Corvid cognition

Copyright © 2005 Elsevier Ltd All rights reserved.

Nicola Clayton and Nathan Emery

aDepartment of Experimental Psychology and Sub-department of Animal Behaviour, University of Cambridge, Cambridge, UK

Available online 7 February 2005.

Article Outline

What is a corvid? There are just over 120 species of corvids, a family of songbirds that includes the crows, ravens, rooks and jackdaws, as well as the more colourful jays, magpies and nutcrackers. Although belonging to the same order as nightingales and other birds with melodious songs (Oscines), corvids tend to be identified by their raucous calls. Little is known about corvid songs, perhaps because they are surprisingly quiet. Corvids can be found throughout the globe, except for the southern most tip of South America and the polar ice caps. In Britain, many of the common species, such as magpies and crows, steal other birds’ eggs and raid agricultural crops. They are therefore treated with disdain by many birdwatchers and farmers.

Why study intelligence in crows? Corvids have not always had such a bad press. Native Americans believed that a raven had created the earth; the Norse god, Odin, consulted two ravens Hugin (Thought) and Munin (Memory) for their wisdom; and Aesop cast corvids as the smart protagonists in many of his fables. Along with their reputation in folklore as the wisest of animals, corvids have the largest brains for their body size of any bird. Perhaps most surprisingly, the crow brain is the same relative size as the chimpanzee brain. Other aspects of corvid biology also give us clues to their intelligence. In the wild, young corvids have an extensive developmental period before they become independent from their parents. This allows them more opportunities to learn the essential skills for later life. Many corvids also live in complex social groups. For example, in the cooperatively breeding Florida scrub-jay, several closely related family members share the responsibility of raising the young with the parents. Furthermore, rooks congregate in large colonies, where juveniles associate with many non-relatives as well as kin. In both cases, this long developmental period provides increased opportunities for learning from many different group members.

Perhaps it is not surprising then that many corvids are also renowned for their innovative feeding skills. For example, Japanese crows in Sendai City have learned to crack nuts safely by dropping them onto pedestrian crossings and waiting until the traffic lights turn red before retrieving the nut’s contents. Rooks at a motorway service station in England have discovered a novel method for gaining access to food thrown in rubbish bins. Two birds cooperate in pulling up the bin liner and then either feeding from the raised food or tossing the contents onto the ground where the waiting crowd of colony mates reap the rewards.

As the crow flies… Most of the corvids that have been studied in detail hide food for the future in times of food abundance and then rely on memory to recover the food caches at a later date when food is scarce. For example, the Clark’s nutcracker is estimated to hide over 30,000 pinyon seeds in many different places during the autumn in preparation for the harsh months ahead. Laboratory experiments have shown that they have highly accurate spatial memories, which enable them to recover these caches up to 9 months later. This is no mean feat when there are so many caches to keep track of, scattered throughout the territory, and when many aspects of the landscape change so dramatically across seasons. It has been suggested that Clark’s nutcrackers rely on remembering the location of large vertical landmarks such as trees and rocks in the environment, because these landmarks are unlikely to be blown away or buried under the snow.

What do scrub-jays recall about past caching events? Although western scrub-jays do not hide as many seed caches as the nutcrackers, they are known to cache a variety of perishable foods, such as insects and fruit, as well as non-perishable nuts and seeds. In the laboratory, these birds demonstrate remarkable memories for what they have cached on a given day, and how long ago, as well as where they hid the various food items during that particular caching episode. This ability to remember the ‘what, where and when’ of specific past events is thought to be akin to human episodic memory, because it involves recalling a particular episode that has happened in the past. Until recently, this ability was thought to be unique to humans.

Avian espionage… Food-caching is a risky strategy, however, because the caches can be stolen by other birds. In addition to hiding their own food caches, corvids also play the role of thief: they watch and remember where other birds have hidden their caches and use this information to steal those caches when the owner has left the scene. When playing the role of thief, speed is of the essence and may make the difference between a successful raid and vicious attack by the owner of the food-cache. Not surprisingly, corvids also employ a number of counter strategies to reduce the risk that their own caches will be stolen by another bird. For example, they attempt to cache out of sight from potential thieves, or wait until the raider is distracted before hiding their caches, and if that is not possible, they hide caches in places that are difficult for the thief to see. When there is little option but to cache when others are around, then the birds will return to the caches once the others have left, and quickly re-hide any remaining caches in new places unbeknown to the potential raider.

