Untrained Birds Research Articles

Size sometimes matters: recognition of known predators with artificially altered body size by untrained birds

Size sometimes matters: recognition of known predators with artificially altered body size by untrained birds

Practical Application and Influence of “Avigen duck” Immunomodulator to White Pekin Ducks Humoral Immune Factors

Factors of non-specific immunity are responsible for protecting birds from a number of viruses and bacteria. Bactericidal proteins are played here lysozyme and complement, interferon, as well as beta-lysine. Adding appropriate active compounds to the bird's diet to activate the innate immune response are subject to studies by many authors. The practical application and influence of the "Avigen Duck". immunomodulator in the cultivation of White Pekin ducks aims to clarify the dynamics of the indicators. It was found that the ducks treated with the immunomodulator had higher non-specific protection expressed in the values of the observed indicators. Complement activity for the experienced group (529.45 ± 17,85 CH50) is significantly higher than that of untrained birds (308.56 ± 10.19 CH50), on the 30th day of their lives (P <0.001). Lysozyme values for the experienced group (6.34 ± 0.86 mg L-1) is more than twice as high as its concentration in control birds - 2.52 ± 0.59 mg L-1. At 30 days of age, the mean concentration of IFN γ in the control group of ducks was 108.86±6.12 pg ml-1, and in the experimental group treated with immunomodulator - 518.06±12.80 pg ml-1, accompanied by an increase in the values of IL-2 and IL-6 and beta-lysine activity. These data show that, despite the short life of the ducks, the concentrations of the investigated factors of non-specific immunity increase significantly and statistically reliably, even after a single treatment with immunomodulator "Avigen Duck". The practical application of the immunomodulator in the duck diet has a strong effect on their non-specific immunity.

Untrained birds\u2019 ability to recognise predators with changed body size and colouration in a field experiment

BackgroundDuring recognition process, multiple parameters of the encountered stimulus may play a role. Previous studies with wild birds identified the importance of several salient features (e.g., eyes, beak, prominent elements of colouration) which birds use to recognise other bird species, such as predators or nest parasites. In the present study, we observed the responses of passerines visiting winter feeders to stimuli in the form of dummies of Eurasian sparrowhawk which were modified in body size and/or colouration but always carried the salient features of raptors (hooked beak, talons) and one species-specific feature of the sparrowhawk (yellow eyes). In the vicinity of a feeder, we placed a dummy of an unmodified sparrowhawk, life-sized sparrowhawk with pigeon, great tit, or robin colouration, a small, great tit-sized sparrowhawk dummy with unmodified or pigeon colouration, or an unmodified pigeon dummy, which functioned as a harmless control. Then we measured how it affected the number of visits.ResultsWe found that birds were less afraid of small dummies regardless of their colouration than they were of life-sized raptor dummies or even the pigeon dummy. This contrasts with the results of a previous laboratory experiment where great tits’ reaction to small dummies was comparably fearful to their response to life-size dummies. In our experiment, birds were also not afraid of life-sized dummies with modified colouration except for a robin-coloured dummy, which caused an equally significant fear reaction as an unmodified sparrowhawk dummy. It is likely that this dummy resembled the colouration of a male sparrowhawk closely enough to cause this effect.ConclusionsBased on our observations, we conclude that birds use contextual features to evaluate the size of other birds. Distance and familiar reference points seem to play an important part in this process.

Adaptive immune response and resting metabolism are unaffected by manipulation of flight intensity, but negatively related to each other

Activation of an immune response (IR) upon exposure to pathogens is crucial to ensure adequate organismal performance and is directly linked to survival. Fitness benefits of the response may be associated with costs in terms of increased energy expenditure and may compete for resources and compromise such fitness benefits. Trade‐offs between immune function and other traits relevant for fitness are well documented, however, it remains unknown if such trade‐offs are energetically mediated. We manipulated the flight activity of 70 zebra finches Taeniopygia guttata to investigate the energy reallocation to the immune system in rested and exercised birds. Four experimental groups exhibiting different flight intensity were used: trained, untrained and birds that either stopped or started flight training after the immune challenge. If costs associated with the IR and flight activity compete for energy, we predicted the extent of inhibition of IR would be dependent on energy allocated to physical activity. Daytime resting metabolic rate was measured before and after the immune challenge, induced using sheep red blood cells (SRBC). Strength of the response was measured as the concentration of anti‐SRBC antibodies six days post‐challenge. We found no evidence for the predicted inhibition of the immune function between trained and untrained birds, as there was no difference in resting metabolic rate between experimental groups. However, resting metabolic rate following the challenge was negatively correlated with the IR. Surprisingly, individuals with relatively low resting metabolic rates following immune challenge were able to up‐regulate their IR, indicating a trade‐off in the use of the energy resource independent of flight activity levels. Our results suggest that energy allocation to mount the IR may represent a constraint that is possibly linked to the circadian pattern of the energy budget but appears to be independent of energetic challenges brought on by different levels of flight activity.

