ArticlePDF Available

Collective decision‐making in aquatic mammals



Collective decision-making is an essential part of day-to-day life for group-living animals. These decisions can be unshared (e.g. leadership) or shared (e.g. consensus). Aquatic mammals face particular challenges when making collective decisions, including a three-dimensional habitat that can make group coordination and collective navigation a challenge. We systematically reviewed literature on decision-making in non-human mammals by examining the types of collective decisions observed and hypotheses used to structure analyses. Most of the current literature was centred around terrestrial species, particularly within primates and artiodactyls. There are no collective decision-making studies on aquatic mammal species outside of cetaceans. Both unshared and shared decision-making have been reported in whales and dolphins, with leadership found in killer whales Orcinus orca and bottlenose dolphins Tursiops sp. and consensus decisions in sperm whales Physeter macrocephalus. Five recommendations for decision-making research include: 1) clearly delineating the temporal components of decision-making, 2) standardising research to allow for comparisons, 3) considering both shared and unshared decision-making, 4) analysing decision-making across behavioural contexts, and 5) avoiding anthropomorphic terminology. Future studies of collective decision-making will help us better understand how non-human mammals overcome environmental and contextual challenges – particularly in the case of aquatic species such as cetaceans, which face challenges related to their aquatic environment and exhibit phenomena such as mass strandings.
Mammal Review ISSN 0305-1838
Collective decision- making in aquatic mammals
Elizabeth ZWAMBORN*Dalhousie University, 1355 Oxford St., Halifax, Nova Scotia, Canada
B3H4J1. Email:
Naomi BOONHakai Institute, PO Box 25039, Campbell River, British Columbia, Canada V9W 0B7.
Hal WHITEHEADDalhousie University, 1355 Oxford St., Halifax, Nova Scotia, Canada B3H 4J1.
Mammal Review (2023) © 2023 The Authors. Mammal Review published by Mammal Society and John Wiley & Sons Ltd.
This is an open access article under the terms of the Creative Commons Attribution License, which permits use,
distribution and reproduction in any medium, provided the original work is properly cited.
1. Collective decision- making is an essential part of day- to- day life for group-
living animals. These decisions can be unshared (e.g. leadership) or shared
(e.g. consensus).
2. Aquatic mammals face particular challenges when making collective decisions,
including a three- dimensional habitat that can make group coordination and
collective navigation a challenge.
3. We systematically reviewed literature on decision- making in non- human mam-
mals by examining the types of collective decisions observed and hypotheses
used to structure analyses.
4. Most of the current literature was centred around terrestrial species, particu-
larly within primates and artiodactyls. There are no collective decision- making
studies on aquatic mammal species outside of cetaceans. Both unshared and
shared decision- making have been reported in whales and dolphins, with
leadership found in killer whales Orcinus orca and bottlenose dolphins Tursiops
sp. and consensus decisions in sperm whales Physeter macrocephalus.
5. Five recommendations for decision- making research include: 1) clearly de-
lineating the temporal components of decision- making, 2) standardising re-
search to allow for comparisons, 3) considering both shared and unshared
decision- making, 4) analysing decision- making across behavioural contexts,
and 5) avoiding anthropomorphic terminology.
6. Future studies of collective decision- making will help us better understand
how non- human mammals overcome environmental and contextual challenges
particularly in the case of aquatic species such as cetaceans, which face
challenges related to their aquatic environment and exhibit phenomena such
as mass strandings.
aquatic mammals, cetacean, collective
decision- making, decision- making, global,
leadership, mammals
Received: 24 October 2022
Accepted: 3 May 2023
Editor: DR
doi: 10.1111/mam.12321
Animals that spend time in groups must align individual
and collective decisions about where to forage, when to
travel, and how to escape predators. It can be argued
that collective decision- making itself is inherent to the
definition of what a group is (Wilson 2000): ‘any set of
organisms, belonging to the same species, that remain
together for a period of time while interacting with one
another to a greater degree than with other conspecifics’.
In contrast, an aggregation may be defined as individuals
attracted to the same area at the same time for non- social
reasons such as abundant food or adequate shelter (Plötz
et al. 1991, Heyman et al. 2001).
Within the current literature on collective decision-
making, decisions are often classified as either unshared
or shared according to the framework set out by Conradt
and Roper (2005). When decisions are unshared there
can be either a single leader (fully unshared) or a few
leaders (partially shared), which may or may not be con-
sistent over time (Conradt & Roper 2005). A leadership
E. Zwamborn, N. Boon and H. WhiteheadCollective decision- making in aquatic mammals
Mammal Review (2023) © 2023 The Authors. Mammal Review published by Mammal Society and John Wiley & Sons Ltd.
event can be defined in terms of time (e.g. the first
individual(s) to initiate a behavioural change; Krueger
et al. 2014) or space (e.g. the individual(s) physically po-
sitioned in front of a group leading movement; Lewis
et al. 2011). There are many examples of unshared deci-
sions in wild animal populations, such as the leadership
of southern resident killer whale Orcinus orca matriarchs
during times of food scarcity (Brent et al. 2015), distrib-
uted leadership in group recruitment of pavement ants
Tetramorium caespitum (Collignon et al. 2014), and un-
shared leadership seen during chacma baboon Papio ursinus
morning departures from their sleeping sites (Stueckle &
Zinner 2008).
Conversely, collective decisions can be made in a shared
manner with a majority decision made by group members
or by reaching a required threshold – such as a quorum
in human societies (Conradt & Roper 2005). Some examples
include meerkat Suricata suricatta quorum- like decisions of
when to return to their sleeping sites (Gall et al. 2017), as
well as the sneezing of African wild dogs Lycaon pictus as
a voting- like mechanism for decisions on movement (Walker
et al. 2017). Sometimes a consensus cannot be reached,
resulting in inaction or even group fission. Societies with
fission- fusion dynamics may avoid conflict, as has been
hypothesised in American bison Bison bison (Merkle
et al. 2015), if individuals can leave a group when they
do not agree with the decisions made by others. Fission
decisions have been classified as ‘combined’ decisions because
animals make their choices individually, such as whether
to stay or leave a given group, in comparison to ‘consensus’
decisions, which are generally undertaken by spatially co-
hesive groups that must make decisions about cooperative
actions such as travel (Conradt & Roper 2005).
Decision- making processes found in mammals are complex
and diverse. Many mammalian species are at least partially
group living, with examples ranging from extremely stable
matrilines to solitary individuals that congregate occasionally
under particular conditions to forage (Bigg et al. 1990, Nowacek
et al. 2011). Mammals are often individually identifiable and
make particularly interesting subjects for research on collec-
tive decision- making due to an abundance of dedicated long-
term studies where the temporal consistency of leadership
can be studied (Krueger et al. 2014, Brent et al. 2015). There
have been several reviews of mammalian decision- making
(see Appendix S1). Published literature has assessed focused
subjects, such as leadership in mammalian societies (Smith
et al. 2016, 2020) and collective movement decisions in non-
human primates (Fischer & Zinner 2011, King & Sueur 2011),
but none have looked at collective decision- making across
mammals more broadly.
Collective decisions in aquatic environments can lead to
additional challenges for both the mammals reaching these
decisions and the researchers studying them. Visibility is
often low or non- existent and the environment is frequently
used in a much more three- dimensional way (e.g. deep
diving) in comparison to terrestrial species (Norris &
Schilt 1988, Hindell et al. 2002). One taxon of aquatic
mammals, cetaceans, includes species that live in groups
and frequently make collective deep dives. During these
coordinated dives, they are subject to extreme pressures
and go to places where they cannot simply return from
in a quick manner without serious consequences (e.g. de-
compression sickness; Fernández et al. 2017). Certain cetacean
species are known for common mass strandings (Moore
et al. 2018). In species such as killer whales and sperm
whales Physeter macrocephalus, the groups are highly mobile,
tight- knit and long- term (Bigg et al. 1990, Christal
et al. 1998). How does the different use of space in an
aquatic environment change how they make collective deci-
sions? How are we to understand the best response or
intervention during mass strandings, when we do not un-
derstand how the species involved make such collective
decisions? Part of the difficulty of examining decision- making
in aquatic mammals, including cetaceans, is the challenge
of collecting continuous observations for species that spend
the majority of their time underwater. Recent advances in
technology, such as drones (Hartman et al. 2020), have
allowed scientists to acquire the data needed to investigate
questions about decision- making further.
In this review, we consider what is known of collective
decision- making for terrestrial non- human mammalian
species and compare this to what has been learned about
collective decision- making in cetacean species (the only
group of aquatic mammals for which collective decision-
making has been studied). Our goal is to suggest new
research directions in this developing field for both aquatic
and terrestrial mammals. Our recommendations will allow
for more focused and comparable studies in future, at
both population and species levels.
We ask the following questions:
1. Which collective decision- making processes are used by
2. What hypotheses have been tested in studies of collective
decision- making in mammals?
3. How can our knowledge of the collective decision- making
processes in mammals be used to direct and advance
our understanding of collective decision- making processes
in aquatic mammal species?
We used a systematic database search to gather literature
on available collective decision- making in non- human
mammalian species and then ran a second search targeting
decision- making literature in cetacean species. The databases
13652907, 0, Downloaded from by Trinity Western University, Wiley Online Library on [12/09/2023]. See the Terms and Conditions ( on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License
Collective decision- making in aquatic mammalsE. Zwamborn, N. Boon and H. Whitehead
Mammal Review (2023) © 2023 The Authors. Mammal Review published by Mammal Society and John Wiley & Sons Ltd.
Web of Science, Biological Abstracts, ProQuest and Scopus
were searched. Identical terms were used for each database
during the respective searches (see Appendix S2). Only
peer- reviewed articles, books, and theses published up until
March 2020 were kept. All citations were uploaded to a
systematic review manager (Covidence Systematic Review
Software 2021) for analysis. Duplicate literature was re-
moved. Two qualified reviewers screened abstracts (see
Fig. 1 for flowchart) and excluded any studies that were
not linked to collective decision- making. There was a 94%
proportionate agreement between the two reviewers in the
selection of studies. A consensus was reached for the re-
maining literature via consultation and discussion between
both reviewers. Both reviewers then evaluated the full text
of each article. We excluded studies unrelated to collective
decision- making, such as research on individual decisions
made in a non- group context. We also excluded any theses
for which the relevant chapters had been published. Studies
on both wild and captive animals were considered. However,
as this review focuses on providing suggestions for fur-
thering the field of decision- making studies in free- ranging
populations of mammals, particularly cetaceans, experi-
mental studies were excluded. We used a quality assessment
to exclude any studies that had inadequate data (see
Table 1).
We then extracted for each study: (1) the decision-
making hypotheses used, (2) the type of decision- making
found (e.g. unshared, partially shared, shared, mixed, etc.),
and (3) the evolutionary explanations proposed by the
authors. Box 1 provides definitions for the types of deci-
sions used in this review, based on Conradt and
Roper (2005) with additional clarifications.