Laboratory experiments have established that western scrub-jays use all these techniques to protect their caches from potential thieves, and only do so if another bird is present at the time of caching. Furthermore, they only move their caches to new hiding places if they have been thieves themselves in the past. Naı̈ve jays, even ones who have watched other birds caching but have never had the opportunity to raid those caches, do not do so. This suggests that experienced birds relate information about their previous experience of being a thief to the possibility of future theft by another bird, and adjust their caching behaviour accordingly. Using your own experience to predict another individual’s future behaviour in relation to your own – ‘putting yourself in someone else’s shoes’ – is thought to be one of the hallmarks of Theory of Mind, another ability that was thought to be uniquely human.

Cultural tool use in crows? New Caledonian crows are extraordinarily skilled at making and using tools. In the wild, they make two types of tool. The hooked tools consist of twigs that are trimmed and sculpted into a functional hook, which the crows use to poke insect larvae out of tree holes. The crows also manufacture stepped-cut Pandanus leaves, which they use in different ways for different jobs: they make rapid back and forth movements for prey under soil, yet slow deliberate movements if the prey is in a hole. These tools are consistently made to a standardized pattern and carried around on foraging expeditions. The only other animals that display this diversity and flexibility in tool use and manufacture are the great apes. Thus, chimpanzees have been observed to manufacture a range of different tools that are used for specific purposes, and different geographical populations of chimpanzees use different tools for different uses, suggesting that there may be cultural variations in tool use. Observations of the crows’ tool use in the wild also suggest similar levels of cultural complexity. For example, there is potential cumulative evolution in the complexity of stepped tools (increasing the number of steps required to make a more complex tool), analogous to minor technological innovations in humans. Crows from different geographical areas have different designs of tool, suggesting that crows may also show cultural variations in tool use.

Laboratory experiments confirm the sophisticated intellectual capabilities of these crows. One tool-using crow, called Betty, can manipulate novel man-made objects to solve a problem, such as reaching food in a bucket only accessible by using a hook to pull the bucket up. When the bent wire was stolen by another bird, Betty found a piece of straight wire that was lying on the floor, bent this wire into a hook and used it to lift up the bucket and reach the food! Betty proceeded to do this consistently. Furthermore, when given a tool box containing a variety of different tools to reach normally inaccessible food, she was able to select one of the correct length and width. So evidence of tool use and manufacture suggests that these crows can sometimes combine past experiences to produce novel solutions to problems.Feathered apes? Corvids are large-brained, social birds. They have an extensive developmental period in which they are dependent on their parents, and so have a long time-window in which to learn many different things from their parents and peers. They show a great propensity to find innovative solutions to novel problems, from the manufacture of tools to the protection of food from competitors. Furthermore, they appear to be particularly adept at predicting the future behaviour of conspecifics. These features are things they share in common with the apes. The common ancestor of mammals and birds lived over 280 million years ago, so it is hardly surprising that they have very different brains. It follows that intelligence in corvids and apes must have arisen independently in two groups with very different brains. Interestingly, the thinking part of the brain is correlated with propensity to innovate in both birds and primates, with the corvids and apes as the ‘star inventors’. So when it comes to intelligence, corvids are feathered apes.

Further reading

Where can I find out more?

R.P. Balda, A.C. Kamil and P.A. Bednekoff, Predicting cognitive capacities from natural histories: examples from four corvid species, Curr. Ornithol. 13 (1996), pp. 33–66.

N.S. Clayton, T.J. Bussey and A. Dickinson, Can animals recall the past and plan for the future?, Nat. Rev. Neurosci. 4 (2003), pp. 685–691.

N.J. Emery and N.S. Clayton, The mentality of crows: Convergent evolution of intelligence in corvids and apes, Science 306 (2004), pp. 1903–1907.

Heinrich, B. (1999). The Mind of the Raven (Harper Collins).

G.R. Hunt and R.D. Gray, Diversification and cumulative evolution in New Caledonian crow tool manufacture, Proc. Roy. Soc. Lond. B. 270 (2003), pp. 867–874.

L. Lefebvre, S.M. Reader and D. Sol, Brains, innovations and evolution in birds and primates, Brain Behav. Evol. 63 (2004), pp. 233–246.

A.A.S. Weir, J. Chappell and A. Kacelnik, Shaping of hooks in New Caledonian crows, Science 297 (2002), p. 981

“Reprinted from Current Biology, Vol 15 / Issue No 3, Author(s) Nicola Clayton and Nathan Emery, Corvid cognition, Page No. 1, Copyright 8 February 2005, with permission from Elsevier.”
Direct Link to Article click here.

Biggest and Smallest Corvids

Most people do not know that there are over 120 species of corvid family of birds—including many jays, choughs and treepies—not just crows, ravens and magpies. Well, I was not certain where to begin with this fascinating family of birds so I decided to start with telling you the biggest and the smallest amongst them.

