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.     

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.     

Pecking: another measurement for filial attachment in group-reared domestic fowl chicks

This study examines different types of attachment measurements and pecking behavior in group-reared domestic chicks imprinted to a silent imprinting object. Immediately upon arriving from the hatchery, groups of heavy strain chicks were imprinted to a colored foam rubber ball for 72 h. The bond between these chicks and the imprinting object was then tested from 8 days until 5 weeks of age. Three days of imprinting sessions demonstrated that a strong attachment could be formed between the imprinted chicks and the imprinting object. In both experimental and control groups, the number of pecks was found to be significantly correlated with the latency measurements. It is, therefore, reasonable to consider the number of pecks of the imprinting object as another measurement for filial attachment.     

Prenatal light exposure affects early feather-pecking behaviour in the domestic chick

Recently we proposed that early feather pecking is a form of social exploration. Social recognition, important for exploration, is a lateralized function in the domestic chick. Lateralization of functions can be influenced by light exposure late in embryonic development. Therefore, we investigated whether this light exposure affected early posthatching feather-pecking behaviour in domestic chicks, Gallus gallus domesticus. White leghorn embryos either were exposed to light or remained in darkness in the last week of incubation. After hatching, they were housed in groups of two light-exposed and two dark-incubated chicks. Light-exposed chicks showed more feather pecking than did their dark-incubated cagemates. Dark-incubated chicks preferred to direct feather pecks to unfamiliar peers than to familiar peers; light-exposed chicks showed no preference. These effects were present in the first week after hatching and remained at least another 3 weeks. These results support the hypothesis that early gentle feather pecking is part of the normal behavioural repertoire of young chicks and influences social exploration. We discuss a possible mechanism underlying these results. We also suggest that it may be worthwhile not to expose embryos to light during the last week of incubation when housing hatchlings in commercial conditions, where feather pecking is a serious problem.     

A probabilistic model of the spatial patterning of pecking in birds : Pilot study with young chicks

The pecking behaviour of young chicks ($\text{Gallus gallus}$) is studied in a situation involving several equivalent targets (mealworms). The question is raised whether the successive pecks are randomly distributed or whether they follow a systematic order based on the spatial arrangement of the targets. Data collected with one-week-old chicks indicate that pecking is compatible with a probabilistic model where the probability to peck at a given place is inversely proportional to the energy used for this particular peck. Pecking by chicks is interpreted as a functional compromise between random sampling and optimal exploitation of the environment.     

Dynorphin(1–13) impairs memory formation for aversive and appetitive learning in chicks

The opioid peptide dynorphin(1–13) impairs memory formation in chicks (5). We examined whether this occurs for both aversively and appetitively motivated learning. Four-day-old chicks were injected with dynorphin(1–13) into the intermediate medial hyperstriatum ventrale and trained on either a peck avoidance (PA) or an appetitive discrimination (AD) task; 2-day-old chicks were trained on PA. In 2-day-old chicks, dynorphin was amnestic for PA at 0.01, 0.03, or 0.1 mM. In 4-day-old chicks, dynorphin impaired memory formation for PA at 0.1 mM, and for AD training at 0.03 mM. Thus, similar doses of dynorphin impair memory formation for both appetitive and aversive conditioning.     

Reducing feather pecking when raising laying hen chicks in aviary systems

Aviary systems for laying hens offer several advantages over battery cages. However, pecking the feathers of conspecifics remains a serious problem that negatively affects the welfare of the birds as well as the economy of a farm. From experimental studies with small groups, it has been shown that feather pecking and foraging behaviour are related and that both behaviour are influenced by early access to litter substrate. We, therefore, hypothesised, that feather pecking in aviaries can be reduced with an adequate management in the first 2 weeks of life.Each of seven pens on six commercial poultry farms, was divided into two identical compartments (matched pair design). In one of the compartments (experimental compartment) chicks were reared for the first 2 weeks of life with access to litter (wood shavings, in one case with additional straw), while the chicks in the other compartment (control) were kept on a plastic grid. Thereafter, all chicks had unrestricted access to litter and there were no differences between the two compartments neither in housing conditions nor in management procedures.Chicks in the experimental compartments spent significantly more time foraging (week 5), showed significantly less feather pecking (weeks 5 and 14) and significantly fewer birds had damaged tail feathers (weeks 5 and 14).The study demonstrates that in aviaries, under commercial conditions, early access to litter substrate has a significant effect on the development of feather pecking. In order to reduce feather pecking and to increase foraging behaviour, it is recommended that laying hen chicks raised in aviary systems do get access to litter from day 1 on.     

