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Although behavior, biology, and ecology of giraffes have been widely studied, little is known about their cognition. Giraffes’ feeding ecology and their fission–fusion social dynamics are comparable with those of chimpanzees (Pan troglodytes), suggesting that they might have complex cognitive abilities. To assess this, we tested 6 captive giraffes on their object permanence, short-term memory, and ability to use acoustic cues to locate food. First, we tested whether giraffes understand that objects continue to exist even when they are out of sight. Giraffes saw one of two opaque containers containing food, then containers were closed, and 2 s later giraffes could choose one. Second, we measured giraffes’ memory repeating the procedure but with a delay of 30 s, 60 s, or 2 min between closing the containers and subjects’ choice. Finally, we investigated whether giraffes could locate food inside one of two identical opaque containers, when the only cue provided was the sound made by food when shaking the baited container, or the lack of sound when shaking the empty container. Our results show that giraffes form mental representations of completely hidden objects, but may not store them for longer than 30 s. Moreover, they rely on stimulus enhancement rather than acoustic cues to locate food, when no visual cues are provided. Finally, we argue that giraffes and other ungulates might be a suitable model to investigate the evolution of complex cognitive abilities from a comparative perspective.
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© 2018, American Psychological Association. This paper is not the copy of record and may
not exactly replicate the final, authoritative version of the article. Please do not copy or cite
without authors' permission. The final article will be available, upon publication, via its DOI:
10.1037/com0000142
Accesing the original paper is strongly recommended, it includes videos of every test
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Object permanence in Giraffa camelopardalis: first steps in
giraffes’ physical cognition
Alvaro L. Caicoya a, Federica Amici b,c, Conrad Ensenyat d and Montserrat Colell a,e
a Department of Clinical Psychology and Psychobiology, Faculty of Psychology, University
of Barcelona, Barcelona, Spain.
b Institute of Biology, Faculty of Life Sciences, University of Leipzig, Leipzig, Germany
c Junior Research Group "Primate Kin Selection", Department of Primatology, Max Planck
Institute for Evolutionary Anthropology, Leipzig, Germany
d Barcelona Zoo, Spain.
e Institute of Neurosciences, University of Barcelona, Barcelona, Spain.
Corresponding author: Álvaro L. Caicoya. alocaico@gmail.com
Acknowledgments:
We thank the staff at the facilities of Barcelona and Leipzig, Oscar Quilez Peña,
Bibiana Martin Prat, Ruben Holland, Rene Forberg, Daniel Volkmann, Kathrin Dorn, Marco
Mehner, Stefan Lohmer, Michael Tempelhof and all the others for endless support and
cooperation. We also thank Fred Bercovitch for his clever commentaries on a previous
version of this manuscript. Last, we would like to thank Maria Luisa Caicoya for helping us
coding all the trials for inter-observer reliability.
This research was supported by a PRIC grant, convocatoria 2016/2017, Fundación
Zoo de Barcelona.
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Abstract
Although behaviour, biology and ecology of giraffes have been widely studied, little
is known about their cognition. Giraffes feeding ecology and their fission-fusion social
dynamics are comparable to those of chimpanzees (Pan troglodytes), suggesting that they
might have complex cognitive abilities. To assess this, we tested 6 captive giraffes on their
object permanence, short-term memory and ability to use acoustic cues to locate food. Firstly,
we tested whether giraffes understand that objects continue to exist even when they are out of
sight. Giraffes saw one of two opaque containers containing food, then containers were
closed, and 2 seconds later giraffes could choose one. Secondly, we measured giraffes’
memory repeating the procedure but with a delay of 30 seconds, 60 seconds or 2 minutes
between closing the containers and subjects’ choice. Finally we investigated whether giraffes
could locate food inside one of two identical opaque containers, when the only cue provided
was the sound made by food when shaking the baited container, or the lack of sound when
shaking the empty container. Our results show that giraffes form mental representations of
completely hidden objects, but may not store them for longer than 30 seconds. Moreover,
they rely on stimulus enhancement rather than acoustic cues to locate food, when no visual
cues are provided. Finally, we argue that giraffes and other ungulates might be a suitable
model to investigate the evolution of complex cognitive abilities from a comparative
perspective.
Key words: Object permanence, short-term memory, acoustic cues, giraffe, cognition,
bayesian statistics.
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Introduction
Giraffes are a neglected species in science, with only 400 scientific papers having
been written about them, as compared to 20,000 papers on white rhinos, for instance
(Dell'Amore, 2016). Besides this, all we know about giraffes is limited to their behaviour,
biology and ecology, while nothing is to our knowledge known about their cognition (Dagg,
2014; Seeber, Ciofolo, & Ganswindt, 2012; Shorrocks, 2016). During the past 15 years, the
number of wild giraffes has plummeted from an estimated 140,000 to around 9,000, and our
limited knowledge about them makes conservation efforts a very difficult task (Muller et al.,
2016).
In the wild, giraffes form fission-fusion groups, with individuals joining subgroups of
different size and composition, which vary from one individual (usually adult bulls) up to
100. Cows usually form small subgroups with calves and other cows, and the probability and
stability of a relationship between two giraffes is determined by kinship and shared space
(Bercovitch & Berry, 2013; Carter, Seddon, Frère, Carter, & Goldizen, 2013; VanderWaal,
Wang, McCowan, Fushing & Isbell, 2014). These fission-fusion social dynamics are thought
to be linked to the evolution of complex cognitive abilities, as for example in chimpanzees
(Pan troglodytes), although subtle differences in fission-fusion dynamics may posit different
cognitive challenges across animal taxa (Aureli et al., 2008).
From an ecological point of view, giraffes have a very diverse diet, eating different
specific leaves and flowers depending on the time of the year (Berry & Bercovitch, 2017).
