This is the 16597th most frequent Russian word.
северу
"Северу" means "to the north" in English.
In this sentence, 'северу' is used to refer to the north region of Russia, indicating the area where the travels took place.
Мы отправились по северу России в поисках приключений.
We traveled across the north of Russia in search of adventures.
Here, 'северу' indicates the northern direction or side relative to the house, used to spatially describe the location of the birds.
К дому под северу прилетели перелётные птицы.
Migratory birds arrived by the northern side of the house.
In this context, 'северу' again refers to the northern regions, used to specify the area concerning the route planning.