Circadian variation in cardiac autonomic activity: reactivity measurements to different types of stressors

The role of endogenous circadian rhythmicity in autonomic cardiac reactivity to different stressors was investigated. A constant routine protocol was used with repeated exposure to a dual task and a cold pressor test. The 29 subjects were randomly divided into two groups in order to manipulate prior wakefulness. Group 1 started at 09:00 h immediately after a monitored sleep period, whereas group 2 started 12 h later. Measures of interbeat intervals (IBI), respiratory sinus arrythmia (RSA, a measure of parasympathetic activity), pre-ejection period (PEP, a measure of sympathetic activity), as well as core body temperature (CBT) were recorded continuously. Multilevel regression analyses (across-subjects) revealed significant (mainly 24 h) sinusoidal circadian variation in the response to both stressors for IBI and RSA, but not for PEP. Individual 24 + 12 h cosine fits demonstrated a relatively large interindividual variation of the phases of the IBI and RSA rhythms, as compared to that of the CBT rhythm. Sinusoidal by group interactions were found for IBI and PEP, but not for RSA. These findings were interpreted as an indication for endogenous circadian and exogenous parasympathetic (vagal) modulation of cardiac reactivity, while sympathetic reactivity is relatively unaffected by the endogenous circadian drive and mainly influenced by exogenous factors.     

Circadian Variation in Cardiac Autonomic Activity: Reactivity Measurements to Different Types of Stressors

The role of endogenous circadian rhythmicity in autonomic cardiac reactivity to different stressors was investigated. A constant routine protocol was used with repeated exposure to a dual task and a cold pressor test. The 29 subjects were randomly divided into two groups in order to manipulate prior wakefulness. Group 1 started at 09:00 h immediately after a monitored sleep period, whereas group 2 started 12 h later. Measures of interbeat intervals (IBI), respiratory sinus arrythmia (RSA, a measure of parasympathetic activity), pre-ejection period (PEP, a measure of sympathetic activity), as well as core body temperature (CBT) were recorded continuously. Multilevel regression analyses (across-subjects) revealed significant (mainly 24 h) sinusoidal circadian variation in the response to both stressors for IBI and RSA, but not for PEP. Individual 24 + 12 h cosine fits demonstrated a relatively large interindividual variation of the phases of the IBI and RSA rhythms, as compared to that of the CBT rhythm. Sinusoidal by group interactions were found for IBI and PEP, but not for RSA. These findings were interpreted as an indication for endogenous circadian and exogenous parasympathetic (vagal) modulation of cardiac reactivity, while sympathetic reactivity is relatively unaffected by the endogenous circadian drive and mainly influenced by exogenous factors.     

Individual differences in respiratory sinus arrhythmia

To investigate the interindividual differences in respiratory sinus arrhythmia (RSA), recordings of ventilation and electrocardiogram were obtained from 12 healthy subjects for five imposed breathing periods (T(TOT)) surrounding each individual's spontaneous breathing period. In addition to the spectral analysis of the R-R interval signal at each breathing period, RSA characteristics were quantified by using a breath-by-breath analysis where a sinusoid was fitted to the changes in instantaneous heart rate in each breath. The amplitude and phase (or delay = phase x T(TOT)) of this sinusoid were taken as the RSA characteristics for each breath. It was found that for each subject the RSA amplitude-T(TOT) relationship was linear, whereas the delay-T(TOT) relationship was parabolic. However, the parameters of these relationships differed between individuals. Linear correlation between the slopes of RSA amplitude versus T(TOT) regression lines and 1) mean breathing period and 2) mean R-R interval during spontaneous breathing were calculated. Only the correlation coefficient with breathing period was significantly different from zero, indicating that the longer the spontaneous breathing period the lesser the increase in RSA amplitude with increasing breathing period. Similarly, only the correlation coefficient between the curvature of the RSA delay-T(TOT) parabola and mean breathing period was significantly different from zero; the longer the spontaneous breathing period the larger the curvature of RSA delay. These results suggest that the changes in RSA characteristics induced by changing the breathing period may be explained partly by the spontaneous breathing period of each individual. Furthermore, a transfer function analysis performed on these data suggested interindividual differences in the autonomic modulation of the heart rate.     

