I've had a hive on a scale for a couple of years now. I believe that bees don't go out to forage unless they can keep the hive at a particular temperature. If it takes 10,000 bees to keep the hive at temperature, andif you have 10,000 bees, you'll get no foragers, however, if you have 30,000 bees, you'll get a lot more foragers. A weak hive will have very little bees foraging when it's, say 60 degrees. A strong hive, like in the video, has thousands foraging when it's 60.