I have since the 1980s been active doing visible migration counts of birds flying over and heading backwards and forwards from their wintering quarters. This poem on the day in question (19th March 1990) was of Meadow Pipits heading back (probably from the Dee Marshes and heading North over Laund Hey in Haslingden, Lancashire, making to their breeding grounds. It was very misty and for most of the times you could not actually see the birds, but you could still hear them above the mist.
You Can hear their little twitter above this mist,
Regular, repeated, their call of contact.
What must their mind attribute,
Its delicacy and fragility, this little soul.
We will never understand,
Though patience we will share,
The Pipit searches too and fro...