Respiratory Sinus Arrhythmia Versus Neck/Trapezius EMG and Incentive Inspirometry Biofeedback for Asthma: A Pilot Study

This pilot study compared biofeedback to increase respiratory sinus arrhythmia (RSA) with EMG and incentive inspirometry biofeedback in asthmatic adults. A three-group design (Waiting List Control n = 5, RSA biofeedback n = 6, and EMG biofeedback n = 6) was used. Six sessions of training were given in each of the biofeedback groups. In each of three testing sessions, five min. of respiratory resistance and EKG were obtained before and after a 20-min biofeedback session. Additional five-min epochs of data were collected at the beginning and end of the biofeedback period (or, in the control group, self-relaxation). Decreases in respiratory impedance occurred only in the RSA biofeedback group. Traub-Hering-Mayer (THM) waves (.03-.12 Hz) in heart period increased significantly in amplitude during RSA biofeedback. Subjects did not report significantly more relaxation during EMG or RSA biofeedback than during the control condition. However, decreases in pulmonary impedance, across groups, were associated with increases in relaxation. The results are consistent with Vaschillo's theory that RSA biofeedback exercises homeostatic autonomic reflex mechanisms through increasing the amplitude of cardiac oscillations. However, deep breathing during RSA biofeedback is a possible alternate explanation.     

Incoherent oscillations of respiratory sinus arrhythmia during acute mental stress in humans

Respiratory sinus arrhythmia (RSA) has been widely used as a measure of the cardiac vagal control in response to stress. However, RSA seems not to be a generalized indicator because of its dependency on respiratory parameter and individual variations of RSA amplitude (A(RSA)). We hypothesized that phase-lag variations between RSA and respiration may serve as a normalized index of the degree of mental stress. Twenty healthy volunteers performed mental arithmetic task (ART) after 5 min of resting control followed by 5 min of recovery. Breathing pattern, beat-to-beat R-R intervals, and blood pressure (BP) were determined using inductance plethysmography, electrocardiography, and a Finapres device, respectively. The analytic signals of breathing and RSA were obtained by Hilbert transform and the degree of phase synchronization (λ) was quantified. With the use of spectral analysis, heart rate variability (HRV) was estimated for the low-frequency (LF) and high-frequency (HF) bands. A steady-state 3-min resting period (REST), the first 3 min (ART1), and the last 3 min (ART2) of the ART period (ranged from 6- to 19 min) and the last 3 min of the recovery period (RCV) were analyzed separately. Heart rate, systolic BP, and breathing frequency (f(R)) increased and λ, A(RSA), and HF power decreased from REST to ART (P < 0.01). The λ was correlated with normalized A(RSA) and the HF power. The decrease in λ could not be explained solely by the increase in f(R). We conclude that mental stress exerts an influence on RSA oscillations, inducing incoherent phase lag with respect to breathing, in addition to a decrease in RSA.     

Influences of breathing patterns on respiratory sinus arrhythmia in humans during exercise

