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Blood plasma calcium concentrations in captive and wild individuals of the cape griffon vulture (Gyps coprotheres)
Corqp. Biochem. Physiol.Vol. 104A, No. 3, pp. 555-559, 1993 Printed in Great Britain
0300-9629/93 $6.00 + 0.00 0 1993 Pergamon Press Ltd
BLOOD PLASMA CALCIUM CONCENTRATIONS IN CAPTIVE AND WILD INDIVIDUALS OF THE CAPE GRIFFON VULTURE (GYPS CoPRoTHERES) ERIKA VAN WYK,*
F.
H. VAN DER BANK*and G. H. VERDOORN~
*Sanlam Research Unit for Environmental Conservation, Department of Zoology and tDepartment of Chemistry and Biochemistry, Rand Afrikaans University, P.O. Box 524, Aucklandpark, 2006, Republic of South Africa (Fax 01 I-489-241 1) (Received I June 1992; accepted 1 July 1992) Abstract-l. A calcium deficiency in young Cape vultures manifests as metabolic bone disease or osteodystrophy which is causal to crippling skeletal misformations. 2. Osteodystrophy has only been diagnosed in nestlings showing visible symptoms of the syndrome and when these signs have developed the effects are irreversible. 3. Blood chemistry levels could supply information to facilitate early prognosis of dangerous afflictions. 4. Blood plasma calcium levels of 42 Cape vultures held in captivity and from natural populations were determined. 5. The results were compared to values considered normal for different bird and mammal species. 6. Possible explanations for the fluctuating calcium concentrations are discussed.
1NTRODUCTION
Approximately 98% of the total body calcium concentration is contained within the skeleton (Taylor, 1985) and the net flux of calcium in the plasma is due to bone resorption (Vaughan, 1981). Although the skeletons of birds are well adapted to the demands of flight it is a common fallacy to assume that problems involving calcium regulation in birds are compounded by lightweight bones. In fact bird skeletons weigh almost the same as those of comparably sized mammals (Prange et al., 1979). It has been found that the regulation of plasma calcium in birds is facilitated in a similar manner as in mammals (Taylor, 1985). It can therefore be assumed that occurring complications, resulting from abnormal calcium levels would be experienced in a fashion coinciding between mammals and birds. Exemplary of such a shared phenomenon is metabolic bone disease or osteodystrophy. This condition materializes as excessive cartilage proliferation, retention of cartilage in ossified areas of bones and the absence of orderly alignment of chondrocytes, which are all symptomatic of an individual with rickets (Mundy and Ledger, 1976). Rickets is however caused by a lack of vitamin D which decreases the ability of the body to absorb calcium, whereas osteodystrophy is a syndrome which arises directly from a calcium deficiency (Mundy et al., 1980). Metabolic bone disease has been labeled as a major contributing factor to the decline in numbers experienced by G. coprotheres (Johnson, 1984) and incidence of the affliction have been witnessed in both adult birds and nestlings on various occasions by Cape vulture conservationists (Verdoorn et al., 1989). The Cape griffon vulture is endemic to southern Africa and carries a “threatened and vulnerable”
F ematological values and serum chemistry levels are sensitive indicators of the physiological status of an individual (Siegel, 1980). Biological data acquired fi-om such a physiological assay could provide excelknt indices describing the overall condition of the animal (Peinado et al., 1990) and prove to be beneficial during attempts to detect pathological s.ates in an organism (Ferrer et al., 1987). Many factors, both external and internal, for example food availability and age are known to affect the levels of tlood components (Chaplin et al., 1984). A large catabase is therefore required against which inforrlation obtained can be compared, in order to facilit lte meaningful interpretations of data resulting from analyses (Wolf et al., 1985). Avian hematology has been utilized for some years i 1 ornithological studies, where differences between the blood constituents of taxonomic groups of birds (mainly domestic species) have been described (Gee t t al., 1981). Studies concerning the normal concent rations of blood parameters in wild birds, especially raptors are not very common (Rehder and Bird, 983) and investigations focused on the variability of ! uch parameters with physiological or environmental lactors are even more scarce (Viiiuela et al., 1991). A physiological examination encompasses many parameters, one of which is the level of plasma calcium in the sample (Ghebremeskel et al., 1991a; Vahala et al., 1991). Calcium is a vital macro element rhat has four major biological functions (Hunn, 1985). Regarding the present study, one of the most critical purposes of this mineral is the structural role which involves the skeletal tissue (Williams, 1976). 555