Indeed, new long-term evidence has shown that giraffes’ diet is much more varied than
previously thought, and their dietary breadth is comparable to that of chimpanzees (Berry &
Bercovitch, 2017). Chimpanzees at Ngogo spend 77% of their feeding time eating 15 species
out of the 102 identified in their diet (ShannonWeiner Diversity Index H´ = 3.282; Watts,
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Potts, Lwanda, & Mitani, 2012), while giraffes from the Luangwa Valley spend a comparable
66% of their feeding time eating 15 out of the 93 plant species in their diet (H´ = 3.699; Berry
& Bercovitch, 2017). Such dietary breadth may also be linked to enhanced cognitive skills,
with dietary complexity being one possible primary driver of cognitive evolution in primates
and other species (see MacLean et al., 2014).
Living in fission-fusion groups and having complex diets make giraffes excellent
candidates for having enhanced cognitive skills. Given our poor knowledge about giraffes’
cognition, a good starting point might be the study of object cognition. Indeed, the ability to
segment the world into discrete objects that exist independently of us through space and time
is one of the most fundamental conceptual structures, and therefore a widely studied area in
comparative psychology (Cacchione & Rakoczy, 2017). A very basic form of object
cognition is object permanence, i.e. the ability to understand that objects continue to exist
even when they are out of sight (Piaget, 1954). Piaget originally designed different object
permanence tasks to assess cognitive development in human infants, dividing them into 6
stages of increasing difficulty. Object permanence develops gradually through these 6 stages
also in a variety of species such as nonhuman great apes (Call, 2001), corvids (Bugnyar,
Stöwe, & Heinrich, 2007) and parrots (Pepperberg, Willner, & Gravitz, 1997). The stage that
an animal is capable of reaching is often used as a measure of the species’ cognitive abilities
as compared to others (e.g. Manger, 2013). Stage 4, for instance, is largely considered the
first true form of object permanence (Cacchione & Rakoczy, 2017). This stage is usually
tested by showing a reward to the subject and then hiding it under one of several identical
opaque containers: if subjects locate the hidden reward at first choice, they are assumed to
have acquired stage 4 of object permanence.
Previous studies have increased memory demands of object permanence tasks by
introducing a delay between the baiting procedure and the moment in which subjects can
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retrieve the food: after the reward has been hidden, the subject waits for a specific period of
time before selecting one of the containers (e.g. Barth & Call, 2006). In this way, memory
demands are increased, and individuals have to remember the food location in the face of
increasing delays. Unsurprisingly, performance declines with increasing delays across several
species (see Cacchione & Rakoczy, 2017). Another modification that has been done to this
paradigm is providing an acoustic cue (e.g. making the baited container produce a noise)
instead of a visual one (e.g. showing the reward being hidden: Call, 2004). In this task, if
subjects understand the causal connection between objects and the noise produced when they
move, they should infer that the noisy container is the one that contains the reward.
Moreover, when the empty container is shaken instead, subjects should use the absence of
noise to infer by exclusion that the unshaken container must be baited. This paradigm has
been already tested with children (e.g. Hill, Collier-Baker, & Suddendorf, 2012), all species
of great apes (Call, 2004), corvids (Shaw, Plotnik, & Clayton, 2013), pigs and boars
(Albiach-Serrano, Bräuer, Cacchione, Zickert, & Amici, 2012), among others. A similar
inference-by-exclusion paradigm (with visual instead of acoustic cues) has also been used
with two relatives of the giraffe, goats and sheep: subjects were shown either an empty or a
full container, and then had to search for food (Nawroth, von Borell, & Langbein, 2014).
Both species correctly solved the usual object permanence test (i.e. when the full container
was shown), but only goats solved it when being provided with mere indirect information and
inference by exclusion was needed (i.e. when the empty container was shown).
To our knowledge, none of these paradigms, nor any other paradigm assessing
cognition, has so far been used to test giraffes. In this study, we therefore aimed to start
exploring giraffes cognition with an object permanence task. This task may be an ideal
experimental tool, testing a basic cognitive skill (which is required for more complex skills to
emerge) and having been widely used in comparative psychology, therefore also allowing
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comparisons across species. In giraffes, object permanence may play an essential role when
dealing with social partners or predators, which may not always be visible but still exist.
However, object permanence may be ecologically less relevant when considering their diet,
as giraffes typically move from tree to tree to eat visible leaves (Leuthold & Leuthold, 1972).
In this respect, testing object permanence in giraffes can be important to understand how
cognitive skills really map the socio- and/or ecological challenges faced by giraffes in their
every-day life and how modular brains are (Amici, Barney, Johnson, Call, & Aureli, 2012).
We conducted 3 different experiments on giraffes. Firstly, we tested stage 4 of object
permanence by visibly hiding food in one of two opaque containers. Secondly, we tested their
short-term memory skills, by increasing the delay between baiting and retrieval up to 2
minutes. Finally, we tested their inferential skills by testing their ability to use the presence or
absence of acoustic cues to locate food. If giraffes’ ecological (i.e. dietary breadth) or social
characteristics (i.e. fission-fusion social dynamics) are linked to their cognitive skills, they
should perform above chance across all experiments, similarly to other species with similar
socio-ecological characteristics that have been shown to master these tasks (e.g. Barth & Call,
2006; Call, 2004).
Method
Ethics statement
The Barcelona Zoo and the Leipzig Zoo controlled and approved all the procedures.
Given that giraffes participated on a completely voluntary basis, and no invasive procedures
were used, no formal approval was required. During the task, moreover, individuals were
never food deprived, and motivation to participate was ensured exclusively by the use of
highly-preferred food (i.e. carrots, carob pellets and apples). Before testing started, we
assessed participants food preferences by presenting them with two food types and making
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them choose one, with each possible comparison being repeated 12 times per individual. The
experiments thus provided a form of enrichment for the subjects and did not present any risks
or adverse effects.
