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Abstract and Summary

The activity rhythm, reproductive cycle, and maintenance, social and reproductive behavior of a pair of captive giant pandas were studied at the National Zoological Park, Washington, D.C. Results from this study and the available literature indicate that:

  • 1) 
    Giant pandas are probably nocturnal, although they may be polycyclic in activity.
  • 2) 
    Males are more active than females, especially in locomotor behavior and scent-marking activity
  • 3) 
    Activity levels are inversely correlated with age.
  • 4) 
    There is a single annual estrous period of one to three days between March and June, preceded by conspicuous behavioral changes in the female consisting of a depressed appetite, increased restlessness and scent-marking, and increased vocalizing. Behavioral changes in the male are similar and are synchronized with the female reproductive cycle.
  • 5) 
    The major communicatory modes are through scent-marking and vocalizations. A variety of postures is used to deposit urine and anogenital gland secretions throughout the environment. Most of the major call types show considerable variation and grading; they are prominent during agonistic and reproductive activities. Visual signals are only poorly developed. Tactile contact is more frequent during social interactions than might be predicted, considering the solitary nature of the species. However, significant tactile contact may be limited to the initial stages of encounters, with avoidance and intolerance occurring thereafter.
  • 6) 
    Both the giant panda's copulatory posture and the temporal patterning of copulation (numerous short mounts and a brief ejaculatory intromission with a long inter-ejaculation interval) differ significantly from sexual behavior reported for other closely related carnivores. Observations suggest that the prior compatibility of a pair is essential for successful reproductive behavior.
  • 7) 
    Comparative data on giant panda reproduction suggest that the 140 day average gestation length (range: 122–163 days) includes a delay, either in implantation or early development. The neonatalimaternal weight ratio may be the smallest among the Eutherian mammals.
  • 8) 
    Three major reproductive characteristics—
  • (a) 
    the occurrence of a weak estrus in the autumn in some females
  • (b) 
    variability in the duration of the “gestation” period and
  • (c) 
    survivorship of only one young despite a litter size of one to three young — and fossil evidence for a much wider previous geographic distribution, suggest that giant pandas may have had a more flexible and opportunistic reproductive strategy during their past evolutionary history, and have recently undergone K-selection, with increasing dietary and habitat specialization.