Pecking preferences and pre-dispositions in domestic chicks: implications for the development of environmental enrichment devices

Environmental enrichment is thought likely to benefit chickens and farmers in many ways; these include reduced fearfulness and feather pecking and improved productivity. Enrichment devices would intuitively be more effective if they reliably attracted and sustained appreciable interest but many fail to do so. This may reflect the fact that the choice of stimuli often reflects availability and human preconceptions rather than a critical consideration of the birds' preferences and pre-dispositions. We had previously identified string as a particularly attractive pecking stimulus for chicks and adult hens (Gallus gallus domesticus) of a laying strain (ISA Brown). In the present study we found that chicks of another laying strain (Lohmann Brown) also pecked sooner and more at a bunch of string than at chains or beads (Experiment 1). White or yellow strings were preferred to red, green or blue ones (Experiment 2) and white string elicited more pecking than did combinations of white and yellow or of all five colours (Experiment 3). Varying the length and width of the bunches of string exerted no detectable effects on pecking (Experiment 4) whereas incorporating small, shiny beads in the white string devices actually reduced pecking (Experiment 5). Virtually all the devices elicited progressively more interest with repeated presentation; this trend was particularly marked for white string. Collectively, the present findings demonstrate that young domestic chicks have clear and specific pecking preferences. Although the magnitude of response varied across experiments, white string consistently elicited the most interest. Our two main conclusions are: (i) white or yellow strings were particularly attractive stimuli that drew increasing interest, at least in the short term, and (ii) simple devices were preferred to more complex ones, or at least to those used here.     

Reaction to frustration in high and low feather pecking laying hens

Reaction to frustration of high (HFP) and low feather pecking (LFP) laying hens was investigated. From a HFP- and a LFP-line five birds with a HFP- and five birds with a LFP-phenotype were selected. Birds from the HFP-line were expected to show more key pecking and covered feeder pecking during frustration than birds from the LFP-line. When a bunch of feathers was presented, birds with a HFP-phenotype were expected to redirect their pecks at the bunch. Birds were trained to peck a key for a food reward in an automated Skinnerbox and subjected to two sessions: a control session, where food was available, and a frustration session, where the feeder was covered with Perspex. These two sessions were repeated in the presence of a bunch of feathers. Unexpectedly, birds from the LFP-line had a stronger reaction to frustration than birds from the HFP-line, expressed in pecking behaviour. When a bunch of feathers was offered, birds with a HFP-phenotype did not show more bunch pecking during frustration than birds with a LFP-phenotype.     

Synaptic Vesicle Proteins and Acetylcholine Levels in Chick Forebrain Nuclei Are Altered by Passive Avoidance Training

In a search for biochemical markers of modified synaptic function following training of day-old chicks on a passive avoidance task, we have assayed two monoclonal antibodies to synaptic vesicle proteins (anti-p65 and anti-SV2) and one raised to postsynaptic densities (411B). We have also measured total acetylcholine (ACh) content. Measurements were made on three forebrain regions known to show metabolic and morphological change consequent on training--the lobus parolfactorius (LPO), paleostriatum augmentatum (PA), and medial hyperstriatum ventrale (MHV)--in the right and left hemispheres 2 and 24 h after training chicks on a passive avoidance task, in which they learn to avoid pecking a bead coated with methylanthranilate [methylanthranilate-trained (M-trained)]. Control chicks were trained on a water-coated bead [water-trained (W-trained)]. Twenty-four hours after training, 411B levels showed no differences between W-trained and M-trained chicks in any region. M-training reduced the titre of anti-p65 by 16% in the left PA and 15% in the left MHV and that of anti-SV2 by 19% in the left PA. M-trained chicks showed reduced total ACh content in the LPO by up to 40% and in the PA by up to 48% but had no change in ACh level in the MHV. The decreases in antibody titre were not seen in forebrains analysed 2 h after training, but tendencies toward increases in levels in the right PA and MHV were observed with all three antibodies. Significant differences between right and left hemispheric regions, independent of training, were observed for all the antibodies and for ACh content.(ABSTRACT TRUNCATED AT 250 WORDS)     

Is there social transmission of feather pecking in groups of laying hen chicks?