Six of the 29 extant mammal orders are represented by
collective decision- making studies. Cetacean decision-
making was better represented than decision- making in
bats, elephants, and carnivorans, but research effort in
mammalian decision- making was predominantly focused
on primates and terrestrial ungulates (see Fig. 2). Many
well- researched groups of mammals (e.g. equids, bats) were
represented by only a few non- experimental studies focus-
ing on how they make their collective decisions.
Within mammalian collective decision- making studies
there was a wide range of species from diverse habitats
and geographical locations. There were several examples
of a species, for example chacma baboons, being studied
on multiple occasions (see Table 2) – sometimes with
different decision- making tactics for different contexts or
Fig. 1. Flowchart for systematic review of collective decision- making studies in mammal species.
13652907, 0, Downloaded from by Trinity Western University, Wiley Online Library on [12/09/2023]. See the Terms and Conditions ( on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License
E. Zwamborn, N. Boon and H. WhiteheadCollective decision- making in aquatic mammals
Mammal Review (2023) © 2023 The Authors. Mammal Review published by Mammal Society and John Wiley & Sons Ltd.
populations (Sellers et al. 2007, Stueckle & Zinner 2008),
which is perhaps unsurprising given our knowledge of
the complexity of many animal societies. However, these
discrepant findings emphasise our limited understanding
of decision- making for species that have only been studied
in one specific context or for a single population.
The largest representative category of mammalian decision-
making is unshared (single leader) decisions, including ex-
amples from five of the six orders included in this review
(Penzhorn 1984, Peterson et al. 2002, Barelli et al. 2008, Ihl
& Bowyer 2011, Mizuno et al. 2017). Many of these studies
looked specifically for physical leadership and individuals who
initiated group movement. The second most prevalent cat-
egory was mixed decision- making, where a combination of
unshared, partially shared, and/or shared decisions were made
to reach a goal such as group movement initiation (Seltmann
et al. 2016, Gall et al. 2017). There were few examples of
species using an entirely shared decision- making process
(Bousquet et al. 2011, Whitehead 2016), and even fewer
examples of partially shared decisions (as defined in Box 1)
(Mech 2000, Lee & Teichroeb 2016). Both shared and par-
tially shared decision types were common components within
the mixed decision category.
Studies of several well- known cetacean populations made
up the entirety of the literature available on collective decision-
making in aquatic mammals. This research covers five species:
democratic consensus movement decisions in sperm whales
(Whitehead 2016), spatial leadership observed in common
bottlenose dolphins Tursiops truncatus and Indo- Pacific bot-
tlenose dolphins Tursiops aduncus (Lusseau 2007, Lusseau &
Conradt 2009, Lewis et al. 2011, 2013a, b) and killer whales
(Foster 2012, Brent et al. 2015), and leadership potential in
Irrawaddy dolphins Orcaella brevirostris (Liew &
Labadin 2017). Evidence for leadership during synchronous
surfacing was not found in Indo- Pacific bottlenose dolphins
(McCue et al. 2020). There have been suggestions made for
leadership in other species, including long- finned pilot whales
Globicephala melas and sperm whales, particularly during
stranding events (de Kock 1956, Mazzariol et al. 2018), but
these observations are largely anecdotal, without detailed
explanation or supporting evidence.
Hypotheses of mammalian collective
decision- making
The hypotheses tested in mammalian decision- making
studies were diverse, ranging from predicted drivers of
Table 1. Quality assessment domains for mammalian decision- making systematic review
Quality domain Considerations
Methods Are methods well- described and sufcient for inclusion? This ensures that only repeatable studies are included in this review.
Sample size Is the study based on an adequate sample size to draw the conclusions made? Inadequate sample sizes are more likely to result
in inaccurate conclusions that are not representative.
Quantitative vs.
Is the study of decision- making purely observational or supported by quantitative analyses? How robust is the conclusion about
collective decision- making – is it well supported by quantitative data or just a statement made in a broader study?
Does the study discuss evolutionary reasons or a functional framework for the observed decision- making? Is there an
evolutionary explanation given for the conclusions of the study?
Study design Is the study experimental or non- experimental? Experimental studies do not always produce results that can be observed in
nature because of the articial environment they take place in.
Other bias Are there any other obvious biases resulting from the study design that should be considered when deciding whether or not to
include this article in this review? Are there funding, professional, environmental, or other considerations that could bias the
outcome of the study?
Box 1. Important denitions for decision-making
SHARED: Equal contribution from all group members
on a given decision (quorum – a majority, sub major-
ity or super majority – or voting) (Conradt &
Roper 2005).
UNSHARED (single leader): A single individual who
makes a given decision (Conradt & Roper 2005). For
addressing the temporal aspect of unshared decisions,
leaders could be:
1. stable – a single individual leads
2. semi- distributed – a subset of individuals who share
leadership over time
3. distributed – all members being able to lead in any
given decision, whether equally or unequally
PARTIALLY SHARED (several leaders): An intermediate
decision between shared and unshared where a subset
of individuals make the decision (Conradt & Roper 2005).
MIXED: Where any combination of shared, unshared,
and partially shared decision- making is used to achieve
an outcome.
For example, where the decision of WHEN to move might
be made separately from the decision of WHERE move-
ment, resulting in a two- part process needed for movement
to take place.
13652907, 0, Downloaded from by Trinity Western University, Wiley Online Library on [12/09/2023]. See the Terms and Conditions ( on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License
Collective decision- making in aquatic mammalsE. Zwamborn, N. Boon and H. Whitehead
Mammal Review (2023) © 2023 The Authors. Mammal Review published by Mammal Society and John Wiley & Sons Ltd.
leadership to different decision- making types and the
mechanisms underlying the decision- making process (see
Table 3). Over 25% of studies (n = 30) did not state clear
hypotheses in the introduction or methods sections. Reasons
for lack of stated hypotheses ranged from studies being
purely observational without specific decision- making goals,
to technical papers where specific hypotheses were not
The most common hypotheses proposed centred around
testing the drivers of leadership (57% of hypotheses, n = 90),
with dominance (n = 26), energetics (n = 21), social con-
nectedness (n = 19), and ecological knowledge (n = 16) being
the most frequently proposed explanations. These drivers
were frequently tested in a similar manner, first by de-
termining the independent variable(s); e.g. dominance rank,
reproductive status, age, etc., for each individual, followed
by using a statistical model (e.g. Generalised Linear Mixed
Model, Analysis of Variance, etc.) to test which factors
successfully predicted observed leadership (Tecot &
Romine 2012, Fernández et al. 2013, Ceccarelli et al. 2020).
There was a wide variety of statistical methods used. The
most common hypothesis was that dominant individuals
were most likely to be leaders, particularly among primates
where high- ranking individuals often play a key social
role within their groups (Leca et al. 2003, Bonnell
et al. 2017). Examples of dominance- driven leadership can
be found in species such as sheep Ovis aries, chacma ba-
boons, wolves Canis lupus, and cattle Bos taurus (Addison
& Simmel 1980, Mech 2000, Peterson et al. 2002, Šárová
et al. 2007, Romero & Castellanos 2010).
Not all mammalian species exhibit dominance hierar-
chies, and other studies were focused on alternative ex-
planations for successful leadership. The hypothesis that
females would be more likely to lead based on higher
energetic needs when gestating or lactating was proposed
as an explanation for species ranging from plains zebra
Equus burchellii and spotted hyenas Crocuta crocuta to
primates such as vervet monkeys Chlorocebus pygerythrus
and red- fronted lemurs Eulemur rufifrons (Fischhoff
et al. 2007, Smith et al. 2010, Lee & Teichroeb 2016,
Sperber et al. 2019). In species where social connectedness
was an important component of societies, it has been
suggested that more connected individuals are frequent
leaders (Strandburg- Peshkin et al. 2015). Socially central
individuals in common bottlenose dolphins, Tibetan ma-
caques Macaca thibetana and highland cattle have been
observed with more followers and better leadership success
(Lusseau 2007, Wang et al. 2016, Sueur et al. 2018).
The ecological knowledge of an individual was sometimes
proposed to be the driver behind leadership. In killer
whales, post- menopausal females were observed leading,
likely because their age and experience meant that they
held the best knowledge of where to find salmon
(Oncorhynchus sp.) when food was scarce (Brent
et al. 2015). Similarly, female Verreaux’s sifakas Propithecus
verreaxi were hypothesised to lead more often because
Fig. 2. Representation of mammalian taxonomic orders from this decision- making review (n = 117), with the percentage of studies for each order.
Cetaceans, part of the order Artiodactyla, make up only 8% of studies overall.
13652907, 0, Downloaded from by Trinity Western University, Wiley Online Library on [12/09/2023]. See the Terms and Conditions ( on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License
E. Zwamborn, N. Boon and H. WhiteheadCollective decision- making in aquatic mammals
Mammal Review (2023) © 2023 The Authors. Mammal Review published by Mammal Society and John Wiley & Sons Ltd.
Table 2. Orders and species of mammals according to observed decision types (aquatic mammal species in bold, represented in the literature only by
cetaceans). References are listed in the same order as the species to which they pertain
Decision Type Order Species References
Shared Artiodactyla Moose Alces alces, sheep Ovis aries, sperm whale
Physeter macrocephalus
Geist(1963), Whitehead(2016), Pérez- Barbería and
Carnivora Meerkat Suricata suricatta Bousquet et al.(2011)
Chiroptera Leisler’s bat Nyctalus leisleri Naďo and Kaňuch(2015)
Primates Chacma baboon Papio ursinus Sellers et al.(2007)
Partially Shared
Primates Chacma baboon, vervet monkey Chrorocebus
Lee and Teichroeb(2016), Bonnell et al.(2017)
Carnivora Wolf Canis lupis Mech(2000)
Unshared (single
Artiodactyla Barbary sheep Ammotragus lervia, caribou Rangifer
tarandus, cattle Bos taurus, common bottlenose
dolphin Tursiops truncatus, elk Cervus canadensis,
European bison Bison bonasus, Giraffe Giraffa
camelopardalis, goat Capra aegagrus, horse Equus
ferus, Indo- Pacic bottlenose dolphin Tursiops
aduncus, Irrawaddy dolphin Orcaella brevirostris,
killer whale Orcinus orca, muskox Ovibos
moschatus, Pyrenean chamois Rupicapra pyrenaica,
roe deer Capreolus capreolus, sheep, wild boar Sus
scrofa, zebu Bos indicus
Altmann(1952), Beilharz and Mylrea(1963), Dickson
et al.(1967), Naumov and Baskin(1969),
Tsarev(1980), Funk(1981), Bresiński(1982), Gray
and Simpson(1982), Sato(1982), Jakimchuk and
Carruthers(1983), Reinhardt(1983), Carranza and
de Reyna(1987), Mrlik(1991), Escos et al.(1993),
Gerard et al.(1993), Rowell and Rowell(1993),
Zaitsev(1999), Lusseau(2007), Šárová et al. (2007),
Lusseau and Conradt(2009), Ihl and Bowyer(2011),
Lewis et al.(2011, 2013b), Foster(2012), Berry and
Bercovitch(2014), Wolter et al.(2014), Brent
etal.(2015), Liew and Labadin(2017), Ramos
etal.(2018), Sueur et al. (2018)
Carnivora Domestic dog Canis familiaris, wolf, spotted hyena
Crocuta crocuta
Mech(2000), Peterson et al.(2002), Bonanni et al.