Subjects and materials
We tested 6 giraffes (Giraffa camelopardalis) ranging from 1 to 21 years of age and
housed at the zoos of Barcelona and Leipzig (see Table 1). All study subjects were
consistently fed a diet of fruit and vegetables. None of the subjects had previous experience
with the materials used in our experiments, and none had ever been tested in any cognitive
task. The tests were carried out in the interior facilities, after isolating the participant giraffe
from the group. Subjects kept visual, auditory and potentially tactile contact with the rest of
the group in all cases. Only the experimenter remained in the enclosure during the tests.
For all the experimental conditions we used two identical opaque containers of
approximately 15x15x3cm. Using only two containers allowed us to test naïve subjects with
an easier set-up, as often is done in literature (e.g. Albiach-Serrano et al., 2012; Chiandetti &
Vallortigara, 2011; Nawroth, von Borell, & Langbein, 2015). Depending on the result of
previous individual preference tests, a piece of carrot or apple was used as a reward in case of
a correct choice; in order to fill the container and facilitate visual discrimination, the food
reward was laid on a bed of carobs or pellets, depending on the diet restrictions at the two
facilities. Every trial was recorded from a video-camera fixed one meter behind the
experimenters back. All experimental conditions were administered in a pseudo-randomized
order, except from the habituation phase, which was administered at the beginning to all
subjects. Trials always started when the subject’s head was in front of the experimenter, with
its head approximately between the two containers.
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All giraffes belonged to the subspecies Giraffa camelopardalis rothschildi. All of them were
born in captivity.
Habituation phase
Only one container was used. The experimenter baited the container out of the
subjects view, and then showed the container to the subject. After 5 seconds the
experimenter closed the container and pushed it toward the subject. If the subject touched the
container, the experimenter opened the lid and let the subject eat the food. After 4 successful
retrievals out of 5 consecutive trials, the giraffe started the experimental phase.
Olfactory control condition
We used the same procedure as in the Habituation phase, but two containers were
used. Out of the subject’s view, the experimenter baited one of the two containers and closed
both of them. Then, the experimenter showed both containers to the subject, holding each one
in one hand, approximately at 80 cm from each other and around 50 cm from the subject.
After 5 seconds, the experimenter simultaneously moved both containers toward the subject,
and let the subject choose. The experimenter made this movement with his eyes closed to
avoid providing inadvertent cues to the subject: he could notice the choice of the giraffe
Table 1
Subjects participating in the study.
Name
Sex
Age (years)
Rearing history
Nuru
F
8
Mother
Yalinga
F
13
Mother
Nakuru
M
1
Mother
Max
M
21
Nursery
Andrea
F
9
Mother
Ashanti
F
16
Mother
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because both containers were light enough to be clearly moved by the giraffe during the
election. If the subject touched the correct container, the experimenter opened the lid and let
the subject eat the food, while removing the unchosen container. If the subject touched the
wrong container, the experimenter opened its lid and showed its content to the subject, then
showed the content of the correct container and removed both. In this condition, the subject
had neither visual nor acoustic cues to locate the food, and could only rely on possible
olfactory cues coming from the container containing the reward. Chance performance (50%
of the trials) in this condition therefore indicated that subjects could not rely on olfactory cues
to locate food.
We followed the same procedure as in the Olfactory control condition, but in this case
the subject could see the baiting procedure. In full view of the subject, the experimenter
showed the content of both containers, holding each one in one of his hands as above, and
after 5 seconds he simultaneously closed the lids of both containers, making their content
invisible. After 2 seconds, the experimenter closed his eyes and approached both containers
to the subject, letting her choose (see an example in Video 1).
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Figure 1. (A) The experimenter shows the content of both recipients to one of the subjects.
(B) The subject makes a choice.Object permanence condition
A
B
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Memory condition
We used the same procedure as in the object permanence condition. The only
difference was the time elapsed between closing the lid and letting the subject choose.
Depending on the condition, the time elapse was 30 sec, 60 sec or 120 sec, instead of 2 sec.
The experimenter stared at the ground during this time, observing his watch (see an example
of the 30sec condition in Video 2).
Acoustic cues condition
We followed the same procedure as in the Object permanence condition, but this time
the opaque lids were closed before being presented to the subject, so that no visual cue was
given with regards to the food location. In the Shake full condition, the experimenter held
both containers slightly beyond the subject’s reach, and then shook 3 times the container
containing the reward. In this way, the carob/pellets inside the container made a loud noise,
similar to the sound of a rattle. After 2 seconds, the experimenter simultaneously pushed both
containers toward the subject and let her choose (see an example in Video 3). In the Shake
empty condition the procedure was identical, but this time the experimenter shook the empty
container, which thus made no sound. In this last condition, a correct choice was coded when
the giraffe selected the unshaken container, as this one contained the food reward.
Design
Each subject went first through a habituation phase. After this, each subject was
administered 12 trials for each of the 7 conditions, in a pseudo-randomized order. Within
each condition, the position of the food reward was also pseudo-randomized, being on the
right side in half of the trials. There was always a 2 minute break between trials. Sessions
continued until the subject stopped approaching the experimenter, usually around 30 minutes
after the first trial.
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Data analyses
An external observer coded 15% of all the trials from the video-recordings. This
observer was naïve to the hypotheses: as soon as the subject made a choice, she stopped the
tape and coded before seeing the experimenter’s reaction to the subject’s choice. Inter-
observer reliability was excellent (κ = 1, n = 75).
We used Bayesian statistics to analyse the results, instead of the traditional null-
hypothesis significance testing (NHST) (see NHST analyses in supplementary material 1).
This was due to various reasons (see Kruschke, 2014). Firstly, Bayesian statistics provide
more information about the analysed parameters, as compared to traditional hypothesis tests
(Kruschke, 2013). Secondly, Bayesian statistics require no corrections for multiple
comparisons and thus provide more statistical power, which is an advantage in case of
multiple testing. Moreover, Bayesian analyses use the highest density interval (HDI) instead
of the confidence interval employed for frequentist analysis. In particular, the HDI informs
about the probability that a certain hypothesis is true, given the data, and does not simply
accept or reject the null hypothesis, as NHST instead do. Therefore, the HDI reduces
uncertainty, indicating the most credible values and covering 95% of data distribution.
