Koala tree-use dynamics vary with tree size and local tree density in a fragmented landscape

Abstract

Movement between trees is essential for arboreal herbivores in fragmented landscapes, but ground travel can increase energetic costs and predation risk. However, the fine-scale data needed to understand how tree-level decisions shape broader patterns of space use have rarely been available. We combined high-frequency GPS and accelerometry to analyse 92 tree visits from nine free-ranging koalas (Phascolarctos cinereus) monitored over approximately 8-10 days in a fragmented agricultural landscape. We predicted that koala tree use would reflect a balance between the benefits of remaining in a given tree and the costs of moving to another, particularly where movement between trees required ground travel. For each visit, we quantified the temporal dynamics of tree departure, residence time, and within-tree activity in relation to tree size, canopy cover, surrounding tree density, and time of day. Koalas remained in trees about four times longer during the day than at night, were about twice as active during night visits, and were most likely to leave trees before dawn. Koalas also became progressively less likely to leave larger trees as a visit continued, suggesting that larger trees may provide greater value for prolonged occupancy. In contrast, koalas left trees sooner where local tree density was higher, indicating shorter residence times where nearby alternatives were more readily available. In fragmented landscapes, retaining large trees and maintaining locally connected tree cover may therefore help preserve tree-use and movement options for koalas.