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A stag digs up the grass to decorate his antlers in Killarney National Park a few weeks ago.

Antler entanglement with vegetation is a common occurrence during the red deer rutting season and is primarily caused by a behaviour called “thrashing,” where stags violently shake their antlers against trees, shrubs, and ground vegetation. This behaviour serves multiple purposes: it helps remove the dried velvet that covered growing antlers earlier in the season, it deposits scent from glands near the eyes onto vegetation to mark territory, it demonstrates strength and aggression to rival males, and it creates visual displays that attract females. During peak rutting activity, stags may thrash vegetation dozens of times per day, and the force involved can uproot small plants entirely, strip bark from trees, and break substantial branches. The Irish name for red deer, “fia rua,” literally means “red deer,” and historical Irish texts frequently reference the autumn roaring season when stags’ bellowing calls could be heard echoing across valleys. The physical demands of rutting are so intense that stags typically lose 10-20% of their body weight during the season, as they spend most of their time and energy on reproductive behaviours rather than feeding. Killarney’s native red deer population represents Ireland’s only surviving indigenous red deer herd, genetically distinct from Scottish red deer introduced elsewhere in Ireland, making behavioural observations like this particularly valuable for understanding the ecology of Ireland’s original red deer. The autumn rut typically peaks in October, which means stags spend about 4-6 weeks in this heightened state of activity, after which successful males are often exhausted and in poor condition heading into winter, requiring the entire spring and summer to recover condition for the following year’s rut.