Hail-induced nest failure and adult mortality in a declining ground-nesting forest songbird

Natural catastrophes are known to impact wildlife populations, however opportunities to directly measure the demographic effects associated with such events are rare. Given the projected increase in severe storms due to climate change, understanding how these weather events influence small wildlife populations will become increasingly important for conservation. During the spring 2017 nesting season, we observed a severe localized hailstorm that afforded us an opportunity to measure the immediate demographic effects on a small breeding aggregation of Golden-winged Warblers (Vermivora chrysoptera). The hailstorm produced approximately 2.5 cm diameter hail and apparently caused the failure of 89% (8/9) of monitored Golden-winged Warbler nests in a patch of early-successional forest in north-central Pennsylvania. Seven of the 8 failed nests contained broken eggs and all nests at the site showed signs of nest cup damage. Two dead Goldenwinged Warbler females were found within 0.5 m of their nests. We suspect that additional mortalities of female and male Golden-winged Warblers occurred because several thorough searches of the early-successional patch revealed little territorial or renesting behavior in the following weeks. We noted hail-caused vegetation damage across the site characterized by varying levels of defoliation and destruction to herbaceous vegetation, Rubus, and even saplings and canopy trees. Storm events such as the one described here are well known to cause mortality in grassland species; however, events that result in forest-dependent passerine mortality are notably less common. We consider here the potential longterm implications of extreme weather events on bird populations, particularly those of conservation concern. .