(2010), Smith et al.(2010)
Perissodactyla Horse, zebra Equus zebra Jezierski and Gebler(1984), Penzhorn(1984),
Krueger et al.(2014), Briard et al.(2015)
Primates Bonobo Pan paniscus, chacma baboon, chimpanzee Pan
troglodytes, Columbian white- faced capuchin
monkey Cebus capucinus, diamemed sifaka
Propithecus diadema, red lemur Eulemur rufus,
hamadryas baboon Papio hamadryas, eastern lesser
bamboo lemur Hapalemur griseus, gelada
Theropithecus gelada, Geoffroy’s spider monkey
Atelinae geoffroyi, Guatemalan black howler Alouatta
pigra, Japanese macaque Macaca fuscata, mantled
howler monkey Alouatta palliata, moustached
tamarin Saguinus mystax, northern plains grey langur
Semnopithecus entellus, Panamanian white- faced
capuchin Cebus imitator, red- bellied lemur Elemur
rubriventer, red- fronted lemur Eulemur rufrons,
Spix’s saddle- backed tamarin Leontocebus fuscicollis,
Tana River red colobus Piliocolobus rufomitratus,
Tibetan macaque Macaca thibetana, Verreaux’s sifaka
Propithecus verreauxi, vervet monkey, white- faced
capwhite- handed gibbon Hylobates lar
Struhsaker(1967), Makwana(1979),
Dunbar(1983), Nakagawa(1990), Boinski and
Campbell(1995), Erhart and Overdorff(1999),
Leca et al.(2003), Smith et al.(2003), Trillmich et
al. (2004), Barelli et al.(2008), Stueckle and
Zinner(2008), Romero and Castellanos(2010),
Jacobs et al.(2011), King et al.(2011), Pyritz
etal. (2011), Tecot and Romine(2012), Bonnell
et al. (2013), van Belle et al. (2013), Foreit(2016),
Lee and Teichroeb(2016), Wang et al.(2016),
Tokuyama and Furuichi(2017), Chambers(2019),
Palacios- Romo et al.(2019), Sperber et al.(2019),
Ceccarelli et al.(2020), Rasolonjatovo and
Proboscidea African bush elephant Loxodonta Africana, Asian
elephant Elephas maximus
Lee and Moss(2012), Mizuno et al.(2017)
Mixed Artiodactyla Caribou, cattle, European bison, giraffe, plains bison
Bison bison, Przewalski’s gazelle Procapra przewalskii,
Innis(1958), Addison and Simmel(1980), Ramseyer
et al.(2009a, b, c), Šárová et al.(2010), You
etal. (2013), Merkle et al.(2015), Ramos et al.
(2015), Lesmerises et al.(2018)
Carnivora African wild dog Lycaon pictus, domestic dog, meerkat Bonanni et al.(2011), Gall et al.(2017), Walker
etal. (2017)
Perissodactyla Horse, plains zebra Equus quagga Fischhoff et al.(2007), Bourjade et al.(2009, 2015),
Ozogány and Vicsek(2014)
13652907, 0, Downloaded from by Trinity Western University, Wiley Online Library on [12/09/2023]. See the Terms and Conditions ( on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License
Collective decision- making in aquatic mammalsE. Zwamborn, N. Boon and H. Whitehead
Mammal Review (2023) © 2023 The Authors. Mammal Review published by Mammal Society and John Wiley & Sons Ltd.
they do not disperse from their natal habitats like males
do and, therefore, would have knowledge of where to
find food (Trillmich et al. 2004). Kinship and personality
(e.g. bold vs. shy) were also hypothesised to be drivers
of successful leadership (Lee & Moss 2012, Briard
et al. 2015), though far less often.
The second most common type of hypotheses were those
that attempted to determine the mechanisms behind the
decision- making process (12% of hypotheses, n = 19). Almost
half of these were focused on whether signal coordination
was important in decision- making (n = 8). Testing for this
hypothesis mainly occurred in primates (Boinski 1993, Boinski
& Campbell 1995), though there were studies on both spot-
ted hyenas and meerkats that also found vocal signals re-
sponsible for group conflict avoidance and group movement
coordination, respectively (Smith et al. 2010, Gall et al. 2017).
Hypotheses in this category also focused on whether
decision- making was spatially driven (n = 3; e.g. whether in-
dividuals in specific positions within a group consistently
led directional changes) or temporally driven (n = 1; e.g.
whether leadership for direction changes depended upon the
first individual to move, regardless of position within the
group); what mechanisms underlay consensus decisions (n = 3),
and even suggested that decision- making in some species
was a process involving multiple decisions (n = 4; Norton 1986,
Petit et al. 2009, Ramseyer et al. 2009a, Seltmann et al. 2013).
The third category of hypotheses tested was composed
of those testing for decision- making type (11% of hypotheses,
n = 18), specifically if there were consensus decisions being
made (broadly, n = 6), what the type of leadership was being
used (stable vs. distributed, n = 7), whether a quorum de-
termined the decision (n = 2), or whether mimetics played
a role in how groups moved (n = 3). A study on Tibetan
macaques discovered that a quorum system was used if the
initiator had a simple majority of followers, but selective
mimetics also played an important role if less than the
majority initially followed (Wang et al. 2015).
There is great potential for future research to expand our
understanding of leadership and shared decisions in non-
human mammals. We have five recommendations for
designing a study on collective decision- making or analysing
opportunistic data collected for other studies.
Like many areas of behavioural research, the literature
available on mammalian collective decision- making suffers
from weak and overlapping definitions. What is leader-
ship? Does the initiator also count as a leader even if
they do not lead the subsequent movement or only func-
tion in triggering a voting process? Are those pivotal first
Decision Type Order Species References
Primates Barbary macaque Macaca sylvanus, black and gold
howler monkey Alouatta caraya, black- and- white
ruffer lemur Varecia variegata, chacma baboon,
Columbian white- faced capuchin monkey, golden
snub- nosed monkey Rhinopithecus roxellana, olive
baboon Papio anubis, Panamanian white- faced
capuchin monkey, red- fronted lemur, rhesus macaque
Macaca mulatta, Tibetan macaque, Tonkean macaque
Macaca tonkeana, yellow baboon Papio cynocephalus
Norton(1986), Boinski(1993), Overdorff et al.
(2005), Sueur and Petit(2008, 2010), King and
Cowlishaw(2009), Petit et al.(2009), Sueur et al.
(2009, 2010a, b, 2011, 2013), Zappala and
Logan(2010), Sueur(2011), Marshall et al.
(2012), Fernández et al.(2013), Seltmann et al.
(2013, 2016), Strandburg- Peshkin et al.(2015),
Wang et al.(2015, 2020), Farine et al.(2016),
Schweitzer et al.(2017), Sperber et al.(2017)
Table 2. (Continued)
Table 3. Hypotheses used in mammalian decision- making studies
Hypothesis category Hypothesis subcategory
of studies
Leadership drivers Dominance 26
Ecological knowledge*16
Social connectedness*19
Personality 3
Other traits 2
Decision- making type Consensus*6
Leadership – stable*5
Leadership – distributed 2
Quorum 2
Mimetic 3
Decision- making
Signal coordination 8
As a process 4
Consensus mechanisms 3
Spatially driven*3
Temporally driven 1
*Hypotheses presented in cetacean decision- making studies.
13652907, 0, Downloaded from by Trinity Western University, Wiley Online Library on [12/09/2023]. See the Terms and Conditions ( on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License
E. Zwamborn, N. Boon and H. WhiteheadCollective decision- making in aquatic mammals
Mammal Review (2023) © 2023 The Authors. Mammal Review published by Mammal Society and John Wiley & Sons Ltd.
followers who are needed to meet a quorum also leaders?
In their framework, Conradt and Roper (2005) defined
unshared decisions as a single dominant individual acting
as leader, which does not consider situations where lead-
ership is not linked to dominance. In aquatic mammals
such as cetaceans, dominance hierarchies are not apparent,
perhaps because a three- dimensional and fluid habitat
limits opportunities for the monopolisation of resources
(Strickland et al. 2017, Rendell et al. 2019). In cetaceans,
social connectedness and ecological knowledge have been
more commonly suggested as drivers of leadership
(Lusseau 2007, Brent et al. 2015).
Conradt and Roper’s (2005) broad definition of partially
shared leadership as ‘a subset of individuals making a given
decision’ has a wide range of interpretations. Having several
leaders for a specific decision, in contrast to several leaders
rotating leadership at various times are quite different sce-
narios, although in both cases, the leadership is temporally
stable with the same individual(s) leading across the study
period. It appears that much of the confusion in terminol-
ogy could be avoided if time was considered and incor-
porated into definitions. Further conflating this terminology
is that distributed leadership (temporally unstable), where
all individuals in the group are observed leading, is some-
times also interpreted as ‘partially shared’. An example of
this would be if some individuals (e.g. females) lead more
often than the others, even though everyone takes a turn
at leading (Lee & Teichroeb 2016). Where then do these
complexities fit into our understanding of decision- making?
We propose that a single decision made by one individual
at a specific point in time to be termed as ‘unshared’,
with a second temporally defined subcategory associated
to capture these nuances (e.g. stable, semi- distributed, dis-
tributed unequally, or distributed equally). Clarifying the
temporal dimension of terminology, as well as the mecha-
nisms of decision- making and potential functions, will not
only help facilitate the comparison of studies but also give
the reader a clear understanding of the goals and scope
of the research.
There is a need for more standardised studies to facilitate
comparisons of populations and species. There has been
an attempt to standardise research methods in several cases,
often as the result of researchers being involved in multiple
similar studies or projects across populations or species
(e.g. Sueur & Petit 2008, 2010, Sueur 2011). Much of the
lack of standardisation may result from studies that use
opportunistic data, where understanding decision- making
is a secondary research goal. Targeted data collection may
be necessary for undertaking comparative studies and fur-
thering the field of decision- making research.
Within mammalian decision- making research, there is also
a need to develop studies, which consider both shared
and unshared decisions. Many of the studies we reviewed
were focused solely on testing a hypothesis for one or
the other. For example, if one is testing specifically for
physical leadership, the absence of an individual leading
in front would not preclude leadership as it could be
acoustic in nature or conducted from a central position
in the group. The risk of not testing for both shared and
unshared decision- making is that the research will be
limited in what it can say about these decisions and po-
tential process complexities. Researchers have observed
different decision- making types within the same species,
indicating that decision- making may be influenced by the
context in which it is made. If there is evidence for a
physical leader when group movement begins, it can be
difficult to determine whether this decision is truly un-
shared or whether the observed ‘leader’ is simply initiating
movement in a direction that has already been agreed
upon by the majority of the group through a shared
decision- making process.
