Circadian Rhythms and Activity Patterns

Circadian rhythms and activity patterns in a pair of captive giant pandas (Ailuropoda melanoleuca)

Principal Investigators: David M. Powell, Loraine R. Tarou & Devra G. Kleiman
Smithsonian National Zoological Park

Collaborators: Zhang Hemin & Zhang Guiquan
China Research & Conservation Center for the Giant Panda

Relatively little biological information is published about giant pandas, despite their tremendous public appeal and over 25 years of research. The basic activity patterns and circadian rhythms of relatively few individuals have been studied. Circadian rhythms are patterns of behavioral, biochemical, and physiological fluctuations that have a 24-hour period. Examples include sleep, temperature fluctuations, and hormonal fluctuations. Circadian rhythms are regulated by an internal clock that is located in the suprachiasmatic nucleus. Light is the most powerful factor that influences the pattern of a circadian rhythm. Cyclical changes in certain functions are important because they allow animals to anticipate periodic events such as nightfall and daybreak. It is also important for resource partitioning between diurnal and nocturnal animals.

Circannual rhythms are patterns of behavioral, biochemical and physiological fluctuations that have a 365-day period. Examples include reproductive status and body weight. Circannual rhythms can be driven by exogenous factors such as food availability and temperature as well as endogenous factors. These types of rhythms are important in that they allow animals to anticipate seasonal changes that may be important for mating, hibernation, seasonal foraging, migration, and other regular environmental changes.

Circadian rhythms have been studied in black, grizzly, and brown bears. Each of these species exhibit a crepuscular pattern of activity during the spring, which characterized by peaks of activity in the morning hours of daybreak and the evening hours surrounding nightfall. During the summer and sometimes fall, their behavior is characterized by an increasing tendency towards diurnal activity. There have been some limited observations of nocturnal activity, especially in fall for black bears. The patterns of behavior observed in these other bears differ according to region, sex, reproductive condition, age, and environmental variables (temperature, rainfall) and there is a high degree of behavioral plasticity.

In George Schaller’s seminal research on wild giant pandas in the Wolong Nature Reserve, he reported activity patterns for pandas that were similar to those of other wild bears. Specifically, he observed two activity peaks from 0400-0600 and 1600-1900. However, pandas differed from other bears in that they exhibited intermittent activity periods over the entire 24-hour period. The probability of a panda being active in a given hour was >0.5 for most animals most of the time. Like other bears, there was individual and seasonal variability in behavior patterns. Activity was relatively constant throughout the year, with the exception of a significant decline in September and a tendency to be more active in summer.

Some studies of circadian rhythms have been conducted with captive giant pandas. The results of these studies suggest that the patterns of behavior in captive pandas may differ from that of their wild counterparts. For example, two 3-year old pandas were studied when they were temporarily housed at the Los Angeles Zoo in 1984. These pandas were housed together from 0900-1700. Researchers observed 3 peaks in activity between the hours of 0600-1000, 1300-1700, and 0300-0400. Similar behavior patterns were observed in two adult pandas (10 and 16 years of age) housed at Tokyo Ueno in 1983. These pandas were always separated from each other. Like the pandas at the Los Angeles Zoo, the Tokyo pandas exhibited 3 peaks in activity. These peaks occurred between the hours of 0600-1000, 1300-1700, and 2100-2400. Finally, the pandas, Ling Ling and Hsing Hsing, which were originally housed at the Smithsonian National Zoological Park also displayed 3 peaks of activity throughout the day. However, the salience of the peak that occurred between 0400 and 0700 was highly variable.

The acquisition of two young pandas at the Smithsonian National Zoological Park provided us with the opportunity to increase the sample size and our understanding of captive pandas whose activity patterns have been documented. Our objectives in this study were to 1) identify biological rhythms in a new pair of young, captive pandas housed at the Smithsonian National Zoological Park, 2) compare their rhythms and activities with those of the previous pair of pandas housed at the Smithsonian National Zoological Park, and 3) identify seasonal changes in activity.

Research Method

The subjects of our study were one 3.5 male “Tian Tian” and one 2.5 year old female female “Mei Xiang”. They were fed indoors at 0700 and were then released outdoors at 0800 with food in exhibits. Mid-day feedings were provided between 1100-1200 and 1430-1530. At 1700 they were moved indoors at 1700 and provided with an evening meal.

Data were collected during two, week-long nighttime observations (1700-0700 hours in May and November 2001), two four-day 24 hour observations (February and March 2001), and daytime observations conducted year round. Instantaneous scan sampling with one minute intervals were used during the 24 hour watches to record information on behavior, location in the exhibit and proximity to the other panda throughout the day. Continuous behavior sampling was used to collect data in the two week-long nighttime watches. The methodology was identical to that used by Kleiman (1974) to study Ling Ling and Hsing Hsing at the Smithsonian National Zoological Park.

Analyses of seasonal patterns of behavior in SNZP giant pandas were also conducted to determine if activity patterns changed on a seasonal basis. Two-hour focal animal observations were balanced across a period of 0800-1800 hours. Scan sampling was conducted at one minute intervals 5 days/week, all year.

Findings

Despite being separated during the nighttime hours of 1700-0700, the SNZP giant pandas were highly synchronous in their behavior patterns. The results from the 24-hour watches revealed that daytime active periods for both animals were observed between 0700-1000 and 1400-1600. These peaks coincided with feedings. A third peak in activity was observed and varied in timing with season. During the winter, there was an active period that occurred between 2100-0000. During the summer, this peak was observed from 1900-2100. The observation of three distinct peaks in activity was similar to that observed in the other captive pandas studied to date. This differs from the activity peaks that were observed by Schaller in wild giant pandas, which exhibited only two distant peaks in activity. Furthermore, captive giant pandas were generally less likely to be active in a given hour than wild pandas. The results of the two nighttime watches revealed that the previous and current pandas housed at the National Zoo showed similar levels of resting and feeding during the night.

Analysis of seasonal patterns of behavior in SNZP giant pandas showed that feeding and resting changed the most over the course of a year. There were age/sex differences in the patterns of resting and feeding. Both animals spent less time feeding in summer versus winter. Moreover, overall activity was higher in the cooler months than in the warmer months of the year. The reverse was true for wild pandas, but both show a decline in August/September. The male’s time spent active was always higher than time spent resting.

In conclusion, giant pandas at same facility were synchronous in their behavior, even when tactile, visual, auditory and olfactory access to each other was limited. Captive giant pandas have similar activity patterns due in part to husbandry. Captive and wild giant pandas differed in overall activity and timing of active periods. Previous and current SNZP giant pandas were similar in nocturnal behavior. Resting and feeding behavior varied on an annual basis and sex and/or age differences exist in circannual patterns of behavior and activity.

Implications for Conservation and Captive Management

Determining the normal pattern of circadian and cirannual rhythms is very important. Disruption of these rhythms due to biological factors or environmental factors may have deleterious affects on the health of an individual. Some of the questions that we may be able to ask now are: How fixed/plastic are rhythms? Can they be modified for the better or for the worse? Also, it is important for managers of captive animals to know how animals, particularly those that are active during the night, behave when they are gone for the day. Results of studies such as this may have implications for the psychological and physiological well-being of the animals being studied.