Persistence of respiratory sinus arrhythmia (RSA) has been described in humans during intense exercise and attributed to an increase in ventilation. However, the direct influence of ventilation on RSA has never been assessed. The dynamic evolution of RSA and its links to ventilation were investigated during exercise in 14 healthy men using an original modeling approach. An evolutive model was estimated from the detrended and high-pass-filtered heart period series. The instantaneous RSA frequency (FRSA, in Hz) and amplitude (ARSA, in ms) were then extracted from all recordings. A(RSA) was calculated with short-time Fourier transform. First, measurements of FRSA and ARSA were performed from data obtained during a graded and maximal exercise test. Influences of different ventilation regimens [changes in tidal volume (VT) and respiratory frequency (FR)] on ARSA were then tested during submaximal [70% peak O2 consumption (VO2peak)] rectangular exercise bouts. Under graded and maximal exercise conditions, ARSA decreased from the beginning of exercise to 61.9 +/- 3.8% VO2peak and then increased up to peak exercise. During the paced breathing protocol, normoventilation (69.4 +/- 8.8 l/min), hyperventilation (81.8 +/- 8.3 l/min), and hypoventilation (56.4 +/- 6.2 l/min) led to significantly (P < 0.01) different ARSA values (3.8 +/- 0.5, 4.6 +/- 0.8, and 2.9 +/- 0.5 ms, respectively). In addition, no statistical difference was found in ARSA when ventilation was kept constant, whatever the FR-VT combinations. Those results indicate that RSA persists for all exercise intensities and increases during the highest intensities. Its persistence and increase are strongly linked to both the frequency and degree of lung inflation, suggesting a mechanical influence of breathing on RSA.     

Human sinus arrhythmia: inconsistencies of a teleological hypothesis

Respiratory sinus arrhythmia (RSA) may serve an inherent function in optimizing pulmonary gas exchange efficiency via clustering and scattering of heart beats during the inspiratory and expiratory phases of the respiratory cycle. This study sought to determine whether physiological levels of RSA, enhanced by slow paced breathing, caused more heart beats to cluster in inspiration. In 12 human subjects, we analyzed the histogram distribution of heart beats throughout the respiratory cycle during paced breathing at 12, 9, and 6 breaths/min (br/min). The inspiratory period-to-respiratory period ratio was fixed at approximately 0.5. RSA and its relationship with respiration was characterized in the phase domain by average cubic-spline interpolation of electrocardiographic R wave-to-R wave interval fluctuations throughout all respiratory cycles. Although 6 br/min breathing was associated with a significant increase in RSA amplitude (P < 0.01), we observed no significant increase in the proportion of heart beats in inspiration (P = 0.34). Contrary to assumptions in the literature, we observed no significant clustering of heart beats even with high levels of RSA enhanced by slow breathing. The results of this study do not support the hypothesis that RSA optimizes pulmonary gas exchange efficiency via clustering of heart beats in inspiration.     

Effects of hypercapnia and hypoxemia on respiratory sinus arrhythmia in conscious humans during spontaneous respiration

Normally, at rest, the amplitude of respiratory sinus arrhythmia (RSA) appears to correlate with cardiac vagal tone. However, recent studies showed that, under stress, RSA dissociates from vagal tone, indicating that separate mechanisms might regulate phasic and tonic vagal activity. This dissociation has been linked to the hypothesis that RSA improves pulmonary gas exchange through preferential distribution of heartbeats in inspiration. We examined the effects of hypercapnia and mild hypoxemia on RSA-vagal dissociation in relation to heartbeat distribution throughout the respiratory cycle in 12 volunteers. We found that hypercapnia, but not hypoxemia, was associated with significant increases in heart rate (HR), tidal volume, and RSA amplitude. The RSA amplitude increase remained statistically significant after adjustment for respiratory rate, tidal volume, and HR. Moreover, the RSA amplitude increase was associated with a paradoxical rise in HR and decrease in low-frequency-to-high-frequency mean amplitude ratio derived from spectral analysis, which is consistent with RSA-vagal dissociation. Although hypercapnia was associated with a significant increase in the percentage of heartbeats during inspiration, this association was largely secondary to increases in the inspiratory period-to-respiratory period ratio, rather than RSA amplitude. Additional model analyses of RSA were consistent with the experimental data. Heartbeat distribution did not change during hypoxemia. These results support the concept of RSA-vagal dissociation during hypercapnia; however, the putative role of RSA in optimizing pulmonary perfusion matching requires further experimental validation.     