That decision- making can be a mix of shared and un-
shared processes is often overlooked. Events, such as group
movement, that are initiated by an individual, who then
triggers a consensus decision on direction by the group,
have been found in several species including Panamanian
white- faced capuchins Cebus imitator, and meerkats
(Boinski 1993, Gall et al. 2017). Thus, shared and unshared
decisions are not mutually exclusive. For example, barbary
macaques Macaca sylvanus have a two- fold process where
the first part of the decision to move is shared by group
members who display pre- departure behaviour to signal
a readiness for movement, followed by an unshared deci-
sion when an initiator starts travel (Seltmann et al. 2013).
Fig. 3 outlines a framework for exploring decision- making
as a process.
A decision- making process may be simple or complex – and
may require several hypotheses and analyses to clarify.
Important questions to consider include: is the decision
shared or unshared? If unshared, is there one leader or
several? If leadership, is this leadership temporally consistent?
Does the process start with leadership and result in a shared
decision, or vice versa? If the decision is shared, does it
result in group consensus or fission into subgroups?
Studies that incorporate decision- making for a population
or species across different contexts are crucial for broader
understanding of how collective decisions are made. This
was done in an observational study of mountain zebras
Equus zebra, where dominant mares led most herd move-
13652907, 0, Downloaded from by Trinity Western University, Wiley Online Library on [12/09/2023]. See the Terms and Conditions ( on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License
Collective decision- making in aquatic mammalsE. Zwamborn, N. Boon and H. Whitehead
Mammal Review (2023) © 2023 The Authors. Mammal Review published by Mammal Society and John Wiley & Sons Ltd.
ments, but stallions were observed consistently
taking over leadership when the group went to drink
(Penzhorn 1984). Many studies were focused on specific
events or choices (Berry & Bercovitch 2014, Gall et al. 2017),
resulting in important findings, yet a poor understanding
of collective decision- making beyond these behavioural
contexts. If there are older female leaders in an endangered
population who lead groups to food during scarcities
(ecological knowledge), then prohibiting the removal of
these older females and protecting known traditional for-
aging habitat would be important. However, other decisions
within this population (e.g. where they breed, who defends
against predators, etc.) may not use the same decision-
making strategies. Conservation measures based on a single
context or study might be limited in their ability to protect
the population and detrimental if the assumption is made
that the population consistently makes decisions in the
same manner.
How can shifts in behaviour, including those not as-
sociated with the initiation of group movement, tell us
more about how decisions are made? Collecting consistent
temporal (timing) and spatial (position) data, in addition
to information on individual gestures, orientation, and
even acoustic signals associated with group decisions will
be important for facilitating the study of collective decision-
making across contexts.
Studies on decision- making often use language that is an-
thropomorphic, implying assumptions about the underlying
drivers of the decisions being made. Examples of these are
words like ‘democratic’, used when referring to shared
decisions, and ‘despotic’ when discussing a leadership or
otherwise unshared decision. Do animals really count, as
is implied when using the term ‘quorum’, or are they more
sensitive to a different sort of threshold? Are the leaders
of groups truly ‘despots’? We should be careful when using
wording that implies the intentions of the decision- makers
in cases where this is still often unknown. Using terms
such as shared and unshared in place of democratic and
despotic, as well as threshold instead of quorum, are less
assumptive and more objective.
Why are continued efforts to study collective
decision- making in aquatic mammals
Perhaps the greatest challenge for aquatic mammals when
it comes to collective decision- making is the environment
in which they live and how they use it. Many cetaceans
have been observed diving to great depths to forage, the
deepest of these being recorded for Cuvier’s beaked whales
Ziphius cavirostris reaching to 2992 m (Schorr et al. 2014).
Even species that are generally thought of as inhabiting
surface waters have been occasionally shown to dive deeper,
such as killer whales, where a 1087 m deep dive was re-
corded for an individual in the Southern Ocean (Towers
et al. 2019). Not only are these species diving to great
depths where low visibility in addition to high- pressure
limit communication options and constrain movement
patterns, but many of these departures and returns to the
surface are also tightly coordinated with other conspecifics
(Aguilar de Soto et al. 2020). Additionally, ocean environ-
ments are often patchy and unpredictable in resources
(Martin et al. 2002), meaning that collective travel deci-
sions are a critical part of life.
Fig. 3. Decision- making framework for a given collective decision or series of decisions, including consideration of temporal components.
13652907, 0, Downloaded from by Trinity Western University, Wiley Online Library on [12/09/2023]. See the Terms and Conditions ( on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License
E. Zwamborn, N. Boon and H. WhiteheadCollective decision- making in aquatic mammals
Mammal Review (2023) © 2023 The Authors. Mammal Review published by Mammal Society and John Wiley & Sons Ltd.
All but one of the studies on cetacean decision- making
found evidence of leadership in collective decisions, with
examples in both long- term stable groups and societies
with fission- fusion dynamics (Lewis et al. 2011, Brent
et al. 2015). This comes as a bit of a surprise, as mo-
nopolising resources in the ocean is difficult, given its
patchy and unpredictable nature, and the added dimen-
sionality of the habitat. Because of this, both territoriality
and dominance are less commonly observed in cetaceans
(Strickland et al. 2017, Rendell et al. 2019). We would
expect unshared decision- making to be less common than
in terrestrial mammals, as leadership is frequently ob-
served in species with strong dominance hierarchies
(Peterson et al. 2002, Sueur et al. 2013). There are several
possible reasons for the unexpected frequency of leader-
ship in cetaceans. Firstly, in female- centred societies, such
as those found in killer whales, the group may value
the ecological knowledge of certain individuals and fol-
low their lead at times when this information is needed
(Brent et al. 2015). Secondly, several of these studies
looked at small inshore dolphin populations (Lusseau &
Conradt 2009, Lewis et al. 2011), where competition and
potential temporal monopolisation of restricted resources
within a small area may be more common. Thirdly,
shared decisions might be more difficult to detect in
cetaceans, particularly when studies are designed to look
for physical leadership among animals that spend much
of their time underwater.
It is important to consider how space use in three-
dimensional aquatic environments with extreme pressure
gradients and generally low or non- existent visibility impacts
how collective decisions are made. An obvious problem
would be the difficulty of maintaining communication
between conspecifics over large distances and depths (Tyack
& Clark 2000). Groups of sperm whales can spread out
over several kilometres to hunt independently, yet they
must make collective decisions on how to move direction-
ally (Whitehead 2016) and then find each other when
they return to the surface. Life in aquatic environments
is compounded by an additional challenge. Light travels
poorly and chemical signals do not function well, meaning
that communication is often limited to acoustic signals
(Tyack & Clark 2000). The use of sound is likely to be
a much more integral element of collective decision- making
in cetaceans than for most terrestrial species (perhaps with
the exceptions of bats and humans). While we know that
cetaceans have developed advanced acoustic abilities to
communicate (as well as forage and navigate in toothed
whales), the importance and function of these signals in
collective decision- making remains largely unknown (Tyack
& Clark 2000). It can be argued that the collection of
acoustic data is just as important or even more critical
than the collection of movement data for studying how
cetaceans make collective decisions, given that this is their
primary means of communication.
Studies of decision- making also have the potential to
contribute valuable insight into cetacean sociality. For
example, finding a relationship between social connected-
ness in Indo- Pacific bottlenose dolphins, and discovering
who leads within different social contexts (Lusseau 2007),
allows us to address questions about the evolution and
function of their social structure. Decision- making studies
can also help us understand the psychology of individuals.
Research in horses and elephants found that personality
can predict who leads (Lee & Moss 2012, Briard et al. 2015).
While no studies in cetaceans have been focused on how
personality and leadership are connected, a recent study
in wild common bottlenose dolphins that looked at traits
(e.g. shyness, boldness) in individuals showed that this
would be an attainable next step (Díaz López 2020).
Fig. 4. Suggested data collection methods and data types for studying decision- making (including acoustic aspects) in aquatic mammals.
13652907, 0, Downloaded from by Trinity Western University, Wiley Online Library on [12/09/2023]. See the Terms and Conditions ( on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License
Collective decision- making in aquatic mammalsE. Zwamborn, N. Boon and H. Whitehead
Mammal Review (2023) © 2023 The Authors. Mammal Review published by Mammal Society and John Wiley & Sons Ltd.
A phenomenon unique to cetaceans that involves
decision- making is mass stranding. Various potential
causes for strandings have been proposed (including
military sonar exposure, navigational errors, and illness),
and in many cases, it can be hard to determine the
exact cause (Moore et al. 2018; see Appendix S3 for
further discussion on the causes of mass strandings).
Sometimes, individuals have been observed close to the
shore in the hours or days before a stranding takes
place (Best & Reeb 2010). The singularity of mass strand-
ings has resulted in much discussion and reporting from
groups dedicated to rescue and response, but there are
few peer- reviewed articles on potential causes. Literature
pertaining to pre- stranding behaviour is even more scarce
(Best & Reeb 2010). This is in part because strandings
are typically identified as an issue only after they occur.
Current technology and social media sharing means that
access to footage of strandings that are ‘in progress’,
showing behaviour as whales linger in nearshore waters
and swim towards the beach, is more readily available.
Understanding more about day- to- day and pre- stranding
cetacean collective decision- making would likely allow
us to prevent or mitigate some (particularly anthropo-
genically triggered) stranding events.
Studies of mammalian collective decision- making have
advanced significantly in recent years. We have made
five recommendations to move the study of decision-
making forward: 1) make clear delineations between
temporal and non- temporal aspects of decision- making,
2) standardise methods to allow comparisons, 3) consider
both shared and unshared decision- making, 4) consider
decision- making in context, and 5) avoid anthropomor-
phising decision- making by non- human mammals. While
cetaceans are not the only group of aquatic mammals
that make collective decisions, they represent the entirety
of available literature on decision- making for these ani-
mals. A better understanding of collective decision-
making across species will help us understand how these
mammals have adapted to an environment with unique
challenges not faced by their terrestrial counterparts.
Additionally, research has the potential to provide new
insights into both the function of social structures and
the psychology of individuals (e.g. the role of personal-
ity). With new technology, data needed to answer many
of these research questions are becoming readily available
(Fig. 4). Learning from the successes and challenges in
collective decision- making studies conducted across other
mammalian species is important in advancing the field
of aquatic mammal behaviour and maximising future
research opportunities.
We thank Laura Feyrer, Dara Orbach, and Shelley Adamo
for their helpful comments during manuscript preparation.
Open access was funded and made possible by Dalhousie
We are grateful for the research funding provided by the
Natural Sciences and Engineering Research Council of
Canada (Canadian Graduate Scholarship – Doctoral) and
the Amy R. Samuels Cetacean Behaviour and Conservation
Award (to EZ).
