The Agab Pride

Xpl-17 Xpl-18

A GPS collar was fitted to Xpl-18 between Jul & Oct 2005.

Due to constraints imposed by the terrain, observations on marked lions are restricted to daytime radio tracking. Anecdotal observations suggest that lions move extensively at night and that they may utilise habitats not reflected by the conventional radio tracking data. To address this concern a GPS radio collar (courtesy of Ingrid Wiesel) was fitted to a lioness (Xpl-18) of the Agab Pride, for a three-month period in July 2005. The GPS radio collar was programmed to record daily position coordinates (fixes) every two hours, between 17h00 and 10h00 (UTC). Over the three months the GPS radio collar recorded 893 fixes during 104 nights (Table 1). The lioness moved an average calculated distance of 8.3 km per night, but utilised only 22% of the pride’s known home range (Table 1). Over the same period Xpl-18 was also located 17 times, using conventional VHF tech-niques (see Methods). These aerial radio-tracking locations reflected only 8% of the known home range, and 34% of the area recorded by the GPS collar (Fig. 1).

Category GPS collar Aerial tracking (VHF)
No. of fixes 893 17
No. of nights (data units) 104 17 (days)
No. of fixes per night 8.6 +- 1.3 -
Mean distance moved per night 8.3 +- 5.8 km -
Range of distances moved 0.08 - 24.1 km -
Total distance moved 858 km -
Home range (MCP) 592 sqr km 201 sqr km
Percentage of known home range 22 % 8%

Extended nocturnal movements to the north and northeast, and outside the ephemeral river sys- tems (GPS collar data), was not captured by the conventional daytime methods. The GPS data on nocturnal movements of Xpl-18 revealed interesting patterns, not previously known, and in support of the anecdotal information on extended movements at night.

Fig. 1. Locations of Xpl-18 from a GPS radio collar & aerial radio tracking Fig. 2. Layout of nocturnal movements of Xpl-18 during six nights (see Table 2)

In order to demonstrate these findings, a sub-set of six nocturnal movements, is presented (Fig. 2). The movements of Xpl-18 were often erratic, as she crossed over mountains, and between different tributaries of the ephemeral river systems. With the exception of 23 July 2005 (blue line), there were frequent and considerable changes in the direction of movements. The distance between one day-time-resting-spot and the next, is substantially less than the actual distance moved during the night, as recorded by the GPS collar (Table 2). Conventional radio- tracking techniques (daytime loca- tions) clearly produce inadequate data on movements and habitat use, when compared with the GPS collar data.

Table 2. Summary of distances moved during six nights by Xpl-18 (Agab Pribe), as recorded by a GPS radio collar between 11 July and 22 October 2005.

Date

Colour

Distances (km)

Proportion

GPS data

Day resting

23 Jul 05

Blue

16.0

14.8

93 %

19 Aug 05

White

15.7

7.3

46 %

23 Aug 05

Yellow

17.3

9.4

54 %

16 Sep 05

Red

16.2

2.2

14 %

28 Aug 05

Green

22.2

17.4

78 %

29 Jul 05

Orange

24.1

7.2

30 %