The largest corvids are the Common Raven (Corvus corax) and the Thick-billed Raven (Corvus crassirostris), both of which regularly exceed 1400 grams (3 lbs) and 65 cm (26 inches). ((http://en.wikipedia.org/wiki/Corvidae))

I will do thorough posts about these specific birds in the next couple of days. For now I will share a picture of each.

Dwarf Jay
Dwarf Jay


Common Raven
Common Raven


Thick-billed Raven
Thick-billed Raven

Crow Cam Today =)

We put out peanuts without shells today for the first time. They were a hit. The crows like not having to open the shells and they attracted two more kinds of birds as well. =) Fun!

The crows seemed to be done for the day. The bowl was still about 1/4 full but they flew off. However, when a stellar jay showed up and started eating some of the peanuts, they came back cawing and trying to scare him off. He flew away but then when they flew off, he flew back. It was rather comical to watch. =) I think the new peanuts attracted him.

Fan-tailed Raven

Today, I decided to introduce the Fan-tailed Raven officially known as the Corvus rhipidurus. This corvid is native to Eastern Africa and the Arabian Peninsula. It is much smaller than most other corvids at around 18 inches long. It has a thick bill, short tail and large wings. It looks thinner than the Common Raven and is completely black with a purplish-blue gloss in the right lighting. If it is an older Fan-tailed Raven it can appear slightly coppery-brown.

Their voice is described as guttural croaks mixed with the sound of frog-call.

It lives in desert or open dry country that includes crags for nesting. It is one of the most aerial of birds traveling huge distances in search of food, its large wings being adapted to gliding on thermals in a rather vulture-like way.

The Fan-tailed Raven eats insects, invertebrates, grains taken from other animal’s dung, human food scraps, parasites of other animals and garbage. It will also eat a variety of fruit.

I like this bird. It is interesting, too bad I live so far from it. Does anyone you know or do you live near it? Have any stories you wish to tell?

The Jungle Crow

The Jungle Crow (Creative Commons)
The Jungle Crow (Creative Commons)

The Jungle Crow also known as Corvus macrorhynchos, Indian Corby, Large-billed crow and the thick-billed crow. This is the bird I thought I’d focus on today. It is found all over Asia. Like most crows they are able to adapt to most any situation. There are three types of Jungle Crows: the Eastern Jungle Crow (Corvus levaillantii), the Indian Jungle Crow (Corvus culminatus) and the Eastern Large-billed Crow (Corvus japonensis).

All forms have a relatively long bill with the upper one quite thick and arched, making it look heavy and almost Raven-like. Generally, all forms have dark greyish plumage from the back of the head, neck, shoulders and lower body. Their wings, tail, face and throat are glossy black. The depth of the grey shading varies across its range to almost black in the Indian form.

These birds have long bills with a thick, arched upper bill. This makes them look a bit like the Raven. Most have a dark grayish color around their necks, heads, shoulders and lower bodies. Their wings, tail, face and throat are often glossy black.

The range of this species is extensive and stretches from the northeastern Asian seaboard to Afghanistan and eastern Iran in the west, and south to India down to the Malaysian peninsula in the southeast. The Philippines also have a regional form. It occurs in woodland, parks and gardens, cultivated regions with a least some trees, but is a bird of more open country in the south of its range where it is not in competition with the Raven and Carrion Crow of the north. ((http://en.wikipedia.org/wiki/Jungle_Crow))

They can and will eat just about anything, including trash, often leading to their reputation as being pests. They also regularly kill and eat domestic chickens, more so than any other species of Crow. This reinforces their “pest” status with farmers.

They like to nest way up high in a fork in trees and their nests are typically a platform of twigs or a cup of sticks lined with grass roots, wool, rags, vegetable fibers etc. There have even been nests made of wire. How resourceful are they?

To see videos of these birds click
here
.

Common Ravens and Egg


Common Ravens and Egg

Originally uploaded by poecile05

This is the second raven baby/egg photograph and post. Thanks to the photographer, poecile05, for sharing this on flickr and allowing us to blog it.

If you read yesterday’s post, you know how much a baby raven can and must consume. I shared with you a small part of a book I read, “Mind of the Raven” by Bernd Heinrich.

The high maintenance baby ravens don’t stop with just a need for attention and an enormous amount of food. They also require some special attention to see to their “bathroom” needs, if you will. You may recall from yesterday’s post that nestlings eat A LOT of food. For every action there is an equal and opposite reaction.

Yep! That is right. Almost every amount that goes into the baby ravens must come out. Since they can’t lift themselves up to hang over the side of the nest for at least a couple of weeks, their parents must take care of this expediently. Remember, if they eat six woodfrogs and two mice IN ONE FEEDING, then you can imagine how much waste that much food produces after EACH and EVERY FEEDING! They would quite literally be drowning in a bowl (their nest) full of their own liquid dung (also known as ‘mutes’).

