Sayyiduna Ibn Abbas (may Allah be pleased with them both) said that the Noble Prophet (peace and blessings be upon him) forbade the killing of four creatures: the ant, the honeybee, the hoopoe, and the small bird.
Hadith Referenceسنن دارمي / من كتاب الاضاحي / 2038
The "sard" is a bird whose head and beak are large, it is half black and half white, and it has large wings.
The aforementioned four types of animals are not particularly harmful to human life; rather, there is some benefit in them. Therefore, the Messenger of Allah (sallallahu alayhi wa sallam) forbade killing or slaying them. For example, the honeybee produces honey, which is a very beneficial thing. The ant carries away fallen grains, bread, and rice from the house, thereby removing filth, stench, and impurity.
The hoopoe (hudhud) has little meat and is also tasteless; similarly, the bird "sard" is of this kind. There is no benefit in killing them. Secondly, all these animals and the entire creation glorify Allah (do tasbih), so they should not be prevented from this glorification.
«﴿أَلَمْتَرَأَنَّاللّٰهَيُسَبِّحُلَهُمَنْفِيالسَّمَاوَاتِوَالْأَرْضِوَالطَّيْرُصَافَّاتٍكُلٌّقَدْعَلِمَصَلَاتَهُوَتَسْبِيحَهُ﴾ [النور : 41]» and similarly it is mentioned in [سورة الحج : 18].