Flight training in a migratory bird drives metabolic gene expression in the flight muscle but not liver, and dietary fat quality influences select genes.

Training and diet are hypothesized to directly stimulate key molecular pathways that mediate animal performance, and flight training, dietary fats, and dietary antioxidants are likely important in modulating molecular metabolism in migratory birds. This study experimentally investigated how long-distance flight training, as well as diet composition, affected the expression of key metabolic genes in the pectoralis muscle and the liver of European starlings (Sturnus vulgaris, n = 95). Starlings were fed diets composed of either a high or low polyunsaturated fatty acid (PUFA; 18:2n-6) and supplemented with or without a water-soluble antioxidant, and one-half of these birds were flight trained in a wind-tunnel while the rest were untrained. We measured the expression of 7 (liver) or 10 (pectoralis) key metabolic genes in flight-trained and untrained birds. Fifty percent of genes involved in mitochondrial metabolism and fat utilization were upregulated by flight training in the pectoralis (P < 0.05), whereas flight training increased the expression of only one gene responsible for fatty acid hydrolysis [lipoprotein lipase (LPL)] in the liver (P = 0.04). Dietary PUFA influenced the gene expression of LPL and fat transporter fatty acid translocase (CD36) in the pectoralis and one metabolic transcription factor [peroxisome proliferator-activated receptor (PPAR)-α (PPARα)] in the liver, whereas dietary antioxidants had no effect on the metabolic genes measured in this study. Flight training initiated a simpler causal network between PPARγ coactivators, PPARs, and metabolic genes involved in mitochondrial metabolism and fat storage in the pectoralis. Molecular metabolism is modulated by flight training and dietary fat quality in a migratory songbird, indicating that these environmental factors will affect the migratory performance of birds in the wild.

Acute effects of intense exercise on the antioxidant system in birds: does exercise training help?

The acute effects of an energy-intensive activity such as exercise may alter an animal's redox homeostasis, although these short-term effects may be ameliorated by chronic exposure to that activity, or training, over time. Although well documented in mammals, how energy-intensive training affects the antioxidant system and damage by reactive species has not been investigated fully in flight-trained birds. We examined changes to redox homeostasis in zebra finches exposed to energy-intensive activity (60 min of perch-to-perch flights twice a day), and how exercise training over many weeks affected this response. We measured multiple components of the antioxidant system: an enzymatic antioxidant (glutathione peroxidase, GPx) and non-enzymatic antioxidants (measured by the OXY-adsorbent test) as well as a measure of oxidative damage (d-ROMs). At no point during the experiment did oxidative damage change. We discovered that exposure to energy-intensive exercise training did not alter baseline levels of GPx, but induced exercise-trained birds to maintain a higher non-enzymatic antioxidant status as compared with untrained birds. GPx activity was elevated above baseline in trained birds immediately after completion of the second 1h flight on each of the three sampling days, and non-enzymatic antioxidants were acutely depleted during flight after 13 and 44 days of training. The primary effect of exercise training on the acute response of the antioxidant system to 2h flights was increased coordination between the enzymatic (GPx) and non-enzymatic components of the antioxidant system of birds that reduced oxidative damage associated with exercise.