Feather pecking is an abnormal behaviour where laying hens peck the feathers of conspecifics, damaging the plumage or even injuring the skin. If it occurs in a flock, more and more birds show it within a short period of time. A possible mechanism is social transmission. Several studies have shown that laying hen chicks, Gallus gallus domesticus, are able to modify their own behaviour when observing the behaviour of other chicks, for example, when feeding and foraging. As there is good experimental evidence that feather pecking originates from foraging behaviour, we hypothesized that feather pecking could also be socially transmitted. To test this, we reared 16 groups of 30 chicks. After week 4, the birds were regrouped into 16 groups of 20 chicks into each of which we introduced either five chicks that showed high frequencies of feather pecking or, as controls, five chicks that had not developed feather pecking. We then determined the feather-pecking rate and the frequency of foraging, dustbathing, feeding, drinking, preening, moving, standing and resting of all birds in a group. Data from the introduced birds were analysed separately and excluded from the group data. Chicks in groups with introduced feather-pecking chicks had a significantly higher feather-pecking rate than chicks in the control groups. In addition, birds in groups with introduced feather peckers showed significantly lower foraging frequencies than those in the control groups, although the housing conditions were identical and there were no differences in either the number or the quality of the stimuli relevant to foraging behaviour. The study therefore suggests that feather pecking is socially transmitted in groups of laying hen chicks. Copyright 2000 The Association for the Study of Animal Behaviour.     

Ontogenetic development of conditioned food aversion in chickens

Development of conditioned food aversion (CFA) was studied in 25-, 35-, and 45-day Leghorn chicks. Food-deprived birds had 10-min access to normal food on days 1 and 2, and to green coloured food CS on day 3. Injection of LiCl (0.15 M, 3–4% body weight) administered 10 min after CS on day 3 served as the US. Control groups were injected with the same volume of saline. Retention was tested on day 4 in three 3-min presentations of normal food alternating with two presentations of green food. Number of pecks and amount of food consumed were measured. Significant neophobic rejection of green food was observed in 25- but not in 35- and 45-day-old control birds. Neophobia in the youngest chicks was further accentuated by CFA which could be observed in pure form in the 45-day-old experimental group. Comparison of pecking rate and food intake showed that CFA in younger birds was accomplished predominantly by inhibition of pecking, and in older birds also by reduction of peck volume. It is concluded that protection against poisoning in chickens shifts between 25 and 45 days of posthatching age from neophobia to CFA.     

Relationship between feather pecking and ground pecking in laying hens and the effect of group size

The aim of this experiment was to study the relationship between feather pecking and ground pecking in laying hens and the effect of group size on feather pecking behaviour. Hisex White hens were kept in floor pens in group sizes of 15, 30, 60 and 120 birds, each with four replicates. Behavioural observations were performed at four different ages and focused on the number of feather pecks and aggressive pecks, both given and received. The part of the body pecked and the location of the bird was recorded as well as the number of pecks made to the floor, feeder and drinker.The results showed that most feather pecking activity occurred in the largest group size (120 birds) and there was some evidence of an increasing frequency of aggressive pecks with increasing group size. The parts of the body which were targets for feather pecking varied depending on the location of the bird giving the peck and the bird receiving it. When looking at the behaviour of individuals, birds doing a lot of feather pecking also showed more ground pecking.     

