Bird use of grain fields and implications for habitat management at airports

Airport properties often include agricultural land cover that can attract wildlife species hazardous to aircraft, despite recommendations against row crops near air operations areas. However, few studies have directly quantified bird use of corn, wheat, and soybean fields relative to bird-aircraft collision (strike) hazard levels to support land cover recommendations. Therefore, we compared bird use among corn, wheat and soybean fields and predicted that corn and wheat would attract bird species recognized as hazardous to aviation. We also anticipated that soybeans would pose minimal attraction to such birds. Here, hazard ranking (low to extremely high) reflects the percentage of strikes involving a species that resulted in damage to aircraft. We investigated bird use among 22 corn, wheat, and soybean fields near Oak Harbor, OH, using approximately weekly point transects from 2013 to 2014. We used generalized distance sampling models and analysis of variance using distance matrices to determine bird abundance and community responses to row crop land coverages and crop height. We observed 4331 birds of 40 species, with most birds observed in wheat fields (n=2555 birds) and standing stubble (n=2409 birds). Large flocks occurred more in corn and wheat fields than soybean fields, but soybean fields harbored greater cumulative hazard scores than corn, likely due to consistent detections of small, non-flocking birds in soybean fields. Crop type and height had greater influence on medium- and high-hazard level bird species than other hazard levels. Density of medium- and high-hazard level birds increased with increasing crop height in soybean and wheat fields with wheat fields having slightly greater densities than soybeans. Corn fields also had the greatest bird densities in the tallest crop height categories. Categories of very and extremely high-hazard level bird species were rarely detected, but their abundance peaked in crops 0–15cm, similar to low-hazard level bird species. However, model selection results included null models for very and extremely high-hazard level bird species suggesting minimal effects. Overall, our results suggest that all three crop types can harbor birds hazardous to aircraft, and crop height can enhance bird use. Although not directly tested in our study, land management surrounding airports may benefit most from alternative land covers (e.g., biofuel crops), but additional research is necessary.