Comparing post-release survival and habitat use by captive-bred Cabot’s Tragopan (Tragopan caboti) in an experimental test of soft-release reintroduction strategies

Restoring a viable population by reintroduction is the ultimate goal of a large number of ex situ conservation projects for endangered animals. However, many reintroductions fail to establish a population in the wild, partly because released animals cannot acclimate to the native environment of the release site, resulting in very low survival rates. Acclimation training is a technique to resolve this problem, although it does not have positive results in all species. We tested whether acclimation training and soft-release could improve the reintroduction success for captive-bred Cabot’s Tragopan (Tragopan caboti), an endangered pheasant in southern China. Reintroduction of captive-bred Cabot’s Tragopan was carried out in the Taoyuandong National Nature Reserve, China from 2010 to 2011. We built a soft-release enclosure for acclimation training in the typical montane habitat of this pheasant. Nine birds were acclimated to the environment of this release site in this cage for more than 50 days before release (“trained birds”), while 11 birds remained only in the cage for 3 days prior to release (“untrained birds”). Released birds were tagged with a collar radio-transmitter. Post-release monitoring revealed that the survival rate of trained birds was higher than that of untrained birds after 50 days (trained: 85.7%; untrained: 20.0%). Cox regression analysis showed that there was a significant difference in the mortality rates between the trained and untrained birds. In addition, a survey of the habitat of the experimental and the control groups showed significant differences in habitat selection between the groups. Our study suggests that pre-release acclimatization training is an important factor that can lead to improved survival and habitat selection of captive-bred reintroduced tragopans.

The role of body size in predator recognition by untrained birds

It is supposed that body size serves as an important cue in the recognition of relevant stimuli in nature. As predators of varying body size pose differing levels of threat, their potential prey should be able to discriminate between them. We tested the reaction of great tits (Parus major) to the dummies of their common predator (the European sparrowhawk—Accipiter nisus) in natural and reduced body sizes under laboratory conditions. All of the tested dummies possessed local raptor-specific features (hooked beak, claws with talons, and conspicuous eyes), but differed in global species-specific features: body size (large – the size of a sparrowhawk, small – the size of a great tit) and colouration (sparrowhawk, great tit, robin, and pigeon). The sparrowhawk-coloured dummies evoked fear regardless of their size while both great tit- and pigeon-coloured dummies evoked no fear reaction. The body size was used as the cue only for the discrimination of the robin-coloured dummies. The differences in reactions to the dummies with robin colouration (species unimportant to the great tits) could be explained as that the tits are able to recognize these birds in nature, but not so undoubtedly as the predator or the conspecific.

The role of key features in predator recognition by untrained birds

The most important role in the recognition and categorization of predators (as well as other animals) is usually attributed to so-called key features. Under laboratory conditions, we tested the role of yellow eyes (specific for the genus Accipiter in European raptors) and hooked beak (common for all European birds of prey) in the recognition of the sparrowhawk (Accipiter nisus) by untrained great tits (Parus major) caught in the wild. Using wooden dummies, we interchanged either one of these potential key features or the body of the sparrowhawk (predator) and domestic pigeon (harmless bird). The tested tits showed three types of behaviour in the presence of the dummies: fear, interest without fear, and lack of interest. Eye interchange lowered fear of the sparrowhawk, but did not cause fear of the pigeon. Beak interchange did not lower fear of the sparrowhawk. Eye interchange caused increased interest in both species. Thus, a specific sparrowhawk feature is necessary for correct sparrowhawk dummy recognition but a general raptor feature is not. On the other hand, a specific sparrowhawk feature on a pigeon dummy is not enough to prompt sparrowhawk recognition. Thus, key features play an important, but not exclusive, role in predator recognition. An increased interest in some of the modified dummies implies that the tits have a general concept of a sparrowhawk. The individual variability in behaviour of tits is discussed.

Robustness of flight leadership relations in pigeons

Collective animal movements produce spectacular natural phenomena that arise from simple local interactions among group members. Flocks of homing pigeons, Columba livia, provide a useful model for the study of collective motion and decision making. During homing flights, flock members are forced to resolve potentially divergent navigational preferences in order to stay together and benefit from flying in a group. Recent work has demonstrated that some individuals consistently contribute more to the movement decisions of the flock than others do, thereby generating stable hierarchical leader/follower networks. Yet, what attributes of a flying pigeon reliably predict leadership remains an open question. We examined the flexibility of an individual's hierarchical leadership rank (i.e. its ordinal position when flock members are ranked according to the average time differences with which they lead or follow others) as a function of changes in its navigational knowledge. We manipulated already established hierarchical networks in three different flocks, by providing certain individuals with additional homing experience. We found that such training did not consistently lead to an increase in birds' leadership ranks, and that, in general, the nature of leader/follower interactions between trained and untrained birds remained unaffected. Thus, leadership hierarchies in pigeon flocks appear resistant to changes in the navigational knowledge of a subset of their members, at least when these changes are relatively small. We discuss the implications of our results in light of the potential benefits of structural stability in decision-making networks.

