[EBB Sightings] How do shorebirds sense the next low tide?

A friend and I were at Frank's Dump on Sunday about an hour after high tide (4:30P). Mostly gulls and godwits were still roosting. At around 5:30P they all began flying out for the hunt over a period of about one hour.

The roosts at FD have no view of the Bay. Another "no-view" roost, for example, is Lake Merritt where mostly gulls and cormorants roost.

In these situations, how do they sense the coming low tide?  How do they sense the most adventitious time to fly out given the great variability in tide heights, wind loads on them, etc.? 

I've googled this and have found no discussions about it. Here are some random theories I've come up with:

1. Territorial familiarity- change in water depth around the roost.
2. Occasional fly-ups to get a view.
3. Hematite in the brain which senses gravitational pull.
4. Brain interval timer.
5. Kin from other roosts with a view flying over and out.

Does anyone know of any research on this?