Ecology of the lappet-faced vulture Torgos tracheliotus in Saudi Arabia

Shobrak, Mohammed (1996) Ecology of the lappet-faced vulture Torgos tracheliotus in Saudi Arabia. PhD thesis, University of Glasgow.

Abstract

1- Food availability for the lappet-faced vultures was examined between 1993 and 1995. Several methods were used to estimate the number of ungulates in the area, such as aerial surveys, ground counts, questionnaires and the Ministry of Agriculture reports. The density of domestic livestock was estimated as 2.66 LSU's (LSU= Livestock Unit, one LSU equal one camel or ten sheep or ten goats). Based in studies in northern Saudi Arabia the expected carrying capacity of livestock in the study area is 0.3. This mean that the number of domestic livestock outside the reserve was nine times the predicted carrying capacity of the study area. A high mortality rate among the domestic herds provided a reliable food source for all the scavenging species in the study area. The wild ungulates were also examined, but their number was low, and their distribution was restricted to inside the reserve. There was no evidence of food shortage for the vulture population.

2- The pellets analysed from the lappet-faced vulture roost and nests sites at Mahazat as- Sayd reserve showed that they were heavily reliant on domestic ungulate carcasses. The birds might occasionally feed on live prey such as rodents and spiny-tailed lizards, but this was not a major source of food. However, there was no evidence of any seasonal variation in the type of carcasses used by the lappet-faced vultures.

3- The way in which different scavenging species located and exploited the carcasses was examined. Observations at carcasses placed in random sites showed that the brown-necked raven was the first species to arrive to the carcass. The lappet-faced vulture was the last species to find the carcass. They started foraging singly or in pairs and they moved in different directions, which would allow them to form a network in the sky and search effectively for food over a large areas. The number of vultures increased rapidly once the carcass had been discovered. The mammalian scavengers found few of the carcasses and were nocturnal.

4- The competition over the food supply was determined by measuring the amount of food removed by each of the scavenging species. Observations at the carcasses showed that the amount of food utilised by the avian scavengers was 30.4%, most of which was consumed by the lappet-faced vultures. The bill structures of the smaller scavenging birds are not adapted for tearing the skin of carcasses. However, different species of scavengers attended the carcasses at different times of the day. The small species fed in the early morning and late evening and the lappet-faced vulture concentrated on feeding in the midday. Therefore, there was no evidence that competition at the food sources had any effect on the lappet-faced vulture population.

5- The most important factor influencing the timing of breeding is probably the climate. Eggs are laid in winter to minimise the thermal stress on both the egg and the incubating adults. The number of active nests inside the reserve was far higher than outside the reserve, because the reserve provides an undisturbed area for breeding. Human disturbance is probably the main factor affecting the vulture population in the study area.

6- Observations at the nest suggested that the lappet-faced female may incubate the egg more than the male. The critical time in the lifetime of the lappet-faced vulture was probably the post-fledging dependence period, which could last up to 4-5 months. The majority of birds which died were found in this period.

7- During the first six months after fledging the distance covered by the fledging nestling increased significantly with age. There was a seasonal cycle of the lappet-faced vultures abundance at the reserve. The results from the movements of birds fitted with the satellite transmitters supported this cycle and suggested that some birds engage in short-distance migration within Saudi Arabia.

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Additional Information: Supported by a British Council scholarship.
• Keywords: Ecology.
• Colleges/Schools: College of Medical Veterinary and Life Sciences
• Supervisor's Name: Houston, Dr. David and Newton, Dr. Stephen
• Date of Award: 1996
• Depositing User: Enlighten Team
• Unique ID: glathesis:1996-71669
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 17 May 2019 09:31
• Last Modified: 02 Sep 2021 09:51
• Thesis DOI: 10.5525/gla.thesis.71669
• URI: https://theses.gla.ac.uk/id/eprint/71669