The Flying Behavior of Homing Pigeons, Columba livia, Immediately after Release

After release, homing pigeons are often observed to fly around at the release site before they depart. To assess the significance of this behavior, the bearings of pigeons were taken 1,2,3 and 4 min after release and analysed with respect to the mean vanishing direction of the group (Table 1) and the individual vanishing bearing of each bird (Fig. 3, Table 2). The data come from a series of experiments involving young untrained pigeons that were shown to orient using information obtained on the outward journey, older untrained pigeons (older than 12 weeks) and trained pigeons using local information (see R. Wiltschko & Wiltschko 1985). Analysis of behavior at the release site revealed that most groups of pigeons headed into the direction in which they finally departed almost immediately after release. Their flight directions showed a highly significant relationship to the vanishing bearing from the first min onward. Noteworthy exceptions were the young untrained control birds that seemed to fly around erratically, their bearings after one minute still unrelated to the individual vanishing bearing. Because these birds were shown to use information obtained during the outward journey, this finding indicates that flying around at the release site has nothing to do with determining the current home direction. Instead it might possibly serve to collect local release site information and match it with the home course as determined by information collected en route, thus to integrate it into the navigational ‘map’ of the spatial distribution of navigational factors.

Emas Rhea americana Linnaeus (Rheiformes, Rheidae) se lembram do treinamento anti-predação?

The antipredator training is a powerful tool now being used to help the reintroduced animals to recognise and escape from their predators. Testing the memory capacity of the animals after antipredator training is important to evaluate if the application of the training is worthwhile. A group of 15 captive-born greater rheas was studied at Belo Horizonte Zoo. Eight birds were antipredator trained and seven birds were not. After the end of the antipredator training sessions, we run four memory tests at 40, 55, 70 and 88 days after training was completed. The memory tests consisted of showing a predator model to the rheas and recording their behavioural responses. It was measured the capacity of antipredator information storage, the influence of the group size on the behaviour of the birds and the influence of the antipredator training on the elicitation of the correct behavioural responses of the birds when confronted by a predator. The results showed that the rheas retained predator recognition for almost three months, that the group size affected the responses of the birds (more defence behaviours expressed when tested alone) and that the antipredator training is essential to elicit the adequate antipredatory responses, since untrained birds behaved in a tranquil manner when confronted by a predator model. We concluded that antipredator training is worthwhile for future reintroduction programs for greater rheas, since their memory capacity is considerable.

Do captive-born greater rheas Rhea americana Linnaeus (Rheiformes, Rheidae) remember antipredator training?

The antipredator training is a powerful tool now being used to help the reintroduced animals to recognise and escape from their predators. Testing the memory capacity of the animals after antipredator training is important to evaluate if the application of the training is worthwhile. A group of 15 captive-born greater rheas was studied at Belo Horizonte Zoo. Eight birds were antipredator trained and seven birds were not. After the end of the antipredator training sessions, we run four memory tests at 40, 55, 70 and 88 days after training was completed. The memory tests consisted of showing a predator model to the rheas and recording their behavioural responses. It was measured the capacity of antipredator information storage, the influence of the group size on the behaviour of the birds and the influence of the antipredator training on the elicitation of the correct behavioural responses of the birds when confronted by a predator. The results showed that the rheas retained predator recognition for almost three months, that the group size affected the responses of the birds (more defence behaviours expressed when tested alone) and that the antipredator training is essential to elicit the adequate antipredatory responses, since untrained birds behaved in a tranquil manner when confronted by a predator model. We concluded that antipredator training is worthwhile for future reintroduction programs for greater rheas, since their memory capacity is considerable.

