CardiovascularOxford Team Discovers Crows Can Use Complex Sequences Of Tools To Reach A Reward
New experiments by scientists at the University of Oxford revealed that
New Caledonian crows can spontaneously use up to three tools in the
correct
sequence to achieve a goal, something never before observed in non-human
animals without explicit training. While "sequential tool use" is
routinely interpreted as evidence for advanced cognitive abilities, the
researchers decided to examine these claims in more detail, teasing apart
what
the crows really understood about the tasks and their own actions with
tools. This careful approach provided not only novel insights into the
cognitive abilities of New Caledonian crows, but it also highlighted the
need for more comprehensive analyses of seemingly sophisticated animal
behaviour. A report of the research appears August 5 in the open-access,
peer-reviewed journal PLoS ONE.
New Caledonian crows are renowned for their tool-using abilities. In the
wild, they use a range of tool types for extracting invertebrate prey from
holes and crevices, and in captivity, they have been shown to make, or
select, tools of appropriate dimensions to retrieve food rewards in
various
experimental contexts. In previous experiments, the Oxford team reported
that a crow (named "Betty"), was capable of spontaneously inventing new
tool designs, either bending strips of metal into hooks or unbending them
to make them reach further, according to what was required by the tasks.
In
all these cases, however, objects were used to act on pieces of food.
Using tools to act on non-food objects - for example, to make or retrieve
other tools - is considered to be a hallmark of human intelligence, and may
have been a crucial step in our evolution. One form of this behaviour,
"sequential tool use," has been observed in a number of non-human
primates,
and has recently been reported for New Caledonian crows by a research team
from Auckland University, New Zealand.
While sequential tool use has often been interpreted as evidence for
advanced cognitive abilities, such as planning and analogical reasoning,
the
behaviour itself can be underpinned by a range of different cognitive
mechanisms, but this had never been examined explicitly. In their new
study, the
Oxford scientists tested seven captive New Caledonian crows on a range of
randomly intermixed tasks, requiring the use of up to three different
tools
in a sequence to retrieve food. Their study incorporated several novel
features, including a suite of critical control conditions to test whether
tool
retrieval by crows was indeed goal-directed, and a manipulation of the
subjects" pre-testing experience to examine the determinants of successful
performance.
Five subjects successfully used tools in a sequence (four from their very
first trial), and four subjects repeatedly solved the most demanding
three-tool condition. In this, food was placed at a depth so that it was
only reachable with one particular tool, but getting that tool required
the
use of two others. The crows had to use a short, available tool to drag in
a longer, otherwise out-of-reach tool, and then use that longer tool to
retrieve the correct, longest one. They could then use the longest tool to
reach the for the food morsel.
Pre-training on each element in the sequence was not required for
successful sequential tool use - an explanation that could not be ruled
out in
earlier studies on primates and crows. Painstaking analysis of tool
choices, tool swapping and improvement over time allowed the team to
conclude that
successful subjects did not probe for tools at random: for example, when
birds swapped tools, it was usually to get a longer one. At the same time,
however, they could find no firm evidence to support previous claims that
sequential tool use demonstrates analogical reasoning or human-like
planning.
While the ability of crows to use three tools in sequence reveals a
competence beyond that observed in any other non-human species, including
non-human primates, this study also emphasises the importance of parsimony
in comparative cognitive science. Seemingly intelligent behaviour can be
achieved without the involvement of high-level mental faculties, and
detailed analyses are necessary before accepting claims for complex
cognitive
abilities.
Further information on this research, including photos and additional
movie clips of the crows using and making tools can be found at:
http://www.NewCaledonianCrow.com
Funding:
This work was funded by a BBSRC studentship (to JHW), a BBSRC
grant (BB/C517392/1 to AK), a Brasenose College Junior Research Fellowship
(to
AASW), and a Rhodes scholarship and Linacre College Junior Research
Fellowship (both to CR). We received money from the Cogito Foundation
(grant to
AK) and the University of Oxford (to CR) during the final stages of
manuscript preparation. The funders had no role in study design, data
collection
and analysis, decision to publish, or preparation of the manuscript.
Competing interests:
The authors have declared that no competing interests
exist.
Citation:
Wimpenny JH, Weir AAS, Clayton L, Rutz C, Kacelnik A (2009)
"Cognitive Processes Associated with Sequential Tool Use in New Caledonian
Crows."
PLoS ONE 4(8): e6471.. doi:10.1371/journal.pone.0006471
PLoS ONE