Data from our study are freely available online at Figshare
DOI: 10.6084/m9.figshare.23661132
Addison WE, Simmel EC (1980) The relationship between
dominance and leadership in a flock of ewes. Bulletin of
the Psychonomic Society 15: 303– 305.
Aguilar de Soto N, Visser F, Tyack PL, Alcazar J, Ruxton
G, Arranz P, Madsen PT, Johnson M (2020) Fear of
killer whales drives extreme synchrony in deep diving
beaked whales. Scientific Reports 10: 13.
Altmann M (1952) Social behavior of elk, Cervus canadensis
nelsoni, in the Jackson hole area of Wyoming. Behaviour
4: 116– 143.
Barelli C, Boesch C, Heistermann M, Reichard UH (2008)
Female white- handed gibbons (Hylobates lar) lead group
movements and have priority of access to food resources.
Behaviour 145: 965– 981.
Beilharz RG, Mylrea PJ (1963) Social position and
movement orders of dairy heifers. Animal Behaviour 11:
529– 533.
van Belle S, Estrada A, Garber PA (2013) Collective group
movement and leadership in wild black howler monkeys
(Alouatta pigra). Behavioral Ecology and Sociobiology 67:
31– 41.
Berry PSM, Bercovitch FB (2014) Leadership of herd
progressions in the Thornicroft’s giraffe of Zambia.
African Journal of Ecology 53: 175– 182.
Best PB, Reeb D (2010) A near mass stranding of cetaceans
in St Helena bay, South Africa. African Journal of Marine
Science 32: 163– 166.
Bigg MA, Olesiuk PF, Ellis GM, Ford JKB, Balcomb KC
(1990) Social organization and genealogy of resident killer
whales (Orcinus orca) in the coastal waters of British
Columbia and Washington state. Report of the
International Whaling Commission 12: 383– 405.
13652907, 0, Downloaded from by Trinity Western University, Wiley Online Library on [12/09/2023]. See the Terms and Conditions ( on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License
E. Zwamborn, N. Boon and H. WhiteheadCollective decision- making in aquatic mammals
Mammal Review (2023) © 2023 The Authors. Mammal Review published by Mammal Society and John Wiley & Sons Ltd.
Boinski S (1993) Vocal coordination of troop movement
among white- faced capuchin monkeys, Cebus capucinus.
American Journal of Pathology 30: 85– 100.
Boinski S, Campbell AF (1995) Use of trill vocalizations to
coordinate troop movement among white- faced capuchins:
a second field test. Behaviour 132: 875– 901.
Bonanni R, Cafazzo S, Valsecchi P, Natoli E (2010) Effect
of affiliative and agonistic relationships on leadership
behaviour in free- ranging dogs. Animal Behaviour 79:
981– 991.
Bonanni R, Natoli E, Cafazzo S, Valsecchi P (2011)
Free- ranging dogs assess the quantity of opponents in
intergroup conflicts. Animal Cognition 14: 103– 115.
Bonnell TR, Campennì M, Chapman CA, Gogarten JF,
Reyna- Hurtado RA, Teichroeb JA, Wasserman MD,
Sengupta R (2013) Emergent group level navigation: an
agent- based evaluation of movement patterns in a
folivorous primate. PLoS One 8: e78264.
Bonnell TR, Clarke PM, Henzi SP, Barrett L (2017)
Individual- level movement bias leads to the formation of
higher- order social structure in a mobile group of
baboons. Royal Society Open Science 4: 170148.
Bourjade M, Thierry B, Maumy M, Petit O (2009)
Decision- making in Przewalski horses (Equus ferus
przewalskii) is driven by the ecological contexts of
collective movements. Ethology 115: 321– 330.
Bourjade M, Thierry B, Hausberger M, Petit O (2015) Is
leadership a reliable concept in animals? An empirical
study in the horse. PLoS One 10: e0126344.
Bousquet CAH, Sumpter DJT, Manser MB (2011) Moving
calls: a vocal mechanism underlying quorum decisions in
cohesive groups. Proceedings of the Royal Society B:
Biological Sciences 278: 1482– 1488.
Brent LJN, Franks DW, Foster EA, Balcomb KC, Cant MA,
Croft DP (2015) Ecological knowledge, leadership, and
the evolution of menopause in killer whales. Current
Biology 25: 746– 750.
Bresiński W (1982) Grouping tendencies in roe deer under
agrocenosis conditions. Acta Theriologica 29: 427– 447.
Briard L, Dorn C, Petit O (2015) Personality and affinities
play a key role in the organisation of collective
movements in a group of domestic horses. Ethology 121:
888– 902.
Carranza J, de Reyna LA (1987) Spatial organization of
female groups in red deer (Cervus elaphus L.). Behavioural
Processes 14: 125– 135.
Ceccarelli E, Rangel Negrín A, Coyohua- Fuentes A, Canales-
Espinosa D, Dias PAD (2020) Sex differences in
leadership during group movement in mantled howler
monkeys (Alouatta palliata). American Journal of
Primatology 82: 1– 9.
Chambers LM (2019) Follow the Leader: Correlates of
Juvenile Leadership in Wild Chimpanzees. PhD thesis, The
George Washington University, Washington, D.C., USA.
Christal J, Whitehead H, Lettevall E (1998) Sperm whale
social units: variation and change. Canadian Journal of
Zoology 76: 1431– 1440.
Collignon B, Cervantes Valdivieso LE, Detrain C (2014)
Group recruitment in ants: who is willing to lead?
Behavioural Processes 108: 98– 104.
Conradt L, Roper TJ (2005) Consensus decision making in
animals. Trends in Ecology & Evolution 20: 449– 456.
Covidence Systematic Review Software (2021) Veritas Health
Innovation, Melbourne, Australia. http://www.covid
Díaz López B (2020) When personality matters: personality
and social structure in wild bottlenose dolphins, Tursiops
truncatus. Animal Behaviour 163: 73– 84.
Dickson DP, Barr GR, Wieckert DA (1967) Social
relationship of dairy cows in a feed lot. Behaviour 29:
195– 203.
Dunbar RIM (1983) Structure of gelada baboon reproductive
units: IV. Integration at group level. Zeitschrift für
Tierpsychologie 63: 265– 282.
Erhart EM, Overdorff DJ (1999) Female coordination of
group travel in wild Propithecus and Eulemur.
International Journal of Primatology 20: 927– 940.
Escos J, Alados CL, Boza J (1993) Leadership in a domestic
goat herd. Applied Animal Behaviour Science 38: 41– 47.
Farine DR, Strandburg- Peshkin A, Berger- Wolf T, Ziebart B,
Brugere I, Li J, Crofoot MC (2016) Both nearest
neighbours and long- term affiliates predict individual
locations during collective movement in wild baboons.
Scientific Reports 6: 27704.
Fernández VA, Kowalewski M, Zunino GE (2013) Who is
coordinating collective movements in black and gold
howler monkeys? Primates 54: 191– 199.
Fernández A, Sierra E, Diaz- Delgado J, Sacchini S, Sánchez-
Paz C, Suárez- Santana M et al. (2017) Deadly acute
decompression sickness in Risso’s dolphins. Scientific
Reports 7: 13621.
Fischer J, Zinner D (2011) Communication and cognition in
primate group movement. International Journal of
Primatology 32: 1279– 1295.
Fischhoff IR, Sundaresan SR, Cordingley J, Larkin HM,
Sellier MJ, Rubenstein DI (2007) Social relationships and
reproductive state influence leadership roles in movements
of plains zebra, Equus burchellii. Animal Behaviour 73:
825– 831.
Foreit K (2016) Leading Behaviour, Positioning, and Group
Spacing as Indicators of Dominance in Hapalemur Griseus.
PhD thesis, Northern Illinois University, DeKalb, USA.
Foster EA (2012) Exploring the Mechanisms and Functions
Underpinning the Social Networks of an Endangered
Population of Killer Whales, Orcinus Orca. PhD thesis,
University of Exeter, Exeter, UK.
Funk E (1981) The behavior of 2 red deer family groups
an enclosure observation. Zeitschrift Fur Jagdwissenschaft
27: 33– 41.
13652907, 0, Downloaded from by Trinity Western University, Wiley Online Library on [12/09/2023]. See the Terms and Conditions ( on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License
Collective decision- making in aquatic mammalsE. Zwamborn, N. Boon and H. Whitehead
Mammal Review (2023) © 2023 The Authors. Mammal Review published by Mammal Society and John Wiley & Sons Ltd.
Gall GEC, Strandburg- Peshkin A, Clutton- Brock T, Manser
MB (2017) As dusk falls: collective decisions about the
return to sleeping sites in meerkats. Animal Behaviour
132: 91– 99.
Geist V (1963) On the behaviour of the North American
Moose (Alces Alces Andersoni Peterson 1950) in British
Columbia. Behaviour 20: 377– 416.
Gerard JF, Richard- Hansen C, Maublanc ML, Bideau E
(1993) Probable exaptations within the “distributed” herd.
Revue d’Ecologie (la Terre et la Vie) 48: 239– 248.
Gray GG, Simpson CD (1982) Group dynamics of free-
ranging barbary sheep in Texas. Journal of Wildlife
Management 46: 1096– 1101.
Hartman K, van der Harst P, Vilela R (2020) Continuous
group follows operated by a drone enable analysis of the
relation between sociality and position in a group of
male Risso’s dolphins (Grampus griseus). Frontiers in
Marine Science 7: 283.
Heyman WD, Graham RT, Kjerfve B, Johannes RE (2001)
Whale sharks Rhincodon typus aggregate to feed on fish
spawn in Belize. Marine Ecology Progress Series 215:
275– 282.
Hindell MA, Harcourt R, Waas J, Thompson D (2002)
Fine- scale three- dimensional spatial use by diving,
lactating female Weddell seals Leptonychotes weddellii.
Marine Ecology Progress Series 242: 275– 284.
Ihl C, Bowyer RT (2011) Leadership in mixed- sex groups of
muskoxen during the snow- free season. Journal of
Mammalogy 92: 819– 827.
Innis AC (1958) The behaviour of the giraffe, Giraffa
camelopardalis, in the eastern Transvaal. Proceedings of the
Zoological Society of London 131: 245– 278.
Jacobs A, Watanabe K, Petit O (2011) Social structure
affects initiations of group movements but not
recruitment success in Japanese macaques (Macaca
fuscata). International Journal of Primatology 32:
1311– 1324.
Jakimchuk RD, Carruthers DR (1983) A preliminary study
of the behaviour of barren- ground caribou during their
spring migration across Contwoyto Lake, N.W.T., Canada.
Acta Zoologica Fennica 175: 117– 119.
Jezierski T, Gebler E (1984) Observations on behavior of
polish feral horses. Zeitschrift Fuer Tierzuechtung Und
Zuechtungsbiologie 101: 143– 152.
King AJ, Cowlishaw G (2009) All together now: behavioural
synchrony in baboons. Animal Behaviour 78: 1381– 1387.
King AJ, Sueur C (2011) Where next? Group coordination
and collective decision making by primates. International
Journal of Primatology 32: 1245– 1267.
