I could easily believe this. But I'd need to understand more of the details of the experiments they used to determine this.
I'm a dog person. Ever since I can remember I was raised around dogs. When I was 15 my family moved from AK to KY (driving down the ALCAN Hwy). We stopped at my grandparents' house in OH for some time. Anyway, I don't get along with all of my relatives, so I used the time to train my mom's poodle. I had some experience training a number of different breeds, but none with a poodle.
I was startled. In two days I had trained her to do a very complicated obstacle course in the bedroom, one part of which consisted of going around the leg of a chair exactly three times. She could do this even without me in the room - so it possible she was getting cues from someone, but I don't think it's likely.
Anyway, I'm sorta convinced at this point that some dogs can count. These counters may not have the same depth of understanding of the concept of number that humans have, but I'm pretty sure they (at least some of them) have an elementary concept of it.
I also did a very limited bit of training for rats - but I don't recall anything that indicated an understanding of number. OTOH, I wasn't trying to train for it, either.
I wouldn't be too surprised if all the higher mammals had some members with a primitive concept of number.