Cardiorespiratory interactions during resistive load breathing

The addition to the respiratory system of a resistive load results in breathing pattern changes and in negative intrathoracic pressure increases. The aim of this study was to use resistive load breathing as a stimulus to the cardiorespiratory interaction and to examine the extent of the changes in heart rate variability (HRV) and respiratory sinus arrhythmia (RSA) in relation to the breathing pattern changes. HRV and RSA were studied in seven healthy subjects where four resistive loads were applied in a random order during the breath and 8-min recording made in each condition. The HRV spectral power components were computed from the R-R interval sequences, and the RSA amplitude and phase were computed from the sinusoid fitting the instantaneous heart rate within each breath. Adding resistive loads resulted in 1) increasing respiratory period, 2) unchanging heart rate, and 3) increasing HRV and changing RSA characteristics. HRV and RSA characteristics are linearly correlated to the respiratory period. These modifications appear to be linked to load-induced changes in the respiratory period in each individual, because HRV and RSA characteristics are similar at a respiratory period obtained either by loading or by imposed frequency breathing. The present results are discussed with regard to the importance of the breathing cycle duration in these cardiorespiratory interactions, suggesting that these interactions may depend on the time necessary for activation and dissipation of neurotransmitters involved in RSA.     

Cardiac rhythm effects of .125-Hz paced breathing through a resistive load: Implications for paced breathing therapy and the polyvagal theory

This study examined the psychophysiological effects of slow-paced breathing while subjects breathed through external respiratory resistive loads. Twenty-four normal volunteers completed four 5-min trials of paced breathing (.125 Hz) through an inspiratory resistive wire mesh screen (0 to 25 cm H₂O/L/s). Each trial was followed by a 5-min rest trial. There was evidence for hyperventilation and/or fatigue during paced breathing. Also, respiratory sinus arrhythmia (RSA) was elevated in the first minute of paced breathing, and then declined toward baseline. Heart period decreased during paced breathing trials, and fell significantly below baseline during rest periods. These data suggest decreased vagus nerve activity and/or sympathetic activation, following an initial increase in parasympathetic activity during paced breathing. They are not consistent with the use of .125-Hz paced breathing as a relaxation technique, particularly during respiratory resistive stress. Finally, although RSA and average heart period changed synchronouslywithin paced breathing and rest conditions, they diverged incomparisons between pacing and rest. This dissociation suggests that different mechanisms mediate these two cardiac parameters. These data are consistent with Porges' theory that vagal influences on tonic heart rate are mediated by the combined effect of vagal projections from both the nucleus ambiguus and the dorsal motor nucleus, while RSA is mediated only through the nucleus ambiguus alone.     

Microgravity alters respiratory sinus arrhythmia and short-term heart rate variability in humans

We studied heart rate (HR), heart rate variability (HRV), and respiratory sinus arrhythmia (RSA) in four male subjects before, during, and after 16 days of spaceflight. The electrocardiogram and respiration were recorded during two periods of 4 min controlled breathing at 7.5 and 15 breaths/min in standing and supine postures on the ground and in microgravity. Low (LF)- and high (HF)-frequency components of the short-term HRV (< or =3 min) were computed through Fourier spectral analysis of the R-R intervals. Early in microgravity, HR was decreased compared with both standing and supine positions and had returned to the supine value by the end of the flight. In microgravity, overall variability, the LF-to-HF ratio, and RSA amplitude and phase were similar to preflight supine values. Immediately postflight, HR increased by approximately 15% and remained elevated 15 days after landing. LF/HF was increased, suggesting an increased sympathetic control of HR standing. The overall variability and RSA amplitude in supine decreased postflight, suggesting that vagal tone decreased, which coupled with the decrease in RSA phase shift suggests that this was the result of an adaptation of autonomic control of HR to microgravity. In addition, these alterations persisted for at least 15 days after return to normal gravity (1G).     

Monitoring the wild black bear's reaction to human and environmental stressors

Background

Bears are among the most physiologically remarkable mammals. They spend half their life in an active state and the other half in a state of dormancy without food or water, and without urinating, defecating, or physical activity, yet can rouse and defend themselves when disturbed. Although important data have been obtained in both captive and wild bears, long-term physiological monitoring of bears has not been possible until the recent advancement of implantable devices.

