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Effects of Isolation on Stress Responses to Novel Stimuli in Subadult Chickens ( Gallus gallus )
Abstract
Extensive research has examined the effects of social isolation in neonatal and adult animal
populations, but few studies have examined the effect of social isolation in early adulthood.
Animals reaching reproductive age often experience extensive social changes as they leave their
natal site, and a social stressor like isolation may uniquely affect this age group. Furthermore,
adolescence is a time when sex differences in behavior become more pronounced. As such, the
effects of social stressors are likely to vary by sex. In the present study, we used non-invasive
methods to evaluate stress responses to social change in male and female subadult chickens
(Gallus gallus). Half of the birds experienced regular sessions of social isolation over the course
of two weeks while the other half were never isolated. Subsequently, all of the animals were
exposed to a suite of three novel probes, including an open field test. We monitored the birds’
behavioral (head movements) and physiological (fecal glucocorticoid metabolites, FGM)
response to the tests. Our results indicate that, for subadult chickens, the effect of social isolation
is sex-dependent: male FGM and behavioral responses did not change with subsequent
experiences, in contrast to females. Females also exhibited more social reinstatement behavior
compared to males. Our results are consistent with the expectations of differences between the
sexes based on changes in the social environment due to sex-biased dispersal patterns. For both
sexes, the FGM and behavioral responses varied independently, which highlights the necessity
for multiple measures of stress in animal populations.
... Extensive research has investigated the effects of social isolation in other animal populations (Mendoza and Mason, 1986;Rukstalis and French, 2005;Chauke et al., 2011) with a few in broiler chickens (Goerlich et al., 2012;Weldon et al., 2016). Therefore, this study focused on the effects of dietary vitD 3 and UVB light source on growth performance, CORT, 25-OH-D 3 status, gastrointestinal tract (GIT) component weights, gut histology and welfare indicators of broiler chickens challenged with social isolation. ...
... Conversely, the control birds remained in their home pens during the test periods; they were never captured, handled, or out of visual and vocal contact with others. Both groups experienced regular husbandry activities (i.e., the presence of humans changing food, water and bedding material) in their home pen (Goerlich et al., 2012;Weldon et al., 2016). ...
Stressors are commonly encountered by all farmed species, including chickens, but the impact of these stressors on the animal and their productivity can be influenced by the environmental conditions in which they are kept. This study investigated the effects of dietary vitamin D3 (vitD3) and ultraviolet light (UVB) on growth performance, organ weight, serum corticosterone levels (CORT), serum 25-hydroxy vitamin D (25-OH-D3) status, gut histology, and welfare indicators of broiler chickens challenged with social isolation stress. One day (d) old Ross 308 broiler chicks (n = 192) were individually weighed, wing-tagged, and allocated to non-isolated (control) and isolated groups; control birds were never isolated, while isolated birds were subjected to regular sessions of social isolation for about 15-min periods over the course of 3 d a week for 2 weeks starting from d 10 (1.30 h total exposure) with inter treatment interval of 48 h. Birds were treated with either dietary vitD3 at 4,000 IU/kg (HD) or UVB light (UVB). The UVB lamp (24 Watt 12% UVB D3, 55 cm) with wavelength: 280–315 nm, intensity; 28.12 μW/cm2 hung 50 cm above the substrate was used for the broilers in all the treatment groups but were filtered to remove UVB in the HD group. Growth performance measure; body weight gain, feed intake, and feed conversion ratio were estimated at the end of starter (day 10), grower (day 24), and finisher periods (day 38). Broilers were feather and gait scored to measure welfare at 22/35 and 24/37 days of age, respectively. The selected birds were weighed and euthanized to obtain serum to determine 25-OH-D3 and CORT levels, GIT weights, and gut histology. Subjecting the birds to 2-week social isolation (for 15 min, three times per week) increased CORT levels but did not alter GP and 25-OH-D3 levels of broilers. However, UVB-treated broilers demonstrated better welfare, duodenal absorptive capacity, and reduced FCR compared to HD chickens. Results suggest some beneficial effects of UVB lighting on welfare indicators and the potential to support early life growth of commercial broilers reared indoors, which are often challenged with stressors.
... During the first stage of the familiarization (Fig. 3), with the test set up, pairs of chickens (one low ranger and one high ranger) were placed in the apparatus and were allowed to explore it for 10 min. Familiarization in pairs was used to facilitate exploration of the arena and reduce the stress of the social isolation (Fontana et al., 2016;Weldon et al., 2016), the new environment (apparatus structure, cups) and the new food (mealworms). The 8 cups in the apparatus were 10 cm high and 2 cm deep. ...
... These results support what was evidenced by other studies in domestic chickens: males and females differ in social attachment and social reinstatement patterns, with females being more sociable, and therefore less prone to be in social isolation, than their male counterparts (Vallortigara, 1992;Vallortigara et al., 1990). Males also show weak physiological and behavioral responses during social isolation when compared to females (Weldon et al., 2016). Social isolation may be a common situation in the range since there is a negative relationship between stocking density (animal/m 2 ) and distance from the poultry house that results in low individual proximity to social partners. ...
... Thus, chickens in the isolation treatment were exposed to capture, handling, feed and water restrictions. Both groups received the same husbandry activities (change of food, water, bedding materials and humans) in their pens (Goerlich et al., 2012;Weldon et al., 2016). ...
Within intensive poultry production systems, broilers are reared indoors, at fast growth rates in controlled environments with little access to natural light, which together impacts the expression of natural behaviours. Birds can see into the ultraviolet spectrum and the provision of ultraviolet-B (UVB) light may support the expression of natural behaviour and endogenous synthesis of vitamin D 3 (vitD 3). Commercially, chickens regularly encounter stressors, and both the environment and diet can influence their response to stressors. This study was designed to compare the impacts of providing dietary vitD 3 at 4000 IU/kg (VitD) compared with provision via UVB light on the behaviour of broilers challenged with periodic social isolation stress. One-day-old Ross 308 broiler chicks (n = 192) were randomly allocated to non-isolated (control) and periodically isolated groups and were provided with either, additional dietary vitD 3 , or UVB light, in a 2 × 2 factorial design. UVB lamps were provided in all pens (12% UVB D3 of 55 cm length, 24-Watt, 280-315 nm wavelength and 28.12 µW/cm2 intensity) but in the VitD treatment, there were filters to remove UVB. Behaviour was recorded from video footage using instantaneous scans measuring the number of birds engaged in each behaviour six times per day on 12 days spread across days 2-39, resulting in 72 scan samples per pen. Body weight was measured weekly and analysed to provide context for understanding the activity of broilers. Body weight was modelled using growth curves and poisson models were used to analyse behaviour, controlling for the number of birds visible in scans. Chickens performed less active behaviour when they had been periodically isolated. Chickens spent more time sitting inactive (and less sitting active) and sleeping when they received UVB light but were not isolated. Sunbathing was lower in isolation treatments compared to controls, but this effect was reduced when they received UVB lighting. The growth rate of chickens was highest in the isolation and VitD treatment and higher for VitD compared to UVB treatments. Higher activity on days 2 and 39 was associated with a lower growth rate. These results indicate some benefits of supplementation of UVB light in terms of observing natural behaviour when chickens are exposed to stressors. However, we did not observe large differences in behaviour in chickens receiving UVB light compared to those provided with VitD. Further research is needed to investigate the benefits and optimal level of UVB light to support the behaviour and welfare of broilers.
... Thus, chickens in the isolation treatment were exposed to capture, handling, feed and water restrictions. Both groups received the same husbandry activities (change of food, water, bedding materials and humans) in their pens (Goerlich et al., 2012;Weldon et al., 2016). ...
... Therefore, 99% of breeders experience isolation stress for more than 2 weeks. It has been suggested that the severity of isolation stress is higher for females than males and that multiple periods of 2week long isolation events dampen the stress response over time (Weldon et al., 2016). The reason for sex-dependent severity of isolation stress is the natural dispersal pattern in males. ...