To assess performance, we used the Bayesian alternative to a one-sample t-test and
assessed whether each condition had its 95% HDI above chance (i.e. 6 out of 12 correct
choices, 50%). Our dependant variable was the percentage of correct responses. A correct
choice was scored if the subject chose the baited container by touching it with her lips or
tongue. In those conditions resulting in a preference for the baited container, we repeated the
analysis including only the first three trials, to assess performance before extensive learning
could take place. If subjects in these conditions had simply learned to associate cups with
food (e.g. the noisy cup and the food in the Acoustic cues condition), their performance
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should drop to chance levels in the first three trials. We applied a t distribution, as this has
fatter tails than the normal distribution and can better accommodate outliers in the model. We
used minimally informative priors as described by Kruschke (2013), i.e. normal priors with
large standard deviation for (µ), broad uniform priors for (σ), and a shifted-exponential prior
for (ν).
Since giraffes moved freely during the tests, we coded their body orientation in order
to know if they used it as an aid to make their choices (e.g. by maintaining their head oriented
toward the baited container throughout the trial). We thus counted the number of trials in
which giraffes maintained their heads oriented towards the same container from the end of
stimuli presentation (i.e. closing the lids in the visual conditions, or stopping containers
movements in acoustic conditions) until the choice was made.
Results
In the Olfactory control condition (95% HDI: .32 - .57) giraffes performed at chance
level (50% correct choices), showing that they could not rely on olfactory cues to locate
hidden food.
Subjects performed above chance level in the Object permanence condition (95%
HDI: .67 - .75) and in the 30 sec Memory condition (95% HDI: .55 - .72). Equivalent results
were obtained if only including the three first trials of these two conditions (95% HDI > .5).
In the 60 sec Memory condition (95% HDI: .43 - .71) and in the 120 sec Memory condition
(95% HDI: .4 - .82) giraffes performed at chance levels (Figure 2).
In the Shake full condition (95% HDI: .68 - .92) subjects performed above chance
level but in the Shake empty condition giraffes performed below chance (95% HDI: .34 -
.37). See supplementary material for the complete data (See Figure 2).
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Figure 2. Mean ± SEM of correct choices in the forced-choice task. Values above 0.5
indicate a preference for the baited container. A 95% HDI above chance level (50%) is
indicated by an asterisk.
Figure 3. In gray, the percentage of trials in which giraffes maintained their heads oriented
toward the correct (Correct) or the incorrect (Errors) container, from the end of the stimuli
presentation, until their choice. In black, the percentage of trials in which giraffes did not
maintain head orientation toward the container throughout the trial.
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The percentage of trials in which giraffes maintained the head orientation toward the same
container throughout the trial was relatively high in the Object permanence (43%), Shake full
(58%) and Shake empty (76%) conditions, but much lower in the 30 sec (7%), 60 sec (1%)nd
120 sec (0%) Memory conditions (Figure 3).
Discussion
Chance performance in the Olfactory condition confirmed that giraffes in the other
conditions were not simply relying on smell to locate hidden food. Giraffes were able to
locate food both in the Object permanence condition (2 sec delay) and in the 30 sec Memory
condition, but not when delays were increased in the 60 sec and 120 sec Memory conditions,
suggesting a memory or an attention limit. Giraffes could further use the presence of acoustic
cues to locate food in the Shake full condition, but not the absence of acoustic cues to infer
food location in the Shake empty condition.
Chance performance in the olfactory condition demonstrates that subjects failed to
select the container containing food in the absence of visual and acoustic information.
Therefore, our results in the other conditions cannot be attributed to giraffes relying on
inadvertent cues provided by the experimenter or by food smell to solve the task. Moreover,
they are also not the result of learning, as giraffes either correctly solved the task from the
very first trials (Object permanence, 30 sec Memory and Shake full conditions), and correctly
performed also in the following trials, or failed to master a condition, even after being
administered multiple trials (60 sec and 120 sec Memory, and Shake empty conditions).
Giraffes reached stage 4 of object permanence, as they consistently performed above
chance level in our first condition. Understanding that objects exist even if being completely
hidden may be the result of different socio-ecological pressures. In giraffes, for example,
object permanence may be useful to track conspecifics something important when living in
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groups (Zucca, Milos, & Vallortigara, 2007). However, object permanence is also a
widespread ability in vertebrates (Cacchione & Rakoczy, 2017). Therefore, it is likely that
this ability is shared with other species as a result of homology, and does not reflect specific
selective pressures experienced since giraffes diverged from other taxa. Future studies should
address whether giraffes also show further stages of object permanence. Goats, for instance,
have been tested with a similar experiment, showing stage 6 of object permanence (i.e. being
able to successfully track invisible displacements; Nawroth et al., 2015). Given the socio-
ecological challenges faced by giraffes, it would come as no surprise if they could also reach
stage 6.
The Memory conditions tested whether giraffes can use their short-term memory
(Carruthers, 2013) to remember the location of hidden food. Their success in the 30 sec
condition indicates that giraffes can store information for up to 30 seconds later. Their failure
in the 60 sec and 120 sec conditions, however, indicates that their short-term memory might
not last long when compared with other mammals (Lind, Enquist, & Ghirlanda, 2015). Dogs,
for example, can store information for at least 240 seconds (Fiset, Beaulieu, & Landry, 2003),
and cats for at least 60 seconds (Fiset & Doré, 2006). Even in the 30 sec condition, their
accuracy (i.e. 72%) is far from the one shown by chimpanzees (i.e. 86%) with the same delay
and three containers (Barth & Call, 2006). From an evolutionary perspective, however, this
limit in short-term memory is surprising, as giraffes’ fission-fusion social system would
especially benefit from the ability to remember the position of others through time (see Aureli
et al., 2008). Moreover, it is possible that giraffes may show a much better performance when
tested in a long-term memory task. For instance, fights between bulls at first encounters are
common, but these fights create dominance hierarchies and the same bulls rarely fight again
(Shorrocks, 2016; but see Bercovitch & Berry, 2015). Given that adult bulls seldom
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encounter each other, this ability to recognize other individuals and remember the outcome of
previous fights may indicate a good long-term memory.