Results

Insertable cardiac monitors that were developed for use in human heart patients (Reveal® XT, Medtronic, Inc) were implanted in 15 hibernating bears. Data were recovered from 8, including 2 that were legally shot by hunters. Devices recorded low heart rates (pauses of over 14 seconds) and low respiration rates (1.5 breaths/min) during hibernation, dramatic respiratory sinus arrhythmias in the fall and winter months, and elevated heart rates in summer (up to 214 beats/min (bpm)) and during interactions with hunters (exceeding 250 bpm). The devices documented the first and last day of denning, a period of quiescence in two parturient females after birthing, and extraordinary variation in the amount of activity/day, ranging from 0 (winter) to 1084 minutes (summer). Data showed a transition toward greater nocturnal activity in the fall, preceding hibernation. The data-loggers also provided evidence of the physiological and behavioral responses of bears to our den visits to retrieve the data.

Conclusions

Annual variations in heart rate and activity have been documented for the first time in wild black bears. This technique has broad applications to wildlife management and physiological research, enabling the impact of environmental stressors from humans, changing seasons, climate change, social interactions and predation to be directly monitored over multiple years.     

Hemodynamic response pattern predicts susceptibility to stress-induced elevation in arterial pressure in the rat

Cocaine or air jet stress evokes pressor responses due to either a large increase in systemic vascular resistance (vascular responders) or small increases in both cardiac output and vascular resistance (mixed responders) in conscious rats. Repeated cocaine administration results in elevated arterial pressure in vascular responders but not in mixed responders. The present study examined the hypothesis that the pattern of cardiovascular responses to an unconditioned stimulus (UCS; air jet) is related to responses to a conditioned stimulus (CS; tone followed by brief foot shock) in individual rats. Our data demonstrate that presentation of the UCS produced variable cardiac output responses that correlated with responses to the CS (n = 60). We also determined whether individual cardiovascular response patterns to acute stress correlated with predisposition to a sustained stress-induced elevation in arterial pressure. Rats were exposed to three different stressors presented one per day successively for 4 wk and during a poststress period of 3 wk while arterial pressure was recorded periodically. Mean arterial pressure was elevated in all rats during chronic stress but, during the poststress period, remained at significantly higher levels in vascular responders but not mixed responders. Therefore, we conclude that acute behavioral stress to a conditioned stimulus elicits variable hemodynamic responses that predict the predisposition to a sustained stress-induced elevation in arterial pressure.     

Increased energy expenditure but decreased stress responsiveness during molt

Baseline and stress-induced corticosterone (CORT), heart rate (fH), and energy expenditure were measured in eight captive European starlings Sturnus vulgaris during and following a prebasic molt. The fH and oxygen consumption (V O2 ) were measured simultaneously across a range of heart rates, and energy expenditure (kJ/d) was then calculated from data. Energy expenditure and fH were strongly and positively correlated in each individual. Baseline fH and energy expenditure were significantly higher during molt. Molting starlings expended 32% more energy over 24 h than nonmolting birds, with the most significant increase (60%) occurring at night, indicating a substantial energetic cost to molt. Furthermore, the cardiac and metabolic responses to stress during molt were different than during nonmolt. Birds were subjected to four different 30-min acute stressors. The fH and CORT responses to these stressors were generally lower during molt. Although restraint caused a 64% increase in daily energy expenditure during nonmolt, no other stressor caused a significant increase in energy expenditure. Overall, our data suggest that molt is not only energetically expensive but that it also alters multiple stress response pathways. Furthermore, most acute stressors do not appear to require a significant increase in energy expenditure.     

