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A range of acoustic characteristics typically carry information on individual identity in mammalian calls. In addition, physical similarities in vocal production anatomy among closely related individuals may result in similarities in the acoustic structure of vocalizations. Here, acoustic analyses based on source-filter theory were used to determine whether giant panda bleats are individually distinctive, to investigate the relative importance of different source-(larynx) and filter-(vocal tract) related acoustic features for coding individuality, and to test whether closely related individuals have similarities in call structure. The results revealed that giant panda bleats are highly individualized and indicate that source-related features, in particular, mean fundamental frequency, amplitude variation per second, and the mean extent of each amplitude modulation, contribute the most to vocal identity. In addition, although individual pairwise relatedness was not correlated with overall acoustic similarity, it was highly correlated with amplitude modulation rate and fundamental frequency range, suggesting that these acoustic features are heritable components of giant panda bleats that could be used as a measure of genetic relatedness. The ecological relevance of acoustically signaling information on caller identity and the potential practical implications for acoustic monitoring of population levels in this endangered species are discussed.

Sex differences in spatial cognition have been reported for many species ranging from voles to humans. The range size hypothesis predicts that sex differences in spatial ability will only occur in species in which the mating system selects for differential range size. Consistent with this prediction, we observed sex differences in spatial ability in giant pandas, a promiscuous species in which males inhabit larger ranges than females, but did not observe sex differences in Asian small-clawed otters, a related monogamous species in which males and females share home ranges. These results provide the first evidence of sex differences in spatial ability in the order Carnivora, and are consistent with the range size hypothesis.

The luteal phase of the giant panda has been exclusively assessed by studying urinary hormone patterns in a very few individuals. To better understand hormonal dynamics of protracted progestagen excretion in this endangered species, we monitored hormonal metabolites in the fibrous faeces of multiple females in the USA and China. Giant pandas that were anoestrual during the breeding season excreted baseline progestagen throughout the year. In contrast, there were two distinctive periods when progestagen excretion increased in females that experienced behavioural oestrus, the first being modest, lasting for 61-122 days, and likely reflecting presumptive ovulation. This increase was far surpassed by a secondary rise in progestagen excretion associated with a rejuvenated luteal capacity or hormone production from an extra-gonadal source. The duration of this 'secondary' rise in progestagen excretion averaged w45 days and terminated in a decline to baseline coincident with parturition or the end of a non-parturient luteal interval. Data revealed that, even with a complex, biphasic progestagen profile, the longitudinal patterns produced by giant pandas were relatively consistent among animals and across years within individuals. However, progestagen excretion patterns throughout this period could not be used to discriminate among non-pregnant, pregnant or pseudopregnant states.