Movement and Home Range of Nile Crocodiles in Ndumo Game Reserve, South Africa

Peter M Calverley,Colleen T Downs

doi:10.4102/koedoe.v57i1.1234

Abstract

The study of movement patterns and home range is fundamental in understanding the spatial requirements of animals and is important in generating information for the conservation and management of threatened species. Ndumo Game Reserve, in north-eastern KwaZulu-Natal, bordering Mozambique, has the third largest Nile crocodile (Crocodylus niloticus) population in South Africa. Movement patterns of 50 Nile crocodiles with a total length of between 202 cm and 472 cm were followed over a period of 18 months, using mark-resight, radio and satellite telemetry. The duration of radio transmitter attachment (131 ± 11.4 days) was significantly and negatively related to total length and reproductive status. Satellite transmitters failed after an average of 15 ± 12.5 days. Home range was calculated for individuals with 10 or more radio locations, spanning a period of at least 6 months. There was a significant relationship between home range size and total length, with sub-adults (1.5 m – 2.5 m) occupying smaller, more localised home ranges than adults (> 2.5 m). The largest home ranges were for adults (> 2.5 m). Home ranges overlapped extensively, suggesting that territoriality, if present, does not result in spatially discrete home ranges of Nile crocodiles in Ndumo Game Reserve during the dry season. Larger crocodiles moved farther and more frequently than smaller crocodiles. The reserve acts as a winter refuge and spring breeding site for an estimated 846 crocodiles, which also inhabit the Rio Maputo during the summer months. Nile crocodile movement out of the reserve and into the Rio Maputo starts in November and crocodiles return to the reserve as water levels in the floodplain recede in May.Conservation implications: Movement patterns of Nile crocodiles show the important role the reserve plays in the conservation of Nile crocodile populations within the greater Ndumo Game Reserve–Rio Maputo area.

Highlights

The historical range of the Nile crocodile (Crocodylus niloticus) in South Africa included every major river and estuary on the eastern seaboard of the country, extending as far south as the Eastern Cape (Pooley 1982)
Between March and May 2009, ten Nile crocodiles caught were fitted with radio transmitters at Lake Nyamithi
Improvements in tracking technologies are allowing for more accurate studies on movement and home range of wildlife

Summary

Introduction

The historical range of the Nile crocodile (Crocodylus niloticus) in South Africa included every major river and estuary on the eastern seaboard of the country, extending as far south as the Eastern Cape (Pooley 1982). Populations are restricted to the northern and eastern portions of the country between the Limpopo River in the north and the Tugela River in the south (Combrink 2004; Van Vuuren 2011). In recent years the crocodile populations in some of these South African rivers and lakes have undergone severe setbacks (Botha et al 2011; Combrink et al 2011; Ferreira & Pienaar 2011). NGR in north-eastern KwaZulu-Natal (KZN) is home to the third largest Nile crocodile population in South Africa (Mathews 1994). It borders on Mozambique and little is known about the movement of Nile crocodiles into surrounding areas, including Mozambique

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