This Scientific Opinion considers the welfare of domestic fowl (Gallus gallus) related to the production of meat (broilers) and includes the keeping of day-old chicks, broiler breeders, and broiler chickens. Currently used husbandry systems in the EU are described. Overall, 19 highly relevant welfare consequences (WCs) were identified based on severity, duration and frequency of occurrence: 'bone lesions', 'cold stress', 'gastro-enteric disorders', 'group stress', 'handling stress', 'heat stress', 'isolation stress', 'inability to perform comfort behaviour', 'inability to perform exploratory or foraging behaviour', 'inability to avoid unwanted sexual behaviour', 'locomotory disorders', 'prolonged hunger', 'prolonged thirst', 'predation stress', 'restriction of movement', 'resting problems', 'sensory under- and overstimulation', 'soft tissue and integument damage' and 'umbilical disorders'. These WCs and their animal-based measures (ABMs) that can identify them are described in detail. A variety of hazards related to the different husbandry systems were identified as well as ABMs for assessing the different WCs. Measures to prevent or correct the hazards and/or mitigate each of the WCs are listed. Recommendations are provided on quantitative or qualitative criteria to answer specific questions on the welfare of broilers and related to genetic selection, temperature, feed and water restriction, use of cages, light, air quality and mutilations in breeders such as beak trimming, de-toeing and comb dubbing. In addition, minimal requirements (e.g. stocking density, group size, nests, provision of litter, perches and platforms, drinkers and feeders, of covered veranda and outdoor range) for an enclosure for keeping broiler chickens (fast-growing, slower-growing and broiler breeders) are recommended. Finally, 'total mortality', 'wounds', 'carcass condemnation' and 'footpad dermatitis' are proposed as indicators for monitoring at slaughter the welfare of broilers on-farm.
... Social isolation can alter responses to stress and can alter social behavior in animals and humans (Alexander et al., 1988;Hawkley et al., 2012;Cacioppo et al., 2015), and isolation has been used as a stressor in many animal studies (Panksepp et al., 1980;Sufla et al., 1994;Kato et al., 2022). In poultry, social isolation may cause physiological and behavioral stress responses and has been used as a stress treatment in experiments (Goerlich et al., 2012;Weldon et al., 2016;Ogbonna et al., 2022). Distress vocalizations are considered to be stress-related behaviors induced by isolation stress treatment (Gallup and Suarez, 1980;Fause et al., 1983). ...
The aim of the present study was to investigate effects of isolation at an early age on behavioral and physiological responses of chickens to an isolation challenge at two weeks of age. Birds were assigned to a control group or to one of three treatments where chicks were isolated for 5 min per day. The groups were 1) no isolation (control); 2) early isolation (EI; 2 to 4 days of age); 3) late isolation (LI; 5 to 7 days of age); or 4) full isolation (FI; 2 to 7 days of age). All groups of chicks were challenged with isolation for 5 min at two weeks of age, with distress vocalizations (DV), stepping and jumping behavior measured. Hypothalamic and blood samples were collected at the end of isolation challenges. There were no significant differences between groups in body weight gain at 2 weeks of age. Latency of jump was lower in the LI group compared with the control group, but DV and number of steps were not affected by isolation treatment during the neonatal period. There were no significant differences among groups in plasma glucose or FFA concentrations. Gene expression for hypothalamic corticotropin-releasing hormone, was lower in the EI than the control group, with no differences in expression between control and LI or control and FI groups. There were no significant differences among groups in the expression of arginine vasotocin, thyrotropin-releasing hormone, neuropeptide Y, proopiomelanocortin, and orexin genes. These results suggest that isolation in the first week of life may affect responses to isolation of chicks when they are older, and that there may be a critical period of several days for this effect to occur.
... Movement in a novel environment likely entails a trade-off between motivation to reinstate social contact, motivation to explore the environment and motivation to avoid detection by potential predators 51 . In a previous study on domestic young chicks, it was concluded that young female chicks have a higher motivation for social reinstatement than males in a novel environment 52 , and a short latency to leave a start box has previously been linked to stress in chickens 51 . This in turn suggests that a short latency to move for our young female chicks most likely reflects a high motivation for social reinstatement. ...
Cognitive processes are often biased by emotions. In humans, affective disorders are accompanied by pessimistic judgement, while optimistic judgement is linked to emotional stability. Similar to humans, animals tend to interpret ambiguous stimuli negatively after experiencing stressful events, although the long-lasting impact on judgement bias has rarely been investigated. We measure judgement bias in female chicks (Gallus gallus domesticus) after exposure to cold stress, and before and after exposure to additional unpredictable stressors. Additionally, we explore if brain monoamines can explain differences in judgement bias. Chicks exposed to cold stress did not differ in judgement bias compared to controls, but showed sensitivity to additional stressors by having higher motivation for social reinstatement. Environmental complexity reduced stress-induced negative judgement bias, by maintaining an optimistic bias in individuals housed in complex conditions even after stress exposure. Moreover, judgement bias was related to dopamine turnover rate in mesencephalon, with higher activity in individuals that had a more optimistic response. These results demonstrate that environmental complexity can buffer against negative effects of additive stress and that dopamine relates to judgement bias in chicks. These results reveal that both internal and external factors can mediate emotionally biased judgement in animals, thus showing similarities to findings in humans.
Under commercial conditions, laying hen chicks are exposed to a range of stressful events immediately after hatch. Here, we studied whether environmental enrichment was able to reduce the stress sensitivity of these chicks. A total of 50 hatchery chicks (HC) and 50 control chicks (CC) were raised in enriched pens (E), while 53 HC + 53 CC were raised in standard non-enriched floor pens (NE). HC weighed less on day one, but there was no effect of hatchery treatment at later ages. HC were more pessimistic in a cognitive judgement bias test and emitted more distress calls when socially isolated, indicating that hatchery stress affected behaviour and stress sensitivity. However, enrichment did not affect the behaviour in any of these tests. We found no effects of hatchery stress in a novel environment, but indications that enrichment may have increased fearfulness of HC. The sensitivity of the hypothalamic-pituitary-adrenal (HPA) axis was reduced in HC-E compared to HC-NE, indicating that enrichment buffered the physiological stress sensitivity in HC; however, the opposite pattern was found in CC. In conclusion, our results show complex and somewhat contradictory effects on the ability of enrichment to buffer the consequences of stress in commercial hatcheries.
The Supplementary Tables and References list published papers dealing with faecal cortisol/corticosterone metabolites in different species grouped by class/order/family
It's regularily updated now - see last update 27th Feb 2020!
Social discrimination in male and female domestic chicks (Gallus gallus) was investigated by using (a) latencies of approach response, (b) simultaneous free choice, and (c) intersubject aggressive-pecking tests. In approach-response tests, females showed shorter latencies when tested with cagemates than when tested with strangers, whereas males showed shorter latencies when tested with strangers than when tested with cagemates. In simultaneous-choice tests, females spent more time near a cagemate, whereas males spent more time near a strange chick. In aggressive-pecking tests, both sexes pecked more at strangers than at cagemates; aggressive pecking at strangers, however, was higher in males than in females. It is argued that gender effects in social discrimination can be accounted for in terms of stronger social attachment in females and aggressive responses in males.
We reviewed the avian literature for quantitative studies of sex biases in dispersal and found continued and strengthened support for the general pattern of female biased dispersal established by Greenwood in 1980. We report sex differences in dispersal patterns in natal and breeding dispersal as measured by 1) proportion leaving and 2) distance moved. Greenwood's review found evidence for male biased dispersal only within four species of the Anatidae. We find there is now evidence for male biased dispersal in twenty-two species representing twelve families.
Popular procedures to control the chance of making type I errors when multiple statistical tests are performed come at a high cost: a reduction in power. As the number of tests increases, power for an individual test may become unacceptably low. This is a consequence of minimizing the chance of making even a single type I error, which is the aim of, for instance, the Bonferroni and sequential Bonferroni procedures. An alternative approach, control of the false discovery rate (FDR), has recently been advocated for ecological studies. This approach aims at controlling the proportion of significant results that are in fact type I errors. Keeping the proportion of type I errors low among all significant results is a sensible, powerful, and easy-to-interpret way of addressing the multiple testing issue. To encourage practical use of the approach, in this note we illustrate how the proposed procedure works, we compare it to more traditional methods that control the familywise error rate, and we discuss some recent useful developments in FDR control.
