# Male removal sparks aggression, infant kidnapping and death in captive geladas (Theropithecus gelada)

Luca Pedruzzi, Martina Francesconi, Alessia Cudini, Paolo Oliveri, Elisabetta Palagi, Alban Lemasson

## ► To cite this version:

Luca Pedruzzi, Martina Francesconi, Alessia Cudini, Paolo Oliveri, Elisabetta Palagi, et al.. Male removal sparks aggression, infant kidnapping and death in captive geladas (Theropithecus gelada). Applied Animal Behaviour Science, 2025, 292, pp.106836. 10.1016/j.applanim.2025.106836. hal-05374093

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# Male removal sparks aggression, infant kidnapping and death in captive geladas (Theropithecus gelada)

Luca Pedruzzi<sup>a,b,*</sup>,<fnref n="1" />ᵇ, Martina Francesconi<sup>b</sup>, Alessia Cudini<sup>b</sup>, Paolo Oliveri<sup>b</sup>, Elisabetta Palagi<sup>b,c,<fnref n="2" /></sup>, Alban Lemasson<sup>a,d,<fnref n="2" /></sup>

## ARTICLE INFO

### Keywords:

- Aggression

- Animal welfare

- Infant handling

- Monkeys

- Thanatology

## ABSTRACT

In group-living species, social stability relies on individual relationships and group composition—crucial factors for captive animal management. Gelada monkeys (*Theropithecus gelada*) form core units of a dominant male and strongly bonded related females. Here, we analysed the consequences of removing males from a gelada group, as part of standard management procedures essential for maintaining genetic variability. Compared to the control group (n = 30 females), the test group (n = 33 females) showed a marked increase in aggression. One adult and older female engaged in repeated infant kidnappings involving four younger mothers, resulting in the deaths of two infants, which she continued to carry and groom post-mortem for days. These events began after male removal, suggesting a destabilizing effect of male absence on social dynamics. Our findings raise critical questions about the role of gelada males in regulating female competition. We emphasize the importance of considering social roles—not just demographic balance—when implementing animal transfers in managed populations. Understanding the behavioural consequences of group restructuring is essential to improve welfare outcomes and prevent maladaptive behaviours in socially complex species under human care.

## 1. Introduction

The dynamics of male–female relationships contribute to the stability of social groups in complex species-specific ways (Davidian et al., 2022; Grueter et al., 2020; Hemelrijk et al., 2020). Geladas (Theropithecus gelada), monkeys endemic to the Ethiopian Highlands, are known for their complex multi-level social structure in which the core unit consists of a dominant adult male, several typically related females, and their offspring (Snyder-Mackler et al., 2012). Strong female-female bonds—fostered by female philopatry—support cohesion within units. Some studies suggest these bonds may maintain group stability even in the absence of a male (Matsuda et al., 2012; Mori, 1979; Snyder-Mackler et al., 2012). Yet, males seem to assert comforting and policing activities among females (Palagi et al., 2018). Male loss, defined here as the disappearance of the group male(s) without imminent replacement, does not include regular male takeovers where the resident male is

immediately replaced; rather, it is rare in the wild and typically occurs under exceptional conditions (Kifle, 2024; Mori, 1979). Here, we examine how the social dynamics of a gelada group under human care changed following the management procedure of male removal, comparing it with a control group in the same facility. Specifically, we analyse the aggression frequencies and a series of infant kidnappings carried out by an adult female toward younger mothers, resulting in infant death and extended post-mortem care. We explore whether these events reflect disruptions caused by male removal and question the assumption that female-bonded groups remain socially stable in the absence of males.

<footnote><sup>a</sup> EthoS (Ethologie Animale et Humaine) - U.M.R 6552, Université de Rennes, Université de Normandie, CNRS, Rennes 35000, France</footnote>

<footnote><sup>b</sup> Unit of Ethology, Department of Biology, University of Pisa, via Alessandro Volta 6, Pisa 56126, Italy</footnote>

<footnote><sup>c</sup> Natural History Museum, University of Pisa, Via Roma 79, Pisa, Calci, Italy</footnote>

<footnote><sup>d</sup> Institut Universitaire de France, 1 Rue Descartes, Paris Cedex 75231, France</footnote>

<footnote>* Corresponding author at: EthoS (Ethologie Animale et Humaine) - U.M.R 6552, Université de Rennes, Université de Normandie, CNRS, Rennes 35000, France. E-mail addresses: luca.pedruzzi@phd.unipi.it, luca.pedruzzi@etudiant.univ-rennes.fr (L. Pedruzzi).</footnote>

<footnote n="1">¹ ORCID: 0000-0003-4716-3440</footnote>

<footnote n="2">² These authors share senior authorship</footnote>
<figure><img src="image_4.png" /><figcaption>Fig. 1. Video frames of the kidnapper stealing infants from mothers a), b), c) carrying a dead infant with her mouth, and d) biting an infant.</figcaption></figure>

<caption>**Table 1**</caption>

Estimated parameters (Coeff), Standard Error (SE), and results of the Likelihood Ratio Tests ($\chi^2$) of the GLMM. Significant *P* values are bold; df= degree(s) of freedom; - = not applicable.