Giraffes used their body orientation as a cue to choose in 52% of their correct trials in
the Object permanence condition, but only in 9% of their correct trials in the 30 sec condition
(see Figure 3). This indicates that, although body orientation may be used as a cue in these
tasks, it is not essential for giraffes to succeed. Also note that the most successful subject,
Ashanti, barely used body orientation as a cue to solve Object permanence and Memory trials
(only in 1 out of 48 trials), confirming that relying on body orientation is no key to success.
In the Acoustic cues condition we tested whether giraffes were able to make
inferences about food position by relying on acoustic cues. Although they performed very
well in the Shake full condition, performance in the Shake empty condition suggests that
giraffes relied on stimulus enhancement (i.e. go toward the container being shaken) rather
than acoustic cues to make their choices, and were not able to infer by exclusion the location
of food. In these conditions, giraffes more heavily relied on body orientation to make their
choice, keeping their head oriented toward the shaken container in 90% of the wrong Shake
empty trials (Figure 3). This may indicate that their attention got trapped by the movement of
the container. However, it is worth noting that this is an especially challenging test. For
instance, not a single chimpanzee out of a sample of 12 performed significantly above chance
levels when an empty container was shaken in an analogous experiment (Call, 2004). Only
with larger sample sizes (e.g. 30 individuals) do primates start to achieve significant results in
these tasks (Call, 2004). Similar patterns have been found in other primate species, being
unusual to find individual performances above chance levels (Maille & Roeder, 2012; Marsh,
Vining, Levendoski, & Judge, 2015; Sabbatini & Visalberghi, 2008). One of the possible
explanations for our outcome is that giraffes have cognitive restraints: although they could
use acoustic cues to locate food when the full container was shaken, inference by exclusion
Giraffes physical cognition
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was cognitively too demanding to allow them success in the Shake empty condition. In
contrast to apes, however, giraffes did not simply select the baited container at chance levels,
in the Shake empty condition, but went for the empty shaken container significantly more
than chance, showing evidence of stimulus enhancement (rather than simply lack of inference
by exclusion). It is therefore likely that, even in the Shake full condition, subjects simply
went for the baited container because it was shaken, and not because it made noise. This
would also be in line with the leaf-based diet of wild giraffes: as leaves produce no sound
when shaken, the ability to associate sound with food may have not been especially selected
for.
Using stimulus enhancement to locate food, of course, need not be the result of
evolutionary pressures, but may depend on our giraffes’ captive condition. Being captive
animals, they could have learned throughout their lives to associate food to human cues (e.g.
shaking), rather/more than to physical cues (e.g. acoustic cues). Regarding this last
explanation, it is usually thought that domesticated species are better able to understand
human communicative cues (e.g. Kaminski, Riedel, Call, & Tomasello, 2005). Our results,
however, would rather suggest that developmental experience may easily allow also wild
animals to rely on human cues to locate food. Indeed, stimulus enhancement is traditionally
considered an early indicator of social learning (Spence, 1937; Thorpe, 1956). Further
experiments are needed to test these different possibilities, by for example testing giraffes’
ability to use human cues, testing their abilities to make inferences by exclusion in the visual
rather than acoustic modality, or providing them with acoustic cues while separately
controlling for stimulus enhancement.
Overall, our results indicate that giraffes can successfully form mental representations
of objects and store them in memory for short periods of time, and likely rely on stimulus
enhancement to locate food, when only acoustic cues are provided. Our results are in line
Giraffes physical cognition
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with recent, perhaps unexpected findings of complex cognitive capacities in other ungulates
(e.g. Briefer, Haque, Baciadonna, & McElligott, 2014; Nawroth et al., 2014; Nawroth et al.,
2015; Marino & Allen, 2017), and converge in suggesting that ungulates might have better
cognitive skills than previously thought. Importantly, our results also show that giraffes are
attentive and motivated enough to become valuable subjects in future cognitive tests. Given
the variety of socio-ecological characteristics across ungulate taxa (see Shultz & Dunbar,
2006), this opens up to the possibility of comparing cognitive performance across ungulate
species, to test evolutionary hypotheses about the emergence of complex cognitive abilities.
Recently, evolutionary hypotheses have been mainly contrasted by comparing performance
across primates and corvids: extending this approach to other taxa may not only provide an
easier alternative, but also allow us to better understand the limits of evolutionary theories
that have so far only been tested across few species. Such investigations may help to
reconstruct the evolution of cognitive skills and to gain a real comprehensive view of their
socio-ecological foundations.
Giraffes physical cognition
21
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... Ungulates are one of many neglected taxa in comparative cognition, although they are an ideal model to test cognitive skills from a comparative perspective, as demonstrated by several recent studies [22][23][24][25][26][27][28][29][30][31]. Although most of these studies have focused on domesticated ungulate species (but see [27,32]), ungulates also include many non-domesticated species with an impressive variety of socio-ecological characteristics [33], allowing the reliable contrast of different evolutionary hypotheses. ...
... Ungulates are one of many neglected taxa in comparative cognition, although they are an ideal model to test cognitive skills from a comparative perspective, as demonstrated by several recent studies [22][23][24][25][26][27][28][29][30][31]. Although most of these studies have focused on domesticated ungulate species (but see [27,32]), ungulates also include many non-domesticated species with an impressive variety of socio-ecological characteristics [33], allowing the reliable contrast of different evolutionary hypotheses. Moreover, there are very few studies that have explored the link between cognition and socio-ecological characteristics in ungulates, and all have used neuroanatomical measures as cognitive proxies [33][34][35]. ...