Human studies suggest that prior emotional responses are stored within the brain as associations called somatic markers and are recalled to inform rapid decision-making. Consequently, behavioural and physiological indicators of arousal are detectable in humans when making decisions, and influence decision outcomes. Here we provide the first evidence of anticipatory arousal around the time of decision-making in non-human animals. Chickens were subjected to five experimental conditions, which varied in the number (one versus two), type (mealworms or empty bowl) and choice (same or different) of T-maze goals. As indicators of arousal, heart-rate and head movements were measured when goals were visible but not accessible; latency to reach the goal indicated motivation. We found a greater increase in heart-rate from baseline to the goal-viewing period, more head movements and shorter latencies in all conditions including mealworms compared to those with empty bowls. More head movements when two mealworm bowls were available compared to just one, and prior to occasions when hens accessed an empty bowl rather than declining to move, showed that arousal preceded and influenced decision-making. Our results provide an important foundation for investigating arousal during animal decision-making and suggest that the somatic-marker hypothesis might not only apply to humans.
Two experiments investigating sex differences in the open-field behavior of young chicks are reported. In the first experiment,
ambulation latencies of 10-day-old male and female chicks in a novel environment were measured. Half of the chicks were kept
in social isolation for 2 days prior to testing; the other half were socially reared until tested. Results showed that in
socially reared chicks ambulation latencies were significantly higher in males than in females, whereas in isolation-reared
chicks there were no significant sex differences. In the second experiment, latencies of ambulation were measured in socially
reared 10-day-old chicks placed in a novel environment with or without a visible predator (i.e., a human being). Sex differences
were evident in both conditions, with males showing higher ambulation latencies than females. It is argued that sex differences
in open-field behavior of chicks may be due to a stronger motivation for social reinstatement in females, which reduces the
usual antipredatory reactions of chicks placed in a novel environment.
The common approach to the multiplicity problem calls for controlling the familywise error rate (FWER). This approach, though, has faults, and we point out a few. A different approach to problems of multiple significance testing is presented. It calls for controlling the expected proportion of falsely rejected hypotheses – the false discovery rate. This error rate is equivalent to the FWER when all hypotheses are true but is smaller otherwise. Therefore, in problems where the control of the false discovery rate rather than that of the FWER is desired, there is potential for a gain in power. A simple sequential Bonferroni-type procedure is proved to control the false discovery rate for independent test statistics, and a simulation study shows that the gain in power is substantial. The use of the new procedure and the appropriateness of the criterion are illustrated with examples.
Sex-biased dispersal is an almost ubiquitous feature of mammalian life history, but the evolutionary causes behind these patterns still require much clarification. A quarter of a century since the publication of seminal papers describing general patterns of sex-biased dispersal in both mammals and birds, we review the advances in our theoretical understanding of the evolutionary causes of sex-biased dispersal, and those in statistical genetics that enable us to test hypotheses and measure dispersal in natural populations. We use mammalian examples to illustrate patterns and proximate causes of sex-biased dispersal, because by far the most data are available and because they exhibit an enormous diversity in terms of dispersal strategy, mating and social systems. Recent studies using molecular markers have helped to confirm that sex-biased dispersal is widespread among mammals and varies widely in direction and intensity, but there is a great need to bridge the gap between genetic information, observational data and theory. A review of mammalian data indicates that the relationship between direction of sex-bias and mating system is not a simple one. The role of social systems emerges as a key factor in determining intensity and direction of dispersal bias, but there is still need for a theoretical framework that can account for the complex interactions between inbreeding avoidance, kin competition and cooperation to explain the impressive diversity of patterns.
Dispersal is a fundamental process affecting the genetic structure of populations, speciation, and extinction. Nevertheless, our understanding of the evolution of dispersal is limited by our paucity of knowledge on dispersal decisions at the individual level. We investigated the effect of interactions between residents and juvenile dispersers on individual dispersal and settlement decisions in Siberian jays (Perisoreus infaustus). In this group-living bird species, some offspring remain on the parental territory for up to 3 years (retained juveniles) whereas other offspring disperse within 2 months of fledging (dispersers). We found that retained juveniles constrained settlement decisions of dispersers by aggressively chasing dispersers off their territory, resulting in dispersers continuing to disperse and settling in groups without retained juveniles. Experimental removal of male breeders during the dispersal period also demonstrated that dispersers were unable to settle in high-quality breeding openings, which were instead filled by older nonbreeding residents. Rather, dispersers immigrated into groups without retained offspring where they became subordinate group members, queuing for a breeding opening. Also, they preferably settled in groups with short queues where no same-sex juveniles were present. Dispersal did not inflict a cost to dispersers through increased mortality. However, the presence of immigrants was costly for breeders because it increased the rate of conflicts during the breeding season which negatively affected nestling condition. These results demonstrate that resident individuals constrain both dispersal and settlement decisions of dispersers. Social interactions between residents and dispersers can thus be a key factor to understand the evolution of dispersal. Copyright 2008, Oxford University Press.
Substantial strain differences in tonic immobility were found between different breeds of chickens. Crossbreeding between strains showing different immobility durations yielded hybrids that exhibited intermediate reactions. For purpose of relating the strain differences in tonic immobility to more conventional measures of emotionality, data were collected on open-field activity, defecation, and adrenal weight. Overall, the results implicated strain-specific differences in emotionality as being the basis for the observed differences in immobility. Latency to defecate in an open field, however, was highly correlated with latency to ambulate. It was argued that defecation, rather than being an absolute measure of fear or emotionality, may in fact be an intermediate response to gradual fear reduction.
This review examines the consequences of social deprivation on brain chemistry and behavior on rats. Although social deprivation produces wide-ranging behavioral and neurochemical effects, it appears that these effects are determined by a number of factors, the most critical factor being the age or developmental stage during the period of deprivation. Roughly, the effects examined in this review may be separated into three major developmental stages and each is related to deprivation of specific types of social interaction: preweaning/neonatal, postweaning/adolescent, and adult. The effects of social deprivation during each of these stages appears to be neurochemically and behaviorally specific. However, much of the research to date has failed to examine deprivation during specific stages, often combining deprivation of different types. Nonetheless, these modifications of experience produce animals of differing phenotypes, which could be characterized as pathological in nature in many instances, and may model particular aspects of human psychopathologies or perhaps the propensity to develop those phenotypic features.
The effects of the duration of isolation and age during isolation on open-field behavior in rats were examined. An inner wall divided the floor of the field into two areas, a peripheral alley and the center square, and the subjects' behavior in each area was measured. An increase in the tendency to avoid the center square was found in rats isolated during their juvenile stage, which disappeared if they were reared in pairs for a long period after isolation. On the other hand, subjects isolated during their postmaturity stage displayed an increased tendency to approach the center square whereas isolation during sexual maturity had no effect. The duration of isolation showed no consistent effect; rather, the effect depended on the age of the subjects during isolation. These findings suggest that isolation affects the open-field behavior of rats in various ways, depending on their age during isolation.
1. A non-invasive technique for stress assessment is needed. Therefore, an enzyme immunoassay (EIA) for measurement of glucocorticoid metabolites in chicken droppings was established and validated.
2. Radiolabelled corticosterone was administered intravenously to detect the time course of excreted metabolites. The metabolites were then characterised by chemical and immunological methods to find a suitable antibody.
3. Reversed-phase high-performance liquid chromatography (RP-HPLC) separations of the peak concentration samples revealed that corticosterone was extensively metabolised, mainly to more polar substances.
4. HPLC fractions were tested in several EIAs for glucocorticoid metabolites, where the highest quantities were detected by a newly established cortisone assay, measuring metabolites with a 3,11-dione structure.
5. The biological relevance of this cortisone EIA was confirmed by stimulation of adrenocortical activity by adrenocorticotropic hormone (ACTH).
6. With this newly developed EIA it should be possible to measure adrenocortical activity non-invasively in chickens and other galliformes, thus providing a tool for a variety of research fields, such as poultry production, ethology and behavioural ecology.