The Effect of Transport on Hematologic Parameters in Trained and Untrained Harris's Hawks (Parabuteo unicinctus) and Peregrine Falcons (Falco peregrinus)

Birds of prey are found increasingly in captive situations. When sick, these animals show only very subtle signs of disease, making the detection of disease difficult. For this reason, the analysis of hematologic parameters is a very useful technique for the avian veterinarian. However, birds are most frequently transported to the veterinary clinic for a health check-up. This study investigates the effects of transport-related stress on heterophil and lymphocyte morphology and hematologic parameters of peregrine falcons (Falco peregrinus) and Harris's hawks (Parabuteo unicinctus). Twelve birds of each species, all adults, mixed males and females, were analyzed. Each group of 12 was comprised of 6 trained (accustomed to being transported) and 6 untrained birds. Samples of blood were taken from all birds in their place of origin and again 1 week later after 1 hour (35 km) of transport. Both samples were taken in similar conditions (eg, time of day, duration after feeding, environmental temperature, sample handling) so that any variation would be caused only by transport-related factors. Both untrained groups showed a significant (P < .05) increase in the heterophil/lymphocyte ratio (H/L). Whereas untrained peregrines showed no other significant change, untrained Harris's hawks had a significant leukopenia, lymphopenia, and eosinopenia. Trained Harris's hawks showed a significant monocytosis, whereas trained peregrines showed no significant change. Transport had no apparent influence on heterophil or lymphocyte morphology. Although the difference between pre- and posttransport was significant in some parameters, all values in the 4 groups remained within the reference ranges for the species. Therefore, we can conclude that 1-hour transport for trained or untrained members of these 2 species to a clinic need not be factor that requires the clinician's consideration when interpreting a hematologic sample. However, the 2 species reacted differently to transport. Further studies on other species are suggested. The H/L ratio is proposed as the most sensitive measure of stress response in the blood picture of raptors, and possible uses are suggested.

A sport-physiological perspective on bird migration: evidence for flight-induced muscle damage.

Exercise-induced muscle damage is a well-described consequence of strenuous exercise, but its potential importance in the evolution of animal activity patterns is unknown. We used plasma creatine kinase (CK) activity as an indicator of muscle damage to investigate whether the high intensity, long-duration flights of two migratory shorebird species cause muscle damage that must be repaired during stopover. In two years of study, plasma CK activity was significantly higher in migrating western sandpipers (a non-synchronous, short-hop migrant), than in non-migrants. Similarly, in the bar-tailed godwit (a synchronous, long-jump migrant), plasma CK activity was highest immediately after arrival from a 4000-5000km flight from West Africa to The Netherlands, and declined before departure for the arctic breeding areas. Late-arriving godwits had higher plasma CK activity than birds that had been at the stopover site longer. Juvenile western sandpipers making their first southward migration had higher plasma CK activity than adults. These results indicate that muscle damage occurs during migration, and that it is exacerbated in young, relatively untrained birds. However, the magnitude of the increases in plasma CK activity associated with migratory flight were relatively small, suggesting that the level of muscle damage is moderate. Migrants may avoid damage behaviourally, or have efficient biochemical and physiological defences against muscle injury.

Learning-related alterations in the visual responsiveness of neurons in a memory system of the chick brain.

The intermediate and medial hyperstriatum ventrale (IMHV) of the chick brain is known to be essential for the learning process of imprinting. The activity of neurons was recorded from the left IMHV of 2-day-old unanaesthetized chicks while the chicks were free to move in a running wheel. The chicks were either raised in complete darkness or visually trained (imprinted) with a set duration of exposure to a visual image. The first group of these birds was trained by exposure for 100 min to a rotating red box and the second was trained by similar exposure to a rotating blue cylinder. A third group was left untrained. Training more than doubled the proportion of sites that responded to the stimulus used to train the bird, relative to the proportion of sites responsive to the other stimulus and to the proportion of sites responsive in the untrained birds; the learning-related increase was selective and highly significant. Behavioural monitoring indicated that the enhanced responsiveness could not be explained by overt differences in the alertness, attentiveness or movements of the birds. No significant effect of training was found on the proportion of sites responsive to a rotating stuffed jungle fowl or to the sound of a maternal call. The response at certain sites selectively signalled the presence of the training stimulus, while at others the response showed generalization across stimulus shape or colour. There was a non-specific effect of training upon the pattern of spontaneous discharges of the neurons: the numbers of spikes occurring in clusters (bursts) was significantly reduced in trained birds compared with the dark reared controls.