... Although high levels of fission-fusion dynamics have been observed in another African subspecies (Syncerus caffer caffer), forest buffalo groups are rather cohesive [50], living in small groups of around 15 individuals with stable group size and composition [51,52]. Moreover, we compared the performance of these two species to giraffes (Giraffa camelopardalis), which we had previously tested with the same experimental protocol (see below [27]). Giraffes are browsers with a remarkable dietary breadth [53] that live in open habitats, in fissionfusion societies [27]. ...
Article
Full-text available
Background Comparative cognition has historically focused on a few taxa such as primates, birds or rodents. However, a broader perspective is essential to understand how different selective pressures affect cognition in different taxa, as more recently shown in several studies. Here we present the same battery of cognitive tasks to two understudied ungulate species with different socio-ecological characteristics, European bison ( Bison bonasus ) and forest buffalos ( Syncerus caffer nanus ), and we compare their performance to previous findings in giraffes ( Giraffa camelopardalis ). We presented subjects with an Object permanence task, Memory tasks with 30 and 60 s delays, two inference tasks based on acoustic cues (i.e. Acoustic inference tasks) and a control task to check for the use of olfactory cues (i.e. Olfactory task). Results Overall, giraffes outperformed bison and buffalos, and bison outperformed buffalos (that performed at chance level). All species performed better in the Object permanence task than in the Memory tasks and one of the Acoustic inference tasks (which they likely solved by relying on stimulus enhancement). Giraffes performed better than buffalos in the Shake full Acoustic inference task, but worse than bison and buffalos in the Shake empty Acoustic inference task. Conclusions In sum, our results are in line with the hypothesis that specific socio-ecological characteristics played a crucial role in the evolution of cognition, and that higher fission-fusion levels and larger dietary breadth are linked to higher cognitive skills. This study shows that ungulates may be an excellent model to test evolutionary hypotheses on the emergence of cognition.
... Clearly, ungulates are thus a promising taxa to test how cognitive skills are distributed. Nonetheless, very few studies have so far tested ungulate cognition, for spatial cognition (Osthaus et al. 2013;Abramson et al. 2018), object permanence (Nawroth et al. 2015a;Caicoya et al. 2019), categorization skills (Meyer et al. 2012), ability to use human cues (Nawroth et al. 2015b(Nawroth et al. , 2016) and a few other capacities (Nawroth et al. 2014;Knolle et al. 2017;Pitcher et al. 2017). The field of quantity discrimination is no exception, with three times more studies on primates than on all other mammals altogether (Agrillo and Bisazza 2018). ...
... We tested two male and three female giraffes (Giraffa camelopardalis) ranging from 1 to 21 years of age, housed at the zoos of Barcelona and Leipzig. All study participants were fed a regular diet of fruit and vegetables, and had limited experience with experimental tasks (see Caicoya et al. 2019). Participants were never food or water deprived during this study, and participation was on a completely voluntary basis. ...
... This study was the first one we are aware of to assess quantity discrimination in a non-domesticated ungulate species, and one of the few studies in mammals with low encephalization quotient. Giraffes performed well in most conditions, confirming them as a promising model to study animal cognition (see, e.g., Caicoya et al. 2019, finding evidence of object permanence, and short term memory in this species). However, our study had a very small sample size. ...
Article
Full-text available
Many species, including humans, rely on an ability to differentiate between quantities to make decisions about social relationships, territories, and food. This study is the first to investigate whether giraffes (Giraffa camelopardalis) are able to select the larger of two sets of quantities in different conditions, and how size and density affect these decisions. In Task 1, we presented captive giraffes with two sets containing a different quantity of identical foods items. In Tasks 2 and 3, we also modified the size and density of the food reward distribution. The results showed that giraffes (i) can successfully make quantity judgments following Weber’s law, (ii) can reliably rely on size to maximize their food income, and (iii) are more successful when comparing sparser than denser distributions. More studies on different taxa are needed to understand whether specific selective pressures have favored the evolution of these skills in certain taxa.
... None of the study subjects had ever been tested in a neophobia test before, and none had, to the best of our knowledge, come in contact with objects with the same shape and color as the ones used in this study, although all species occasionally participated in enrichment activities. None of the study subjects had ever participated in an experimental task, except for 3 of the 6 giraffes, which had participated in (i) a task on physical cognition in which they had been exposed to two small plastic containers (~ 15 × 15 × 3 cm) that could contain food (Caicoya et al. 2019), (ii) a quantity discrimination task in which they had been tested with two white trays containing food , and (iii) an inhibition task in which they Gray and Simpson 1982;3 Elmi et al. 1992, Am Abbas et al. 19954 Gauthier-Pilters and Dagg 1981;5 Berry and Bercovitch 2017;6 Muller et al. 2018;7 González-Pech et al. 2015, Mellado 20168 Nowak and Paradiso 1983;9 Puig et al. 2001, Baldi et al. 200410 Bank et al. 2002, Marino andBaldi 2008;11 Posse and Livraghi 1997;12 Nowak and Walker 1999;13 Gilbert and Woodfine 2004;14 Newby 1984;15 Slivinska and Kopij 2011;16 Grum-Grzhimailo 1982;17 Gebert and Verheyden-Tixier 2001;18 Gibson andGuinness 1980, Clutton-Brock et al. 1982;19 Fox and Streveler 1986;20 2-60 20,21 10 Yes had been exposed to a plastic cylinder with food (ALC et al., unpublished data). All groups included males and females of different age and ranks (see Online Resource, Table S1) and differed in their socio-ecological characteristics, including dietary breadth, social group size, and domestication (see Table 1). ...