Information on genetic structure can be used to complement direct inferences on social systems and behaviour. We studied the genetic structure of the solitary grey mouse lemur (Microcebus murinus), a small, nocturnal primate endemic to western Madagascar, with the aim of getting further insight on its breeding structure. Tissue samples from 167 grey mouse lemurs in an area covering 12.3 km2 in Kirindy Forest were obtained from trapping. The capture data indicated a noncontinuous distribution of individuals in the study area. Using 10 microsatellite markers, significant genetic differentiation in the study area was demonstrated and dispersal was found to be significantly male biased. Furthermore, we observed an overall excess of homozygotes in the total population (F(IT) = 0.131), which we interpret as caused by fine-scale structure with breeding occurring in small units. Evidence for a clumped distribution of identical homozygotes was found, supporting the notion that dispersal distance for breeding was shorter than that for foraging, i.e. the breeding neighbourhood size is smaller than the foraging neighbourhood size. In conclusion, we found a more complex population structure than what has been previously reported in studies performed on smaller spatial scales. The noncontinuous distribution of individuals and the effects of social variables on the genetic structure have implications for the interpretation of social organization and the planning of conservation activities that may apply to other solitary and endangered mammals as well.
We demonstrated that neonatal isolation (1-h pup isolation; postnatal days 2-9) impairs context-induced fear conditioning in adult male rats and tends to enhance this effect and foot shock sensitivity in females. In this study, we examine the effects of brief (i.e., handling; 15 min) and prolonged (3 h) maternal separations (postnatal days 1-21) on fear conditioning and foot shock sensitivity in adult male and female rats. Identical training and test conditions from our prior study were employed so comparisons of the three early life stressors could be made. Context- and cue-elicited freezing and ultrasonic vocalizations (USVs; 22 kHz) were measured after 10 tone-shock training trials in Experiment 1. In Experiment 2, foot shock responses (flinch, jump, sonic vocalizations) to escalating shock levels were assessed. Brief maternal separation impaired context- and cue-conditioned fear in rats of both sexes as assessed by USVs. Prolonged maternal separation only impaired context fear in female rats. There were no effects on foot shock sensitivity. Results of this and other studies suggest that early life stress impairs fear conditioning in adult rats whereas stress experienced in adulthood has the opposite effect. These opposing effects may reflect developmental differences on stress-induced alterations on hippocampal regulation of the hypothalamic-pituitary-adrenal axis.
The common approach to the multiplicity problem calls for controlling the familywise error rate (FWER). This approach, though, has faults, and we point out a few. A different approach to problems of multiple significance testing is presented. It calls for controlling the expected proportion of falsely rejected hypotheses — the false discovery rate. This error rate is equivalent to the FWER when all hypotheses are true but is smaller otherwise. Therefore, in problems where the control of the false discovery rate rather than that of the FWER is desired, there is potential for a gain in power. A simple sequential Bonferronitype procedure is proved to control the false discovery rate for independent test statistics, and a simulation study shows that the gain in power is substantial. The use of the new procedure and the appropriateness of the criterion are illustrated with examples.
This report attempts to describe objectively the complete vocal repertoire and the vocal code of the Red Junglefowl (Gallus gal/us), most probable wild ancestor of the domestic fowl. An unconfined color-banded flock was watched over a period of 6 years at the San Diego Zoo. The general behavior and vocalizations are essentially the same in Red Junglefowl and the domestic fowl. Different vocal signals can be recognized by their so-nograms and by the common element in the various situations in which a signal is given. Twenty-four vocal signals are described but because of intergradation between some signals and between different situations no absolute size of vocal repertoire can be fixed. A spec-trographic (structural) key to the vocal signals of the Red Junglefowl is given and with the sonograms should enable one to identify the typical calls. Different elements can be combined to produce specific vocal signals, in effect a code. Brief, soft repetitive notes of low frequency are attraction calls. Loud harsh sounds with high frequencies are alarm cries. Harsh sounds emphasizing low frequencies are threat sounds. These rules hold for many other birds. Junglefowl also have special calls that appear to indicate well-being, or mild disturbance and frustration. The evolution of the vocal signals of the Red Junglefowl is discussed in relation to Darwin' s (1872) three principles of com-munication and to modem ethology.
Using video recordings of hens, Gallus gallus domesticus, as they approached different kinds of objects, I examined how change in object distance is associated with a change from lateral to binocular viewing. The birds tended to view distant objects laterally while they preferentially viewed objects less than 20–30 cm away frontally; this was true whether they were looking at another bird or at an inanimate object. However, as well as switching between lateral and frontal viewing, the hens also swung their heads from side to side with movements so large that the same object appeared to be viewed with completely different parts of the retina, and even with different eyes, in rapid succession. When confronted with a novel object, the hens walked more slowly but continued to show large head movements. This suggests that, unlike mammals, which gaze fixedly at novel objects, hens investigate them by moving the head and looking at them with different, specialized, parts of their eyes. Many aspects of bird behaviour, such as search image formation, vigilance and visual discriminations, may be affected by the way they move the head and eyes. Copyright 2002 The Association for the Study of Animal Behaviour. Published by Elsevier Science Ltd. All rights reserved.
The response of animals to handling by humans has been extensively evaluated in domesticated livestock, but rarely examined in wildlife species. Twelve captive wombats (Lasiorhinus latifrons) were subjected to two treatments in a replicated design: (1) daily handling, involving 15min of tactile contact 5 d/wk for 12 wk and (2) no-handling, involving no contact apart from that received during routine husbandry. The effect of handling was assessed via overt responses to human approach and touch, a stressor, and a novel stimulus. Daily handling reduced the wombat's flight distance in response to human approach; more in the first handling replicate (−0.16±0.02m/wk) than in the second (−0.06±0.02m/wk). A behavioural reactivity score also declined faster in the first than second handling replicate. Synthetic ACTH was used to validate the measurement of faecal cortisol metabolites in L. latifrons by EIA. Faecal cortisol metabolite secretion consistently increased in reaction to a handling procedure involving forced human contact (indicating a lack of habituation) but the magnitude of this response was not reduced by regular handling. Regular handling therefore changed the human–wombat relationship by lowering reactivity to and avoidance of the human handler, but did reduce the stress response, suggesting that the wombats entered into a state of learned helplessness.
Weaning is a complex process resulting in a number of physiological challenges that may have prolonged effects on foal welfare. We predicted that intensified maternal behaviour during early development reduces the negative effects associated with the weaning process. In this study, we subjected foals (n=5) to 10min separations from the dam at 2, 4, 6, 8, 10, and 12 weeks of age and measured changes in a number of tactile and non-tactile maternal interactions. During weaning at 6±0.5 months, we investigated the changes in salivary cortisol, heart rate and behavioural markers of stress in foals from the separation treatment group and compared them with control foals (n=5). Mares initiated contact with their foals 0.3±0.06 times during 30min and this increased to 1.77±0.06 times after separations (P
The effects of modifying the amount of human contact on the behavioural (withdrawal responses to humans), physiological (corticosterone and immunological) and production (hen-day egg production) responses of laying hens were examined in a total of 144 hens (White Leghorn×Australorp) housed in two-bird conventional cages in two treatments: (1) ‘Minimal’ — in which birds received regular but limited human contact during egg collection (daily), inspections (daily) and feeding (twice weekly); the birds' vision of humans was limited to what they could see through a 5 cm gap between the bottom of a blind and the egg tray. (2) ‘Additional’ — in which birds received a total of 15 min additional (to routine husbandry) human contact per day for 5 days per week. The treatments were imposed for 17 weeks from 19 weeks of age and then all birds received routine husbandry. Measurements were taken on 12 cages per treatment at three periods over the following 3 weeks. At each sampling period there were two behaviour tests (3 days apart) to measure withdrawal responses of birds to an approaching human using birds remaining in their cages (approaching human test — AHT) and birds removed from their cages and placed on a table at the end of an enclosed corridor (shute test — ST). At the end of the ST, a blood sample was taken for corticosterone analysis and 3 days after the AHT, a measure of cell-mediated immunity (CMI) was made. Hen-day egg production was measured from 23 to 36 weeks of age. In both behaviour tests there were fewer withdrawal responses in the ‘Additional’ treatment and they were maintained over time. A lower proportion of birds moved away from the human in the ST (0.41 vs. 0.64; P<0.06) and the number of times (max.=3) that birds were in the front 10 cm of the cage and oriented forwards in the AHT were greater (2.12 vs. 1.22 and 2.54 vs. 1.80, respectively; P<0.01). The corticosterone response at the end of the ST was greater in the ‘Minimal’ treatment (P<0.05) and there were no changes with time. CMI was greater in the ‘Additional’ treatment only at the first sampling period (2.1 vs. 1.4 mm; P<0.01) and hen-day egg production was higher in the ‘Additional’ treatment over the experiment (89.4 vs. 83.1%; P<0.05). Compared with the ‘Minimal’ treatment, increasing the amount of human contact reduced the level of fear of humans shown by birds, on the basis of their withdrawal responses in the two behavioural tests and decreased corticosterone response to handling, with consequent effects on production. The mechanism may involve a chronic stress response since adverse changes in cell-mediated immunological responsiveness were found in the ‘Minimal’ treatment. The results indicate that human contact may be an important determinant of bird behaviour, production and possibly welfare.
