Weather and traffic
The precise timing of the migration of birds largely depends on weather conditions, such as wind direction or temperature. While some species fly to their winter quarters as far afield as Africa, others migrate just to keep ahead of the frost. Strong headwinds will keep the former grounded, while a marginal change in temperature will result in big swings in numbers for the latter. Hence our interest in the weather. You can enlarge the pictures by clicking on them. For a broader view, here's an european radar image.
During the migration season the University of Amsterdam gives a three day forecast of bird density in dutch airspace.
The German Airforce has a program in which they compute a relative bird density in a part of the European airspace that is interesting to us. You'll find it here.
Fortunately we're never hampered by the tide at the birdringing station, but to birders who want to observe the waders on the mudflats of the Waddensea the next few links will come in handy: the tide now, and later.