Article
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Neophobia (the fearful reaction to novel stimuli or situations) has a crucial effect on individual fitness and can vary within and across species. However, the factors predicting this variation are still unclear. In this study, we assessed whether individual characteristics (rank, social integration, sex) and species socio-ecological characteristics (dietary breadth, group size, domestication) predicted variation in neophobia. For this purpose, we conducted behavioral observations and experimental tests on 78 captive individuals belonging to 10 different ungulate species—an ideal taxon to study inter-specific variation in neophobia given their variety in socio-ecological characteristics. Individuals were tested in their social groups by providing them with familiar food, half of which had been positioned close to a novel object. We monitored the individual latency to approach and eat food and the proportion of time spent in its proximity. Using a phylogenetic approach and social network analyses, we showed that across ungulate species neophobia was higher in socially more integrated individuals, as compared to less integrated ones. In contrast, rank and sex did not predict inter-individual differences in neophobia. Moreover, species differed in their levels of neophobia, with Barbary sheep being on average less neophobic than all the other study species. As group size in Barbary sheep was larger than in all the other study species, these results support the hypothesis that larger group size predicts lower levels of neophobia, and confirm ungulates as a highly promising taxon to study animal behavior and cognition with a comparative perspective. Significance statement In several species, individuals may respond fearfully to novel stimuli, therefore reducing the risks they may face. However, it is yet unclear if certain individuals or species respond more fearfully to novelty. Here, we provided food to 78 individual ungulates with different characteristics (e.g., sex, rank, social integration, group size, domestication, dietary breadth) in different controlled conditions (e.g., when food was close to novel or to familiar objects). Across species, we found that socially integrated individuals responded more fearfully in all species. Moreover, being in larger groups decreased the probability of fearfully responding to novelty.
... Our study should clearly be considered as a first preliminary step in the investigation of problem solving in non-domesticated ungulate species. Overall, it confirms ungulates as a promising model to study innovation and, more generally, cognition [28,30,[59][60][61][62]. Despite their relatively small brain size [50,51], bison showed some ability to solve novel problems, although their exact understanding of the functional aspects of the tasks is unclear. ...
Article
Full-text available
The ability to solve novel problems is crucial for individual fitness. However, studies on problem solving are usually done on few taxa, with species with low encephalization quotient being rarely tested. Here, we aimed to study problem solving in a non-domesticated ungulate species, European bison, with two experimental tasks. In the first task, five individuals were presented with a hanging barrel filled with food, which could either be directly accessed (control condition) or which could only be reached by pushing a tree stump in the enclosure below it and stepping on it (experimental condition). In the second task, five individuals were repeatedly fed by an experimenter using a novel bucket to retrieve food from a bag. Then, three identical buckets were placed in the enclosure, while the experimenter waited outside with the bag without feeding the bison, either with a bucket (control condition) or without it (experimental condition). In the first task, no bison moved the stump behind the barrel and/or stepped on it to reach the food. In the second task, two individuals solved the task by pushing the bucket within the experimenter's reach, twice in the experimental and twice in the control condition. We suggest that bison showed a limited ability to solve novel problems, and discuss the implications for their understanding of the functional aspects of the tasks.
Thesis
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In this thesis I explore the extent to which researchers of animal cognition should be concerned about the reliability of its scientific results and the presence of theoretical biases across research programmes. To do so I apply and develop arguments borne in human psychology’s “replication crisis” to animal cognition research and assess a range of secondary data analysis methods to detect bias across heterogeneous research programmes. After introducing these topics in Chapter 1, Chapter 2 makes the argument that areas of animal cognition research likely contain many findings that will struggle to replicate in direct replication studies. In Chapter 3, I combine two definitions of replication to outline the relationship between replication and theory testing, generalisability, representative sampling, and between-group comparisons in animal cognition. Chapter 4 then explores deeper issue in animal cognition research, examining how the academic systems that might select for research with low replicability might also select for theoretical bias across the research process. I use this argument to suggest that much of the vociferous methodological criticism in animal cognition research will be ineffective without considering how the academic incentive structure shapes animal cognition research. Chapter 5 then beings my attempt to develop methods to detect bias and critically and quantitatively synthesise evidence in animal cognition research. In Chapter 5, I led a team examining publication bias and the robustness of statistical inference in studies of animal physical cognition. Chapter 6 was a systematic review and a quantitative risk-of-bias assessment of the entire corvid social cognition literature. And in Chapter 7, I led a team assessing how researchers in animal cognition report and interpret non-significant statistical results, as well as the p-value distributions of non-significant results across a manually extracted dataset and an automatically extracted dataset from the animal cognition literature. Chapter 8 then reflects on the difficulties of synthesising evidence and detecting bias in animal cognition research. In Chapter 9, I present survey data of over 200 animal cognition researchers who I questioned on the topics of this thesis. Finally, Chapter 10 summarises the findings of this thesis, and discusses potential next steps for research in animal cognition.
Article
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Article
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Scientific disciplines face concerns about replicability and statistical inference, and these concerns are also relevant in animal cognition research. This paper presents a first attempt to assess how researchers make and publish claims about animal physical cognition, and the statistical inferences they use to support them. We surveyed 116 published experiments from 63 papers on physical cognition, covering 43 different species. The most common tasks in our sample were trap-tube tasks (14 papers), other tool use tasks (13 papers), means-end understanding and string-pulling tasks (11 papers), object choice and object permanence tasks (9 papers) and access tasks (5 papers). This sample is not representative of the full scope of physical cognition research; however, it does provide data on the types of statistical design and publication decisions researchers have adopted. Across the 116 experiments, the median sample size was 7. Depending on the definitions we used, we estimated that between 44% and 59% of our sample of papers made positive claims about animals’ physical cognitive abilities, between 24% and 46% made inconclusive claims, and between 10% and 17% made negative claims. Several failures of animals to pass physical cognition tasks were reported. Although our measures had low inter-observer reliability, these findings show that negative results can and have been published in the field. However, publication bias is still present, and consistent with this, we observed a drop in the frequency of p-values above .05. This suggests that some non-significant results have not been published. More promisingly, we found that researchers are likely making many correct statistical inferences at the individual-level. The strength of evidence of statistical effects at the group-level was weaker, and its p-value distribution was consistent with some effect sizes being overestimated. Studies such as ours can form part of a wider investigation into statistical reliability in comparative cognition. However, future work should focus on developing the validity and reliability of the measurements they use, and we offer some starting points.
