Male-Biased Partial Migration in a Giraffe Population

Abstract

Partial migration is a common movement phenomenon in ungulates, wherein part of the population remains resident while another portion of the population transitions to spatially or ecologically distinct seasonal ranges. Although widely documented, the causes of variation in movement strategies and their potential demographic consequences are not well-understood. Here, we used GPS telemetry data and individual-based photographic surveys to describe evidence for the partial migration of giraffe (Giraffa camelopardalis) in the tropical savanna habitat of Murchison Falls National Park, Uganda. Seasonal movements in giraffe have been described but have not been systematically investigated within the framework of partial migration. We characterized movement behaviors of eight female GPS tracked giraffe across one full year using a model-driven approach of net-squared displacement metrics. To further evaluate these space use patterns at the population-level, we used closed robust design multi-state capture recapture models derived from individually based photographic surveys collected seasonally over three years. We also characterized environmental conditions associated with seasonal space use by conducting ground-based vegetation surveys and analyzing remotely sensed phenology data. Our results from both individually based telemetry models and population-level multi-state models suggest intra-population variation in seasonal space use strategies with three dominant movement classes: (1) Residents in deciduous savanna characterized by Acacia sieberiana, Acacia senegal, Harrisonia abyssinica, and Crateva adansonii in the far western end of the park. (2) Residents in the broadleaf savannas characterized by Pseudocedrela kotschyi, Stereospermum kunthianum, Termalia spp., and Combretum spp. in the central sector of the park (3) Male-biased migrants that transitioned seasonally between the acacia savanna in the wet seasons and the broadleaf savanna in the dry seasons. Our results offer insights into how giraffe navigate spatiotemporally dynamic environments at both individual and population levels, providing ecological mechanisms for the emergent population dynamics of these large-bodied topical browsers.

A review of the social behaviour of the giraffeGiraffa camelopardalis: a misunderstood but socially complex species

“…Female home ranges are smaller than those of males (Foster 1966, Langman 1973, Leuthold & Leuthold 1978, Leuthold 1979, Fennessy 2009, VanderWaal et al 2014b, Deacon & Smit 2017, Knüsel et al 2019). Female ranging patterns indicate residency within a defined area, even in unfenced ecosystems, whereas males exhibit dispersal and migration (Fennessy 2009, Bercovitch & Berry 2013a, Carter et al 2013a, b, VanderWaal et al 2014a, Knüsel et al 2019, Brown & Bolger 2020). While birth site is variable (Bercovitch & Berry 2015b), this probably reflects selection for temporally variable habitat and forage factors.…”

Skeletal Dysplasia-Like Syndromes in Wild Giraffe

“…comm.). Notably, however, despite the high giraffe encounter rates during surveys in Murchison Falls NP and the relatively high subadult/adult survival in the park (Brown & Bolger, 2020), the Ugandan giraffe has not been observed during surveys since May 2017. The last reported observation of the Namibian giraffe was in July of 2020.…”

Foot shape and radiographs of free-ranging Nubian giraffe in Uganda

“…All giraffe were apparently healthy young adults living in the predominantly savanna, Borassus palm woodland, and riverine woodland on the north side of MFNP [ 34 ]. Animals were estimated to be between 1–6 years old, with estimated weights between 300–800 kg.…”