It turns out that sheep are far more intelligent than their reputation for barnyard slowness would lead one to believe. In recent research published in PLoS ONE1, Professor Jenny Morton of the Department of Pharmacology at the University of Cambridge and her colleague Laura Avanzo reported that domestic sheep can perform extremely well on tests of designed to measure cognitive abilities, possibly as well as any animal other than primates.
Professor Morton, who had been studying Huntington’s disease, wanted to find out whether transgenic sheep with a specific genetic defect might be useful in preclinical research regarding potential treatments for this neurodegenerative disease. Because Huntington’s is characterized by cognitive deterioration, Morton was particularly interested in seeing how well sheep would perform cognitively, since suitable research subjects for neurologic disorders like Huntington’s inevitably must undergo systematic cognitive testing relevant to the disease.
Accordingly, Morton and Avanzo devised a series of tests that they gave to seven female Welsh Mountain sheep, six of whom completed the whole study. No word on why all of the ungulate volunteers were female, although my guess is that the males were off rollicking around with male bottlenose dolphins who were avoiding sponge fishing duty.
The tests were designed to measure the ability of the sheep to perform in three areas (discrimination learning, reversal learning and “attentional set-shifting”), which are relevant to what the researchers refer to as executive function – that is, the “ability to learn associations between stimuli, actions and outcomes, and to then adapt ongoing behavior to changes in the environment.” While the sheep took a large number of very specific tests, the tests fell into the following general categories:
- Simple discrimination tests. Sheep must choose between two feed buckets that are identical except one is blue the other is yellow. One color contains a food reward; the other is empty. Later “retention tests” repeat the original tests after time has passed to see how well the sheep remember.
- Simple discrimination reversal tests. Sheep must relearn the correct answer after sneaky researchers reverse the color of the bucket containing the food reward. (Note: we encountered this type of testing in the earlier AnimalWise post about the clever Anole lizards). Again, later “retention tests are given.
- Compound discrimination tests. The rewarded color is the same as in 1 above, but the relevantly-colored objects are now “perforated sports cones” rather than buckets. Additional buckets of irrelevant colors (one black, one green) are placed next to the sports cones, with the food reward in whichever bucket happens to be next to the correctly-colored sports cone.
- Intradimensional shift tests. Now, the sheep are presented with new shapes (rhomboids and cones) and new colors (purple and green). The sheep must still make a correct choice based on color, but need to learn the new color to apply.
- Intradimensional shift reversal tests. Same as 4, but sheep must relearn correct answer after the researchers change the rewarded color.
- Extradimensional shift tests. Again, the sheep are presented purple or green cones or rhomboids, but this time they must figure out now that the reward is based on choosing the correct shape, rather than a particular color.
- Extradimensional shift reversal test. Same as 6, but sheep must relearn after researchers swap which shape is rewarded.
Of the above tests, 1 & 3 measure “discrimination learning”; 2, 5 & 7 measure “reversal learning”; and 4 & 6 measure “attentional set-shifting.”
In a nutshell, the sheep did amazingly well.
They very quickly learned to pass the initial simple discrimination test (within seven sets of eight discriminations). When presented with the first reversal test, their performance initially dropped off, but they learned the new correct answer within three days of testing (11 sets of discriminations). For the compound discrimination testing, their performance again dropped slightly at the outset, but within two days they had this new puzzle figured out as well. Moreover, the retention tests showed that the sheep were able to remember the correct answer after time had passed (six weeks in the case of the simple discrimination test; two weeks for the simple reversal test).
At first, the sheep performed no better than chance on the more difficult intradimensional shift test, but they soon were performing at over 90% correct. They also experienced a large drop off in performance on the extradimensional shift test, but improved gradually until they reached 80% correct on the fourth day of testing. The sheep learned also were able to learn the reversals (within eight sets of discriminations for the intradimensional reversal and within 10 sets for the extradimensional reversal).
Morton and Avanzo summarized the results as follows:
We show that not only can normal can sheep perform discrimination reversal learning tasks, but they can also perform attentional set shifting tasks that test executive function. To our knowledge, this is the first time that these executive functions have been demonstrated in any large animal, apart from primates.
They were surprised by this success, conceding that they hadn’t been expecting the sheep to do well on the more difficult tests and indicating that they were “driven more by curiosity than expectation” in even giving the tests to them.
So, given these results, sheep seem to have gotten a bum rap for intelligence. There are relatively few studies on ovine intelligence, although research has shown that they can learn and remember how to navigate complex maze2 and that they are very good at remembering faces3. And then there’s my favorite, that they’ve learned to roll their way across hoof-proof metal cattle grids in order to raid villagers’ valley gardens4!
One reason for the mistaken impression about sheep cognition may be that we have a bit of a blind spot when it comes to intelligence. We expect it in ourselves and a few other select animals, but even scientists can be quite surprised when it pops up elsewhere. Perhaps the main lesson here is that we should do our best to remain open to finding intelligence in unexpected places – if nothing else, this sort of a mental stretch will be a good test of our own cognitive abilities.
1Morton, A., & Avanzo, L. (2011). Executive Decision-Making in the Domestic Sheep PLoS ONE, 6 (1) DOI: 10.1371/journal.pone.0015752.
2LEE, C., COLEGATE, S., & FISHER, A. (2006). Development of a maze test and its application to assess spatial learning and memory in Merino sheep Applied Animal Behaviour Science, 96 (1-2), 43-51 DOI: 10.1016/j.applanim.2005.06.001.
3Kendrick, K., da Costa, A., Leigh, A., Hinton, M., & Peirce, J. (2007). Sheep don’t forget a face Nature, 447 (7142), 346-346 DOI: 10.1038/nature05882.
4See, e.g., BBC News, “Crafty sheep conquer cattle grids,” July 30, 2004.