Global biodiversity loss causes a critical threat to humanity, and corporate funding is essential to bridge the significant financial gap in conservation efforts. Firms are therefore expected to integrate biodiversity into their business and to disclose related actions. However, reporting and action remain voluntary in countries such as Japan. Under such conditions, funding may not be provided at all, or it may be pursued mainly as philanthropy with only small amounts funded. To investigate these challenges, our study empirically analyzes the patterns and determinants of biodiversity initiatives using disclosure data from Japanese firms. The results demonstrate that information on conservation finance is scarce and investments embedded in business operations are uncommon. We also find that firm size and board characteristics are key determinants of engagement. These findings emphasize the limitations of the current voluntary approach and highlight the need for policy interventions to mainstream biodiversity in business.