Daytime cardiac autonomic activity during one week of continuous night shift

Shift workers encounter an increased risk of cardiovascular disease compared to their day working counterparts. To explore this phenomenon, the effects of one week of simulated night shift on cardiac sympathetic (SNS) and parasympathetic (PNS) activity were assessed. Ten (5m; 5f) healthy subjects aged 18-29 years attended an adaptation and baseline night before commencing one week of night shift (2300-0700 h). Sleep was recorded using a standard polysomnogram and circadian phase was tracked using salivary melatonin data. During sleep, heart rate (HR), cardiac PNS activity (RMSSD) and cardiac SNS activity (pre-ejection period) were recorded. Night shift did not influence seep quality, but reduced sleep duration by a mean of 52 +/- 29 min. One week of night shift evoked a small chronic sleep debt of 5 h 14 +/- 56 min and a cumulative circadian phase delay of 5 h +/- 14 min. Night shift had no significant effect on mean HR, but mean cardiac SNS activity during sleep was consistently higher and mean cardiac PNS activity during sleep declined gradually across the week. These results suggest that shiftwork has direct and unfavourable effects on cardiac autonomic activity and that this might be one mechanism via which shiftwork increases the risk of cardiovascular disease. It is postulated that sleep loss could be one mediator of the association between shiftwork and cardiovascular health.     

INDIVIDUALITY IN THE WHISTLE CALL OF THE ASIATIC WILD DOG CUON ALPINUS

ABSTRACT

The Asiatic wild dog or dhole Cuon alpinus is a threatened social canid that uses a repetitive whistle call to maintain group contact in dense habitats. Spectrographic analysis revealed significant differences between the whistles of captive dholes, allowing callers to be reliably identified. The most important discriminatory characteristics were the period from the start of one syllable to the next, the fundamental frequency, and the maximum frequency. The individual distinctiveness of the whistle is discussed in terms of its functional significance and possible survey applications.     

Respiratory sinus arrhythmia in the denervated human heart

We performed this study to test whether the denervated human heart has the ability to manifest respiratory sinus arrhythmia (RSA). With the use of a highly sensitive spectral analysis technique (cross correlation) to define beat-to-beat coupling between respiratory frequency and heart rate period (R-R) and hence RSA, we compared the effects of patterned breathing at defined respiratory frequency and tidal volumes (VT), Valsalva and Mueller maneuvers, single deep breaths, and unpatterned spontaneous breathing on RSA in 12 normal volunteers and 8 cardiac allograft transplant recipients. In normal subjects R-R changes closely followed changes in respiratory frequency (P less than 0.001) but were little affected by changes in VT. On the R-R spectrum, an oscillation peak synchronous with respiration was found in heart transplant patients. However, the average magnitude of the respiration-related oscillations was 1.7-7.9% that seen in normal subjects and was proportionally more influenced by changes in VT. Changes in R-R induced by Valsalva and Mueller maneuvers were 3.8 and 4.9% of those seen in normal subjects, respectively, whereas changes in R-R induced by single deep breaths were 14.3% of those seen in normal subjects. The magnitude of RSA was not related to time since the heart transplantation, neither was it related to patient age or sex. Thus the heart has the intrinsic ability to vary heart rate in synchrony with ventilation, consistent with the hypothesis that changes, or rate of changes, in myocardial wall stretch might alter intrinsic heart rate independent of autonomic tone.     

Cocaine-induced ventricular fibrillation: protection afforded by the calcium antagonist verapamil

There is increasing evidence that the use of cocaine can trigger lethal cardiac events, including ventricular fibrillation. The mechanism responsible for these lethal cardiac arrhythmias remains to be determined. Therefore, 13 mongrel dogs were instrumented so that heart rate, left ventricular pressure (LVP), and d(LVP)/dt could be measured. After a 3- to 4-wk recovery period, the left circumflex coronary artery was occluded for 2 min, beginning with the last minute of an exercise stress test and continuing for 1 min after the cessation of exercise. None of the dogs developed cardiac arrhythmias during the control exercise plus ischemia test. On a subsequent day, the test was repeated after the injection of cocaine HCl (1.0 mg/kg). Cocaine significantly (P less than 0.01) elevated heart rate, systolic LVP, and d(LVP)/dt, and it elicited cardiac arrhythmias in 12 of the 13 animals during the exercise plus test. In fact, 11 animals developed ventricular fibrillation. Verapamil, a calcium channel antagonist (250 micrograms/kg), attenuated the hemodynamic effects of cocaine and prevented the development of ventricular arrhythmias. These data suggest that cocaine can induce ventricular fibrillation during myocardial ischemia and that these lethal arrhythmias may be prevented by a calcium channel antagonist.     

