Beethoven's musical style
The compositions that Beethoven wrote in his formative period can be generally characterized by the composer's efforts to master the predominant classical language of the period. His works from this period can be subdivided into two, based on the composer's residence. First, various juvenalia, written when the adolescent Beethoven was in residence in Bonn and heavily indebted to the works of contemporaries, especially Mozart and his teacher, Christian Gottlob Neefe. These early efforts can be seen in a set of three piano sonatas and piano quartets (WoO 36) that Beethoven wrote before 1792. The Quartets, for instance, are each specifically modelled after three Violin sonatas Mozart published in 1781 – K 296, 379 and 380 – and Beethoven would later draw upon this familiarity in the composition of several of his own Violin Sonatas.
Yellowhammer
Beethoven's student, Carl Czerny, and biographer Anton Schindler, both suggested that the composer got the idea for the first four notes of his 5th symphony from the yellowhammer's call, although it is more likely that the opening of the 4th Piano Concerto was actually the work in question. Beethoven also used the yellowhammer theme in two piano sonatas, no. 21 in C major (the "Waldstein", Op.53) and No. 23 in F minor (the "Appassionata", Op.57).