The associations between individuals in a free-living population of red junglefowl are visualised in a cluster analysis. The flock structure is shown for the population when females are with and without chicks, and the differences described. Various kinds of groupings are present, from solitary individuals to mixed-sex flocks. The strongest associations maintaining flock cohesion are shown to be female-female pairings and it is these which break down when the females produce their chicks.
A spectrographic analysis was made of the following sound signals of the domestic fowl: (a) sounds made by chicks, including distress calls, pleasure notes and fear trills; (b) sounds made by broody hens that serve to attract chicks, including clucking, food calls, and the roosting call; and, (c) warning signals, including the alarm call for aerial predators, the alarm call for ground predators, the alerting call of a broody hen, fear squawks of a hen held in the hand, threat sounds of cocks, and crowing of a rooster. Distress notes of chicks are composed of descending frequencies only, whereas ascending frequencies are the prominent component of pleasure notes. The spectrographic analysis revealed the following common elements in sounds that attract chicks: (i) repetitiveness or segmentation, (2) brief duration of the component notes, and (3) the presence of relatively low frequencies. Warning signals as a group have in common features that are the opposite: (1) relatively long duration. (2) relatively little segmentation or repetitiveness, and (3) absence of very low frequencies. Experimental tests with artificial sounds confirmed these conclusions.
Three different breeds of poultry, representing different degrees of domestication, were observed in semi-natural conditions in order to study differences in foraging behaviour, activity levels and social behaviours which could be caused by correlated responses to selection for increased production. The breeds used were: (i) red junglefowl (Gallus gallus); (ii) Swedish bantam, which is a domestic breed that has not undergone selection for production traits; and (iii) Hy-Line, a White leghorn laying hybrid, selected mainly for food conversion efficiency. The birds were offered ad libitum food simultaneously from sites where the food was freely available and from sites where the birds had to search and scratch for food which was mixed with wood-shavings. The behaviour was observed three times per day (48 min/d), 3 d per week in eight groups (four birds per group) of each breed between 7 and 18 wks of age. Junglefowl and bantam obtained a significantly higher proportion of their food from the site that required effort. The opposite case was true for the Hy-Line. Overall, bantams performed significantly more foraging behaviour than Hy-Lines. The Hy-Line breed was more inactive and less involved in social interactions than the junglefowl and the bantam. The results support the idea that selection for high production results in modified behavioural strategies. Behaviours that are of high energetic cost, such as extensive foraging and social interactions, were of lower in frequency in the laying hens compared to junglefowl and bantam, allowing the laying hens to save energy that can be reallocated to production traits.
Residents and migrants use their environment very differently – the former remain in a given habitat throughout the year, whereas the latter are repeatedly confronted with unfamiliar environments. The difference in ecology may influence decision-making processes whether, when and to which extent to explore an unfamiliar environment. We have investigated spatial neophobia and spatial neophilia – two important novelty reactions that may underlie decision-making – in two closely related warbler species, the resident Sardinian warbler and the migratory garden warbler. Individuals of both species could access an unfamiliar room from a familiar cage. We assessed the conflict between the motivation to enter the novel room (spatial neophilia) and the motivation to avoid it (spatial neophobia) as the frequency and duration of perching on the dowel in the cage, which led to the unfamiliar room before entering it. Furthermore, we measured the latency to enter the novel room and compared the number of individuals of each species entering the room. The combination of the parameters measured allowed assessing the degree of both neophobia and neophilia. Finally, the time spent on each branch in the novel room was taken as a measure for spatial exploration. The migrants perched less often and spent less time on the dowel leading to the room, and entered the novel room quicker than the residents. Additionally, more migrants than residents entered the room. The migrants’ decision to enter the novel room can best be explained with a combination of low spatial neophobia coupled with high spatial neophilia, whereas the residents’ decision-making is best explained with high spatial neophobia coupled with high spatial neophilia. The differences in neophobia support the migrant-neophobia hypothesis. When in the room, the migrants spent less time on each branch than the residents, possibly indicating that the former collect less spatial information than the latter.
Animals are increasingly exposed to novel environmental conditions because of human activities. An organism's ability to cope with these challenges is critical to its survival. The decision of whether or not an animal should investigate environmental changes involves a trade-off between the risk and the potential benefit of a novel resource. Novelty often elicits approach (exploratory) as well as avoidance behaviour in animals, and the extent of each of these behaviours may influence learning about the environment. We formulated and tested several hypotheses to determine how external factors (complexity of a novel stimulus) and internal factors (experience with objects) might influence exploration latencies to touch a novel object based on either cost or benefit considerations. Garden warblers were confronted with a simple and a complex novel object in their familiar cages, and latencies until first touch were measured. Additionally, corticosterone levels before and after the experiment were measured to assess whether differences in baseline levels might explain variations in latency to approach and whether presentation of novel objects is stressful. The complex object was touched significantly later than the simple object. Experienced birds investigated both types of objects later than inexperienced birds. Although birds showed marked approach–avoidance behaviour with the complex object, none of the objects elicited a corticosterone stress response. The results indicate that garden warblers consider both costs and benefits when exploring novel objects, and that the relative influence of costs and benefits varies with external and internal factors.
This article is part of a Special Issue "Neuroendocrine-Immune Axis in Health and Disease." The regulation and function of the hypothalamic-pituitary-adrenocortical (HPA) axis and glucocorticoids have been well conserved across vertebrate species. Glucocorticoids influence a wide range of physiological functions that include glucose regulation, metabolism, inflammatory control, as well as cardiovascular, reproductive, and neuronal effects. Some of these are relatively quick-acting non-genomic effects, but most are slower-acting genomic effects. Thus, any stimulus that affects HPA function has the potential to exert wide-ranging short-term and long-term effects on much of vertebrate physiology. Here, we review the effects of social isolation on the functioning of the HPA axis in social species, and on glucocorticoid physiology in social mammals in particular. Evidence indicates that objective and perceived social isolation alter HPA regulation, although the nature and direction of the HPA response differs among species and across age. The inconsistencies in the direction and nature of HPA effects have implications for drawing cross-species conclusions about the effects of social isolation, and are particularly problematic for understanding HPA-related physiological processes in humans. The animal and human data are incommensurate because, for example, animal studies of objective isolation have typically not been modeled on, or for comparability with, the subjective experience of isolation in humans. An animal model of human isolation must be taken more seriously if we want to advance our understanding of the mechanisms for the effects of objective and perceived isolation in humans.
Early-life stimulation (e.g. brief handling) attenuates the behavioral and neuroendocrine responses to stressors encountered in adulthood, particularly with respect to activation of hypothalamic-pituitary-adrenal (HPA) activity. In contrast, if neonates were subjected to a more severe stressor, such as protracted separation from the dam or exposure to an endotoxin, then the adult response to a stressor was exaggerated. These early-life experiences program HPA functioning, including negative feedback derived from stimulation of hippocampal glucocorticoid receptors, and corticotropin-releasing hormone (CRH) and arginine vasopressin (AVP) coexpression in PVN neurons, to modify the response to subsequent stressor experiences. The persistent variations of HPA activity observed in handled/stimulated animals may stem from alterations in dam–pup interactions (e.g. increased arched-back feeding, licking, grooming). In addition genetic makeup is critical in determining stress reactivity. For instance, BALB/cByJ mice are more reactive to stressors than C57BL/6ByJ mice, exhibiting greater HPA hormonal alterations and behavioral disturbances. BALB/cByJ also fail to acquire a spatial learning response in a Morris water-maze paradigm, which has been shown to be correlated with hippocampal cell loss associated with aging. Early-life handling of BALB/cByJ mice prevented these performance deficits and attenuated the hypersecretion of ACTH and corticosterone elicited by stressors. The stressor reactivity may have been related to maternal and genetic factors. When BALB/cByJ mice were raised by a C57BL/6ByJ dam, the excessive stress-elicited HPA activity was reduced, as were the behavioral impairments. However, cross-fostering the more resilient C57BL/6ByJ mice to a BALB/cByJ dam failed to elicit the behavioral disturbances. It is suggested that genetic factors may influence dam–pup interactive styles and may thus proactively influence the response to subsequent stressors among vulnerable animals. In contrast, in relatively hardy animals the early-life manipulations may have less obvious effects.
