This study investigates the use of AI tools in academic writing through analysis of AI usage declarations in journals. Using a mixed-methods approach combining content analysis, statistical analysis, and text mining, this research analyzed 168 AI declarations from 8,859 articles across 27 categories. Results show that ChatGPT dominates academic writing assistance (77% usage), with significant differences in tool usage between native and non-native English speakers (p = 0.0483) and between international and non-international teams (p = 0.0012). The study reveals that improving readability (51%) and grammar checking (22%) are the primary purposes of AI tool usage. These findings provide insights for journal policy development and understanding the evolving role of AI in academic writing.