556
ERIKA VAN WYK
status (Brooke, 1984). The birds are specialist feeders (Houston, 1975) and through no fault of their own, the specialization which evolved in order to gain an advantage over competition from other avian scavenger species at a carcass (Gin, et al., 1990), is now detrimental to the survival of the species. Possessing long necks, devoid of feathers and shovel-shaped tongues, Cape vultures are adapted to feed inside a carcass (Butchart, 1989). The birds consume mainly the muscle meat and intestines which contain inadequate calcium concentrations to satisfy the dietary needs of the vultures (Mundy and Ledger, 1976). In addition to supplementing the insufficient calcium levels in their own diet, the adult G. coprotheres rely on bone fragments, left by bonecrushing spotted hyenas (Crocuta crocuta) and other iarge carnivores, to enhance the calcium content of the food provided to nestlings (Butchart, 1990). The ongoing infiltration of man into the natural habitat of the Cape vulture has brought about a change in land-use patterns (Jilbert, 1983). Scavengers and carnivores are not compatible with ruralization or civilization and have been eradicated from these areas. The absence of bone-crushing animals have resulted in a scarcity of bone fragments and thus supplementary calcium, which is essential to normal skeletal development in the rapidly growing vulture nestlings (Coetsee, 1986). Gyps coprotheres nestlings have been reported having paper thin bones which break, bend or fold when the wings are flexed, giving rise to malformations. Many maiden flights attempted by these young birds are therefore also their last as corpses of such deformed nestlings are found at the foot of cliffs and on ledges at breeding colonies (Steyn, 1985). Calcium levels, in conjunction with other minerals such as magnesium offer good indexes as to the mineral dynamics of an individual (Lochmiller et al., 1985) and as most other hematology parameters, should fall within certain limits that could be characteristic for the species or at least for groups of related species (Ferrer et al., 1987). The object of the present study was to determine the calcium values in samples obtained from G. coprotheres individuals and to compare these results to results reported for other raptor species. References to fluctuating calcium levels caused by various factors in different bird and mammal species and the use of calcium values as indicative blood chemistry parameters was examined
et al.
in order to supplement the existing information bank of avian physiology, as data regarding threatened species are very uncommon. MATERIAL
AND METHODS
Sample collection Gyps copratheres individuals were sampled at six localities in South Africa during the period February 1990-January 1991 (Table 1). A total of 42 blood samples were obtained of which 21 were from birds held in captivity and the remaining samples from birds located in two geographically separated breeding colonies. Both colonies are situated in the Transvaal and with the exception of one adult bird, samples were taken from nestlings more than 40 days old. The captive vultures were sampied at four different institutions and ranged in age from immature to adult. Due to the extensive techniques required to positively identify the gender of monomorphic vultures (Fry, 1983) no differentiation based on sex was included in the study. Blood samples were taken from the underwing by means of a brachial venipuncture. Aliquots of 2 ml were directly transferred to polypropylene test tubes which contained heparin as anticoagulant. The test tubes were in turn placed in liquid nitrogen and transported to the laboratory. The blood samples were centrifuged at 2000g for 10 min to facilitate plasma separation and the plasma was stored at -20°C to await further analysis. Analytical methods
Chemical analyses were preformed using a Corning 940 Calcium Analyzing Instrument following the procedure and using the reagent systems as described by the manufacturers (Corning Scientific Instruments, Medfield, MA). The total plasma calcium levels are expressed as mg% (mg/dl). Each individual sample was subjected to three consecutive runs through the calcium analyzer in order to ensure maximum accuracy of values measured. Ranges, mean values (Z), and standard errors (SE) per location were obtained from levels detected in each individual. information regarding the concentrations detected in each Cape vulture is available on request from the authors. Upper and lower extremes were excluded from calculations of mean calcium concentrations for each location in order to obtain a more realistic index.
