Despite only focusing on one female Chinese pangolin, LF28, our study, to our knowledge, is the first to provide highly detailed records on the nursing behavior of this poorly studied but critically endangered species. During the entire tracking period, the body weight of LF28 increased from 2 kg at the age of 1 year to 3 kg at the age of 2 years, and LF28 reached her maximum body weight of 4 kg at the age of 3 years. Based on the uninterrupted monitoring between Dec 2014 and June 2016, LF28 gave birth to her first offspring when she was 3 years old and another one at the age of 4 years (Fig. 1). Both infants were born in early December, which were in accordance with the peak birth season of the species10. Our observations confirmed that the Chinese pangolin is a seasonal breeder in the wild, and they give birth once a year10,11. Also, they can give birth in consecutive years with a litter size of one17.
Other studies (n = 4) have found that the lightest weight, or youngest age, a female Chinese pangolin can give birth at the age of 2 years or weight of 3 kg11,17,18, which indicated that they can conceive at an age of 1–2 years. Therefore, the first birth of LF28, which took place when she was 3 years old, might suggest a delay in pregnancy or sex maturation. However, information concerning the average primipara age for this species is not available to date, more research, especially in the wild, is necessary.
Our results indicate that female Chinese pangolins will carry their offspring frequently from one nursing burrow to another during the entire nursing period. In the case of LF28, nursing burrows were only some of the resting burrows utilized and were predominantly located within the core area (MCP75) of her home range (Fig. 4), despite the close proximity to human settlements. This suggests that familiarity of the environment or food resource availability should be important considerations in nursing burrow selection.
Nursing burrows were normally used only once during the same nursing period, with durations varying from 1 day to more than 1 month (Fig. 5). This frequent relocation behavior should be important to avoid predation of the newborn. Our monitoring showed that small carnivores, such as ferret-badgers or crab-eating mongoose, will enter the nursing burrow, which may suggest they are searching for prey. Therefore, this could reflect a potential threat to the infant pangolin, especially when the mother is absent for foraging8.
Burrows where LF28 gave birth were not only used for the longest duration after birth, they were also used before parturition. Similar to our findings, a previous study reported that both males and females will collect and pull hay into the resting burrow in the wintertime3. Therefore, in addition to providing insulation, the hay could also serve as necessary bedding for the delivery and nursing of offspring. Other functions of hay that have been proposed include false barriers that can act as predator deterrent structures19.
Our records revealed at least two different adult male pangolins approaching and entering the nursing burrows multiple times throughout the nursing period. Most of these visits lasted only minutes, whereas a few lasted longer. During one long visit, in March, mating behavior was observed, therefore the occurrence of post-partum estrus, or even ovulation, may be likely for this species. In captivity, mating behavior was also observed between February and July10,20. Although there is no direct evidence yet, these adult male visits suggest that at least some of them were for mate-searching. It has been proposed that while mammalian females spend more energy on parental care, males often invest more energy towards seeking mates21. For solitary and fossorial species such as the pangolin, a male’s mate-finding tactics can be critical for mating success, especially due to the low population density22,23. Male pangolins most likely depend on olfactory cues to locate females in heat. In mammals, female chemical signals have important roles in sexual attraction and facilitating sexual receptivity24,25,26,27. Female Chinese pangolins tend to defecate close to the burrow during the nursing period (N.C.M. Sun unpubl. data), therefore, despite the frequent relocation behavior expressed by the mother, it was likely to generate sufficient olfactory information for male pangolins.
It is also possible that female pangolins will mate more than once, even with different males, during the same nursing period. Sun et al.17 have reported that certain female Chinese pangolins exhibited a lack of mate fidelity based on microsatellite marker assessments. Our observation provides additional support for this phenomenon. Multiple mating with the same or different males has been observed in several solitary carnivores28,29,30,31. For males, frequent pre-copulatory encounters with females may offer advantages that increase opportunities for mating compared to males that are less familiar with females32,33. Hypotheses concerning the advantages of females exhibiting promiscuity have also been widely proposed, including direct benefits (e.g., stimulation of reproduction, fertilization assurance, mate retention etc.) and genetic benefits (e.g., choice of paternity, sperm competition, inbreeding avoidance etc.)34,35.
Interestingly, during two separate visitations adult males exhibited excavation behavior, and both events took place shortly after parturition. This excavation behavior at a parturition burrow has never been reported before for male pangolins, therefore, further research is needed to better understand the role male pangolins play in parental care.
The fetus of LF28’s second offspring detected in the ultrasonographic image in Aug. 15 provided additional information on the gestation length of the species. Following the fetal and extra-fetal structure development of small-sized (3–8 kg) dogs described in Luvoni and Grioni36 and Kim and Son37, we estimated the gestation period of this fetus may have lasted 30–40 days or less. The implantation of the blastocyst, therefore, most likely occurred in early July. This infant pangolin was born on Dec. 8 later that year, and the gestation length was estimated to be around 150 days, which was shorter than previous reports4,9,10. This was the first estimation of gestation length of the Chinese pangolin based on physiological evidence under natural conditions.
Our findings of the gestation period, which took place later in the year (July–December), coupled together with the occurrence of post-partum estrus and mating earlier in the year (December–May), suggests that delayed implantation likely takes place in this species, as proposed by Chin et al.11. This also explains why there was such an extensive variation in the gestation length, from 180 to more than 372 days, determined based on the observation of mating behavior and parturition in captivity10,11,18. More studies on the reproductive physiology for this species are necessary.
Lastly, the present study also demonstrated that the difficulties associated with researching the life history and behaviors of the elusive pangolin could be alleviated with the use of technologies (e.g., camera trapping, radio tracking, etc.). This is especially true for non-migratory fossorial species if one has an appropriate knowledge of their home range or residential environment. There are more and more new technologies and devices that have been developed and applied to wildlife research in the field, which should greatly improve our understanding and promote conservation efforts of endangered species such as the pangolin.
Source: Ecology - nature.com
