Weak Declension of Masculine Nouns
There exists a group of masculine nouns which, except in the nominative case, receive an additional ending in all other cases. If the noun ends in '-e', the ending is 'n'; if it ends in a consonant, the ending is 'en', with exceptions being 'der Bauer' and 'der Herr'.
Here are some subgroups
a/ nouns with Latin origin: Dirigent, Kollege, Student, Präsident, Kandidat, Polizist
b/ names of animals ending in '-e': Löwe, Affe, Hase, Rabe, Falke
c/ other nouns ending in '-e': Junge, Glaube, Funke, Gedanke
d/ the only exception is 'Herz', from the neuter gender 'dem Herzen, des Herzens''