Table I. Blood plasma calcium levels of Gyps coprorheres sampled at six localities Localities Captive individuals De Witdt Johannesburg Tygerberg World of Birds Natural populations Manoutsa Scheerpoort
Coordinates
iv
Range
Mean f SE
25’41’S,27’56’E 26‘ IO’S, 27’47% 3Y 46’5,18’: 48’E 34“ 03’5.18” 20’E
9 3 7 2
6.99-10.67 10.0~10.58 7.89-10.32 9.92-9.95
9.52 i 0.959 10.30 *0.217 9.41 i 0.800 9.94 i 0.0 IS
24’ 26’s, 30” 41’E 25” 45’S, 27’45’E
1 14
8.76-10.44 6.22-l I .06
9.18 k0.561 8.82 k 1.391
Griffon vulture blood plasma calcium RESULTS
The lowest calcium concentration (6.22 mg%) was recorded in a Cape vulture from the Scheerpoort colony followed by 6.98 mg% in an individual located at De Wildt Cheetah Research and Breeding Station. The highest calcium level (11.06 mg%) was detected at Scheerpoort and is well above the upper range values calculated for the remaining locations (Table 1). The arithmetic means calculated for the four locations where the vultures are held in captivity are higher than the means determined for the two natural plrpulations. The highest average blood plasma calci urn concentrations were found for vultures from the Jrrhannesburg Zoo and World of Birds. Individuals from Scheerpoort, which include representatives of the upper and lower limits of the range for all samples a ialysed, have the lowest average value (8.82 mg%).
DISCUSSION
The dispersion of the values around their means aopear to coincide with data obtained by other authors who have studied raptor species (Balash e’ al., 1976; Ferrer et al., 1987) and the maximum r:tnge values are within limits reported for other birds of prey. Calcium concentrations for nine captive raptor species were published by Ferrer et al. (1987) where tie lowest minimum range value was 7.2 mg% (calcukited for 13 individuals of the black kite, Miluus migruns). Three Cape vulture individuals were found t,) have levels below 7.2 mg% and the mean value of 8.82 mg% determined for Scheerpoort birds (Table 1) i:. lower than averages obtained for eight out of rine raptor species studied by Ferrer et al. (1987). The latter authors obtained blood calcium values fJr the griffon vulture (Gyps fuluus), which ranged f-om 7.5 mg% to 10.9 mg%. The De Wildt and 5,cheerpoort birds have lower-limit range values less than 7.5 mg% and only samples from Scheerpoort contained levels higher than the upper-limit range 1alue of 10.9 mg% (Table 1). Blood physiology parameters, as mentioned pre\ iously, can be affected by numerous factors of which several will be discussed in order to supply possible zxplanations regarding the fluctuations detected in the present study. Stress has been labeled as an influencing factor on blood physiology parameters, c,specially when caused by handling and transport of animals. Calcium concentrations however, do not :eem to vary significantly when animals are subjected to these circumstances. In research conducted on the channel catfish (Icmlurus punctatus) pre-stress plasma calcium levels were 0.2 mg% higher than lfalues obtained after the fish had been subjected to severe handling and transport related tension (Ellsaesser and Clem, 1987). When the latter is taken into consideration with the fact that care was taken
557
to minimize stress during the sampling procedure of Cape vulture individuals, it can be disregarded as being causal to the variation in calcium levels in this study. It is a well documented fact that sexually mature females of a species in general display higher calcium levels than male individuals (LeaMaster et al., 1990). Female macaroni penguins (Eudyptes chrysoiophus) showed mean levels of 5.4mg% compared to the 2.4mg% measured in males (Ghebremeskel et al., 1991b). Levels within the female birds may as much as double, as the female accumulates adequate body reserves before the onset of egglaying (Sturkie, 1976). This can be demonstrated by calcium concentrations of 9.3 mg% (range 7.4-10.5 mg%) measured in nonbreeding females of the brown pelican (Pelicanus occident&) whereas levels of 15.5 mg% (range 10.8-22.5 mg%) were detected in breeding individuals (Wolf et al., 1985). Gender is a factor that should be considered as far as the captive individuals are concerned due to the fact that the birds varied in age from immature to mature. It can however be disregarded for the