Meaning: This means that the owl quickly flew down to catch its prey.
Choice of Words: Owl is the subject, swooped is the verb, down is the adverb, fast is the adverb.
Alternative Expressions
The owl dived down rapidly.
Meaning: The owl flew down from the sky very quickly, headfirst.
Choice of Words: The word "dived" also means to fly down quickly, but it can also imply that the owl is flying headfirst. The word "rapidly" means very quickly.
The owl plummeted down with great speed.
Meaning: The owl fell or dropped down from the sky very quickly and steeply.
Choice of Words: The word "plummeted" means to fall or drop down quickly and steeply. The phrase "with great speed" tells us that the owl is falling very quickly.