A note on the effect of gestation housing environment on approach test measures in gilts

Systems’ welfare evaluation, including behavioural testing, is becoming increasingly popular in farm animal assurance schemes. The aims of this study were to investigate whether fairly short-term exposure to gestation housing systems, which varied in physical, environmental and human-input factors, influenced behavioural and physiological measures during a human approach test—often used to identify problems in human–animal interactions. Twenty-four Large White×Landrace gilts were initially subjected to identical human contact and daily husbandry. Forty-two days after service, the gilts were randomly assigned to either an indoor housing system (n=16) or an outdoor housing system (n=8), which differed physically and in the amount of human contact and daily husbandry. The indoor system used an electronic sow feeder (ESF), was more space-limited and thermally-controlled and had human contact centered on cleaning out. The outdoor system was more extensive, had much greater space accessible, was not thermally-controlled and had human contact that centered around feeding. The human approach test was carried out on all gilts 30–44 days after entry to the gestation system. At testing, each individual was fitted with heart rate monitor and then moved into a test arena. After 2 min an unfamiliar human entered the pen and stood motionless for 3 min against one wall and then approached the gilt and touched her snout. Throughout the experimental period, behaviour and sound within the test arena were recorded continuously. During the 2 min familiarisation period, outdoor gilts had lower heart rates (108.2 bpm versus 123.7 bpm, P<0.05) and tended to perform fewer short vocalisations (0.5 calls per min versus 3.4 calls per min, P<0.1). Outdoor-housed gilts also carried out less locomotor behaviour (2.2 sections crossed versus 4.0 sections crossed, P<0.05) and tended to perform fewer short (1.4 calls per min versus 5.0 calls per min, P<0.1) and long vocalisations (0.2 calls per min versus 1.8 calls per min, P<0.1) over the 3 min test period. Outdoor gilts tended to be slower to approach within 0.5 m of the human (69.9 s versus 19.3 s, P<0.1) but they then took less extra time to make physical contact (3.3 s versus 52.7 s, P<0.1). Mean heart rate was significantly lower in outdoor sows over the whole 3 min period (99.5 bpm versus 115.5 bpm, P<0.05). The results demonstrate that short-term exposure to different housing systems did influence behavioural and physiological measures during a standard human approach test and thus, systems differences should be taken into account before making judgements about the human–animal relationship on any commercial farm, based on results of behavioural tests of this type.     

Signature-whistle production in undisturbed free-ranging bottlenose dolphins (Tursiops truncatus)

Data from behavioural observations and acoustic recordings of free-ranging bottlenose dolphins (Tursiops truncatus) were analysed to determine whether signature whistles are produced by wild undisturbed dolphins, and how whistle production varies with activity and group size. The study animals were part of a resident community of bottlenose dolphins near Sarasota, Florida, USA. This community of dolphins provides a unique opportunity for the study of signature-whistle production, since most animals have been recorded during capture-release events since 1975. Three mother-calf pairs and their associates were recorded for a total of 141.25 h between May and August of 1994 and 1995. Whistles of undisturbed dolphins were compared with those recorded from the same individuals during capture-release events. Whistles were conservatively classified into one of four categories: signature, probable signature, upsweep or other. For statistical analyses, signature and probable signature whistles were combined into a 'signature' category; upsweep and other whistles were combined into a 'non-signature' category. Both 'signature' and 'non-signature' whistle frequencies significantly increased as group size increased. There were significant differences in whistle frequencies across activity types: both 'signature' and 'non-signature' whistles were most likely to occur during socializing and least likely to occur during travelling. There were no significant interactions between group size and activity type. Signature and probable signature whistles made up ca. 52% of all whistles produced by these free-ranging bottlenose dolphins.