natural samples as samples were only taken from nestlings. The exceeding 10.0 mg% recorded for two birds from De Wildt and two from Tygerberg Zoo respectively in this study (Table I), may thus be indicative of female Cape vultures sampled. The age of the animal is yet another important factor which determines the calcium levels present in the body. Active bone formation takes place during the first few months of a young bird and therefore levels measured in such individuals are higher than blood plasma calcium levels for adult birds (Kan and Cress, 1987). Viriuela et al. (1991) examined nestlings, sub-adults and adults of red kites (Miluus milvus) and found the calcium levels of the nestlings to be 10.76 mg% compared to the 9.54 mg% detected in the sub-adult and adult samples. Wolf et al. (1985) reported that calcium concentrations decrease with age in the brown pelican. Definite distinctions could be made between fledglings and immature to adult groups as far as calcium levels were concerned where mean values were calculated as 11.5 mg% and 9.0mg% respectively (Wolf et al., 1985). Variation in values from the Cape vultures in captivity (Table 1) may be due to age fluctuations of birds within and between sampling areas. Although the average values obtained for the nestlings from the natural populations are lower than the mean values obtained for the individuals in captivity, it should be noted that the highest level (11.06 mg%) was measured in an individual from natural colonies. A bird from Manoutsa and one from Scheerpoort contained calcium levels higher than 10.0 mg% (Table 1). Food availability is not a factor the captive Cape vultures have to contend with due to the fact that calcium supplements are added to the food the birds receive. It has been reported that the calcium levels in individuals should not fluctuate greatly, even over
558
ERIKA VAN WYK et al.
a period of years, when they are maintained on a stable diet (Gromadzka-Ostrowska et al., 1985). A restricted food intake could definitely influence total plasma calcium levels (Lochmiller et al., 1985). The latter authors detected significantly lower values of calcium in adult male collared peccaries (Tayussu tajucu) after they had been fed on a restricted diet for three weeks. Under natural conditions Cape vultures are subjected to numerous environmental variables of which food availability is one of the greatest. The nestling is dependent on the adult bird not only for the required quantity of food but also for a certain quality of food (Brown et al., 1982). When carcasses and bone fragments are in low supply, the stronger, more aggressive parents will acquire larger portions of the quarry and therefore the nestlings of these birds will be in better condition. The reason why the wide calcium level range was detected in the Scheerpoort colony (Table 1) is not clear as the food supplied for these vultures at vulture feeding sites include fragmented bones. In reports for Cape vulture monitoring projects in 1977 and 1978 Mundy et al. (1980) noted that thirteen young birds with osteodystrophy were found at the Scheerpoort and Robert’s Farm colonies in the Magaliesberg. During their 1990 report of the two colonies Verdoorn et al. (1992) observed no immediate signs of the affliction. This positive phenomenon is a result of a direct step towards the conservation strategy being devised for this endemic vulture species. Vulture restaurants were set up at various points within the vicinity of the colonies, providing not only carcasses but also bone fragments for the Cape vultures to feed on (Friedman and Mundy, 1983; Verdoorn et al., 1992). It could be speculated that certain parent birds do have a great diligence and capacity to locate bone chips before other birds do, which would explain the fluctuations in calcium levels within nestlings of similar age groups. Data concerning normal blood plasma calcium values for G. coprotheres are absent from the literature surveyed. It was therefore not possible to assess whether the values obtained in this study are characteristic for this species or perhaps an indication of specifically in the breeding serious problems, colonies. Birds with higher serum mineral values are not a cause for concern but the low levels experienced by individuals could be indicative of pathological states which may lead to the development of osteodystrophy. Whatever the case may be, evidence suggests that a decreased immunity and increased susceptibility to infection may result from mineral deficiencies during malnutrition (Chandra and Dayton, 1982) and that young birds are less able to recover from severe calcium fluctuations (Brown et al., 1970). It could therefore be asked why low calcium concentrations were detected in the Scheerpoort colony which is known to have hosted nestlings with meta-
