Monitoring of Arabian oryx at reintroduction sites

Mahazat as-Sayd Protected Area

During 1990-92, a team of rangers under the supervision of the reserve's manager tracked and located oryx daily. As the population grew and animals dispersed into many small groups it became increasingly difficult to account for all of the oryx each day. Since May 1995 regular transect surveys have been carried out in the reserve. Between 1990 and 1997, the population increased steadily up to about 400 individuals. In 1998 and 1999, because of severe drought conditions, the population levelled off around 350-400 individuals. Good rainfalls, and therefore enhanced forage conditions in 2001 and 2002 allowed the population to recover. By May 2002, the population was estimated to have reached about 500 individuals [Mésochina, pers. com.].

Population dynamics

Because the reserve is fenced, emigration and predation are not limiting the oryx population growth. We have recently developed a computer model that evaluates the probability of extinction of the Mahazat as-Sayd oryx population under various management strategies [Treydte et al., 2001]. The most successful management plan consisted of removing every year all oryx above 70% of the carrying capacity. Management is required to avoid larger fluctuations of the population and to maintain the Mahazat as-Sayd oryx population within the limits of a desirable population size.

Productivity of Arabian oryx at Mahazat as-Sayd Protected Area

Births

During 2005, a total of 81 new oryx calves were recorded, which is one of the highest numbers of calves recorded during the last nine years. However, it is important to note that the majority of the females credited with calves during 2005 were not individually identifiable (this also applies to the previous eight years). It is therefore likely that at least some of these calves have been recorded more than once. It is not known to what extent re-recording has taken place (Ismail and Strauss 2005).  While in 2006, 62 new oryx calves were recorded of that only 24 (38%) of the calves were born from the marked females (Ismail and Strauss 2006).

In total, 62 new oryx calves were recorded during 2006.   While all of the new oryx calves recorded were born to females which were wild-born in Mahazat as-Sayd, only 24 (38%) of the calves were born to identifiable (i.e., marked) females (Ismail and Strauss 2006).

Mortalities

There were 13 oryx mortalities, including two poaching incidents, recorded in the Mahazat as- Sayd Protected Area during 2005. The majority (n=7 or 53%) of the mortalities were recorded were adult males, while four carcasses of female oryx were also recorded. The remaining two animals were sub-adults at the time of death and their sexes could not be determined when they were found. Six of the animals that were found dead were marked individuals, including two animals that were released into the area during March 2005 (Ismail and Strauss 2005).

There were 47 oryx carcasses located in Mahazat as-Sayd during 2006. They were 4 (9%) calves, 16 (33%) sub-adult males, 11 (25 %) adult females and 16 (33 %) adult males (Ismail and Strauss 2006).

Status of marked Arabian oryx in Mahazat as-Sayd Protected Area

The status of 80 individually identifiable oryx was confirmed through the use of the sectors during 2005, with six of these animals being found dead. At the end of 2005 the maximum number of marked oryx still potentially alive in the area was therefore adjusted to 139 animals (Ismail & Strauss 2005b). From January 2006 to 16 November 2006 the number of individually identifiable marked oryx located through the use of sectors equalled 78, with one of these animals being found dead. On 16 November 2006 the maximum number of marked animals potentially still alive in the area was 144 animals. Similar proportions of the marked oryx were located during both 2005 (80/145 = 0.551) and 2006 (79/146 = 0.541) when only considering those observations made while covering the sectors. The status of c. 45% of the marked animals remained unconfirmed through sectors or additional observations at the end of the reporting period (Strauss & Ismail 2006).

Poaching of Arabian oryx and other species

During the reporting period poachers entered the Mahazat As-Sayd Protected Area on four occasions through the fence along the Al-Khurmah road (Ismail and Strauss 2005).

• 18 September 2005: an adult ostrich and a sand gazelle were killed;
• 15 October 2005: two pregnant female oryx were killed by poachers. Observations following the incidents showed that the poachers eviscerated the two females on site before removing the carcasses. Two fetuses were also discovered among the internal organs.
• 8 December 2005: the external fence is again cut along the Al-Khurmah road. Investigation showed that no further attempt was made to poach animals at this time.
• 15 December 2005: two gazelles are poached.
• No poaching recorded in 2006

Total population of Arabian oryx at Mahazat as-Sayd Protected Area

The oryx population in 2006 was estimated at 896 ± 330 oryx.

'Uruq Bani Ma'arid Protected Area

Monitoring and population dynamics

A summary of the status of the marked oryx in the area as known, from where it can be seen that 101 marked oryx are still presumed to be alive in (and around) the protected area.

