Long-term tracking reveals variable partial migration and nomadism in an Endangered bustard

Abstract

Nomadism is characterised by irregular movement patterns that vary within and among years, as individuals respond to dynamic environmental conditions across space and time. Nomadic bird movements are poorly understood because their high variability challenges traditional monitoring techniques. To effectively manage nomadic populations, we need better understanding of their movement patterns. Ludwig’s Bustard Neotis ludwigii is a nomad in the semi-arid shrublands in southern Africa that is presumed to follow seasonal rainfall patterns. It is classified as Endangered owing to power line collisions, but conservation efforts are hampered by limited understanding of its movement ecology. We analysed GPS tracking data for six Ludwig’s Bustards lasting up to 12.7 years, the longest for any nomadic bird, to assess individual space-use, movement intensity (distance, duration and frequency) and regularity (timing and direction). Movement patterns and home ranges varied considerably among individuals and across years, irrespective of tracking time. Two bustards were partial seasonal migrants, while four were nomadic. Home range size spanned 4 600 to 158 200 km². Most individuals’ home ranges contained more than one core area, linked by erratic movements, and ranges expanded in the dry season. We recorded 49 long-distance (>137 km) and 212 short-distance (6–130 km) movements. Five of six bustards completed long-distance movements, the longest of which was 642 km in eight days. Long-distance movements were typically westerly in winter and easterly in summer, following large-scale rainfall patterns, whereas the timing and direction of short-distance movements were irregular and variable. Individuals spent 0–3.5% of time within protected areas. Our study provides new insights into the movement ecology of Ludwig’s Bustards, which exhibit both nomadic behaviour and facultative partial migration. These flexible strategies reflect adaptation to an unpredictable semi-arid environment. By revealing previously unknown movement patterns, our long-term tracking contributes novel understanding of nomadic behaviour and informs conservation of this threatened species.