Many thanks to all that replied. The hives are not in a row, one is far away and the one in question is close to another one. The overall volume of traffic is not very much different, it is the nature of it that puzzles me. Why two have heavy pollen traffic and the third one does not? Is it an indication of something? Or is it just an indication of my ignorance? Curiosity killed the cat, but it is still a good way to learn things.