European crow hybrid zone poem

A poem by Jochen Wolf, that describes the European crow hybrid zone.

Crows are generally believed to be black,
but some think that they are grey.

fact is, both parties are right,
and anyway all crows are black at night.

but during day they meet along a narrow hybrid zone
where they eat and play.
and sometimes mate, and assortatively clone.
black with black and grey with grey.
so the question is: why do black and grey stay away.

to answer this riddle we climbed many pines,
and raised a good deal of young, for food that they shout.
we sequenced genomes and programmed
until the keyboard shines

and kind of
figured it out.