<table><thead><tr><th>Fixed Effects</th><th>Coeff</th><th>SE</th><th>χ<sup>2</sup></th><th>df</th><th>P</th></tr></thead><tbody><tr><td colspan="6"><strong>Model - daily aggression in the Test and Control groups</strong></td></tr><tr><td>Intercept</td><td>-2.160</td><td>0.123</td><td>-</td><td>-</td><td>-</td></tr><tr><td colspan="6"><strong>Tested variables</strong></td></tr><tr><td>Group (Test)</td><td>0.109</td><td>0.097</td><td>95.976</td><td>1</td><td><strong>0.000</strong></td></tr><tr><td>Period (April 1st – April 26th)</td><td>-0.440</td><td>0.174</td><td>6.295</td><td>1</td><td><strong>0.012</strong></td></tr><tr><td>Group*Period</td><td>1.063</td><td>0.135</td><td>62.067</td><td>1</td><td><strong>0.000</strong></td></tr></tbody></table>

$N_{\text{observations}}$= 88, $N_{\text{days}}$= 44. Random factors: Day, Variance= 0.18, SD= 0.42.

2021; Plowman et al., 2005). Although geladas have been described as “female-bonded” (Dunbar, 1979; Tinsley Johnson et al., 2014) and wild units seem to remain stable even in the absence of the male (Matsuda et al., 2012; Mori, 1979; Snyder-Mackler et al., 2012), our findings suggest that male presence may play a more central role in regulating female social dynamics—at least under captive conditions. While the effects appear to be temporary, the study raises relevant questions about male contribution in intra-unit cohesion in geladas.

Following male removal, infant-directed abnormal behaviours increased sharply, involving one older female and four younger mothers. The kidnapper tried to snatch the four infants available in the group, with two being permanently kept and dying likely from starvation. The mothers never actively retrieved their infants, possibly deterred by the kidnapper's size, age, or rank (Maestripieri, 1993). Infant handling and kidnapping by non-mothers have been observed in other species, sometimes by young females as a way to gain experience or by dominant older females as a form of between-female competition detrimental for mothers and infants (Kleindorfer and Wasser, 2004; Quiatt, 1979; Silk, 1980). The latter is more likely in the present case, where male absence

probably inhibited competitive maternal behaviours. Interestingly, the kidnapper kept carrying and grooming the corpses of deceased infants after their death. Post-mortem infant care is well documented in primates (Casetta et al., 2023; Fashing et al., 2011). Hypotheses to explain this include lack of awareness, grief processing, or persistent infantile cues (Bercovitch, 2020; Fernández-Fueyo et al., 2021; Gonçalves and Carvalho, 2019; Watson and Matsuzawa, 2018). Post-mortem care by the kidnapper lasted for several days, despite visible decomposition (Fig. 1c), until only intact skeletons remained. Similar patterns have been reported in wild geladas, with environmental factors possibly slowing decomposition and prolonging post-mortem care (Fashing et al., 2011). Initially, the corpses were carried ventrally, as when alive, which may indicate an initial failure to recognize their death (Gonçalves and Carvalho, 2019).

In monkeys, grooming often appears to function as a form of social currency (Tiddi et al., 2010), with non-mother females exhibiting strong interest in neonates and using grooming to manipulate maternal tolerance (Frank and Silk, 2009; Maestripieri, 1993). Here, qualitative observations indicates that grooming initiated by the kidnapper often preceded attempts to approach or handle the infants, suggesting a strategic use to gain access. Moreover, grooming between the mothers and the kidnapper increased in both directions after kidnapping (Table 2), possibly as mothers tried to stay close to their infants.

The study highlights the often-overlooked role of gelada males in maintaining group stability and mitigating stress-related social disruptions. The observed inhibitory effect of males on female kidnapping behaviour likely reflects their broader social influence over females rather than an adaptive strategy targeting specific offspring. Further, we provide new data on the factors affecting infant kidnapping and post-mortem care in geladas. Most importantly, our study provides useful information for the welfare of primate populations under human care (Orient and Guillén-Salazar, 2021), underscoring the importance of considering the social roles of specific group members when modifying
<figure><img src="image_5.png" /></figure>