In order to prevent this from happening, the parents scoop up the “mute” with their beaks as it is coming out and dumps it over the side of the nest. They are the equivalent of live pooper-scoopers. Not so fun, not so simple. Imagine how much time this takes and then recall how much food they need. You can see clearly how much time parenting takes in a raven’s life.

We are lucky as humans that we only need to go to the local grocery store to obtain food for our young. Imagine the raven’s life…

Corvus frugilegus (The Rook)


Communique

Originally uploaded by Mark Cummins

Another excellent photograph found on flickr. This one is by Mark Cummins. If you click on the photograph it will take you to the URL where it is originally posted.

I am not 100% certain what particular bird this is in the corvidae family. However, I think it might be a rook but I am reluctant to say this for certain with authority because I am not so familiar with rooks to recognize off the top of my head. It looks like a rook and it looks like it the same bird I previously posted by the same photographer and it was a rook. So, I imagine it is either the same bird or a similar one. =)

This is the Corvus frugilegus which means “food-gathering” in Latin. They are more commonly referred to as the Rook. I have not had the great pleasure of seeing this bird in person but I am very excited to learn about it. It looks like a harsher, thinner crow. It appears, to me, to have had a hard-knock-life. I like how it wears its character, much like I relish the quirks in people; a wrinkle earned through years of laughter and tears, an innocent freckle just above the wrist, the shy happiness in a crooked smile, the confident swing of a left-leaning gait.

From what I’ve learned about the Rook, you can differentiate it from similar corvids by looking for the “bare gray-white skin around the base of the adult’s bill in front of the eyes or the feathering around the legs; it looks shaggier and laxer than the congeneric Carrion Crow.” ((Wikipedia))

It seems it is found all over Europe and east of Europe. I read that it is found in Great Britain quite frequently.

Where Rooks Live...
Normal Range of Habitat for the Rook (Where Rooks Live...)

Much like all corvids, it is a survivor. It will eat just about anything depending on where it lives. It prefers earthworms and insect larvae but will eat cereal grain, fruit, insects, crustaceans, small animals, acorns, bird eggs, and will pilfer through the trash for food scraps in urban areas. ((Wikipedia))

The Rook nests together in a colony. This is commonly referred to as colonial nesting which means nesting with many other birds in a safe place and living commune-style. The Rooks learn from one another and find food together. They protect one another but they are still predatory birds, so they can be found stealing from another from time to time. They prefer to nest way up high in trees. They typically have 3-5 eggs which are incubated for 16-18 days and the fledglings are cared for by their parents and other rooks for about a month.

Once fully fledged, they get together with other single rooks and sometimes even jackdaws and fly around, presumably deciding who they will mate with in the future. Or perhaps just enjoying the free, young, single life…flying around without a care.

You can hear a rook here.
It sounds much like most crows but maybe a little throatier which matches how they look, for me anyways. =) I like their throaty “caw”.

Rooks are interesting birds. And so they are written about…people speculate about their abilities and even conjure up powers for these intelligent birds. I found the following on Wikipedia… it is a direct copy and paste but interesting.

Like many other members of the Corvidae family, the Rook features prominently in folklore. Traditionally, Rooks are said to be able to forecast weather and to sense the approach of death. If a rookery — the colonial nesting area of rooks — were abandoned, it was said to bring bad fortune for the family that owned the land. Another folk-tale holds that rooks are responsible for escorting the souls of the virtuous dead to heaven. William Butler Yeats may be making reference to the latter tale in his poem The Cold Heaven.

In Neil Gaiman’s Sandman comic book series, Abel reveals that the parliament would surround a single rook, with that one telling a story. If the story was not liked, the parliament would attack and kill the speaker.

In Brian Jacques’s Redwall series, rooks make an appearance in Mattimeo. Rooks, along with magpies and other similar birds make up the army of General Ironbeak, one of the villains in the book.

In Susan Cooper’s The Dark Is Rising series, rooks are seen as agents of the Dark and the sign-seeker, Will Stanton is warned never to fully trust one.

In Phillip Pullman’s book Northern Lights Lyra Belacqua and Roger Parslow catch and heal an injured rook on the college rooftop.

In Stephen King’s Dark Tower entry Wizard and Glass, one of the characters, Cuthbert Allgood, carries a rook’s skull tied around his neck, claiming it as a good luck charm.

I am now an official fan of the Rook. I may always have been but I simply did not know it.

Do YOU have a Rook story to share with me? I would love to hear one (or many!) If so, e-mail me below.

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