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To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.anbehav.2008.12.005 Byline: Andrew M. Robbins (a), Tara Stoinski (b), Katie Fawcett (b), Martha M. Robbins (a) Abstract: Natal dispersal is often attributed to inbreeding avoidance, competition for resources or competition for mates, but the patterns and frequency of dispersal vary considerably among and even within species. We examined the possible reasons for dispersal and philopatry of natal nulliparous female mountain gorillas, Gorilla gorilla beringei, in the Virunga volcano region, including comparisons with non-natal and/or parous females. Competition among females is generally weak and ineffective in this population, and inbreeding avoidance has been considered the ultimate cause of natal dispersal. Yet fewer than half of nulliparous females left their natal group when the dominant male was old enough to be their father, so they did not rely entirely upon dispersal to avoid such risk of inbreeding. Almost all natal nulliparous females were with at least one sexually active male who was not old enough to be their father, so the presence or absence of such mating alternatives also did not determine whether they left. Natal nulliparous females were more likely to leave groups with only one adult male, where infanticide losses have been higher than in multimale groups. Thus natal dispersal seemed to be influenced by infanticide avoidance, which has been considered the ultimate cause of secondary dispersal. Natal nulliparous females have more time to encounter suitable destinations than other females, which may be a proximate reason why they were more likely to transfer despite having the same ultimate cause of dispersal. Author Affiliation: (a) Max Planck Institute for Evolutionary Anthropology, Germany (b) Dian Fossey Gorilla Fund International, U.S.A. Article History: Received 18 March 2008; Revised 5 June 2008; Accepted 4 December 2008 Article Note: (miscellaneous) MS. number: 08-00194R

Understanding the reproductive biology of endangered mountain gorillas ( Gorilla beringei beringei) is essential for optimizing conservation strategies, determining any demographic impact of socioecological changes, and providing information for comparative studies of primates. Non-invasive techniques have been used to assess the reproductive function of many primates and the importance of validating the measurements of hormones metabolites is widely recognized because they may vary even within closely related species. To determine if it is possible to non-invasively monitor ovarian activity in wild mountain gorillas, we used enzyme immunoassays (EIA) to quantify both urinary and fecal excretion of immunoreactive pregnanediol-3-glucuronide (iPdG), defined as all metabolites detected by a pregnanediol-3-glucuronide immunoassay (PdG EIA). Simultaneously, we performed the liquid chromatography mass spectrometry (LC-MS) to quantify the excretion of pregnanediol in urine and feces. Samples were analyzed over nine cycles of five females from the habituated gorillas monitored by Karisoke Research Center, Rwanda. As an additional indicator for ovulation timing, estrone conjugates (E1C) were measured in a subset of urine samples. The concentrations of iPdG and pregnanediol measured in the same samples were significantly correlated. Urinary concentrations of iPdG and pregnanediol fluctuated over the menstrual cycle but did not reveal any cyclic pattern, whereas a typical preovulatory urinary E1C surge and postovulatory increases of fecal iPdG and pregnanediol were detected. The luteal peaks of iPdG and pregnanediol levels in feces were on average 2.8 and 7.6 times higher, respectively, than averaged levels in the corresponding follicular phase. The relative number of days with observed matings was higher within the presumed fertile window than in the preceding period. Overall, the results indicate that fecal analysis of iPdG and pregnanediol is suitable for detecting ovulation in female mountain gorillas. Urinary measurements using both EIA and LC-MS appeared to be uninformative for monitoring ovarian activity in this primate. Am. J. Primatol. 76:180-191, 2014. © 2013 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

Understanding the life history correlates of ontogenetic differences in hominoid brain growth requires information from multiple species. At present, however, data on how brain size changes over the course of development are only available from chimpanzees and modern humans. In this study, we examined brain growth in wild Virunga mountain gorillas using data derived from necropsy reports ( N = 34) and endocranial volume (EV) measurements ( N = 86). The youngest individual in our sample was a 10-day-old neonatal male with a brain mass of 208 g, representing 42% of the adult male average. Our results demonstrate that Virunga mountain gorillas reach maximum adult-like brain mass by 3-4 years of age; adult-sized EV is reached by the time the first permanent molars emerge. This is in contrast to the pattern observed in chimpanzees, which despite their smaller absolute brain size, reportedly attain adult brain mass approximately 1 year later than Virunga mountain gorillas. Our findings demonstrate that brain growth is completed early in Virunga mountain gorillas compared to other great apes studied thus far, in a manner that appears to be linked with other life history characteristics of this population. Am. J. Primatol. 75:450-463, 2013. © 2012 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

Monitoring temporal and spatial changes in the resource availability of endangered species contributes to their conservation. The number of critically endangered mountain gorillas ( Gorilla beringei beringei) in the Virunga Volcano population has doubled over the past three decades, but no studies have examined how food availability has changed during that period. First, we assessed if the plant species consumed by the gorillas have changed in abundance and distribution during the past two decades. In 2009-2010, we replicated a study conducted in 1988-1989 by measuring the frequency, density, and biomass of plant species consumed by the gorillas in 496 plots (ca. 6 km2) in the Karisoke study area in Volcanoes National Park, Rwanda. We expected to observe a decreased presence of major gorilla food plants as a likely result of density-dependent overharvesting by gorillas. Among the five most frequently consumed species (composing approximately 70% of the gorilla's diet, excluding bamboo), two have decreased in availability and abundance, while three have increased. Some species have undergone shifts in their altitudinal distribution, possibly due to regional climatic changes. Second, we made baseline measurements of food availability in a larger area currently utilized by the gorillas. In the extended sampling ( n = 473 plots) area (ca. 25 km2), of the five most frequently consumed species, two were not significantly different in frequency from the re-sampled area, while two occurred significantly less frequently, and one occurred significantly more frequently. We discuss the potential impact of gorilla-induced herbivory on changes of vegetation abundance. The changes in the species most commonly consumed by the gorillas could affect their nutrient intake and stresses the importance of monitoring the interrelation among plant population dynamics, species density, and resource use. Am. J. Primatol. 75:267-280, 2013. © 2012 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]