Clever Crows

Along with "language use" the other distinguishing ability that has always been held to mark humans off as separate/superior from the rest of the animal kingdom is "tool use" - man the tool maker. An exception had to be made in the 1970's when it was observed that chimps regularly use tools to access ants nests, to crack open nuts and for weapons. Then in 1996 Gavin Hunt from Auckland University discovered that the New Caledonian crow (Corvus Moneduloides) makes stick and leaf tools to extract grubs from crevices and dead wood. This ability appears to be confined to this one particular species found only on two adjacent islands. It was not perhaps too much of a shock for us to accept that chimps might have some crude tool making ability - after all we mostly accept that we derive from related stock some 6 million years ago - however it might give us a little more pause to take in that similar abilities have evolved quite separately in birds that diverged from our ancestral stock line at least 300 million years ago.


Some of the tool-use activity appears to be innate, that is captive chicks reared only by humans and never shown any tool-use will fashion crude leaf tools from Pandanus leaf and use these to extract food (http://users.ox.ac.uk/~kgroup/tools/animal_tool.shtml). However in the wild the tools are far more sophisticated and also there are regional differences in tool design suggesting that social learning is involved.


I was fortunate to be able to spend a month on Mare Island in 2008 observing the crows in conjunction with a University of Auckland study attempting to determine the extent of social learning involved in tool-use. It was initially a slightly surreal sensation seeing lots of crows effortlessly making these leaf tools.


The following short clip from an experimental feeding table on Mare Island New Caledonia shows; stick tool use, then leaf tool making from a pandanus leaf (at 35sec.) and leaf tool use (at 56sec. till the end). You can hear young chicks calling from canopy nests not far from the feeding table:

Two pandanus leaf tools with a pandanus leaf showing where a tool was cut from:

The following clip is a scary/unbelievable/extraordinary recording made of Betty, a New Caledonian crow held in captivity at Oxford. Two crows were part of a "Choice" experiment where there were two wire "sticks", one with a bend which would allow it to be used as a hook to access a small bucket of food from inside a glass tube, the other a straight "stick". Would the crow more likely choose the useful bent stick? There were two crows in this experiment and at the start of this clip Betty's mate grabbed the hooked stick and she was left with the less useful straight stick. This is only the fifth trial in the experiment and the only exposure the crows have had with wire.

The following clip shows a crow fishing - dropping crumbs of dry bread on the surface of the pond. I think it was taken in Israel.





The following clip is of Prof Russell Gray at Auckland University discussing the probable social learning aspect to account for the regional differences in tool design.

Solar bodies - no need to eat !

The leaf shaped green sea slug Elysia chlorotica, found widely on the Eastern seaboard of the USA, has incorporated chloroplasts (the same structures responsible for photosynthesis in all plants) into its body cells which allows it to obtain its energy needs by sunbathing rather than by having to eat.

Photo by N E Curtis and R Martinez from Wired.com article 11/1/10.


Scientists have shown that after a young slugs initial feed of a particular green algae, from whence it obtains its chloroplasts, it can survive the rest of its life - about a year - without having to eat another meal. The slug, now solar-powered, no longer needs a mouth.

I first heard of this plant/animal in Frank Ryans' book Virolution in which he explores the central role of viruses in evolution and cell metabolisim. Elysia initially needs to feed on Vaucheria algae to acquire a sufficient "skin-full" of chloroplasts. The mystery though has been how the process of photosynthesis continues long after the initial chlorophyll reserves acquired from Vaucheria have been used up (photosynthesis requires continual replenishing of this light absorbing pigment).

It seems that in the evolutionary past there has been a natural transfer of genes from the algae to the slug which allows Elysia to produce the chlorophyll pigment proteins itself. These genes are found even in unhatched sea slugs which have never been exposed to algae. While bacteria and other microbes freely exchange genetic information (e.g. the fast build-up of resistance by bacteria to antibiotics), there are not many examples of genes transfering between two different kingdoms of life. Ryan writes that there is gathering evidence that the gene transfer was probably accomplished by a retrovirus that is commonly found throughout the body of the slug. Aggressive reproduction by the same virus is implicated in the quick death of the slug soon after it has laid its eggs the following spring. Ryan speculates that we are looking here at an example of "aggressive symbiosis" where the virus that had previously enabled the slugs idyllic lifestyle now switches behaviour to cull the now redundant adults after they have laid their eggs. He sees this is as a previously unnoticed evolutionary mechanisim perhaps as important as the better known mechanisims of natural selection, adaptation and genetic drift.

So, viruses help design the creatures they inhabit. Over evolutionary time they shape their own hosts. Which virus(es) designed us? Gives a new meaning to "Lord of Hosts".

A good green argument here of course for human genetic engineering. Splice chloroplast genes into our skin cells and we can all retire to the beach. Perhaps those little green Martians have already stolen a march on us here.

Youtube clip of Elysia still with a mouth :


Rumpho ME, Worful JM, Lee J, et al. "Horizontal Gene Transfer... " Nov '08 Proceed. Nat. Acad. Sciences.

Pierce SK, "Chlorophyll a manufacture in Elysia..." Jan '10 Ann. Meeting Soc. Integrative and Comparative Biology.