Two salient but previously unacknowledged aspects of open-field testing involve contact with a potential predator, as a consequence of placement in the open field by a human, and separation from imprinted companions. As a result we propose that open-field behaviour in chickens (Gallus gallus) represents a compromise between opposing tendencies to reinstate contact with conspecifics and minimize detection in the face of possible predation. Five experiments were conducted to test various implications of this model. Manipulations designed to enhance the predatory overtones of open-field testing were found to postpone reinstatement behaviours (e.g. distress calling and escape attempts) and prolong behaviours that serve to minimize detection (e.g freezing). Unlike the more traditional view of open-field behaviour as an index of general emotionality, our model suggests that the principal reason for movement is based on attempts to reinstate social contact. In support of the model, birds tested in the presence of cagemates showed significantly longer durations of freezing than those tested individually. The same was true for birds maintained in social isolation for two days prior to testing. The applicability of this approach to conceptualizing the behaviour of chickens in the open field is discussed, and the supposed relationship between fear and distress calling is critically evaluated.
Many species of birds and mammals are faithful to their natal and breeding site or group. In most of them one sex is more philopatric than the other. In birds it is usually females which disperse more than males; in mammals it is usually males which disperse more than females. Reproductive enhancement through increased access to mates or resources and the avoidance of inbreeding are important in promoting sex differences in dispersal. It is argued that the direction of the sex bias is a consequence of the type of mating system. Philopatry will favour the evolution of cooperative traits between members of the sedentary sex. Disruptive acts will be a feature of dispersers.
The behaviour of chickens following posterior dorsal telencephalic ablations was studied in response to humans, strange hens, aerial predators, ground predators and a visual startle stimulus. The ablations had no effect on the birds' response to either the aerial or ground predator but there was a significant reduction in pacing after the visual startle stimulus. Following posterior telencephalic ablation the birds showed significantly fewer attacks and threats in encounters with unfamiliar hens but showed exaggerated escape/avoidance behaviour to humans in both their home pens and in experimental testing cages. The reasons for this avoidance behaviour to humans are discussed but no definite conclusions could be drawn.
Pair-bonded relationships form during periods of close spatial proximity and high sociosexual contact. Like other monogamous species, marmosets form new social pairs after emigration or ejection from their natal group resulting in periods of social isolation. Thus, pair formation often occurs following a period of social instability and a concomitant elevation in stress physiology. Research is needed to assess the effects that prolonged social isolation has on the behavioral and cortisol response to the formation of a new social pair. We examined the sociosexual behavior and cortisol during the first 90-days of cohabitation in male and female Geoffroy's tufted-ear marmosets (Callithrix geoffroyi) paired either directly from their natal group (Natal-P) or after a prolonged period of social isolation (ISO-P). Social isolation prior to pairing seemed to influence cortisol levels, social contact, and grooming behavior; however, sexual behavior was not affected. Cortisol levels were transiently elevated in all paired marmosets compared to natal-housed marmosets. However, ISO-P marmosets had higher cortisol levels throughout the observed pairing period compared to Natal-P marmoset. This suggests that the social instability of pair formation may lead to a transient increase in hypothalamic-pituitary-adrenal (HPA) axis activity while isolation results in a prolonged HPA axis dysregulation. In addition, female social contact behavior was associated with higher cortisol levels at the onset of pairing; however, this was not observed in males. Thus, isolation-induced social contact with a new social partner may be enhanced by HPA axis activation, or a moderating factor.
Sex differences in dispersal distance are widespread in birds and mammals, but the predominantly dispersing sex differs consistently between the classes. There has been persistent debate over the relative importance of two factors - intrasexual competition and inbreeding avoidance - in producing sex-biased dispersal, and over the sources of the difference in dispersal patterns between the two classes. Recent studies cast new light on these questions.
In adolescence, gender differences in rates of affective disorders emerge. For both adolescent boys and girls, peer relationships are the primary source of life stressors though adolescent girls are more sensitive to such stressors. Social stressors are also powerful stressors for non-human social species like rodents. In a rat model, we examined how social isolation during adolescence impacts stress reactivity and specific neural substrates in adult male and female rats. Rats were isolated during adolescence by single housing from day 30 to 50 of age and control rats were group housed. On day 50, isolated rats and control rats were re-housed in same-treatment same-sex groups. Adult female rats isolated as adolescents exhibited increased adrenal responses to acute and to repeated stress and exhibited increased hypothalamic vasopressin mRNA and BDNF mRNA in the CA3 hippocampal subfield. In contrast, adult male rats isolated as adolescents exhibited a lower corticosterone response to acute stress, exhibited a reduced state of anxiety as assessed in the elevated plus maze and reduced Orexin mRNA compared to adult males group-housed as adolescents. These data point to a markedly different impact of isolation experienced in adolescence on endocrine and behavioral endpoints in males compared to females and identify specific neural substrates that may mediate the long-lasting effects of stress in adolescence.
Avian eggs contain a variety of steroid hormones, which have been attributed as a tool for maternal phenotypic engineering. The majority of studies focuses on androgens, but also significant amounts of progesterone as well as other steroid hormones have been measured. The question if corticosterone is also present in eggs of chickens is currently under debate. The only analytical validation performed so far has failed to demonstrate corticosterone in the yolk of chickens, suggesting that antibodies for corticosterone measurement cross-react with other steroids present in the yolk. In order to investigate this assumption and to characterise potential cross-reacting hormones in more detail, we performed high-performance liquid chromatographic (HPLC) analyses of chicken yolk extracts and determined the concentration of immunoreactive corticosterone, progesterone and cortisol. The progesterone antibody revealed several immunoreactive substances, including progesterone, pregnenolone and two substances with lower polarity. The corticosterone enzyme immunoassay detected immunoreactive substances at exactly the same elution positions as the progesterone assay and a very small peak at the elution position of corticosterone. Immunoreactive cortisol was not found. In addition, inner and outer regions of the yolk sphere were analysed separately via HPLC. We found different concentrations of immunoreactive substances between the inner and outer yolk regions, probably reflecting the steroidogenic activity of the follicle cells during oocyte growth. We conclude that in homogenised yolk extracts without previous clean-up, the measured corticosterone concentrations may actually reflect those of progesterone and its precursors, most probably being 5 alpha- and 5 beta-pregnanes and pregnenolone.
There is accumulating evidence that individuals leave their natal area and select a breeding habitat non-randomly by relying upon information about their natal and future breeding environments. This variation in dispersal is not only based on external information (condition dependence) but also depends upon the internal state of individuals (phenotype dependence). As a consequence, not all dispersers are of the same quality or search for the same habitats. In addition, the individual's state is characterized by morphological, physiological or behavioural attributes that might themselves serve as a cue altering the habitat choice of conspecifics. These combined effects of internal and external information have the potential to generate complex movement patterns and could influence population dynamics and colonization processes. Here, we highlight three particular processes that link condition-dependent dispersal, phenotype-dependent dispersal and habitat choice strategies: (1) the relationship between the cause of departure and the dispersers' phenotype; (2) the relationship between the cause of departure and the settlement behaviour and (3) the concept of informed dispersal, where individuals gather and transfer information before and during their movements through the landscape. We review the empirical evidence for these processes with a special emphasis on vertebrate and arthropod model systems, and present case studies that have quantified the impacts of these processes on spatially structured population dynamics. We also discuss recent literature providing strong evidence that individual variation in dispersal has an important impact on both reinforcement and colonization success and therefore must be taken into account when predicting ecological responses to global warming and habitat fragmentation.