It is interesting to note that although fewer days per year were spent on monitoring the oryx in 2005 & 2006, in comparison to 2004, efficiency in identifying the marked oryx was higher in both 2005 (0.5 animals/day) and 2006 (0.5 animals/day) than during 2004 (0.3 animals/day). This despite the fact that animals have undoubtedly become more unapproachable from 2004 onwards as the wild-born animals increased, while the number of working radio-collars decreased, and monitoring intensity of both biologist and protected area rangers decreased significantly (Strauss 2006).

This suggests that a combination of intimate knowledge of the difficult terrain – due to extensive previous experience by monitoring staff in the area - and Arabian oryx biology and behaviour is essential for effective monitoring of this reintroduced population.

* Total number of days of intensive monitoring by a biologis

The status of many of the marked oryx remains unconfirmed in the area with some of the animals (n=2) not seen since 1999. During 2004, for example, 19 marked oryx were confirmed alive but could not again be positively identified during 2005 and 2006(Strauss 2006).

Productivity of Arabian oryx at 'Uruq Bani Ma'arid Protected Area

Births

Successful calving has been recorded in four of the marked females that could be identified during 2005. Although the absolute number of new calves attributed to identifiable females is low, it should be noted that only 16 females were positively identified during the reporting period. Consequently 25.0% of the marked females located were found with calves at heel during this time. At least another five of the identified females were recorded as pregnant at various times of the reporting period. The outcomes of these pregnancies are not known, again due to the difficulties in identifying the animals during any particular monitoring period.

Mortalities

One mortality was recorded among the marked oryx during 2005, and this was attributed to poaching. The remains of a further four oryx were also located. Due to the fact that a copy of the pre-2005 monitoring database is not available to NWRC it is unclear whether some of these animals have previously been recorded as dead.

Population size

In 2004 the Arabian oryx population in the area was estimated as between 107 and 150 animals (Chassot et al. 2005), following a total count in the escarpment areas that are generally frequented by oryx during the summer months. Due to various logistical constraints this survey was not repeated during 2005 or 2006, although work has started on developing a combination of aerial and ground survey techniques to estimate the population sizes of all ungulates in the area (Wacher, 2006).

As per Strauss (2005) a population estimate, using the monitoring data collected during July 2005. This monitoring period was chosen because the 15 marked animals identified during that visit were the most seen during any of the monitoring periods. The estimate below depends on the following three assumptions:

• There are an estimated 72 marked oryx assumed to be alive in the population
• All animals are equally likely to be seen on more than one occasion during the monitoring period
• This makes it possible to estimate the total number of marked animals seen but not identified. On average each identified oryx was seen 1.7 times, while a further 15 observations were made of marked oryx that could not be identified during July. It is therefore estimated that an additional 9 marked oryx (15/1.7) were located and not positively identified.
• A marked animal that has been identified remains identifiable during all subsequent observations of the monitoring period.

Using the method described by Minta and Mangel (1989) population estimates were therefore generated using the program NOREMARK (White 1996) and the following parameter values:

• Total oryx seen: 84
• Number of marked oryx: 24 (15 identified + 9 estimated)
• Number of marked animal sightings: 35 (note that the “9 estimated” marked animals are regarded as being seen only once; this is the most conservative approach)
• Observations of unmarked oryx: 84-35 = 49
• Total number of marked oryx alive in population: 72
• Population size (N) = 173 oryx (CI: 145-208)

References

Anajariyya & Muhammed 2005. Arabian Oryx – Captive Breeding - NWRC Annual Report 2005, unpublished report.

Anajariyya & Muhammed 2006. Arabian Oryx – Captive Breeding - NWRC Annual Report 2006, unpublished report.

Chassot, P., 2004. Field Biologist’s report in ‘Uruq Bani Ma’arid – NWRC Monthly Report for December 2004, unpublished report (22pp).

Ismail, K. & Strauss, W. M. 2005. Ungulate monitoring in Mahazat as-Sayd Protected Area - NWRC Annual Report 2005, unpublished report.

Ismail, K. & Strauss, W. M. 2006. Ungulate monitoring in Mahazat as-Sayd Protected Area - NWRC Annual Report 2006, unpublished report.

Strauss, W. M. 2006. Arabian oryx and Sand gazelle monitoring in Mahazat as-Sayd Protected Area – NWRC Annual Report 2006, unpublished report.

Strauss, W. M. 2005. Uruq Bani Ma’arid Protected Area – NWRC Annual Report 2005, unpublished report.

Strauss, W. M. 2006. Uruq Bani Ma’arid Protected Area – NWRC Annual Report 2006, unpublished report.

Wacher, T.J., 2006. Monitoring Results: Uruq Bani Ma’arid; August 2006. King Khalid Wildlife Research Centre Gazelle Reintroduction Programme, unpublished report (12 pp).

White, G.C., 1996. NOREMARK Software Reference Manual. Department of Fishery and Wildlife, Colorado State University. (34pp)