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
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
Sexual Segregation
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)
Monthly variation in sexual segregation in spider monkeys in
2009
1
Jan Mar May Jul Sep Nov
0.5
0
SSA
S
Month
(Segregation)
(Aggregation)
Objectives 1. Compare rates of
aggression by Males to females Males to males Females to males Females to females
2. Compare the contexts in which these aggressive interactions occurred
Runaway Creek Nature Reserve
Study Group
34 - 38 group members over course of study 2008-2011
All individuals habituated and individually recognizable
Year Male Females
Adult Subadult Adult Subadult2008 3 2 11 32009 3 2 12 22010 5 2 12 42011 5 3 13 2
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
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
Results
80% M-F (N=154)15% F-F (N=30)3% F-M (N=5)2% M-M (N=4)
80%
2%
3% 16%
Proportion of aggressive interactions
M-FM-MF-MF-F
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%)
Food Fusion Sexual Other0%
10%
20%
30%
40%
50%
Context of Ag-gression
M-F F-F
FroFalso
Fngus
Fugly
Ficus
Fanta
Frugv
Frckls
FranjFury
FigFlameFlirt
Flora
Flowr
Forgt
Faita
Ferde
Fryjk
Forst
FlipFrog Fidle
0.050.470.89
FroFalso
Fngus
Fugly
Ficus
Fanta
Frugv
Frckls
FranjFury
FigFlameFlirt
Flora
Flowr
Forgt
Faita
Ferde
Fryjk
Forst
FlipFrog Fidle
0.050.470.89
Sociogram of asymmetric matrix of dyadic aggression rates
(arrow points from director to receiver)
Males
Females
Aggression rate/hour
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
Acknowledgments Brittany Dean, Kayley
Evans, & Jane Champion
Stevan Reneau, Gilroy Welch, & Birds Without Borders
Dr. Tak Fung Natural Sciences and
Engineering Research Council of Canada, University of Calgary, & National Geographic
XY = total number of males and females sampledk = total number of subgroups sampledi = selected subgroupNi = subgroup sizeXiYi = number of males and females is a subgroup
𝑆𝑆𝐴𝑆=1− 𝑁𝑋𝑌 ∑
𝑖=1
𝑘 𝑋 𝑖𝑌 𝑖
𝑁 𝑖