The social behavior of feral horses was studied in the western United States. Stable harem groups with a dominant stallion and bachelor ♂♂ groups occupied overlapping home ranges. Groups spacing, but not territoriality, was expressed. Harem group stability resulted from strong dominance by dominant stallions, and fidelity of group members. Eliminations of group members were usually marked by urine of the dominant stallion. ♂‐♂ aggression involved spacing between harems and dominance in bachelor groups. Marking with feces was important in ♂‐♂ interactions. Foaling occurred in May and early June, following the post‐partum estrous. All breeding was done by harem stallions. Young were commonly nursed through yearling age. These horses showed social organizations similar to other feral horses and plains zebras.
Zusammenfassung
Von Mai bis November 1970 wurden verschiedene Wildpferd‐Gruppen in den westlichen Vereinigten Staaten untersucht. Die Pferde lebten das ganze Jahr in stabilen Harems mit einem dominanten Hengst oder in weniger stabilen Gruppen aus jungen ♂♂. Weidegebiete überschnitten sich sehr stark, Territorien waren nicht feststellbar. Der Abstand zwischen Gruppen wurde vom dominanten Hengst gewahrt. Der Tageslauf umfaßte regelmäßig Grasen, Ruhen und bei Trockenheit Wanderungen zur Wasserstelle.
Wiederkehrende Verhaltens‐ und Verständigungsweisen werden beschrieben. Unbemerkt von den Pferden wurde das Verhalten in Minutenabständen protokolliert. Zusätzlich wurden sechs Gruppen daran gewöhnt, aus nächster Nähe beobachtet zu werden. Die Konstanz der Haremsgruppen wurde durch starke Dominanz des Hengstes und die Treue der Gruppenmitglieder gewahrt. Die Exkremente der Stuten wurden oft von den Haremshengsten mit Urin markiert.
Sowohl Stuten als auch Hengste wiesen gruppenfremde Pferde ab. Kämpfe zwischen Hengsten und Zusammentreiben der Stuten dienten meist dazu, die Harems getrennt zu halten; selten ging es darum, zusätzliche Stuten zu bekommen.
Harems‐♀♀ zeigten nur wenig entwickelte Rangordnungen. Halberwachsene Hengste wurden von den dominanten ♂ ♂ wegen ihrer starken Unter‐würfigkeit geduldet. Führer, erkennbar am Hüteverhalten wie am Initiieren von Aktivitäten waren meist die dominanten Hengste. In den Junggesellen‐Gruppen bestand eine lineare Rangordnung. Das dominante ♂ behandelte die Gruppe wie seinen Harem. Bei Interaktionen zwischen Harems‐Hengsten wie zwischen Junghengsten spielte Koten eine große Rolle. Die Rangordnung in Junghengst‐Gruppen war beim Koten erkennbar: der Rangniedrigste kotete zuerst, die jeweils Ranghöheren folgten. Alle ♂ ♂ benutzten dieselben Kotplätze, die weitverstreut an Pfaden und Wasserstellen lagen.
Im Mai und Anfang Juni fohlten die Stuten, die sofort wieder rossig und dann ausschließlich vom Haremshengst gedeckt wurden. Die Stuten verteidigten ihre Fohlen sehr stark, und auch die dominanten Hengste zeigten Verteidi‐gungsverhalten. Die Fohlen saugten von sich aus und wurden selten abgewiesen. Einjährige wurden gewöhnlich von Stuten gesäugt, die selbst keine oder ihre neugeborenen Fohlen verloren hatten. Fohlen tranken 1,85mal pro h, einjährige 0,97mal pro h, und zwar durchschnittlich 1,5 min lang. In 76% aller Fälle hörten die Tiere freiwillig zu trinken auf.
Pferde haben eine sehr ursprüngliche Sozialstruktur, die bei wilden Ponies und Pferden der bei den meisten Zebras ähnlich ist.
Involuntary separation from close social companions is widely held to lead to pathophysiological outcomes. Presumably, the relationship with, or category of, the separated individual determines the nature of the physiological response. Here, experiments examining the consequences of brief involuntary separation on the activity of the stress-responsive hypothalamic-pituitary-adrenal (HPA) system are reviewed. Only those studies designed specifically to assess the effect of the absence of the social partner are considered. Evidence for HPA activation in response to social separation has been obtained in a number of species; yet, many studies find no effect of separation of affiliative partners on HPA activity. The occurrence of an HPA response to separation does not appear to be related to the phylogenetic position or cognitive capacity of the species studied, nor is it a universal response to mother-infant separation. Rather, it is suggested that the pattern of results can be largely understood in the context of attachment. Separation of partners exhibiting signs of emotional attachment leads to an immediate and persistent HPA response, whereas separation of partners that are affiliative, but do not exhibit attachment, has little or no effect on HPA activity.
Repeated isolation of neonatal rats produces persistent changes in physiology and behavior. In Experiment 1, we examined changes in plasma corticosterone (CORT) levels as a possible mechanism for the effects of isolation. Pups that were isolated from their mother and the nest for 1 h per day on postnatal days (PND) 2-9 were compared to control litters of pups that were either nonhandled or handled but not isolated. On PND 2, compared to nonhandled pups, handled pups had elevated CORT levels that returned to baseline levels within 30 to 60 min of return to the home cage. No significant elevation of CORT levels were found in handled pups on PND 9. The CORT levels of isolated pups were over twice those of nonhandled pups on PND 2 and four times those of nonhandled pups on PND 9. In Experiment 2, we investigated whether the increased CORT release in response to isolation on PND 9 was the result of the pups' treatment on the previous six days as against an effect of maturation. Plasma CORT levels were measured in rat pups that were either isolated, handled or nonhandled on PNDs 2-8 during the conditions of isolation, handling and nonhandling on PND 9. There were no differences among the groups in basal plasma levels of CORT. Handling on PND 9 did not result in elevated CORT levels in any of the groups. All three groups showed a significant increase in plasma CORT levels after isolation on PND 9. However, the CORT response to isolation of pups previously isolated on PND 2-8 were significantly higher than pups that were either handled or nonhandled on PNDs 2-8. Thus, daily episodes of isolation potentiate the hypothalamic-pituitary-adrenal response to stress.
Two different types of social relationships exist in mammalian social systems: dominance relationships and social bondings. This article shows that both are crucial for the management of stress. The following general conclusions are derived: (1) In stable social systems, established dominance relationships result in predictable behaviour. As a consequence, low positions in the hierarchy do not necessarily lead to enhanced endocrine stress responses. Under conditions of instability, however, distinct increases in the activities of the pituitary-adrenocortical- and the sympathetic-adrenomedullary systems are found; (2) The ability to establish and to respect dominance relationships is a prerequisite to build up stable social systems. Whether this ability is realized, however, depends on social experiences made during behavioural development. The time around puberty seems to be essential for the acquisition of those social skills needed to adapt to unfamiliar conspecifics in a non-stressful and non-aggressive way; (3) Stress responses can be ameliorated by the presence of members of the same species. This phenomenon is called social support. In general, social support cannot be provided by any conspecific, but the ability to give social support is restricted to bonding partners. In most mammalian species mothers are important bonding partners for their infants. In some species bondings also occur between adult individuals; and (4) On a physiological level the bonding partner reduces the activities of the pituitary-adrenocortical- and the sympathetic-adrenomedullary systems. On a psychological level he/she can be regarded as a 'security-giving and arousal-reducing structure'. This is true irrespective of whether the bonding partner is the mother, in the case of an infant, or a male or a female in the case of an adult individual.
The influence of neonatal handling on behavior and immune function was assessed in Orange-winged Amazon parrots (Amazona amazonica). Chicks (n=11) were gently handled daily from 25 days of age until 38 days post-fledging, while control chicks (n=9) were not handled. At 10 days post-fledging ( approximately 66 days of age), chicks were given tests to evaluate tameness (e.g., willingness to perch on an offered finger). They were then restrained for 10 min, either by being held while perching (handled group) or, because they would not perch, by being restrained in a towel (nonhandled group). Serum corticosterone levels were measured and immune status was assessed by: the delayed-type hypersensitivity (DTH) response to phytohemagglutinin-P (PH-P) injection; the humoral response to a killed Newcastle disease virus (NDV) challenge; and heterophil:lymphocyte ratio (H:L). Handled chicks were tamer by all measures of tameness. DTH was greater in nonhandled chicks (P</=0.002), as were serum corticosterone levels (Wilcoxon, P</=0.05), while NDV antibody titers were possibly reduced (P</=0.09). H:L ratios did not differ. We conclude that handling conditioned the birds to be held in a manner that appeared not to be stressful. The greater DTH response of nonhandled chicks suggests that either their DTH response was enhanced by the acute stress of being restrained in a towel, and/or the DTH response of handled chicks was suppressed as a result of the repeated physiologic stress from handling during the neonatal period. In either event, handling produced marked differences in response to types of restraint that would be typically encountered in the husbandry of Amazons in captivity.
