Sudden increase in activity. Nectar flow?

[scrapiron]

For almost 2 days, one of my hives is just crazy with activity. Almost like orientation flights, just with very little crawling up the front of hive before launch. No fighting. Some pollen coming in, but mostly nectar I assume.? I usually have a nice beard in the evening and morning before sunrise. Now there is no beard ever, just bees workin their butts off.  The activity is to the point of a big traffic jam on the landing board, and bees colliding and falling to the ground. Hive is a standard 10 frame that was nectar/honey bound. I added another deep on top and they refuse to use it.
Shortly after seeing the activity, my friend across the street called and his is doing it too. What causes this? I hear of the nectar flows, but I am a 1st year beek and I am not sure if this is whats going on or what.
Most confusing is why my other 2 hives are "normal".

[BeeV]

Somethings blooming. Like you, my girls have been BUSY bringing in pollen for the last two days. First I have seen in probably a month. I don't know if they are getting any nectar but definitely pollen. Did your two normal hives have plenty of stores and the active one not? That might explain the difference.

You might try putting that deep on the bottom to see if they will use it.

[BlueBee]

Here in Michigan, we don’t usually have a dearth except for those long 6 months we call winter.  So I really don’t know how bees react coming out of a dearth.  However whenever I see a sudden increase in activity around any of my hives, it is almost always robbing.  Again, we are in different climates so what you are seeing may be normal down there.  

Robbing is more of a frenzied swarm of bees around the entrance than the more relaxed orientation flights.  When I suspect robbing on a full sized hive, I reduce the entrance for a day or two and the problem usually goes away.  

[scrapiron]

Well things seem to be slowing down. I have the biggest beard ever on the hive this evening. It was like a 48 hour rush of somekind. Now everyone is resting on the front porch! Strange.

It wasnt robbing. This is a strong colony (my best).

[Michael Bach]

This time of year you can get strong flows that last only a couple days.  Bees do work like crazy when there is a strong nectar source and then slow down when the flow slows or if they need a break to process the nectar.  I have discovered that they do need tome to process and organize the nectar when it is coming in so fast.