<figure><img src="image_6.png" /><figcaption>**Fig. 2.** a) Frequency of aggression according to the Group (blue = Test group-G2; pink = Control group-G1) and Period (April 1st–April 24th vs April 26th–May 22nd) (x axis). April 25th corresponds to the day in which males were removed from G2. Boxes display the median value, first and third quartiles, whiskers are extended to the most extreme value inside the 1.5-fold interquartile range; b) Effect of male removal on daily aggression: model predictions (green line with 95 % CI) and observed differences in aggression frequency between Test and Control groups (dots) as a function of time since male removal. We calculated the daily frequency of aggression as: Agonistic events/Observation time for the group\*Number of subjects in the group.</figcaption></figure>

<caption>**Table 2**</caption>

Summary of frequencies of focal behaviours involving the kidnapper, the four infants and their mothers. Frequencies are calculated in the different periods, either before *vs* after male removal *vs* after infant death or before *vs* after kidnapping *vs* after infant death (only for the two mothers whose infant was permanently kidnapped). Frequencies are calculated with observation time calculated *ad hoc* for each infant and/or mother. NA = not applicable (e.g., post-mortem period for the two survived infants).

<table><thead><tr><th></th><th>Before male removal</th><th>After male removal</th><th>Post-mortem</th></tr></thead><tbody><tr><td>Infant 1 (Roll's)</td><td>Kidnapping events (attempts/hour)</td><td></td><td></td></tr><tr><td>Infant 1 (Roll's)</td><td>0</td><td>0.290135397</td><td>NA</td></tr><tr><td>Infant 2 (Neomamma's)</td><td>0.0813</td><td>0.583133971</td><td>NA</td></tr><tr><td>Infant 3 (Schiarita's)</td><td>0</td><td>0.23923445</td><td>NA</td></tr><tr><td>Infant 4 (Tris')</td><td>NA</td><td>1.881331404</td><td>NA</td></tr><tr><td>Infant 1</td><td>Infant carrying (min/hour)</td><td></td><td></td></tr><tr><td>Infant 1</td><td>0</td><td>13.2</td><td>10.32</td></tr><tr><td>Infant 2</td><td>0</td><td>1.62</td><td>NA</td></tr><tr><td>Infant 3</td><td>0</td><td>0.06</td><td>NA</td></tr><tr><td>Infant 4</td><td>0</td><td>12.48</td><td>49.14</td></tr><tr><td>Infant 1</td><td>Grooming from kidnapper to infants (min/hour)</td><td></td><td></td></tr><tr><td>Infant 1</td><td>0</td><td>0.636</td><td>1.23</td></tr><tr><td>Infant 2</td><td>0</td><td>0.0912</td><td>NA</td></tr><tr><td>Infant 3</td><td>0.0261</td><td>0.0177</td><td>NA</td></tr><tr><td>Infant 4</td><td>0</td><td>0.4548</td><td>0.75</td></tr><tr><td>Infant 1</td><td>Before kidnapping</td><td>After kidnapping</td><td>Post-mortem</td></tr><tr><td>Infant 1</td><td>Grooming from kidnapper to mothers (min/hour)</td><td></td><td></td></tr><tr><td>Mother 1 (Roll)</td><td>0</td><td>0.174</td><td>0.2544</td></tr><tr><td>Mother 4 (Tris)</td><td>0</td><td>0.618</td><td>0</td></tr><tr><td>Mother 1 (Roll)</td><td>Grooming from mothers to kidnapper (min/hour)</td><td></td><td></td></tr><tr><td>Mother 1 (Roll)</td><td>0</td><td>1.452</td><td>3.300</td></tr><tr><td>Mother 4 (Tris)</td><td>0</td><td>0.0210</td><td>0</td></tr></tbody></table>

group compositions for management purposes.

### CRediT authorship contribution statement

**Alban Lemasson:** Writing – review & editing, Validation, Supervision, Investigation, Conceptualization. **Paolo Oliveri:** Methodology, Investigation, Formal analysis, Data curation. **Elisabetta Palagi:** Writing – review & editing, Supervision, Methodology, Investigation, Formal analysis, Data curation, Conceptualization. **Martina Francesconi:** Writing – review & editing, Methodology, Investigation, Data curation. **Alessia Cudini:** Writing – review & editing, Methodology, Investigation, Formal analysis, Data curation. **Luca Pedruzzi:** Writing – review & editing, Writing – original draft, Visualization, Methodology, Investigation, Formal analysis, Data curation, Conceptualization.

### Author contributions

Study conception: LP, EP, AL; Data collection: LP, MF, PO; Video analyses: LP, AC, PO; Writing: LP, AC, EP, AL. All authors reviewed the manuscript draft.

### Declaration of Competing Interest

The authors declare no conflicts of interest.

### Acknowledgments

We thank the NaturZoo Rheine, Achim Johann, Nicolas Brüning, and all the keepers for their support during data collection.

### Appendix A. Supporting information

Supplementary data associated with this article can be found in the online version at doi:10.1016/j.applanim.2025.106836.
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