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.
Our laboratory uses a specific test battery for the initial assessment of phenotypic behavioral differences of transgenic, knockout, and inbred strains of mice. Our standard battery includes: open field activity, light-dark exploration, rotarod, prepulse inhibition (PPI), acoustic startle habituation, conditioned fear, Morris water maze, and hot plate. Tests are run in the order listed, from least invasive to most invasive, to decrease the chance that behavioral responses are altered by prior test history. The studies presented here were designed around two questions. The first study asks if differences exist between mice that have undergone testing on different tasks and mice that are naïve to the test experience. The second study asks if the test order affects how an animal performs on subsequent tests. In the first experiment, C57BL/6J male mice were evaluated on all of the tests described above. The behavior of these 'test battery' mice was compared to aged matched naïve mice that were only tested on one test from the battery. Results indicate that on some tests, the behavior of 'test battery' mice was significantly different from the behavior of naïve mice, while on other tests there were no differences. For example, test battery mice responded differently in the open-field, rotarod, and hot-plate test, but behaved similar on the PPI and conditioned fear. Experiments in the second study were performed on male 129/SvEvTac (129S6) and C57BL/6J male mice. An abbreviated battery of tasks was used and the results suggest that certain test variables are sensitive to test order, whereas others are resistant. These two studies demonstrate that some behavioral tests appear to be sensitive to previous testing experience, while other tests are immune.
The corticosterone response to the sight of a natural predator was investigated in free-living and captive great tits (Parus major). Free-living great tits responded to the sight of a stuffed, slowly moving Tengmalm's owl, a major predator of great tits, with warning calls and a change in behaviour around a feeder. Great tits returned to the feeder within a few minutes and began to approach the owl, and there was no increase in plasma corticosterone levels in birds sampled 30-50 min after they first saw the owl. Captive great tits in an aviary were exposed for 30 min to a stuffed Tengmalm's owl, to a stuffed brambling, and to a cardboard box. All three stimulus objects were slowly rotated during the exposure period. Great tits exposed to the owl changed their behaviour immediately, and spent most of the time when the owl was visible flying around the aviary and hanging from the roof, with very few visits to a feeder. Great tits exposed to the brambling and to the moving box also changed their behaviour and made fewer visits to the feeder. The great tits responded to the sight of the owl with a marked increase in plasma corticosterone levels, whereas there was no change in corticosterone levels (mean levels < 11 ng/ml) in birds exposed to the brambling or to the moving box. Mean corticosterone levels were high (37.1 +/- 4.9 ng/ml) 0.5 h after exposure to the owl, remained high (38.9 +/- 6.0 ng/ml) 1 h after exposure, and had returned to basal (5.3 plus minus 1.3 ng/ml) 3 h after exposure to the owl. This is the first demonstration for any bird of a complete corticosterone response to a predator. The sight of a predator initiated a corticosterone response in great tits that could not move more than 3 m away, whereas free-living great tits that could choose how far to fly away from the predator either did not initiate a corticosterone response, or had a small corticosterone response in which corticosterone levels were not significantly different from basal 30-50 min later. The results indicate that the initiation of a corticosterone response in birds depends on whether or not a bird perceives that a stimulus is a threat. Furthermore, they illustrate the importance of not making generalised conclusions based on laboratory experiments.
Retrospective studies in humans have identified characteristics that promote stress resistance, including childhood exposure to moderately stressful events (ie, stress inoculation).
Because of limited opportunities for prospective studies in children, we tested whether exposure to moderate stress early in life produces later stress resistance in a primate model.
Twenty squirrel monkeys were randomized to intermittent stress inoculation (IS; n = 11) or a nonstress control condition (NS; n = 9) from postnatal weeks 17 to 27. At postnatal week 35, each mother-offspring dyad underwent testing in a moderately stressful novel environment for inferential measures of offspring anxiety (ie, maternal clinging, mother-offspring interactions, object exploration, and food consumption) and stress hormone concentrations (corticotropin [ACTH] and cortisol). At postnatal week 50, after acclimation to an initially stressful wire-mesh box attached to the home cage, independent young monkeys underwent testing for inferential measures of anxiety (ie, voluntary exploration and play) in the box.
In the novel environment test, IS compared with NS offspring demonstrated diminished anxiety as measured by decreased maternal clinging (P =.02), enhanced exploratory behavior (P =.005), and increased food consumption (P =.02). Mothers of IS offspring accommodated offspring-initiated exploration (P =.009) and served as a secure base more often compared with NS mothers (P =.047). Compared with NS offspring, IS offspring had lower basal plasma ACTH (P =.001) and cortisol (P =.001) concentrations and lower corticotropin (P =.04) and cortisol (P =.03) concentrations after stress. In the subsequent home-cage wire-box test, IS offspring demonstrated enhanced exploratory (P<.001) and play (P =.008) behaviors compared with NS offspring.
These results provide the first prospective evidence that moderately stressful early experiences strengthen socioemotional and neuroendocrine resistance to subsequent stressors. This preclinical model offers essential opportunities to improve our understanding and enhance prevention of human stress-related psychiatric disorders by elucidating the etiology and neurobiology of stress resistance.
Many neural systems are undergoing marked development over adolescence, which may heighten an animal's vulnerability to stressors. One consequence may be altered sensitivity to drugs of abuse. We previously reported that social stressors in adolescence increased behavioral sensitization to nicotine in adulthood in female, but not male, rats. Here we examined whether social stressors in adolescence alter the functioning of the hypothalamic-pituitary-adrenal (HPA) axis by examining corticosterone release in response to restraint in adulthood. To further assess effects of social stressors on behavioral sensitivity to psychostimulants, we examined locomotor activity in response to nicotine and to amphetamine. In a second set of experiments, we investigated whether the same procedure of social stressors administered in adulthood produces effects similar to that observed when administered in adolescence. Rats underwent daily 1 h isolation followed by pairing with a new cage mate on either postnatal days 33-48 (pubertal stress: PS) or days 65-80 (adult stress: AS). Three weeks later rats tested for either: (a) corticosterone levels were measured in response to restraint, or (b) locomotor sensitization to nicotine (0.25 mg/kg; 5 days) followed by an amphetamine challenge (0.5 mg/kg) 24 h later. Effects of social stressors were evident only in females. PS females had increased locomotor activity to amphetamine compared to controls, and AS females had increased corticosterone release compared to controls. No effect of the social stressors was found in males at either age except for reduced weight gain during the stress procedure. Thus, females are more susceptible to the enduring effects of these moderate social stressors than are males. However, in terms of behavioral sensitivity to drugs of abuse, females may be more susceptible to stressors during adolescence than adulthood, although the reverse appears to be true for HPA function.
In recent years, the noninvasive monitoring of steroid hormone metabolites in feces of mammals and droppings of birds has become an increasingly popular technique. It offers several advantages and has been applied to a variety of species under various settings. However, using this technique to reliably assess an animal's adrenocortical activity is not that simple and straightforward to apply. Because clear differences regarding the metabolism and excretion of glucocorticoid metabolites (GCMs) exist, a careful validation for each species and sex investigated is obligatory. In this review, general analytical issues regarding sample storage, extraction procedures, and immunoassays are briefly discussed, but the main focus lies on experiments and recommendations addressing the validation of fecal GCM measurements in mammals and birds. The crucial importance of scrutinizing the physiological and biological validity of fecal GCM analyses in a given species is stressed. In particular, the relevance of the technique to detect biologically meaningful alterations in adrenocortical activity must be shown. Furthermore, significant effects of the animals' sex, the time of day, season, and different life history stages are discussed, bringing about the necessity to seriously consider possible sex differences as well as diurnal and seasonal variations. Thus, comprehensive information on the animals' biology and stress physiology should be carefully taken into account. Together with an extensive physiological and biological validation, this will ensure that the measurement of fecal GCMs can be used as a powerful tool to assess adrenocortical activity in diverse investigations on laboratory, companion, farm, zoo, and wild animals.