image representing a view of a structurally possible three-dimensional object.     

Social recognition and approach in the chick: lateralization and effect of visual experience

Chicks, Gallus gallus domesticus, tested monocularly on day 3 after hatching recognize familiar versus unfamiliar conspecifics and choose to approach one or other when they use the left eye, whereas they approach familiar and unfamiliar chicks at random when they use the right eye. In experiment 1 we investigated the effects of light exposure of embryos prior to hatching on this particular form of lateralization. Irrespective of whether they hatched from eggs incubated in the dark or from eggs exposed to light during the final days of incubation, chicks using the left eye had higher choice scores (meaning they chose to approach either a familiar or an unfamiliar chick) than chicks using the right eye or both eyes. Therefore, light experience prior to hatching did not influence the lateralization of individual recognition or choice behaviour, although it did affect latency to move out of, and time spent in, the centre of the runway. Experiment 2 showed that visual/social experience posthatching influences choice behaviour: chicks housed in a group in the light for 12 h on day 1 posthatching made a clear choice between familiar and unfamiliar chicks when tested on day 3, but chicks kept in a group in the dark on day 1 did not make a choice, instead alternating between the two stimuli. In experiment 3 we found that posthatching visual/social experience increased the choice scores of chicks using the right eye and thereby removed any lateralization of choice behaviour. The results suggest that visual experience of a social group is required before chicks using their right eye (and left hemisphere) will pay attention to the cues that distinguish one chick from another. Chicks using their left eye (and right hemisphere) recognize the difference between individuals without requiring visual experience with other chicks. Copyright 2002 The Association for the Study of Animal Behaviour. Published by Elsevier Science Ltd. All rights reserved.     

Fruit or aposematic insect? Context-dependent colour preferences in domestic chicks.

Colours are common stimuli in signalling systems. Requirements to function well as a signal sometimes conflict between different signallers, and the same colour stimulus is used to convey completely different messages to the same receiver. Fruits and aposematic insects both use red coloration as a signal, in the former case to signal profitability and in the latter case as a warning signal. In two experiments, we investigated whether the domestic chick, an omnivorous predator, differed in its unconditioned preference or avoidance of red and green stimuli depending on whether or not the stimulus was an insect. The experiments were designed as preference tests between red and green painted prey. The prey were live insects and artificial fruits (experiment 1), and, to investigate the effect of movement, live and dead insects (experiment 2). The chicks did not show any difference in pecking preference between red and green when fruit-like stimuli were used, but when the prey were insects, green prey were strongly preferred to red prey, and prey movement did not affect this bias. Thus, young chicks may recognize prey as insects and then discriminate between different prey colorations, or one type of food may elicit an unlearned colour preference-avoidance response that is absent with another type of food.     

Diurnal variations in learning performance in chickens

Diurnal variations in the learning performance of young chicks were investigated using a visual discrimination task which requires birds to discrminate grains from a background of pebbles. Chicks accustomed to receiving fresh food daily in the morning were found to learn well during the day, in that they pecked almost exclusively at grains; but during the night they pecked indiscriminately at grains and pebbles. This occurred even though food was available ad libitum. Chicks accustomed to receiving fresh food daily in the evening learnt the task during the day, and also late at night. Thus the shape of the performance cycle depends in part on environmental factors. Other factors, such as activity, which may contribute to, or co-vary with, this variation in learning performance were investigated.     

Early rearing enrichments influenced nest use and egg quality in free-range laying hens

In Australia, free-range egg production pullets are typically reared indoors, but adult layers get outdoor access. This new environment may be challenging to adapt to, which could impair egg production and/or egg quality. Adaptation might be enhanced through rearing enrichments. We reared 1386 Hy-Line Brown® chicks indoors with three treatments across 16 weeks: (1) a control group with standard litter housing conditions, (2) a novelty group providing novel objects that changed weekly, and (3) a structural enrichment group with custom-designed structures to partially impair visibility across the pen and allow for vertical movement. Pullets were transferred to a free-range system at 16 weeks of age with daily outdoor access provided from 25 until 64 weeks. Daily egg production at different laying locations (large nests, small nests and floor), weekly egg weights and egg abnormalities were recorded from 18 to 64 weeks old. External and internal egg quality parameters of egg weight, shell reflectivity, albumen height, haugh unit, yolk colour score, shell weight and shell thickness were measured at 44, 52, 60 and 64 weeks. There was a significant interaction between rearing treatment and nest box use on hen-day production from weeks 18 to 25 (P < 0.0001) with the novelty hens laying the most eggs and the control hens the fewest eggs in the nest box. Similarly, from 26 to 64 weeks, the novelty hens laid more eggs in the large nest boxes and fewer eggs on the floor than both the structural and control hens (P < 0.0001). Egg weight and abnormalities increased with age (P < 0.0001), but rearing treatment had no effect on either measure (both P ≥ 0.19). Rearing treatment affected shell reflectivity and yolk colour with the control hens showing paler colours across time relative to the changes observed in the eggs from enriched hens. The novelty hens may have established nest box laying patterns as they were more accustomed to exploring new environments. The differences in egg quality could be related to stress adaptability or ranging behaviour. This study shows that enriching environments during rearing can have some impacts on production parameters in free-range hens.     

A moorable,automated plankton sampler

A moorable, automated plankton sampler is described, designed to obtain series of plankton samples over extended time periods in the absence of a surface vessel. The sampler consists of one or more net-containing boxes, a unit for generating as well as measuring water flow through the net boxes, a programmeable control unit, and a frame. Each net box contains several nets on a vinyl strip, used to move the nets from the storage chamber into the fishing position and then into the preservative chamber. Preservation of samples is in a formalin-brine mixture.Net boxes can be added and the number of nets per box changed; the prototype is described with 1 net box with 10 nets. Volume of water to be filtered, time between sample collections, number of net boxes and the number of nets in each box is programmed into the control unit before sampler deployment. Collections made with the sampler are compared with those made with a SCOR net and a pump.