Portrait v. Landscape

Morning Blue and Green
 There is a difference besides the up/down, side to side.  I wonder when real deal artists make the choice just how they conclude which to choose.  A minor point on such a nice morning.
Shadows at 7am sharp
 Some settings seem to demand the portrait.
Never too early for a curious seagull
While others, like our seagull, just needs room to move side to side while looking for the morsel of bread.