King AJ, Sueur C, Huchard E, Cowlishaw G (2011) A
rule- of- thumb based on social affiliation explains
collective movements in desert baboons. Animal Behaviour
82: 1337– 1345.
de Kock LL (1956) The pilot whale stranding on the
Orkney Island of Westray, 1955. Scottish Naturalist 68:
63– 70.
Krueger K, Flauger B, Farmer K, Hemelrijk C (2014)
Movement initiation in groups of feral horses. Behavioural
Processes 103: 91– 101.
Leca JB, Gunst N, Thierry B, Petit O (2003) Distributed
leadership in semifree- ranging white- faced capuchin
monkeys. Animal Behaviour 66: 1045– 1052.
Lee PC, Moss CJ (2012) Wild female African elephants
(Loxodonta africana) exhibit personality traits of
leadership and social integration. Journal of Comparative
Psychology 126: 224– 232.
Lee HC, Teichroeb JA (2016) Partially shared consensus
decision making and distributed leadership in vervet
monkeys: older females lead the group to forage.
American Journal of Physical Anthropology 161: 580– 590.
Lesmerises F, Johnson CJ, St- Laurent M (2018) Landscape
knowledge is an important driver of the fission
dynamics of an alpine ungulate. Animal Behaviour 140:
39– 47.
Lewis JS, Wartzok D, Heithaus MR (2011) Highly dynamic
fission- fusion species can exhibit leadership when
traveling. Behavioral Ecology and Sociobiology 65:
1061– 1069.
Lewis JS, Wartzok D, Heithaus MR (2013a) Individuals as
information sources: could followers benefit from leaders’
knowledge? Behaviour 150: 635– 657.
Lewis JS, Wartzok D, Heithaus M, Kruetzen M (2013b)
Could relatedness help explain why individuals lead in
bottlenose dolphin groups? PLoS One 8: e58162.
Liew C, Labadin J (2017) Leadership in species: a
bipartite- network- based approach. First international
conference on computer and drone applications
(ICONDA), 66– 70.
Lusseau D (2007) Evidence for social role in a dolphin
social network. Evolutionary Ecology 21: 357– 366.
Lusseau D, Conradt L (2009) The emergence of unshared
consensus decisions in bottlenose dolphins. Behavioral
Ecology and Sociobiology 63: 1067– 1077.
Makwana SC (1979) Infanticide and social change in two
groups of the Hanuman langur, Presbytis entellus, at
Jodhpur. Primates 20: 293– 300.
Marshall HH, Carter AJ, Coulson T, Rowcliffe JM,
Cowlishaw G (2012) Exploring foraging decisions in a
social primate using discrete- choice models. American
Naturalist 180: 481– 495.
Martin AP, Richards KJ, Bracco A, Provenzale A (2002)
Patchy productivity in the open ocean. Global
Biogeochemical Cycles 16: 9- 1– 9- 9.
Mazzariol S, Centelleghe C, Cozzi B, Povinelli M, Marcer F,
Ferri N et al. (2018) Multidisciplinary studies on a
sick- leader syndrome- associated mass stranding of sperm
13652907, 0, Downloaded from by Trinity Western University, Wiley Online Library on [12/09/2023]. See the Terms and Conditions ( on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License
E. Zwamborn, N. Boon and H. WhiteheadCollective decision- making in aquatic mammals
Mammal Review (2023) © 2023 The Authors. Mammal Review published by Mammal Society and John Wiley & Sons Ltd.
whales (Physeter macrocephalus) along the Adriatic coast
of Italy. Scientific Reports 8: 11577.
McCue L, Cioffi W, Heithaus M, Barrè L, Connor R (2020)
Synchrony, leadership, and association in male indo-
pacific bottlenose dolphins (Tursiops aduncus). Ethology
126: 741– 750.
Mech D (2000) Leadership in wolf, Canis lupus, packs.
Canadian Field Naturalist 114: 259– 263.
Merkle JA, Sigaud M, Fortin D (2015) To follow or not?
How animals in fusion- fission societies handle conflicting
information during group decision- making. Ecology Letters
18: 799– 806.
Mizuno K, Sharma N, Idani G, Sukumar R (2017)
Collective behaviour of wild Asian elephants in risky
situations: how do social groups cross roads? Behaviour
154: 1215– 1237.
Moore KM, Simeone CA, Brownell RL Jr (2018) Strandings.
In: Encyclopedia of Marine Mammals, 945– 951. Academic
Press, Cambridge, USA.
Mrlik V (1991) Active protective behaviour of roe deer
(Capreolus capreolus) in an open habitat during the
winter season. Folia Zoologica 40: 13– 24.
Naďo L, Kaňuch P (2015) Swarming behaviour associated
with group cohesion in tree- dwelling bats. Behavioural
Processes 120: 80– 86.
Nakagawa N (1990) Decisions on time allocation to different
food patches by Japanese monkeys (Macaca fuscata).
Primates 31: 459– 468.
Naumov NP, Baskin LM (1969) Leadership in herds of
reindeer as group adaptation. Zhurnal Obshcheĭ Biologii
30: 147– 156.
Norris KS, Schilt CR (1988) Cooperative societies in
three- dimensional space: on the origins of aggregations,
flocks, and schools, with special reference to dolphins and
fish. Ethology and Sociobiology 9: 149– 179.
Norton G (1986) Leadership: decision processes of group
movement in yellow baboons. Primate Ecology and
Conservation 2: 145– 156.
Nowacek DP, Friedlaender AS, Halpin PN, Hazen EL,
Johnston DW, Read AJ, Espinasse B, Zhou M, Zhu Y
(2011) Super- aggregations of krill and humpback whales in
Wilhelmina Bay, Antarctic Peninsula. PLoS One 6: e19173.
Overdorff DJ, Erhart EM, Mutschler T (2005) Does female
dominance facilitate feeding priority in black- and- white
ruffed lemurs (Varecia variegata) in southeastern
Madagascar? American Journal of Primatology 66: 7– 22.
Ozogány K, Vicsek T (2014) Modeling the emergence of
modular leadership hierarchy during the collective motion
of herds made of harems. Journal of Statistical Physics
158: 628– 646.
Palacios- Romo TM, Castellanos F, Ramos- Fernandez G
(2019) Uncovering the decision rules behind collective
foraging in spider monkeys. Animal Behaviour 149:
121– 133.
Penzhorn BL (1984) A long- term study of social
organisation and behaviour of Cape Mountain zebras
Equus zebra zebra. Zeitschrift für Tierpsychologie 64:
97– 146.
Pérez- Barbería FJ, Walker DM (2018) Dynamics of social
behaviour at parturition in a gregarious ungulate.
Behavioural Processes 150: 75– 84.
Peterson RO, Jacobs AK, Drummer TD, Mech LD, Smith
DW (2002) Leadership behavior in relation to dominance
and reproductive status in gray wolves, Canis lupus.
Canadian Journal of Zoology 80: 1405– 1412.
Petit O, Gautrais J, Leca JB, Theraulaz G, Deneubourg JL
(2009) Collective decision- making in white- faced capuchin
monkeys. Proceedings of the Royal Society B: Biological
Sciences 276: 3495– 3503.
Plötz J, Weidel H, Bersch M (1991) Winter aggregations of
marine mammals and birds in the North- Eastern Weddell
Sea pack ice. Polar Biology 11: 305– 309.
Pyritz LW, Kappeler PM, Fichtel C (2011) Coordination of
group movements in wild red- fronted lemurs (Eulemur
rufifrons): processes and influence of ecological and
reproductive seasonality. International Journal of
Primatology 32: 1325– 1347.
Ramos A, Petit O, Longour P, Pasquaretta C, Sueur C
(2015) Collective decision making during group
movements in European bison, Bison bonasus. Animal
Behaviour 109: 149– 160.
Ramos A, Manizan L, Rodriguez E, Kemp YJM, Sueur C
(2018) How can leadership processes in European bison
be used to improve the management of free- roaming
herds. European Journal of Wildlife Research 64: 1– 16.
Ramseyer A, Boissy A, Dumont B, Thierry B (2009a)
Decision making in group departures of sheep is a
continuous process. Animal Behaviour 78: 71– 78.
Ramseyer A, Boissy A, Thierry B, Dumont B (2009b)
Individual and social determinants of spontaneous
group movements in cattle and sheep. Animal 3:
1319– 1326.
Ramseyer A, Thierry B, Boissy A, Dumont B (2009c)
Decision- making processes in group departures of cattle.
Ethology 115: 948– 957.
Rasolonjatovo SM, Irwin MT (2020) Exploring social
dominance in wild diademed sifakas (Propithecus
diadema): females are dominant, but it is subtle and the
benefits are not clear. Folia Primatologica 91: 385– 398.
Reinhardt V (1983) Movement orders and leadership in a
semi wild herd cattle herd. Behaviour 83: 251– 264.
Rendell L, Cantor M, Gero S, Whitehead H, Mann J (2019)
Causes and consequences of female centrality in cetacean
societies. Philosophical Transactions of the Royal Society B
374: 20180066.
Romero T, Castellanos MA (2010) Dominance relationships
among male hamadryas baboons (Papio hamadryas).
Journal of Ethology 28: 113– 121.
13652907, 0, Downloaded from by Trinity Western University, Wiley Online Library on [12/09/2023]. See the Terms and Conditions ( on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License
Collective decision- making in aquatic mammalsE. Zwamborn, N. Boon and H. Whitehead
Mammal Review (2023) © 2023 The Authors. Mammal Review published by Mammal Society and John Wiley & Sons Ltd.
Rowell TE, Rowell CA (1993) The social organization of
feral Ovis aries ram groups in the pre- rut period.
Ethology 95: 213– 232.
Šárová R, Špinka M, Panamá JLA (2007) Synchronization
and leadership in switches between resting and activity in
a beef cattle herd – a case study. Applied Animal
Behaviour Science 108: 327– 331.
Šárová R, Špinka M, Panamá JLA, Šimeček P (2010) Graded
leadership by dominant animals in a herd of female beef
cattle on pasture. Animal Behaviour 79: 1037– 1045.
Sato S (1982) Leadership during actual grazing in a small
herd of cattle. Applied Animal Ethology 8: 53– 65.
Schorr GS, Falcone EA, Moretti DJ, Andrews RD (2014)
First long- term behavioral records from Cuvier’s beaked
whales (Ziphius cavirostris) reveal record- breaking dives.
PLoS One 9: e92633.
Schweitzer C, Gaillard T, Guerbois C, Fritz H, Petit O
(2017) Participant profiling and pattern of crop- foraging
in chacma baboons (Papio hamadryas ursinus) in
Zimbabwe: why does investigating age– sex classes matter?
International Journal of Primatology 38: 207– 223.
Sellers WI, Hill RA, Logan BS (2007) An agent- based model
of group decision making in baboons. Philosophical
Transactions of the Royal Society of London B Biological
Sciences 362: 1699– 1710.
