Almighty Allah declared: So they routed them by Allah 's Leave and David killed Goliath, and Allah gave him (David) the kingdom after the death of Saul and Samuel and wisdom, and taught him of that which He willed. And if Allah did not check one set of people by means of another, the earth would indeed be full of mischief But Allah is full of Bounty to the Alamin (mankind, jinns and all that exist)." Surah 2: 251

David Becomes a Prophet
David became the most famous man among the Israelites. However, he was not inveigled by this; he was not a prisoner of fame or leadership but a prisoner of Allah's love.
Therefore, after killing Goliath he went out into the desert in the company of nature, glorifying Almighty Allah and contemplating His favors.
Verily, We made the mountains to glorify Our Praises with him (David) in the Ashi (i.e. after the mid-day till sunset) and Ishraq (after the sunrise till mid-day). And (so did) the birds assembled: all with him (David) did turn (to Allah i.e. glorified His Praises). We made his kingdom strong and gave him wisdom and so und judgment in speech and decision. Surah 38: 18-20
Creatures such as the plants, birds, beasts, and even the mountains responded to his voice glorifying Allah. Allah had chosen David to be a prophet and revealed the Psalms to him. As He the Almighty said: ... and to David We gave the Psalms. Surah 17: 55

Daivd is Granted the Language of Animals
David recited his scripture and glorified Allah while the mountains joined him in praise and the birds rallied around him. Almighty Allah directed: Be patient (0 Muhammad) of what they say, and remember Our slave David, endued with power. Verily, he was ever oft-returning in all matters and in repentance (toward Allah.) Surah 38: 17
David's sincerity was not the only factor responsible for the birds and beasts joining with him in glorifying Allah, nor was the sweetness of his voice. It was a miracle from Allah. This was not his only miracle, for Allah also endowed him with the faculty of understanding the languages of birds and animals.