Effect of manipulating feathers of laying hens on the incidence of feather pecking and cannibalism

Feather pecking is a problem in commercial laying hens, particularly in loose-housing systems, where many hens can be affected by only a few feather peckers. In addition, feather pecking can become an even larger problem if it spreads throughout the flock. There are several possible ways that feather pecking may spread. The simplest way is that one hen may damage the feathers of a hen, and another hen may find the damaged feathers an attractive pecking target. The aim of this experiment was to determine if damaged feathers were feather-pecked more than undamaged feathers on the same body area, and to determine whether some types of feather-body area manipulations were preferred over others as pecking stimuli. Manipulations involved damaging the feathers on the rump, tail or belly of different hens, with two or three levels of severity of manipulation at each body area. Sixteen groups of 11 Lohmann Brown hens between 26 and 28 weeks were observed with the recipient, the feather pecker and the body area that was pecked all being recorded. The feather pecks were classified separately as either gentle or severe. Damaged feathers received significantly more severe feather pecks than undamaged feathers. There were also more gentle feather pecks to damaged feathers, although this did not reach statistical significance. The feather-body area manipulations that received the greatest number of severe feather pecks were the tail feathers when they were cut very short, the rump feathers when they were trimmed, and the rump when feathers were removed. These results support the suggestion that feather pecking does indeed spread through flocks by damaged feathers becoming an attractive target for feather-pecking behaviour. An unexpected result of performing the feather manipulations was an outbreak of cannibalism in half of the experimental groups. Even though there was no visible damage to the skin of the hens after having the feathers manipulated, 13 of the 16 attacked hens were wounded on the part of the body where the feathers had been damaged in some way.     

Increased Fucosylation of Chick Brain Proteins Following Training: Effects of Cycloheximide

When chicks are trained to avoid pecking a bead coated with methylanthranilate in a one-trial passive avoidance task there is an increase in fucose incorporation in vivo and in vitro in the right forebrain base of methylanthranilate (M)-trained compared to water (W)-trained chicks. The relation of this increase to de novo protein synthesis in vivo and in vitro has been examined. Cycloheximide (Cx), 1 mM, inhibited in vitro fucosylation of chick brain slices by 60% after 3 h. However, the training-related increase in in vitro fucosylation still persisted. When Cx was injected intraventricularly 10 min before training, the subsequent increase in in vitro fucosylation due to training was still apparent. When Cx was injected and [14C]leucine and [3H]fucose incorporation studied in vivo in M-trained and W-trained chicks, there was no increase in fucosylation due to training in the Cx-treated M-trained over the W-trained chicks. These results are taken to indicate that in vitro fucosylation and its increase subsequent to training is not protein synthesis-dependent, but that both in vivo and in vitro there are interactions between Cx and fucosylation steps that are independent of Cx's effects on protein synthesis.     

Categorical counting

Pigeons pecked on three keys, responses to one of which could be reinforced after a few pecks, to a second key after a somewhat larger number of pecks, and to a third key after the maximum pecking requirement. The values of the pecking requirements and the proportion of trials ending with reinforcement were varied. Transits among the keys were an orderly function of peck number, and showed approximately proportional changes with changes in the pecking requirements, consistent with Weber's law. Standard deviations of the switch points between successive keys increased more slowly within a condition than across conditions. Changes in reinforcement probability produced changes in the location of the psychometric functions that were consistent with models of timing. Analyses of the number of pecks emitted and the duration of the pecking sequences demonstrated that peck number was the primary determinant of choice, but that passage of time also played some role. We capture the basic results with a standard model of counting, which we qualify to account for the secondary experiments.     

How to hatch from an egg of great structural strength. A study of the Common Cuckoo

