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Patterns of aggression in spider monkeys at runaway creek nature reserve, Belize

Patterns of aggression in spider monkeys at runaway creek nature reserve, Belize. Kayla Hartwell 1 , Hugh Notman 1,2 , & Mary Pavelka 1. 1 University of Calgary and 2 Athabasca University, Alberta, Canada. Female-Directed Aggression.

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Patterns of aggression in spider monkeys at runaway creek nature reserve, Belize

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  1. Patterns of aggression in spider monkeys at runaway creek nature reserve, Belize Kayla Hartwell1, Hugh Notman1,2, & Mary Pavelka1 1University of Calgary and 2Athabasca University, Alberta, Canada

  2. Female-Directed Aggression • Described in a number of studies (Campbell 2003; Link et al. 2009; Slater et al. 2009) • Low intensity intra-group aggression directed from males to females • “Stereotyped displays and chases” (Link et al. 2009) Photo: Kayley Evans

  3. Sexual Segregation

  4. Quantifying Sexual Segregation • Sexual Segregation and Aggregation Statistic (SSAS) (Bonenfant et al. 2007) • Association = presence in the same subgroup using 30min subgroup scan data • Distinguishes active segregation and aggregation from random association • Calculates index value ranging from 0 (significant aggregation) to 1 (significant segregation)

  5. SSAS 1 Monthly variation in sexual segregation in spider monkeys in 2009 (Segregation) 0.5 0 Jan Mar May Jul Sep Nov Month (Aggregation)

  6. Objectives • Compare rates of aggression by • Males to females • Males to males • Females to males • Females to females • Compare the contexts in which these aggressive interactions occurred

  7. Runaway Creek Nature Reserve

  8. Study Group • 34 - 38 group members over course of study 2008-2011 • All individuals habituated and individually recognizable

  9. Data Collection • Collect scan & focal data • All observations of fission-fusion events & aggression • For aggression: ID of director(s) & receiver(s) & context • ~2000 contact hours over 601 days • 193 aggressive interactions

  10. Contexts of Aggression • Food: receiver was feeding when aggression occurred • Fusion: subgroup fusion occurred within 5min of aggression (food took precedence over fusion) • Sexual: copulation, place sniff, genital inspect occurred immediately following aggression • Other: any other context

  11. Results 80% M-F (N=154) 15% F-F (N=30) 3% F-M (N=5) 2% M-M (N=4)

  12. Context of Aggression • Context of aggression differed between M-F & F-F (X2= 12 df=3 P=.007) • M-F occurred most often during subgroup fusions (38%) or feeding (31%) • F-F occurred most often during feeding (41%) or other (45%)

  13. Aggression rate/hour Males Sociogram of asymmetric matrix of dyadic aggression rates (arrow points from director to receiver) Females

  14. Conclusions • Patterns of female-directed aggression at Runaway Creek are consistent with that found at other Ateles sites • Results support Link et al. 2009: M-F aggression is a form of social control (indirect sexual coercion) • May encourage sexual segregation as females try to avoid attacks from males

  15. Acknowledgments • Brittany Dean, Kayley Evans, & Jane Champion • StevanReneau, Gilroy Welch, & Birds Without Borders • Dr. Tak Fung • Natural Sciences and Engineering Research Council of Canada, University of Calgary, & National Geographic

  16. XY = total number of males and females sampled k = total number of subgroups sampled i= selected subgroup Ni= subgroup size XiYi= number of males and females is a subgroup

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