Historically, the cheetah (Acinonyx jubatus) has been known for its poor reproductive performance in captivity. Although breeding success has improved over the past decade, the percentage of breeders in the captive population is still low and successful propagation unpredictable. Estrus in this species has been reported as "silent" by some, therefore contributing to breeding problems by making appropriate timing of pair introductions difficult. To investigate whether any observable behavioral changes may be associated with estrus, we carried out quantitative behavioral observations and concomitant noninvasive monitoring of estradiol metabolites excreted in feces of 14 captive female cheetahs for periods of 5-22 consecutive weeks. We found that changes in fecal estradiol concentrations correlated significantly with variation in the occurrence of several types of behaviors, including rolling, rubbing, sniffing, vocalizing, and urine spraying. However, the number and types of correlated behaviors varied across females, revealing no single behavior indicative of estrus, but rather a constellation of behaviors that increased in frequency when estradiol concentrations were elevated. There was no significant difference in the overall average estradiol concentrations or peak values of the females that had previously mated and conceived compared to those of the females that had failed to breed. Successful breeders appeared to show significantly higher rates of rubbing and rolling than nonbreeders. However, rates of rubbing, rolling, and urine spraying also were found to increase with age, and older individuals were more likely to have bred. The results of this study indicate that estrus in the cheetah cannot be regarded as "silent" since the frequencies of some behaviors appear to covary with fluctuating estradiol levels. However, behavioral monitoring of estrus may nevertheless be difficult and time-consuming due to individual variation and subtle changes in behavioral frequencies rather than changes in the types of behaviors displayed.