In Israel’s Khai Bar Reserve, a pair of brown-necked ravens has a problem. They’re after the tasty contents of ostrich eggs and there are plenty to go around. The eggs – the largest of any bird – would provide a nutritious meal but they’re so thick that even a pair of ravens can’t puncture them. But they don’t need to. The ravens know that the desert is also home to a master egg-cracker – the Egyptian vulture. All they have to do is wait, and they can rob the robber.
Shai Kabesa from Ben Gurion University first noticed the ravens at work in 2008. Together with Reuven Yosef, she pieced together their strategy in the following years.
The Khai Bar Reserve has no native ostriches – they were hunted to extinction in the area during the 1940s. There is, however, a thriving conservation project that’s breeding the birds in the hope of reintroducing them. Ostriches lay their eggs in a single nest. The dominant female goes first, laying around 15 to 20. Her subordinates follow with 3 to 4 of their own. However, the top pair of ostriches can only incubate around a dozen eggs effectively, and they roll the rest away from the nest. This creates a ring of nutritious treats for any bird skilful enough to break into the eggs.
The Egyptian vulture does so with a special technique – it uses a tool, and is one of the few birds to do so. It picks up rounded stones in its beak and uses them to hammer the egg shells until they crack. Even ostrich eggs eventually give way. But the vultures don’t always get to enjoy the fruits of their labours. Yosef found that on at least three occasions, a pair of ravens, watching nearby but hidden behind a bush, quickly flew in and drove the vultures away.
Yosef thinks that the ravens he saw are the same individuals – they behaved in virtually the same way from one robbery to the next. Their behaviour suggests a keen intelligence. Yosef writes, “Most apparent in the ravens is their innovative thinking and ability to predict the actions of the potential host or prey.”
He thinks that the ravens recognise that ostrich eggs are valuable food but that they cannot break through the shell. They seem to understand the vultures’ technique. They know they have to hide and “be patient”, waiting till the vulture has broken the egg before showing themselves. They know that by hunting together, they can effectively exploit a source of food that they would never be able to reach.
This is possibly overstating the case, at least without putting the birds through any experiments. Animal intelligence is a notoriously tricky thing to study and many previous claims have been overplayed. For example, are they biding their time for the vultures to finish, or are they simply attracted to the glisten of exposed egg whites?
Nonetheless, it’s hardly far-fetched to claim that the ravens are acting intelligently. They and their relatives – crows, rooks, jays and bowerbirds – have demonstrated impressive feats of behaviour time and again. In the same nature reserve, Yosef has found that brown-necked ravens cooperate to hunt a local lizard called a mastigure. When the lizard is away from its burrow, a pair of ravens circles in and blocks the entrance. With its escape route cut off, the lizard is attacked by the other ravens. Only when the lizard is dead do the burrow-blockers join the feast.
Elsewhere in the world, other species of raven are just as resourceful. Common ravens raid the buried larders of Arctic foxes. They’ll also hang around wolves to gain access to fresh carcasses that the wolves rip apart – a very similar strategy to the one that the brown-necked ravens use to pilfer eggs. In captivity, ravens can work out how to reach meat hanging from a perch by a string – they pull the string gradually, stepping on the loops to keep it from dropping. Yosef says, “It appears that the intellectual flexibility and response to ever-changing conditions has allowed this highly intelligent family to persist in extreme conditions—from the freezing tundra to the hot deserts.”
The same can’t be said of the Egyptian vultures. They don’t seem to have come up with a strategy to counter the aggressive ravens. They have large brains for their size and they breed in pairs that could easily see off thieves. But as Yosef writes, “It appears that although they may have large brains and are able to wield tools, they are not innovative enough to outthink the ravens.” Intelligent birds use tools. Really intelligent birds use tool users.
Reference: Yosef, Kabesa & Yosef. 2011. Set a thief to catch a thief: brown-necked raven (Corvus ruficollis) cooperatively kleptoparasitize Egyptian vulture (Neophron percnopterus). Naturwissenschaften Http://dx.doi.org/10.1007/s00114-011-0777-0
More on crows and their relatives:
- Fishing for fat: why learning to use tools is worth it for the New Caledonian crow
- Male bowerbirds create forced perspective illusions that only females see
- Confirming Aesop – rooks use stones to raise the level of water in a pitcher
- Clever New Caledonian crows use one tool to acquire another
- Bird-brained jays can plan for the future
March 20th, 2011 at 2:44 pm
Interesting article, but shouldn’t the headline say “Vultures are tools” instead of “Ravens are tools”?