Technical Report
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http://www.iucnredlist.org/details/full/9194/0 Giraffe (Giraffa cameloprdalis) is assessed as Vulnerable under criterion A2 due to an observed, past (and ongoing) population decline of 36-40% over three generations (30 years, 1985-2015). The factors causing this decline (levels of exploitation and decline in area of occupancy and habitat quality) have not ceased and may not be reversible throughout the species’ range. The best available estimates indicate a total population in 1985 of 151,702-163,452 Giraffes (106,191-114,416 mature individuals), and in 2015 a total population of 97,562 Giraffes (68,293 mature individuals). Historically the species has been overlooked in terms of research and conservation, but in the past five years, considerable progress has been made in compiling and producing a species-wide assessment of population size and distribution by the members of the IUCN SSC Giraffe and Okapi Specialist Group. Some Giraffe populations are stable or increasing, while others are declining, and each population is subject to pressure by threats specific to their local country or region. The populations of Giraffes are scattered and fragmented with different growth trajectories and threats, but the species trend reveals an overall large decline in numbers across their range in Africa.
Book
With its iconic appearance and historic popular appeal, the giraffe is the world's tallest living terrestrial animal and the largest ruminant. Recent years have seen much-needed new research undertaken to improve our understanding of this unique animal. Drawing together the latest research into one resource, this is a detailed exploration of current knowledge on the biology, behaviour and conservation needs of giraffe. Dagg highlights striking new data, covering topics such as species classification, the role of infrasound in communication, biological responses to external temperature changes and motherly behaviour and grief. The book discusses research into behaviour alongside practical information on captive giraffe, including diet, stereotypical behaviour, ailments and parasites, covering both problems and potential solutions associated with zoo giraffe. With giraffe becoming endangered species in Africa, the book ultimately focuses on efforts to halt population decline and the outlook for conservation measures.
Article
en Obtaining longitudinal data about the feeding ecology of long‐lived iteroparous mammals is rare, but enhances our understanding of how the environment influences niche breadth and dietary diversity within a species. We analysed forty years of feeding records obtained from a population of Thornicroft's giraffes (Giraffa camelopardalis thornicrofti) living in the Luangwa Valley, Zambia. Giraffes are browsers that have been reported to feed primarily upon Acacia leaves, but their feeding ecology in some locations conflict with this interpretation. Giraffes in the Luangwa Valley fed on 93 identified plant species, but only a few contributed to the bulk of the diet. Niche breadth was quite large (Shannon‐Weiner Diversity Index H′ = 3.699) and about 13% more diverse during the dry, than wet, season. Key species eaten during the dry season were very consistent across decades, with Kigelia africana and Capparis tomentosa prominent at this time. The evolutionary ecology of giraffes has probably benefitted from a foraging strategy that includes a variable and high‐quality diet during the hot, dry season, when feeding pressures are greatest. Giraffe feeding ecology has evolved in conjunction with their physiology, anatomy and morphology, resulting in an animal that is well adapted for survival in an arid environment. Résumé fr Il est rare d'obtenir des données sur l'écologie alimentaire de mammifères itéropares qui vivent longtemps, mais cela aide à mieux comprendre comment l'environnement influence la taille de la niche et la diversité de l'alimentation au sein d'une même espèce. Nous avons analysé 40 ans de notes sur l'alimentation d'une population de girafes de Thornicroft (Giraffa camelopardalis thornicrofti) vivant dans la vallée de Luangwa, en Zambie. Les girafes sont des brouteurs qui, dit‐on, se nourrissent d'abord de feuilles d'acacia, mais à certains endroits, leur écologie alimentaire ne correspond pas à cette assertion. Les girafes de la vallée de Luangwa se nourrissaient de 93 plantes identifiées, mais l'essentiel du régime ne se composait que de quelques‐unes. La taille de la niche était assez grande (Index de diversité de Shannon‐Weiner H′ = 3.699) et elle était environ 13% plus variée pendant la saison sèche que pendant la saison des pluies. Les espèces clés consommées pendant la saison sèche sont restées très constantes au cours des décennies, Kigelia africana et Capparis tomentosa étant les principales. L'écologie évolutive des girafes a probablement bénéficié d'une stratégie alimentaire qui inclut un régime variable et de grande qualité pendant la saison chaude et sèche, quand la pression alimentaire est la plus forte. L'écologie alimentaire des girafes a évolué en même temps que leur physiologie, leur anatomie et leur morphologie, ce qui donne un animal bien adapté pour la survie dans un environnement aride.
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Previous research has suggested that several primate species may be capable of reasoning by exclusion based on the finding that they can locate a hidden object when given information about where the object is not. The present research replicated and extended the literature by testing 2 Old World monkey species, lion-tailed macaques (Macaca silenus) and a hamadryas baboon (Papio hamadryas), and 2 New World species, capuchin monkeys (Sapajus apella) and squirrel monkeys (Saimiri sciureus). The New World monkeys were tested on the traditional 2-way object choice task, and all 4 species were also tested on a more complex 3-way object choice task. In addition, the squirrel monkeys were tested on a 2-way object choice task with auditory information. The results showed that, whereas the Old World species were able to infer by exclusion on the 3-object task, some of the capuchin monkeys had difficulty on each of the 2- and 3-cup tasks. All but 1 of the squirrel monkeys failed to infer successfully, and their strategies appeared to differ between the visual and auditory versions of the task. Taken together, this research suggests that the ability to succeed on this inference task may be present throughout Old World monkey species, but is fragile in the New World species tested thus far. (PsycINFO Database Record (c) 2015 APA, all rights reserved).
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