Diet of the Egyptian vulture (Neophron percnopterus) - North-Western ...

2 downloads 0 Views 211KB Size Report
Sep 4, 2012 - Bulgarian]. Milchev, B. (2009): Breeding biology of the Long-legged Buzzard. Buteo rufinus in SE Bulgaria, nesting also in quarries. Avocetta.
NORTH-WESTERN JOURNAL OF ZOOLOGY 8 (2): 315-323 Article No.: 121129

©NwjZ, Oradea, Romania, 2012 http://biozoojournals.3x.ro/nwjz/index.html

 

Diet of the Egyptian vulture (Neophron percnopterus) after livestock reduction in Eastern Bulgaria Boyan MILCHEV¹*, Nikolay SPASSOV² and Vasil POPOV³ 1. University of Forestry, Wildlife Management Department, 10 Kl. Ochridski Blvd., 1765 Sofia, Bulgaria. 2. National Museum of natural History, 1 Tzar Osvoboditel Blvd., 1000 Sofia, Bulgaria. 3. Institut of Zoology, 1 Tzar Osvoboditel Blvd., 1000 Sofia, Bulgaria. *Corresponding author, B. Milchev, E-mail: [email protected] Received: 01. March 2011 / Accepted: 04. June 2012 / Available online: 04. September 2012 / Printed: December 2012

Abstract. The diet of six Egyptian vulture Neophron percnopterus breeding pairs has been studied in E Bulgaria since the sharp decline of livestock husbandry. The feeding range was based on 1694 remains and included mainly mammals (67.5% ± 7.3), birds (15.6% ± 4.9) and reptiles (14.3% ± 5.6). Domesticated mammals comprised 46.7 % ± 10.5 (range 31.8–58.2%) of the total diet, and wild mammals 20.8 % ± 14.7 (range 9.0– 44.9%). When livestock numbers decreased in the Strandzha Mountains, the share of livestock carrion and carnivore prey remains dropped in the vultures’ diet. Vultures feeding shifted to scale reptiles. The occurrence of wild animals in vulture's diets differed between years, but the importance of domestic animals remained relatively constant (range 53.5–67.2%). Human food remains were the main origin of livestock’s bones (up to 87.5%). By contrast, in the open habitats of Mt Sakar and nearby the town of Varna, Egyptian vultures took more frequently carnivores and wild birds, and less ungulates and scale reptiles. An important part of the diet is formed by the small and medium sized wild animals, but overall their utilization was low. Young tortoises were taken alive to only one nest. The changes in the food availability and subsequent changes in diets were not the decisive factor for the extinction of the Egyptian vulture in the Strandzha Mountains and Mt Sakar. Key words: Egyptian vulture, Neophron percnopterus, diet composition, diet changes.

Introduction The Egyptian vulture Neophron percnopterus is an opportunistic scavenger that uses a vast variety of animal sources in its diet. It also feeds on livestock excrement, human refuse and hunts for invertebrates and small vertebrates (Cramp & Simmons 1980, del Hoyo et al. 1994, Baumgart 2001, Mebs & Schmidt 2006). Studies in Bulgaria and neighbouring Greece showed the importance of livestock carrion in its diet (Michev 1968, Yankov 1977, Baumgart 1991, Miltschew & Georgiewa 1994, Vlachos et al. 1998). In spite of the plasticity of this diet, the reduced numbers of livestock, enhanced veterinary and sanitary controls, changes to the traditional livestock breeding practices and other changes in the food supply are pointed out as major factors for the shrinking population in Europe (Tucker & Evans1997, Baumgart 2001, Gallardo & Penteriani 2001, Iñigo et al. 2008, Donázar et al. 2009). Kurtev et al. (2008) suggested similar factors as greatly important for the Bulgarian population of the Egyptian vulture (reduced by 55% to 40 pairs in the last 20 years), without any data on their food. Diet related data are important for planning concrete measures to protect this endangered species (IUCN 2011) in specified regions, as

is already occurring for other endangered scavenger species (Margalida et al. 2009, Moreno-Opo et al. 2010). This study presents information on the diet of five (formerly) breeding pairs of the Egyptian vulture in SE Bulgaria and of a pair that still breeds west of the city of Varna in NE Bulgaria, over the period of sharp decline in livestock breeding after 1989.

