Observations on the timing of reproduction in the congeneric Comoro Island fruit bats, Pteropus livingstonii and P. seychellensis comorensis

Weight as an indicator of enclosure suitability in Livingstone's fruit bats (Pteropus livingstonii)

Obesity is common in zoo animals, and both dietary management and the provision of adequate opportunities for exercise are needed to tackle it. We used 30 years of records from Jersey Zoo to compare the weight and forearm length of wild and captive-born Livingstone's fruit bats (Pteropus livingstonii), and to assess the impact on weight of enclosure space. The mean capture weight of wild-caught male Livingstone's bats was 657 g, significantly higher than that of females (544 g). In both wild and captive-born bats, males had significantly longer forearms than females, but there was no effect of birth location. Males weighed more in the mating season than at other times of year. Both sexes gained more weight during development if born in enclosures that restricted flight rather than a large aviary; this was particularly noticeable in females. After reaching maturity at 3 years, weights of bats born in restricted enclosures continued to increase, reached a peak of over 1000 g at 8-10 years, and then declined in both sexes. The weight of bats born in the aviary remained more stable after the age of three. Like wild bats, adult females born in the aviary weighed less than males. However, females born in restricted enclosures weighed more than males born in the same enclosures. Enclosure designs that maximize opportunities for flight can limit excessive weight gain in captive fruit bats and may therefore improve fitness and health, essential in planning for future reintroduction programs.

Predictors of dominance rank and agonistic interactions in captive Livingstone's fruit bats

Male dominance hierarchies have been studied in many animals but rarely in bats (Chiroptera). The dominance rank of social animals may dictate access to resources and mates; therefore, it has important implications for an individual's fitness and is crucial for successful captive management. Between January and December 2018, at both Bristol Zoo Gardens (Bristol, UK) and Jersey Zoo (Jersey, British Isles), we observed 19 male Livingstone's fruit bats Pteropus livingstonii using focal follows for 345 h overall, noting the outcome of all agonistic interactions. We recorded instigators of interactions, along with winners and losers, and analyzed these data using the R-package "EloRating" to create Elo-rating temporal plots of dominance ranks. We used generalized linear mixed models and multiple linear regression to analyze interaction data and test hypotheses regarding predictors of dominance rank, frequency of agonistic interaction, and choice of interaction partner. Age was positively correlated with dominance rank up to around year 9, when an asymptote was attained. Highly ranked bats instigated the most agonistic interactions, and largely directed these interactions at bats with much lower rankings than themselves. Hierarchies were extremely stable throughout the data collection period at both sites. We conclude that Livingstone's fruit bats have a stable linear dominance hierarchy, with high-ranking, typically older males instigating the most interactions with lowest ranking males to secure dominance rank. This study adds to the limited discourse on Pteropus social behaviors, indicating that some bat species may have social systems similar in complexity to some nonhuman primates.

Social roles influence cortisol levels in captive Livingstone's fruit bats (Pteropus livingstonii)

A critical component of conserving and housing species ex situ is an explicit scientific understanding of the physiological underpinnings of their welfare. Cortisol has been repeatedly linked to stress, and therefore used as an indicator of welfare for many species. In order to measure cortisol in the Livingstone's fruit bat (Pteropus livingstonii; a critically endangered keystone species) without disturbing the captive population, we have developed and validated a non-invasive, novel hormone extraction procedure and faecal glucocorticoid assay. A total of 92 faecal samples, 73 from the P. livingstonii breeding colony at Jersey Zoo, Channel Islands and 19 samples from P. livingstonii housed at Bristol Zoological Gardens, UK, have been collected and analyzed. Mixed-effect modelling of the influence of physiological state variables on cortisol concentration revealed that lactating females had higher cortisol levels than non-lactating females, indicating that our assay is measuring biologically relevant hormone concentrations. Males and older bats also had higher cortisol than non-lactating females and younger individuals. Further analysis applied social network methodology to compare the cortisol levels of bats with different social roles. We found that individuals that linked social groups possessed higher than average cortisol levels and conversely, individuals with high-quality, positive relationships had lower cortisol levels. These results demonstrate, for the first time in a bat species, social mediation of stress hormones. Lastly, the frequency of vocalisation was found to positively correlate with cortisol concentration in males, suggesting that this behaviour may be used by animal management as a visual indicator of a bat's hormonal status. Hence, this research has provided unique insights and empirical scientific knowledge regarding the relationship between the physiology and social behaviour of P. livingstonii, therefore allowing for recommendations to be made to optimise bat welfare at the individual level.

Social Experience of Captive Livingstone's Fruit Bats (Pteropus livingstonii)

Social network analysis has been highlighted as a powerful tool to enhance the evidence-based management of captive-housed species through its ability to quantify the social experience of individuals. We apply this technique to explore the social structure and social roles of 50 Livingstone's fruit bats (Pteropus livingstonii) housed at Jersey Zoo, Channel Islands, through the observation of associative, affiliative, and aggressive interactions over two data collection periods. We implement binomial mixture modelling and characteristic-based assortment quantification to describe the complexity and organisation of social networks, as well as a multiple regression quadratic assignment procedural (MRQAP) test to analyse the relationship between network types. We examine the effects of individual characteristics (i.e., sex, age, and dominance rank) on social role by fitting models to explain the magnitude of node metrics. Additionally, we utilize a quadratic assignment procedural (QAP) test to assess the temporal stability of social roles over two seasons. Our results indicate that P. livingstonii display a non-random network structure. Observed social networks are positively assorted by age, as well as dominance rank. The frequency of association between individuals correlates with a higher frequency of behavioural interactions, both affiliative and aggressive. Individual social roles remain consistent over ten months. We recommend that, to improve welfare and captive breeding success, relationships between individuals of similar ages and dominance levels should be allowed to persist in this group where possible, and separating individuals that interact frequently in an affiliative context should be avoided.