Seltmann A, Majolo B, Schuelke O, Ostner J (2013) The
organization of collective group movements in wild
barbary macaques (Macaca sylvanus): social structure
drives processes of group coordination in macaques. PLoS
One 8: e67285.
Seltmann A, Franz M, Majolo B, Qarro M, Ostner J,
Schülke O (2016) Recruitment and monitoring behaviors
by leaders predict following in wild barbary macaques
(Macaca sylvanus). Primate Biology 3: 23– 31.
Smith AC, Buchanan- Smith HM, Surridge AK, Mundy NI
(2003) Leaders of progressions in wild mixed- species
troops of saddleback (Saguinus fuscicollis) and mustached
tamarins (S. mystax), with emphasis on color vision and
sex. American Journal of Primatology 61: 145– 157.
Smith JE, van Horn RC, Powning KS, Cole AR, Graham
KE, Memenis SK, Holekamp KE (2010) Evolutionary
forces favoring intragroup coalitions among spotted
hyenas and other animals. Behavioral Ecology 21: 284– 303.
Smith JE, Gavrilets S, Mulder MB, Hooper PL, El Mouden
C, Nettle D et al. (2016) Leadership in mammalian
societies: emergence, distribution, power, and payoff.
Trends in Ecology & Evolution 31: 54– 66.
Smith JE, Ortiz CA, Buhbe MT, van Vugt M (2020)
Obstacles and opportunities for female leadership in
mammalian societies: a comparative perspective. The
Leadership Quarterly 31: 1– 15.
Sperber AL, Werner LM, Kappeler PM, Fichtel C (2017)
Grunt to go— vocal coordination of group movements in
redfronted lemurs. Ethology 123: 894– 905.
Sperber AL, Kappeler PM, Fichtel C (2019) Should I stay or
should I go? Individual movement decisions during group
departures in red- fronted lemurs. Royal Society Open
Science 6: 180991.
Strandburg- Peshkin A, Farine DR, Couzin ID, Crofoot MC
(2015) Shared decision- making drives collective movement
in wild baboons. Science 348: 1358– 1361.
Strickland K, Levengood A, Foroughirad V, Mann J,
Krzyszczyk E, Frère CH (2017) A framework for the
identification of long- term social avoidance in longitudinal
datasets. Royal Society Open Science 4: 170641.
Struhsaker TT (1967) Social structure among vervet
monkeys (Cercopithecus aethiops). Behaviour 29: 6– 121.
Stueckle S, Zinner D (2008) To follow or not to follow:
decision making and leadership during the morning
departure in chacma baboons. Animal Behaviour 75:
1995– 2004.
Sueur C (2011) Group decision- making in chacma baboons:
leadership, order and communication during movement.
BMC Ecology 11: 1– 14.
Sueur C, Petit O (2008) Shared or unshared consensus
decision in macaques? Behavioural Processes 78: 84– 92.
Sueur C, Petit O (2010) Signals use by leaders in Macaca
tonkeana and Macaca mulatta: group- mate recruitment
and behaviour monitoring. Animal Cognition 13: 239– 248.
Sueur C, Petit O, Deneubourg JL (2009) Selective mimetism
at departure in collective movements of Macaca tonkeana:
an experimental and theoretical approach. Animal
Behaviour 78: 1087– 1095.
Sueur C, Deneubourg JL, Petit O (2010a) Sequence of
quorums during collective decision making in macaques.
Behavioral Ecology and Sociobiology 64: 1875– 1885.
Sueur C, Petit O, Deneubourg JL (2010b) Short- term group
fission processes in macaques: a social networking
approach. Journal of Experimental Biology 213: 1338– 1346.
Sueur C, Deneubourg JL, Petit O (2011) From the first
intention movement to the last joiner: macaques combine
mimetic rules to optimize their collective decisions.
Proceedings of the Royal Society B: Biological Sciences 278:
1697– 1704.
Sueur C, MacIntosh AJJ, Jacobs AT, Watanabe K, Petit O
(2013) Predicting leadership using nutrient requirements
and dominance rank of group members. Behavioral
Ecology and Sociobiology 67: 457– 470.
Sueur C, Kuntz C, Debergue E, Keller B, Robic F, Siegwalt-
Baudin F, Richer C, Ramos A, Pelé M (2018) Leadership
linked to group composition in highland cattle (Bos
taurus): implications for livestock management. Applied
Animal Behaviour Science 198: 9– 18.
Tecot SR, Romine NK (2012) Leading ladies: leadership of
group movements in a pair- living, co- dominant,
monomorphic primate across reproductive stages and fruit
availability seasons. American Journal of Primatology 74:
591– 601.
13652907, 0, Downloaded from by Trinity Western University, Wiley Online Library on [12/09/2023]. See the Terms and Conditions ( on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License
E. Zwamborn, N. Boon and H. WhiteheadCollective decision- making in aquatic mammals
Mammal Review (2023) © 2023 The Authors. Mammal Review published by Mammal Society and John Wiley & Sons Ltd.
Tokuyama N, Furuichi T (2017) Leadership of old females
in collective departures in wild bonobos (Pan paniscus) at
Wamba. Behavioral Ecology and Sociobiology 71: 55.
Towers JR, Tixier P, Ross KA, Bennett J, Arnould JPY,
Pitman RL, Durban JW (2019) Movements and dive
behaviour of a toothfish- depredating killer and sperm
whale. ICES Journal of Marine Science 76: 298– 311.
Trillmich J, Fichtel C, Kappeler PM (2004) Coordination of
group movements in wild Verreaux’s sifakas (Propithecus
verreauxi). Behaviour 141: 1103– 1120.
Tsarev SA (1980) Behavior of the wild boar in the northern
limits of its range. Vestnik Leningradskogo Universiteta
Biologiya 2: 15– 21.
Tyack P, Clark C (2000) Communication and acoustic
behavior of dolphins and whales. In: Au W, Popper A,
Fay R (eds) Hearing by Whales and Dolphins, 156– 224.
Springer- Verlag, New York, New York, USA.
Walker RH, King AJ, McNutt JW, Jordan NR (2017) Sneeze
to leave: African wild dogs (Lycaon pictus) use variable
quorum thresholds facilitated by sneezes in collective
decisions. Proceedings of the Royal Society B: Biological
Sciences 284: 20170347.
Wang X, Sun L, Li J, Xia D, Sun B, Zhang D (2015)
Collective movement in the Tibetan macaques (Macaca
thibetana): early joiners write the rule of the game. PLoS
One 10: e0127459.
Wang X, Sun L, Sheeran LK, Sun BH, Zhang QX, Zhang
D, Xia DP, Li JH (2016) Social rank versus affiliation:
which is more closely related to leadership of group
movements in Tibetan macaques (Macaca thibetana)?
American Journal of Primatology 78: 816– 824.
Wang C, Pan R, Wang X, Qi X, Zhao H, Guo S, Ren Y,
Fu W, Zhu Z, Li B (2020) Decision- making process
during collective movement initiation in golden snub-
nosed monkeys (Rhinopithecus roxellana). Scientific Reports
10: 480.
Whitehead H (2016) Consensus movements by groups of
sperm whales. Marine Mammal Science 32: 1402– 1415.
Wilson EO (2000) Sociobiology: The New Synthesis. Harvard
University Press, Cambridge, Massachusetts, USA.
Wolter R, Pantel N, Stefanski V, Moestl E, Krueger K
(2014) The role of an alpha animal in changing
environmental conditions. Physiology & Behavior 133:
236– 243.
You W, Shi J, Lu F, Dong S, Li X, Zhang Z (2013) Traits
and process of group decision- making in Przewalski’s
gazelle (Procapra przewalskii). Acta Theriologica 33:
293– 299.
Zaitsev V (1999) Guides, leaders and scouts in wild boar.
Bulletin of the Moscow Society of Natural Scientists 104:
10– 16.
Zappala J, Logan B (2010) Effects of resource availability on
consensus decision making in primates. Computational &
Mathematical Organization Theory 16: 400– 415.
Additional supporting information may be found in the
online version of this article at the publisher’s website.
Appendix S1. Further details on past mammalian decision-
making reviews.
Appendix S2. Mammalian collective decision- making lit-
erature search terms.
Appendix S3. Further notes and references on the causes
of mass strandings in cetaceans.
13652907, 0, Downloaded from by Trinity Western University, Wiley Online Library on [12/09/2023]. See the Terms and Conditions ( on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License
... There is considerably less known about collective decisions in aquatic mammal species, where the difficulties of observing groups for long periods at sea makes them more challenging to study than their terrestrial counterparts (Zwamborn et al., 2023). Many species of cetaceans live in groups and behave collectively, but little is known about how group decisions are made. ...
... Leadership has also been documented in postmenopausal southern resident killer whales, Orcinus orca, who hold important ecological knowledge and physically lead their matrilines in times of prey scarcity (Brent et al., 2015). Understanding how cetaceans make collective decisions helps elucidate how they overcome the unique challenges of living in aquatic environments, in comparison to terrestrial habitats where decision making is most often studied (Zwamborn et al., 2023). This is especially important for deep-diving odontocetes, where the loss of group cohesion during collective deep dives can result in an increased risk of predation (Aguilar de Soto et al., 2020;Alc azar-Treviño et al., 2021). ...
Full-text available
Little is understood about how social cetaceans make collective decisions. Consensus processes are often beneficial for fitness at both a group and individual level, but most previous studies of decision making in whales and dolphins show evidence of a leader, frequently an individual with greater ecological knowledge or social connectedness. We used drone footage of long-finned pilot whales, Globicephala melas, off Cape Breton Island, Nova Scotia, Canada, to examine the characteristics of initial divers (age class/sex, relative position, accompanying calf) and the timing of when individuals dive (i.e. dive lag) within collective group dives (N=73). Resting groups of pilot whales had threefold higher mean dive lag and interindividual dive intervals than groups in other behavioural states. Females initiated dives more often than expected by chance and initial divers were most frequently located peripherally on the left or right flank of the group. Dive lags following the initial diver had a heavily right-skewed distribution , suggesting that long-finned pilot whales within groups are often responding to a stimulus (e.g. physical leadership, a vocal signal, an approaching vessel). These findings are consistent with the hypothesis that unequally distributed leadership guides the temporal patterning of the collective deep dives of pilot whales.
