Angels are similar to the animal kingdom:
Angels are called animals, domestic and wild, as the verse states “And the face of the lion to the right, and the face of the ox to the left.” The reason for this is because similar to animals, angels do not contain freedom of choice, and their emotions are natural and instinctive. Their love and fear of G-d is not generated anew as a result of comprehension, but rather comes as an instinctive part of their nature. It is for this reason that Tzaddikim are considered to be of a higher level than angels. However, there are select angels who have the unique capability of intellectual thinking and process, hence being able to develop innovative love and fear that comes as result of comprehension.
 Tanya chapter 39 [p. 51b]
 Admur ibid in Hagah