Strange tracks

Reet . . .

I am in grave need of some experts.  We've seen these tracks year after year when it snows.  They always go from the direction of our porch and across the garden.  They are always these perfect rectangular shapes, some short, some super long.  Always as if a ruler has been carefully impressed into the snow from above with ne'r a smudge nor flake of snow out of place.

I've sent pics in the past to BBC naturewatch (who never replied!) and to loads of learn-ed friends -  but to no avail.

I wondered if it was a heron landing??? But what do YOU think

The scale can been seen by the size of the boot tracks nearby (size 10 boots)

Try this to get into the 'strange' mood

These were taken in the dark last night

 and these were my old pics from 2009 with a plastic ladle for a size indicator

 as you can see they are mighty big!!!

Answers not on a postcard, but in the comments box below please.