Full-text available
Relationships between social status and relative position of group-living animals have been described in a variety of species. For wild cetaceans, who spend most of their time underwater, collecting detailed, continuous data to assess such relationships depends highly on group size, formation, shyness of animals and observation platform. We test a new method for focal group sampling using an Unmanned Aerial Vehicle (UAV), focusing on one long-term followed group of 13 male Risso’s dolphins (Grampus griseus) in the Azores, Portugal. We aim to assess the usefulness of a UAV in delivering robust data to evaluate sociality in relation to relative position. Our analysis is based on recordings of synchronous breathing events, which are taken as an indicator of association strength. Twenty-one separate UAV flights were performed during seven surveys in July–August 2017, recording 2,886 breathing events and 571 synchronous dyads. Results showed strong differences in sociality between individuals and identified two strongly associated pairs, one strongly associated trio and six less associated individuals within the group. We subsequently created continuous time series of relative positions by interpolation of the positions recorded with the UAV at breathing events, and applied the Dynamic Time Warping method to assess associations based on relative position. This analysis identified more detailed association patterns than the synchrony analysis, and revealed a correlation between measures of sociality and relative position, at an individual and sub-cluster level, which may indicate dominant relationships. We compared results with those obtained with Photo-ID to assess any observation bias related to using a UAV. We found that 37% more breathing events were recorded with the UAV, and 21% more synchronous dyads detected, compared with Photo-ID, collected over the same observation periods, but, based on synchrony data, both methods yielded very similar results. We conclude that using a UAV for focal group follows of Risso’s dolphins enables a more granular study of association patterns than Photo-ID, by taking into account the relative position of individuals. The correlation found between measures of sociality and relative position holds promise for using UAVs in future studies of dominant relationships in Risso’s dolphins and other cetacean species.
Full-text available
There is increasing evidence that animal personality can affect many aspects of an individual's behaviour, life history and fitness. However, there have been few studies about the link between personality and social organization in the context of wild mammals in their own natural environments. This article reports on ecologically relevant data, linking experimental data from the wild to long-term social association data in a socially and cognitively complex mammal species (bottlenose dolphin, Tursiops truncatus). Here, I used behavioural data to describe personality differences between bottlenose dolphins and social network analysis to assess the relationship between personality and social structure. First, I measured the reaction of photo-identified individuals over time and across contexts as a trade-off between a novelty-seeking behaviour (boldness) and a novelty-averse behaviour (shyness). Second, I applied social network analysis to understand the link between the observed shy–bold continuum and social organization, while controlling for other factors that could contribute to affiliation. This study presents for the first time consistent individual differences in behavioural response to novelty, as a proxy for the shy–bold continuum, in wild bottlenose dolphins. Bold individuals had a central role in the social network with stronger associations than shy individuals, suggesting that bold individuals may play an important role in group cohesion, group stability and the spread of information through the network. Together, these findings provide insights into how a social network is structured by personality in wild bottlenose dolphins, with potential fitness consequences. Furthermore, this study provides additional evidence of the existence of social personalities in nonhuman animals and contributes to the understanding of the role of personality in determining the extent to which mammals associate with others.
Full-text available
Fear of predation can induce profound changes in the behaviour and physiology of prey species even if predator encounters are infrequent. For echolocating toothed whales, the use of sound to forage exposes them to detection by eavesdropping predators, but while some species exploit social defences or produce cryptic acoustic signals, deep-diving beaked whales, well known for mass-strandings induced by navy sonar, seem enigmatically defenceless against their main predator, killer whales. Here we test the hypothesis that the stereotyped group diving and vocal behaviour of beaked whales has benefits for abatement of predation risk and thus could have been driven by fear of predation over evolutionary time. Biologging data from 14 Blainville’s and 12 Cuvier’s beaked whales show that group members have an extreme synchronicity, overlapping vocal foraging time by 98% despite hunting individually, thereby reducing group temporal availability for acoustic detection by killer whales to <25%. Groups also perform a coordinated silent ascent in an unpredictable direction, covering a mean of 1 km horizontal distance from their last vocal position. This tactic sacrifices 35% of foraging time but reduces by an order of magnitude the risk of interception by killer whales. These predator abatement behaviours have likely served beaked whales over millions of years, but may become maladaptive by playing a role in mass strandings induced by man-made predator-like sonar sounds.
Full-text available
Benefits of group life depend in large part on whether animals remain cohesive, which often requires collective decisions about where and when to move. During a group movement, the leader may be considered as the individual occupying the vanguard position of the group progression, when its movement evokes following by other group members. In nondespotic societies, individuals with greater incentives to move frequently are leaders. During 15 months of observations (1,712 contact hours), we investigated two mantled howler monkey (Alouatta palliata) groups at La Flor de Catemaco (Los Tuxtlas, Mexico) to examine whether sex and female reproductive state influenced leadership likelihood in two contexts: movements toward feeding trees; movements associated with loud calls, a group-defense behavior used by males of this genus. Females led and occupied forward positions during group movements toward feeding trees more often than adult males. Adult females led these movements more frequently when they were gestating than when they were lactating or cycling. There were no differences between sexes in the leadership of group movements associated with loud calls. Leadership by gestating females is perhaps the result of their higher nutritional/energetic needs when compared with cycling females, and of their greater mobility when compared with lactating females carrying dependent offspring. Female leadership during movements toward feeding trees may be a mechanism to optimize access to food resources in mantled howler monkeys.
Full-text available
Collective decision-making is important for coordination and synchronization of the activities among group-living animals and the mechanisms guiding such procedure involve a great variety of characteristics of behavior and motivation. This study provides some evidence investigating collective movement initiation in a multi-level social band of the golden snub-nosed monkeys (Rhinopithecus roxellana) located in the Mts. Qinling, China. We collect 1223 datum records relevant to decision initiation from six OMUs. The results indicate that collective movement initiation could be divided into two continual but relatively independent processes: decisions on moving direction and movement implementation. In both processes, adult individuals are more likely to initiate the decision-making, while other adults vote on initiator’s preference, with a threshold, a supporting number required for a success. Thus, voting behavior and quorum fulfillment contribute to a successful decision-making. Adult individuals play important role in making decisions for moving direction and implementation. For a successful collective movement initiation, the individuals being more central in grooming network initiate decisions more frequently than the others, and attract voters more easily. Furthermore, following the initiation, at least four positive voters are required for a direction decision and at least three positive voters are needed for the decision on movement implementation, which could be considered as the threshold of quorum numbers required for a successful decision. This study has provided some very interesting information and scientific evidence in understanding social structure and behaviors of the nonhuman primates with a social structure very similar to humans’. Thus, some results can directly be referred to the comprehension of human social structure and behavior.
Full-text available
Rarely observed in mammals, female dominance is documented in several of Madagascar’s lemurs. Although dominance affects many aspects of primates’ lives, studies have largely focused on dyadic agonistic interactions to characterise relationships. We explored the power structure of three diademed sifaka groups (Propithecus diadema) at Tsinjoarivo during the lean season (July-August, 325 h) using social behaviours, group leadership, displacements and feeding outcomes. Two groups had a hierarchy dominated by the breeding female, while the highest rank was held by the breeding male in the third; in dyadic interactions, breeding females dominated males in all groups. Inconsistencies in hierarchies suggest that groups vary, with rank related to kinship ties of breeders. Aggression and grooming were rare; adult females received aggression at lower frequencies than males. Group movements were led more by females and followed more by males, and female feeding priority was evident in displacements during feeding. However, males and females did not differ in feeding outcomes, as expected (particularly in the lean season) if female dominance (and/or male deference) serves to ensure better access for females. This unexpected pattern (female dominance despite rare aggression, clear female leadership and displacement, yet no observable benefit in grooming or feeding outcomes) defies easy explanation, and reinforces the fact that studies examining female power in lemurs should take a multifaceted approach. Further study is needed to understand this pattern, the physiological and reproductive consequences of female dominance (e.g. detecting subtler variation in food quality or intake rates) and exactly how (and when) the benefits of female dominance are manifested.
Full-text available
Cetaceans are fully aquatic predatory mammals that have successfully colonized virtually all marine habitats. Their adaptation to these habitats, so radically different from those of their terrestrial ancestors, can give us comparative insights into the evolution of female roles and kinship in mammalian societies. We provide a review of the diversity of such roles across the Cetacea, which are unified by some key and apparently invariable life-history features. Mothers are uniparous, while paternal care is completely absent as far as we currently know. Maternal input is extensive, lasting months to many years. Hence, female reproductive rates are low, every cetacean calf is a significant investment, and offspring care is central to female fitness. Here strategies diverge, especially between toothed and baleen whales, in terms of mother–calf association and related social structures, which range from ephemeral grouping patterns to stable, multi-level, societies in which social groups are strongly organized around female kinship. Some species exhibit social and/or spatial philopatry in both sexes, a rare phenomenon in vertebrates. Communal care can be vital, especially among deep-diving species, and can be supported by female kinship. Female-based sociality, in its diverse forms, is therefore a prevailing feature of cetacean societies. Beyond the key role in offspring survival, it provides the substrate for significant vertical and horizontal cultural transmission, as well as the only definitive non-human examples of menopause. This article is part of the theme issue ‘The evolution of female-biased kinship in humans and other mammals’.
Full-text available
Collective movements are essential for maintaining group cohesion. However, group members can have different optimal departure times, depending on individual, social and contextual factors whose relative importance remains poorly known. We, therefore, studied collective departures in four groups of red-fronted lemurs (Eulemur rufifrons) in Kirindy Forest, Madagascar, to investigate the influence of an individual's age, sex, their affiliative relationships and their proximity to other group members at the time of departure on their individual departure decision. We recorded behavioural and spatial data on individual departures during 167 group movements and conducted group scans (181-279 per group) to assess affiliative relationships. All factors influenced individual departures. Both affiliation and proximity determined a mimetic joining process in which dyads with stronger affiliative bonds departed in closer succession, and individuals followed the initiator and predecessors more quickly when they were in closer proximity at departure. While the influence of affiliation is common, the effect of inter-individual distance has rarely been considered in groups with heterogeneous social relationships. Although local rules influenced joining, the overall movement pattern was mainly determined by individual traits: juveniles took protected central positions, while females made up the van and males brought up the rear. Individual needs, expressed in the departure order, to an extent overruled the effect of affiliation. These results highlight the importance of considering individual, social and contextual factors collectively in the study of collective movements.
Male Indo‐pacific bottlenose dolphins in Shark Bay, Western Australia, have converged with humans in the formation of nested male alliances and the use of synchrony in alliance behavior. Further, the strength of association among allied male dolphins varies and the stability of alliances correlates with the rate that males consort with estrus females (and is thus a possible indicator of dominance). To examine the possibility that synchrony reflects alliance association strength and dominance relationships, we analyzed videotapes from focal follows of two groups of males that reflect the range of alliance size and the strength of association between individuals in the population. We examined two variables: leadership during synchronous behaviors, based on which animal in a synchronously surfacing pair surfaced first, and the degree of synchrony, based on temporal differences in synchronous surfacing. We predicted that closer associates would exhibit a greater degree of synchrony and that one dolphin in a dyad would consistently lead. Contrary to our predictions, the degree of synchrony was inversely related to strength of association within alliances. This surprising result suggests that individuals with less secure bonds may strive more to achieve synchrony. We found no evidence of leadership during synchronous surfacing or between synchrony and other behavioral variables. Proximate mechanisms for synchronous behavior, such as entrainment and mutual motor imitation (“the mirror game” paradigm), may inhibit leadership in this context. Our results show that synchrony during surfacing is not a useful behavior to examine for dominance relationships in wild dolphins but it may be a useful tool to examine variation in alliance relationships.