Four Buns in the Oven

In a shrub in my yard—four cardinal eggs. Mama flurried off the nest when I came by with the lawnmower. I'll let them be from now on, hopefully will see some hatchlings in the near future. I am always blown away by what great nests birds build—larger sticks and twigs on the outside, smaller pine needs on the inside. Who told them how to do this?