APPARENT FEED PARTICLE SIZE PREFERENCE BY LAYING HENS

Trials were designed to investigate the effect of feed particle size on apparent feed intake of laying hens. Feed was offered to five different groups of four birds each as either regular crumbles, mash, large crumbles (trained birds), large crumbles (untrained birds) or small crumbles, respectively. Except for the untrained birds, all birds were given a 15-d adaptation period. In each trial hens were offered 200 g of feed at 05:00 h and at each subsequent hour, until 20:00 h, feed was removed from the trough, sieved, weighed, remixed and returned to the feeders. Chemical analysis of the diet and various diet fractions was undertaken. There was marked disappearance of larger particles when birds were fed regular crumbles. However, smaller particles disappeared as the concentration of large ones decreased throughout the day. There was no marked disappearance of particles smaller than 0.60 mm. Feed intake was comparable when regular crumbles or mash rations were fed. Overall feed intake increased when small particles were offered, while intake decreased when the feed was changed abruptly to one of only large particles. It is concluded that particle size in regular crumbled layer feed is not uniform, and that particle size influences disappearance rate. Key words: Layer, particle preference, nutrient preference

Pigeon Homing: The Orientation of Young Birds that had been Prevented from Seeing the Sun

AbstractTo test whether the sun is an essential factor for the development of a functioning orientation system in birds, a group of young pigeons was raised as ‘No‐Sun’‐birds. They were not allowed to see the sun, and they were released to fly around their loft only under total overcast. The control group had an equal number of opportunities to fly under overcast plus additional flights under sun.When released as untrained birds under solid cloud cover, the ‘No‐Sun’‐birds were significantly oriented, whereas the controls were not. Small magnets glued between the wings (north toward the head) reversed the ‘No‐Sun’‐birds' orientation, indicating they used a magnetic compass.These findings show that the orientation system can develop without information from the sun. Differences in the orientation behavior of the ‘No‐Sun’‐birds and normally raised young pigeons are discussed.

Effects of trialkyltins on the schedule-controlled behavior of the pigeon

Male White Carneaux pigeons trained to respond for food under a multiple fixed-ratio fixed-interval schedule of reinforcement were given single injections of trimethyltin (TMT), or triethyltin (TET). A dose of 0.3 mg/kg TMT produced no effect on behavior, while a 1.0 mg/kg dose was a threshold dose and 1.75 mg/kg produced behavioral changes that persisted for months in some birds. TMT produced effects on responding under the multiple schedule at approximately the same doses that produce neuronal damage in the hippocampus and the brain stem of the pigeon. Higher doses given to untrained birds produced signs of extensive neurological damage. A dose of 1.0 mg/kg of TET decreased rates of responding under both schedule components three hours after administration, but behavior usually had recovered by the next day. Doses of 3.0 and 5.6 mg/kg had similar effects, but responding did not recover for several days. Some birds showed significant rate increases, especially under the fixed-interval component several days to several weeks after TET administration. Doses greater than 10 mg/kg TET were lethal. Dose-effect curves for the effects of d-amphetamine, chlorpromazine and morphine on responding under the multiple schedule were determined for some birds before and one month after 1.0 and 1.5 mg/kg of TMT. TMT shifted the dose-effect curve for d-amphetamine to the right, but it did not produce systematic changes in the dose-effect curves for morphine and chlorpromazine.

Transitory corticosterone responses of ducks ( Anas platyrhynchos) to exercise

Horizontal treadmill exercise induced a marked ( P < 0.001) but transitory increase in the level of circulating corticosterone in the plasma of adult male ducks. The decline in corticosterone concentration during exercise is unlikely to be due to a depletion of adrenocortical stores since a marked ( P < 0.001) corticosterone response to adrenocorticotrophin (ACTH) administration was observed immediately after exercise, and was of similar magnitude to that induced in nonexercised controls. The corticosterone response to repeated exercise is also transitory, habituating completely within 28 days of the start of daily training. The corticosterone response ( P < 0.001) to ACTH challenge is not, however, diminished by training. These results indicate that the habituation of the corticosterone response to either acute or repeated exercise is due to a reduction in endogenous ACTH secretion. A similar mechanism appears to be responsible for the habituation of the corticosterone response to handling and confinement in nonexercised control birds. A marked ( P < 0.001) increase in the level of circulating corticosterone was, however, elicited when these birds were exercised, indicating that despite adaptation to handling and confinement the birds remained responsive to the novel stressor of exercise. The corticosterone response of these birds was, however, less than that in untrained birds indicating that the corticosterone response in untrained birds is due to both workload and the stress of handling and confinement.