Yamshīna is an imperfect verb marked with nūn al-niswah, indicating a feminine plural subject. Likewise, yanhaḍna presents the animals' young as rising with feminine plural agreement. Such agreement is attested for animate animal groups and should not be reduced to a simplistic rule that every nonhuman plural must always have singular feminine agreement.
Khilfatan means alternately or in succession. It gives the description a rhythm: some animals move away while others appear in their place.