Material and methods Study area The four studied pairs inhabited the Bulgarian portion of the Strandzha Mountains, which reach elevations up to 300-400 m a.s.l. and which are covered by oak and beech forests (Bondev 1991, see also Milchev 2009, Fig. 1). Three pairs (Nos. 2 - 4) lived within the Malko Tarnovo Municipality (747.4 sq. km). Arable land constitutes only 5 % of their territory and after 1992, the land was almost completely abandoned. Forests were cut out on the level crests to make way for pastures that support the traditional livelihood in that area: extensive pasture livestock husbandry. Livestock ownership has changed from public to private and livestock breeding has proved to be economically unattractive. Thus the number of domestic animals and the amount of their carrion has dropped up sharply starting from 1991/1992 (Table 1, unpubl. data of Malko Tarnovo Municipality). In 1994, livestock, apart

B. Milchev et al.

316 from pigs, were almost entirely sheltered overnight in the villages and their outskirts. The possible preservation of meat in the villages increased. Also, the human population of the Municipality has steadily decreased. As a result, the amount of food refuse sharply decreased, along with the economic crisis. Only the central municipal town of Malko Tarnovo still had regular garbage collection and a garbage dump, while in the villages garbage was simply dumped in their vicinities. Nest No 1 from the Strandzha Mountains was situated in an area with more open habitats nearby on the gentle slopes.

Figure 1. Map of the three study area with breeding Egyptian vultures Neophron percnopterus, E Bulgaria.

Table 1. Changes in livestock numbers in the Malko Tarnovo Municipality (Strandzha Mountains, S Bulgaria) between 1988 and 2000. Population trends with respect the last census appear in brackets.

Bos taurus Carpa hircus Ovis aries Sus scrofa dom. Total

1988 1487 1917 20716 4163 28283

livestock number / years 1995 2000 252 (-83 %) 173 (-31 %) 2878 (+50 %) 1953 (-32 %) 5771 (-72 %) 3973 (-31 %) 4232 (+1.7 %) 1492 (-65 %) 12881 (-54 %) 7418 (-42 %)

The pair in Mt Sakar inhabited the gentle slanting south-western slopes at 70–250 m a.s.l. Open pasturelands prevailed there as well as arable land. The decline in livestock husbandry manifested similar trends to those mentioned for the Strandzha Mountains. The location west of Varna includes the coastal hills of Beloslav Lake rising to 250 m a.s.l. It differs substantially from the previous two by the proximity of large industrial centres. Nearby villages are not as depopulated and arable land is not abandoned on a mass scale. Data collection The material was collected from 1990 under and around four Egyptian vulture nest sites in the Strandzha Moun-

tains (Miltschew & Georgiewa 1994), while they were still occupied. The food remains in the nests were collected throughout the entire period only in Locality No 3, and in the other nests after 1994. The nests were visited in late June – early July, when the nestlings were ringed, and again after the young birds fledged in late August – early September. The nest in Mt Sakar (Borisov 1988) was visited at the same times after 1999. The first material collected there comprised mainly of remains from the previous years. The material from the nest west of Varna (Meyburg et al. 2004) was sampled only once in August 2001 and also comprised of remains from previous years. Food remains consisted of bones, hides, feathers, scales and carcass parts of vertebrates and pellets in various state of preservation. The food components were determined by comparison to collections of the National Museum of Natural History and the author’s comparative collection. The invertebrates and small and medium vertebrates were reported with a minimum number of individuals. The carnivores and the ungulates were reported as the number of bones or skeletal fragments, as it was impossible to determine precisely the number of whole individual specimens for most species. The three distal parts of their limbs: tarsus/carpus, metatarsus/metacarpus and digits, associated with other smaller bones were reported as one skeletal fragment. The same applied to the skull fragments, which usually consisted of several connected bones. The relative significance of these mammals in relation to the overall amount of prey was assessed by comparing their bones/fragments with the numbers of other prey, similarly to Donázar & Ceballos (1988). The food components were categorized into ten groups: invertebrates, fishes, amphibians, tortoises, scaled reptiles, domestic birds, wild birds, small mammals, carnivores, and ungulates. Statistical differences in the frequencies of these ten groups in the diets were computed by chi-square tests. Between-years differences in the diet among the separate localities were determined by comparing diets mainly in years of successful breeding. Food remains in unsuccessful years were usually too few for comparison, but they were included in the overall amount of prey in each locality. Diet differences between the pairs from the Strandzha Mountains before (Miltschew & Georgiewa 1994) and after the change in livestock ownership during 1991/1992 (this study) were compared by combining the carnivores and ungulates into one group, while the food from Locality No 3 in 1990 was added to the food from the period prior to the changes. All statistical tests are two-tailed and significant at p