This study examines how biodiversity disclosure by Australian listed companies in high-risk (“red zone”) sectors evolved from 2008 to 2024 and whether major national and international policy announcements shifted practice from symbolic statements to specific, performance-based reporting. We analyse 3,975 sustainability and annual reports from 864 firms using text-based content analysis (with Python-assisted coding) and segmented fixed-effects panel regressions to track changes in three dimensions of disclosure quality: extent, specificity, and tone. We find that key policy announcements did not lead to immediate or sustained improvements in biodiversity reporting. While there were periods of increased disclosure, these gains were inconsistent and often short-lived. Most disclosures remained general, lacking specific targets or measurable outcomes, and were framed in neutral or positive terms. By contrast, references to voluntary frameworks—the Sustainable Development Goals (SDGs) and the Global Reporting Initiative (GRI)—were consistently associated with longer and more specific biodiversity content, highlighting the value relevance of these frameworks as a signal of commitment and transparency. Firm characteristics also mattered, and larger companies tended to disclose more extensively, but their reports also leaned heavily toward positive messaging, with limited critical or data-driven content. Overall, the results suggest that policy initiatives alone are insufficient to drive sustained change and that company characteristics and voluntary reporting frameworks are influential in shaping disclosure practices. This study contributes to the literature by offering a comprehensive, longitudinal assessment of biodiversity disclosure trends across high-risk sectors in Australia, highlighting the limited long-term effectiveness of policy signals in improving disclosure quality and in designing future sustainability reporting standards.