Residual grains in post-harvest rice fields are key food resources for wintering yellow-breasted buntings (Emberiza aureola)

Migratory birds frequently depend on agricultural lands for food and staging areas during the non-breeding season. However, evidence regarding the use of post-harvest rice fields by the critically endangered yellow-breasted bunting ( Emberiza aureola ) at wintering sites remains scarce. We conducted detailed surveys with 84 visits across 38 post-harvest rice fields in Haikou City, tropical Hainan Island, south China, recording whether yellow-breasted buntings were observed and, when recorded, their group size while measuring rice field flooding status, residual grain density, stubble height, and survey effort. Data were analyzed using a two-stage framework. The first stage used a Bayesian binomial mixed model with field-level random intercepts to model the probability of recording yellow-breasted buntings during a survey. The second stage used a Bayesian zero-truncated negative binomial mixed model to analyze conditional group size on yellow-breasted buntings being recorded. Yellow-breasted buntings were recorded during 19 visits from nine fields, all under non-flooded conditions; none were recorded during the 23 flooded visits. Residual grain density was positively associated with both the probability of recording yellow-breasted buntings (OR = 18.04, 95% CrI: 5.12–93.21) and conditional group size (IRR = 6.22, 95% CrI: 1.58–21.90). However, the independent association between flooding status and the probability of recording yellow-breasted buntings remained uncertain. Our findings indicate that maintaining accessible residual grain resources during the wintering period may help maintain the suitability of post-harvest rice fields as wintering habitats for this critically endangered bird.