March 20th, 2011 at 5:48 pm
Robyn, it’s a play on words. They’re saying the Ravens are schmucks.
March 20th, 2011 at 7:05 pm
Intelligence in Ravens and their relatives is unsurprising to me. When I was in school (15 or so years ago) we used to watch the crows unwrap sandwiches before devouring the insides. It was fascinating to see them hold the sandwhich down with their claws then use their beaks to fold back the edges of the plastic wrap.
March 21st, 2011 at 2:23 am
One of the best blog titles I’ve seen in a long time. Great post too, especially since I did my undergrad in animal behaviore, but the title…award worthy!
March 21st, 2011 at 9:29 am
I have to agree with Robyn. http://www.urbandictionary.com/define.php?term=tool
March 21st, 2011 at 11:22 am
I also agree with Robyn and Bobthenerd…I would think the vultures are the ‘schmucks’, in that they are being used by the ravens.
March 21st, 2011 at 12:33 pm
I agree with Robyn, Bobthenerd & OwlSong! That’s the first thing I thought of when I finished the article… how are the Ravens tools? They seem to be the smart ones in this scenario. I did enjoy the article, despite the seemingly inconsistent title.
March 21st, 2011 at 12:48 pm
I’ve changed the headline. Now for the love of all that is good, will everyone please shut up?
March 21st, 2011 at 1:36 pm
“Intelligence” is such an amorphous, undefined term that its use automatically invites debates that ultimately center on what the word means to each person using it, not to the behavior being studied. It’s kind of a semantic cul de sac. The behaviors observed, like those above, are interesting in and of themselves. A very odd behavior I have personally observed with spawning Atlantic salmon is that sometimes (not all the time), the female will select a nesting site on the stream bottom and start to excavate it with her tail to the proper size, shape and depth. Then after several hours of diligent work she will abandon it and select a new site, often nearby, and start all over again. These sites are called “test redds” by salmon biologists — that is how prevalent the behavior is. Apparently, the salmon decides that Site A is best place to dig a redd, then after several hours, reconsiders and decides it’s not a good site, abandons it, and chooses another site and starts all over. So it appears the salmon made a considered choice, had second thoughts about it after further analysis, and then made a second choice: abandon the first site, forfeit all the labor it had just expended, and start building a brand new excavation in the riverbed. It’s not for me to call this ‘thought’ — but it illustrates a fairly sophisticated, step-wise analytical technique. In a fish !!!
March 22nd, 2011 at 2:15 am
You know, I read the original version of the title to mean that the ravens were being mean bastards, taking advantage of the poor vultures….
March 22nd, 2011 at 2:17 am
re #9;
If you want another example of complicated behavior that appears to be “intelligent”, consider a Portia spider on the hunt. The brain of that little critter is smaller than a pinhead.
March 22nd, 2011 at 6:06 am
Fascinating.
Reminds me (though the vulture-raven thing clearly isn’t mutualism) of the honey badger-honeyguide relationship: http://en.wikipedia.org/wiki/Greater_Honeyguide#Guiding_of_non-human_animals.3F
March 22nd, 2011 at 11:00 am
Crafty Parasite is crafty.
Another great article BTW
March 22nd, 2011 at 7:45 pm
I agree…ravens are tools…especially Ray Lewis.
Sorry Ed, I’ll shut up now. Please continue posting the best articles on this site.
March 22nd, 2011 at 11:03 pm
Is it these guys? http://en.wikipedia.org/wiki/File:Heckle_and_jeckle_promo_picture.png
March 31st, 2011 at 11:31 am
Crows in the UK have also learnt to use traffic crossings to crack nuts. They fly to the crossing, and drop a nut whilst the cars are moving, then wait on a lamppost. When the lights change and the traffic stops, they drop down and pick up the nut, which has been nicely opened by the cars driving over it. They don’t attempt to pick up the nut until the cards have stopped.