Causes of nest failure vary with water depth, nesting substrate, and adverse weather in the endangered wetland-breeding <i>Rostrhamus sociabilis plumbeus</i> (Everglade Snail Kite)

ABSTRACT Understanding the causes of nest failure is important for interpreting species interactions, drivers of population limitation, and wildlife management. Nest-site characteristics such as hydrology and the stability of nesting substrates may alter the level of risk attributed to different types of nest failure, yet identifying how these factors alter types of nest failure remains rare. We evaluated causes of nest failure for 116 nests in a federally endangered wetland bird, Rostrhamus sociabilis plumbeus (Everglade Snail Kite), during the 2020–2021 breeding seasons using passive infrared game cameras. We tested factors including water depth, peak wind speed, and the type of substrate supporting nest structures (woody or herbaceous) as potential drivers of variation in causes of nest failure using multinomial mixed models. Nest failure increased with decreasing water depth for nests built on woody substrates due to an increased risk of predation by terrestrial predators. The effect of water depth on nest abandonment varied based on nesting substrate, with abandonment increasing as water depth increased for nests built on herbaceous substrates. Despite prior concern over high nest collapse rates in herbaceous substrates, collapse occurred in both substrate types and increased with strong winds caused by storms. Our results identify cause-specific patterns of nest failure for a federally endangered bird that can help guide wetland management and highlight that predator communities on nesting birds can vary across environmental gradients.