[17] Where the birds make their nests: as for the stork, the fir trees are her house.
[18] The high hills are a refuge for the wild goats; and the rocks for the conies.
The psalmist describes the fact that plant life and animal life exist in every place that land exists. The author uses some local examples to make his point.
In order to understand further, one could ask a question like, ‘Was it by random accident that certain types of trees grow well in Lebanon and wild goats and coneys can live in high mountains?” The answer is 'No'. After all, the more one understands how complex life is, the more one cannot believe this world is a random accident. This Psalm is mainly about appreciating how God created this world and it is full of examples like these to show how this world was created.
This helps mankind understand that the same God who went to such great trouble to create all sorts of life on this planet, also cares deeply about our our lives. He wants us to live with a sense of joy and appreciation for how wonderful life can be when we trust in His existence.
[19] He appointed the moon for seasons: the sun knoweth his going down.
Truly, we are learning from these verses that the Bible is a scientific book. The truth of this verse states that we can mark the passage of time by the rise and fall of the sun and the rotation of the moon.
Before modern electronics, the sun, moon and the stars were the main way people marked the passage of time. We must never fail to remember that God created the world the way He did for a reason. We are not in control of time, He controls all. He gave each of us a specific but unknown amount of time on this planet and we should appreciate the time we have been allotted and use it wisely to make a difference for Him.