To assess the population of the puku and eventually other antelope species, line transects were conducted. The gained data should serve above all to estimate population density and population size of the antelopes. But the data also provided general information the population (sex ratio, age classes, group sizes and group composition), about habitat preferences and activity patterns (see Chapter 5). Therefore data collection was not limited to the information necessary for the DISTANCE program, but included additional data.
In theory, the transect lines are straight (THOMAS et al. 2002). They are placed at random or systematically – parallel lines are recommended (GREENWOOD & ROBINSON 2009).
Line length depends on the observer’s ability to concentrate, that ceases after 3 to 5 hours (BARRACLOUGH 2000) or 2 to 3 hours (WILSON et al. 1996). The transect lines should be placed with a certain spacing in order to avoid overlap of sightings (WILSON et al. 1996). WILSON et al.
(1996) recommend marking the lines via GPS so one is able to repeat them. The speed at which the observer moves along the line should be slow enough to detect all animals on and along the line, but fast enough to avoid double-counts or elopement of animals (GREENWOOD
& ROBINSON 2009). The distance from observed animals can be determined in two different ways: distances to the line can be assigned to distance intervals. This is advantageous if data collection has to be fast as from aircrafts (WILSON et al. 1996, BUCKLAND et al. 2001). The other way is to measure the distances either by measuring the perpendicular distance to the line or by measuring the radial distance and the sighting angle – the perpendicular distance will be calculated later (GREENWOOD & ROBINSON 2009).
In practice, the transect lines follow roads and thus they are not straight, but “this doesn’t really matter” (SHORROCKS 2007). This was the case for the transect lines driven in this study. In national parks it is not permitted to leave designated roads and tracks – invariably it is often not feasible e.g. due to dense vegetation. The aim was to cover the study regions evenly; aiming further on getting information about habitat use, the transect lines covered different habitat types. The lines were established on the second or third day of the stay without exact knowledge of the distribution of the antelopes. Preferable distance between
line transect was at least 1 km. Transect line length was 2.3 to 6.3 km in Kasanka NP and 2.2 to 3.9 km in Kafue Region (see Chapter 2.3). To facilitate the performance of the data collection, the launch and the end of the line transects were situated at landmarks, especially crossings or trees. The lines were marked and also their situation was checked via GPS (Garmin eTrex Legend). The lines were named according to their characteristics or situations. A vehicle (Toyota Landcruiser BJ 40) was used to carry out the data collection on the line transects. The advantages of using a car concerned safety reasons and eliminated the need of a WPO (Wildlife Police Officer) escort. Additionally, the antelopes are less frightened by cars then by pedestrians (own obs.). Another important aspect was the time saved. More time was available for other research tasks in between the surveys on the lines and more transect lines could be done during a day than it would have been possible if no car had been used. The speed during data collection was 3.5 to 4.5 km/h which was first gear without or with little use of the accelerator. Two persons observed both sides of the transect line: driver and co-driver were able to look out for animals. If possible, driver and co-driver changed between transect lines to avoid bias. As I could not carry out data collection alone I was assisted by students of biology.
Generally, data collection on the transect lines covered different times of the day.
Four start times were set: 7 am, 10 am, 1 pm and 4 pm (Zambian local time, UTC+2). It was aimed to sample each transect line once a day only. In Kasanka NP, data collection on the transect lines took place during four surveys: in July 2009 (from 8th to 29th July 2009, in the cold dry season), in August 2009 (from 23rd to 29th August 2009, in the progressing dry season), in October 2010 (from 7th to 12th October 2010, before the beginning of the first rains, in the hot dry season) in November 2010 (16th to 24th November, after the first rains but still in the hot dry season). Not all the transect lines were driven during each survey.
Generally, each transect was driven 4 times during each survey – beginning data collection at the predefined start times. Only Puku-Loop was sampled twice, i.e. 8 times, in the two surveys 2009. Due to the fact that Kasanka River should not be crossed via the pontoon after sunset, the transect lines Fibwe, Mulembo and Wasa – all situated on the eastern side of Kasanka River – were not sampled at 4 pm in the two surveys 2009. Mulembo was not sampled at all in 2010. For the same reason the transect Nafulwe had to be shortened in 2010. Furthermore, a survey was planned in April 2011. Unfortunately, it could not be conducted due to ongoing inundation on nearly all transect lines. In Kafue Region, data collection on the transect lines in Kafue Region took place from 13th July to 22nd August 2010 in PukuPan & Kaingu-Region (PPKR) and from 29th August to 3rd September 2010 in Kafue NP. The transect lines River and Plains in PPKR were surveyed for a second time from 20th to
21st September 2010. Exceptionally, transect lines were driven twice a day. Unfortunately, the line River could not be sampled at the 10 am start time.
After BUCKLAND et al. (2001), all animals may be recorded regardless how far they are from the line. Following this, all animals observed, bovid species only, were noted during data collection on the transect lines. In the case of detection, the following information was noted: time of the day, species, number of animals in the group, sighting (radial) distance and sighting angle. These are the main information needed for the basic analysis in distance;
thus, getting this information had the priority over the following. These were: angle to northwards direction, GPS coordinates of the vehicle, habitat characteristics, number of adult males, subadult males, adult females, juveniles and neonates in a group (according to the definitions in Table 2-1), actual activity of the individuals (according to the ethogram, see Table A. 13), body condition of adult males, subadult males and adult females (according to the definitions given by RINEY (1960), Figure 2-3). Whether animals belonged to a group, or to which group, was decided intuitively, as it is commonly done in practise (MARTIN &
BATESON 2007): individuals standing relatively near to others were considered as a group.
Table 2-1: Definition of sex and age classes used for the observations along the transect lines.
sex and age
class characteristic of the puku summarizing
term used adult male full grown individual with lyre shaped horns
adult puku bachelor male full grown individual with growing horns that are not yet lyre shaped
female full grown individual without horns
juvenile shoulder height lower than shoulder height of full grown individuals
young puku neonate shoulder height lower than belly of full grown individuals
Figure 2-3: The general appearance of the hind quarters of ungulates in good, medium and poor condition (from RINEY 1960). Good condition: If no angles appear at the points corresponding to a) and c). Medium condition: If any angles appear at the points corresponding to a) and c). Poor condition: if any of the points indicated at b), d) or e) can be observed.
After a detection of animals, the car was stopped, so information could be gathered and noted. Binoculars were used (Steiner, SkyHawk 10x42). Distance from the observer to the animals was measured with a laser rangefinder (Carl Zeiss, Victory 8x26 T* PRF). The angles determined with the use of a compass were rounded to 10°. While determining the sighting angle, the car was presumed to be 0°. To avoid double-counts data collection at one point was restricted to 5 minutes. If disturbed by other human presence (other cars, bikers or pedestrians coming toward or overtaking) data collection was interrupted for 5 minutes.