Reproductive success of Bornean orangutan males: scattered in time but clustered in space

Abstract

The social and mating systems of orangutans, one of our closest relatives, remain poorly understood. Orangutans (Pongo spp.) are highly sexually dimorphic and females are philopatric and maintain individual, but overlapping home ranges, whereas males disperse, are non-territorial and wide-ranging, and show bimaturism, with many years between reaching sexual maturity and attaining full secondary sexual characteristics (including cheek pads (flanges) and emitting long calls). We report on 21 assigned paternities, among 35 flanged and 15 unflanged, genotyped male Bornean orangutans (Pongo pygmaeus wurmbii), studied from 2003 to 2018 in Tuanan (Central Kalimantan, Indonesia). All 10 infants born since mid-2003 with an already identified sire were sired by flanged males. All adult males ranged well beyond the study area (c. 1000 ha), and their dominance relations fluctuated even within short periods. However, 5 of the 10 identified sires had multiple offspring within the monitored area. Several sired over a period of c. 10 years, which overlapped with siring periods of other males. The long-calling behavior of sires indicated they were not consistently dominant over other males in the area around the time of known conceptions. Instead, when they were seen in the area, the known sires spent most of their time within the home ranges of the females whose offspring they sired. Overall, successful sires were older and more often resident than others. Significance statement It is difficult to assess reproductive success for individuals of long-lived species, especially for dispersing males, who cannot be monitored throughout their lives. Due to extremely long interbirth intervals, orangutans have highly male-skewed operational sex ratios and thus intensive male-male competition for every conception. Paternity analyses matched 21 immature Bornean orangutans with their most likely sire (only 10 of 50 genotyped males) in a natural population. Half of these identified sires had multiple offspring in the study area spread over periods of at least 10 years, despite frequently ranging outside this area. Dominance was a poor predictor of success, but, consistent with female mating tactics to reduce the risk of infanticide, known “sires” tended to have relatively high local presence, which seems to contribute to the males’ siring success. The results highlight the importance of large protected areas to enable a natural pattern of dispersal and ranging.

Maternal behavior in Sumatran orangutans (Pongo abelii) is modulated by mother-offspring characteristics and socioecological factors

“…Mothers might also change their behavior in the presence of males depending on their reproductive status, which is closely linked to the age of their current dependent offspring (Fairbanks & McGuire, 1987; Kunz et al, 2022; Scott et al, 2019). Furthermore, it is likely that not all males are a threat, and maternal behavior may vary based on whether a male is a resident or not (Fairbanks & McGuire, 1987; Kunz et al, 2022; van Noordwijk et al, 2023). With a larger sample size, future studies should test the interaction effect of offspring age and male presence/absence and the effect of associating male’s familiarity on maternal investment.…”

“…Furthermore, the orangutans’ predominantly arboreal lifestyle requires maternal care in the form of carrying and bridging to cross gaps in the canopy. Males disperse from their natal area and do not provide paternal care (Arora et al, 2012; Morrogh-Bernard et al, 2011; Nietlisbach et al, 2012; van Noordwijk et al, 2023). This, along with a prolonged period of lactation relative to gestation length (van Schaik, 2000), sexual size dimorphism (Utami Atmoko et al, 2009), and potential for contest competition between males for mating opportunities (Kunz et al, 2023; Spillmann et al, 2017; van Schaik & van Hooff, 1996), puts orangutans at a high risk of infanticide by males, even though there are no confirmed cases (Beaudrot et al, 2009; Knott et al, 2019; van Schaik & Janson, 2000).…”

The development of social attention in orangutans: comparing peering behaviour in wild and zoo-housed individuals

“…The number of offspring is inferred based on observed dependent offspring and genetically confirmed offspring. For adult males with unknown birth dates, we assigned standardized birth dates: for unflanged males twenty years, and for flanged males thirty years before the date on which they were first encountered in the study area (van Noordwijk et al 2023). For orangutans born in the zoos, exact birth dates are known.…”

Play Behavior Varies with Age, Sex, and Socioecological Context in Wild, Immature Orangutans (Pongo spp.)

“…tions) ‡ fromArora et al, 2012;Lenzi, 2014;van Noordwijk et al, 2023 † only selected observers (researchers focusing on immature development) # focal data between 2010 and 2018 from dependent and semi-dependent immatures included, all association partners counted here (own mother, other dependent, semi-dependent and independent immatures, adult females, and unflanged and flanged males) k known birth date Birth months and years in italics indicate estimates for immatures present at the start of the study period…”