Crafty crows know what it takes to make a good tool

December 07, 2017

Biologists at the University of St Andrews have discovered how New Caledonian crows make one of their most sophisticated tool designs - sticks with a neatly-shaped hooked tip.

New Caledonian crows are the only species besides humans known to manufacture hooked tools in the wild. Birds produce these remarkable tools from the side branches of certain plants, carefully 'crafting' a crochet-like hook that can be used for snagging insect prey.

The study, published in Current Biology today (7 December), reveals how crows manage to fashion particularly efficient tools, with well-defined 'deep' hooks.

The hook is widely regarded as one of humankind's most important innovations, with skilful reshaping, a useless piece of raw material is transformed into a powerful tool. While our ancestors started making stone tools over 3 million years ago, hooks are a surprisingly recent advance - the oldest known fish hooks are just 23,000 years old.

Project leader Professor Christian Rutz, from the School of Biology, has conducted field research on New Caledonian crows for over a decade. His team recently noticed that crows' hooked tools vary considerably in size and shape. While some tools only exhibit a small extension at the tip, others have immaculate hooks.

Professor Rutz explains: "We suspected that tools with pronounced hooks are more efficient, and were able to confirm this in controlled experiments with wild-caught crows. The deeper the hook, the faster birds winkled bait from holes in wooden logs."

This finding raised the intriguing question of what it takes to make such well-formed hooks. The researchers started planning their study by imagining how humans would approach a comparable task. "When a craftsperson carves a tool from a piece of wood, two things ensure a quality product: good raw materials and skill," Professor Rutz said.

Researchers found that the same, apparently, applies to New Caledonian crows. The researchers discovered that the depth of the hook was influenced by both the properties of the plant material, and the technique crows used for detaching branches. When birds made controlled cuts with their sharp bills, the resulting hooks were significantly deeper than when they used a 'sloppier' alternative method of simply pulling off branches. Careful cutting may leave more wooden material at the tip of the stick from which the hook can subsequently be 'sculpted'.

Surprisingly, adult crows, which are expected to have considerable tool-making experience, did not produce the deepest hooks and regularly employed the 'quick-and-dirty' manufacture technique. Professor Rutz notes that making very deep hooks may not be the best strategy in the wild: "It probably takes more time and effort to make such tools, and experienced birds may try to avoid these costs. It is also possible that deep hooks break more easily when inserted into narrow holes and crevices."

Professor Christophe Boesch, a world-leading chimpanzee expert and Director of the Max Planck Institute of Evolutionary Anthropology in Leipzig, Germany, comments: "We have recently discovered that chimpanzees routinely use naturally-hooked stems to fish for algae, but they don't actively craft these hooks. The crows can reshape plant material with their pointed bills, which act like 'precision pliers', but this would be very difficult for chimpanzees with their large fingers."

The present study is the first to examine in a non-human animal what factors determine the morphology of crafted tools, and as a consequence, their foraging efficiency. Palaeo-anthropologists try to understand how our ancestors produced relatively complex tool shapes from basic raw materials, such as wood, bone or seashell, but they face the challenge that the manufacture process cannot be directly observed.

The New Caledonian crow, with its remarkable ability to fashion hooked tools from plant stems, provides a fascinating window into humans' evolutionary past.
-end-
NOTES TO NEWS EDITORS / PICTURE DESKS

The paper 'Causes and consequences of tool shape variation in New Caledonian crows' is published in the journal Current Biology (7 December); an advance copy is available upon request. Contact the Communications Office - contact details below.

Please ensure that the paper's DOI https://doi.org/10.1016/j.cub.2017.11.028 is included in all media stories, and that Current Biology is credited as the source. Please note this link will become active after the embargo.

Photos of tool-using crows are available via http://bit.ly/2AtcacD with credits indicated in the file names.

New Caledonian crows live on the remote tropical island of New Caledonia in the South Pacific, where fieldwork for the present study was conducted. Birds were kept in field aviaries for the brief duration of behavioural experiments, before being released back into the wild, so they could re-join their social groups.

Earlier this year, the team exhibited its crow research at the Royal Society Summer Science Exhibition in London; a promotional YouTube video explaining the significance of the research is available here.

Forbes magazine recently selected the fish hook as one of the most important tools of all time, as reported here.

The study was funded by the UK's Biotechnology and Biological Sciences Research Council (BBSRC).

Last year, the team reported in Nature (see here) that a second tropical crow species - the critically-endangered Hawaiian crow - is a highly-skilled tool user. It is not yet known whether Hawaiian crows also make hooked foraging tools.

INTERVIEW REQUESTS

Professor Christian Rutz is available for interview, and can be contacted either directly (christian.rutz@st-andrews.ac.uk), or via the Communications Office (see contact details below).

St Andrews has an in-house ISDN line for radio and a Globelynx camera for TV interviews, which can be booked through the Communications Office.

Issued by the University of St Andrews Communications Office. Contact Christine Tudhope on +44 (0)1334 467 320 / 07526 624 243, or email christine.tudhope@st-andrews.ac.uk

University of St. Andrews

Related Biology Articles from Brightsurf:

Experimental Biology press materials available now
Though the Experimental Biology (EB) 2020 meeting was canceled in response to the COVID-19 outbreak, EB research abstracts are being published in the April 2020 issue of The FASEB Journal.

Structural biology: Special delivery
Bulky globular proteins require specialized transport systems for insertion into membranes.

Cell biology: All in a flash!
Scientists of Ludwig-Maximilians-Universitaet (LMU) in Munich have developed a tool to eliminate essential proteins from cells with a flash of light.

A biology boost
Assistance during the first years of a biology major leads to higher retention of first-generation students.

Cell biology: Compartments and complexity
Ludwig-Maximilians-Universitaet (LMU) in Munich biologists have taken a closer look at the subcellular distribution of proteins and metabolic intermediates in a model plant.

Cell biology: The complexity of division by two
Ludwig-Maximilians-Universitaet (LMU) in Munich researchers have identified a novel protein that plays a crucial role in the formation of the mitotic spindle, which is essential for correct segregation of a full set of chromosomes to each daughter cell during cell division.

Cell biology: Dynamics of microtubules
Filamentous polymers called microtubules play vital roles in chromosome segregation and molecular transport.

The biology of color
Scientists are on a threshold of a new era of color science with regard to animals, according to a comprehensive review of the field by a multidisciplinary team of researchers led by professor Tim Caro at UC Davis.

Kinky biology
How and why proteins fold is a problem that has implications for protein design and therapeutics.

A new tool to decipher evolutionary biology
A new bioinformatics tool to compare genome data has been developed by teams from the Max F.

Read More: Biology News and Biology Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.