This is the 13282nd most frequent Russian word.
морскими
"Морскими" means "marine" or "sea-related" (instrumental plural form of "морской").
Here, 'морскими' is an adjective modifying 'птицами,' indicating birds associated with or living near the sea.
Мы наблюдали за морскими птицами с берега.
We watched the sea birds from the shore.
In this instance, 'морскими' qualifies 'пейзажами,' specifying that the landscapes are related to the sea.
На выставке представлены модели кораблей, вдохновленные морскими пейзажами.
The exhibition features models of ships inspired by marine landscapes.
In this sentence, 'морскими' is the instrumental plural adjective of 'морской,' describing activities or sports related to sea environments.