Investigating seasonal mobility in Irish giant deer Megaloceros giganteus (Blumenbach, 1799) through strontium isotope (⁸⁷Sr/⁸⁶Sr) analysis

Giant deer Megaloceros giganteus (Blumenbach, 1799) fossils are commonly found in Lateglacial deposits throughout Ireland. While their migrational behaviour has been suggested, it has never been researched. We hypothesise that giant deer underwent seasonal migrations, specifically during Late Pleistocene cold periods as a behavioural adaptation. Giant deer required a high nutrient uptake and were maladapted to the cold-dry steppe of the Pleistocene glacials. Migration allowed for optimal nutrient uptake during summer, while avoiding the harsh winter conditions of the glacials by moving to sheltered, low-lying areas. In this study strontium isotope analysis (⁸⁷Sr/⁸⁶Sr) of sequentially sampled dental enamel is conducted for the first time on giant deer that were previously sampled in the same manner for δ¹³C and δ¹⁸O, allowing correlations between the isotope data sets. One specimen from Ballybetagh, Dublin generated results indicating seasonal mobility behaviour. This individual was perhaps pushed to migrate at the Younger Dryas stadial onset as the vegetation giant deer depended on disappeared in Ireland. Adaptive mobility behaviour in response to climate was perhaps imperative to their survival through previous glacial periods, but other Eurasian populations would need to be analysed to make such a general conclusion.