Brood parasitism represents a unique mode of avian reproduction that requires a number of adaptations. For example, to reduce chances of puncture ejection of their eggs by small hosts, brood parasites may have been selected for laying eggs of unusually great structural strength. However, great structural strength of eggshells should hinder hatching. The goals of our study were to establish if chicks of the Common Cuckoo Cuculus canorus have more difficulty with hatching out of their strong eggs than chicks of species with eggs of similar size, and whether they possess any mechanisms facilitating hatching. To achieve these goals, we compared hatching pattern and selected body characteristics of chicks of the Common Cuckoo with those of another altricial species with eggs of a similar size, the Great Reed Warbler Acrocephalus arundinaceus . Although the rate of pecking was similar in the two species, the Common Cuckoo chicks started pecking earlier in relation to their emergence and consequently required more time and a greater cumulative number of pecks for breaking open their eggs than did young Great Reed Warblers. The two species also differed with respect to the pattern of opening their shells; in contrast to the warbler chicks, which enlarged the original pip circularly, the cuckoo chicks opened the egg by systematically creating a long narrow slit until they emerged. Finally, our study of hatched young revealed several differences; the Cuckoo hatchlings were significantly heavier, had a longer forearm, and their egg tooth was located significantly farther from the tip of the beak. The edge used for cutting through the shell was also significantly longer than that of hatchling Great Reed Warblers. To conclude, our data suggest that hatching is more difficult for a Cuckoo than for a Great Reed Warbler and that Cuckoos possess several mechanisms to overcome the problems of hatching from a structurally strong egg.     

Reactions of male domestic chicks to two-dimensional eye-like shapes

There is considerable evidence that eye-shapes are aversive to the domestic chick but controversy remains over the relative importance of various features of the eyes in causing aversion. In this study the potency of various eye-like shapes in causing avoidance was evaluated. It was shown that monochromatic, two-dimensional eye shapes elicit avoidance and fear in young male domestic chicks, and that the eye shapes are not responded to merely as conspicuous objects. Horizontal orientation, pairedness and the presence of both an ‘iris’ and a ‘pupil’ are important recognition cues. The shape of the eye-like stimulus appears to be more important than its size. Circularity of the iris is not an essential feature but further work is necessary before conclusions can be drawn regarding the shape of the pupil although the available evidence does suggest that circularity is important.     

What learning in day-old chickens can teach a neurochemist: focus on astrocyte metabolism

The learning process sets in motion a prolonged, reproducible, and complicated pattern of brain activation, which provides information about biochemical reactions in activated brain. Study of this pattern during one-trial aversive bead discrimination in day-old chick is facilitated by precise timing of sequential metabolic events occurring between a 10-s learning period, in which the chicks learn to associate a red bead with aversive taste, and memory consolidation, indicated by unwillingness to peck at untainted red beads while freely pecking at corresponding blue beads. Inhibition of learning by metabolic inhibitors and restoration of memory by specific substrates at specific times allow determination of specific metabolic events and their neuronal or astrocytic localization. Downstream metabolism of glycogen and of glucose to pyruvate/lactate is segregated into separate pools. Glucose metabolism via pyruvate dehydrogenation provides energy in both neurons and astrocytes and may include gap junction-mediated lactate transport into astrocytes. A key role is played by glycogenolysis, stimulated by β₂-adrenergic and/or 5-HT₂-receptor stimulation along with α₂-adrenergic stimulation of glycogen synthesis. The importance of glycogen reflects that it selectively supports de novo synthesis of transmitter glutamate by combined pyruvate dehydrogenation and carboxylation in astrocytes.     

Conditioning the pecking motions of pigeons

The spatio-temporal courses of head and neck motions of pigeons while pecking at small grains are described. Single and serial pecks are distinguished but the inter- and intraindividual variability of the peck kinetics is stressed. Pigeons were then trained with instrumental conditioning procedures to speed-up their pecking. A partial reinforcement schedule where pigeons had to peck repeatedly before receiving reward led to a mild shortening of inter-peck intervals at lower reinforcement rates but surprisingly, a lengthening at higher rates. A schedule where short inter-peck intervals were differentially rewarded yielded a pronounced abbreviation of the inter-peck intervals, but this was achieved by a reduction of the movement path rather than an increase in motion velocity. A schedule whereby increased approach velocities were differentially rewarded yielded marked movement accelerations. When pigeons were rewarded for diminished approach speeds they also showed significant movement decelerations. Finally, it is shown that pigeons could learn to reliably abort their peck approach movement when a visual stimulus signalling a penalty was occasionally presented during the approach movement. The proportion of successful peck interruptions decreased as these interruption signals occurred later during the approach phase. It is concluded that the pecking of pigeons is neither an innately fixed nor a visually ballistic movement. It is instead a multiply controlled and flexibly adaptable response pattern.