(1) Zugunruhe is restlessness that an animal displays around the usual time of its migration.
(2) Or, zugunruhe is the need to migrate, accompanied by a seasonally occurring restlessness.
(3) In ethology (the study of animal behavior), zugunruhe is the sort of anxious behavior that migratory animals exhibit, especially birds prevented from migrating when they normally would.
Ed is getting nervous. It's either a touch of zugunruhe, and time for him to migrate, or his giardia is acting up again.