bolic bone disease and not in the Manoutsa colony where the incidence of this syndrome is very uncommon, and why do values obtained from the latter colony not fluctuate to the extent of the values detected in the Scheerpoort colony? In order to provide definite answers to questions such as these, further blood chemistry data for this species is required and it is essential to obtain normal values for specific parameters. The detection of blood calcium levels which could give rise to complications resulting from malnutrition is extremely important. The calcium levels in plasma for instance, normally vary between 9.0 and 10.0 mg% in humans. Tetany ordinarily occurs when blood concentrations of calcium fall from natural levels of 9.4 to approx. 6.0 mg% and it is usually lethal when levels are about 4.0 mg%. When the levels rise above approximately 12 mg%, the nervous system is depressed and reflex activities of the central nervous system become sluggish. This effect becomes marked as the blood level of calcium rises above 15.0 mg% and when concentrations exceed around 17.0 mg% in the body fluids. The effect could be rapidly lethal as calcium phosphate is likely to precipitate throughout the blood and soft tissue (Guyton, 1987). There are few pristine places left on planet earth thus vulture populations need to be managed (Eitniear, 1989). In order to devise a successful conservation strategy the maximum knowledge regarding the species involved should be obtained. It is therefore recommended that physiological data be added to such knowledge to strengthen the current strategy and ensure the success of a long term management programme. Acknowledgemenw-The authors wish to thank the Sanlam Research Unit for Environmental Conservation for financial assistance during this study. We would also like to thank Dr Lynn Golly, Mr John Spence, Dr Richard Burroughs, MS Ann van Dyk, Mr Koos Meyer, Mr Walter Mangold, Mr Walter Neser, Mr Heiner Meyer, Mr Danie Terblanche, Mr Albert Froneman, MS Ingrid Becker, Mr Richard Anker-Simmons and Mr Willie Boshoff for their cooperation and assistance during the collection of blood samples from Cape vultures. My gratitude is extended toward Mr Victor Wepener for his assistance during the analysis of the samples. REFERENCES Balash J., Musquera S., Palacios L., Jiminiz M. and Palomeque J. (1976) Comparative hematology of some falconiformes. Condor 78, 258-259. Brooke R. K. (1984) South African Red Data Book-Birds. Foundation for Research Development, CSIR, Pretoria. Brown D. M., Perey D. Y. E. and Jowsey J. (1970) Effects of ultimobranchialectomy on bone decomposition and mineral metabolism of the chicken. Endocrinology 87, 1282-1291. Brown L. H., Urban E. K. and Newman K. (1982) The Birds of Prey of Southern Africa, Vol. 1. Academic Press, London. Butchart D. (1989) Vultures a dying symbol of Africa. Getaway (October), 51-55.
Griffon
vulture
blood
Butchart D. (1990) Vultures and Farmers. Vulture Study Group, Parkview. Chandra R. K. and Dayton D. H. (1982) Trace element regulation of immunity and infection. Nutr. Res. 2, 721-733. Chaplin S. B., Diesel D. A. and Kasparie I. A. (1984) Body temperature regulation in red-tailed hawks and greathorned owls: responses to air temperature and food deprivation. Condor 86, 175-18 1. C)etsee J. (1986) Committee to avoid vulture tragedy. Vulture News 15, 21-22. E tniear J. C. (1989) Vulture populations in a changing world. Vulture News 21, 2-3. E lsaesser C. F. and Clem L. W. (1987) Blood serum chemistry measurements of normal and acutely stressed channel catfish. Comp. Eiochem. Physiol. 88A, 589-594. F:rrer M., Garcia-Rodriguez T., Carrillo J. C. and Castrovieio _ J. (1987), Hematocrit and blood chemistrv values in captive raptors (Gyps fulvus, Buieo buteo, Milvus migrans, Aquila heliaca). Comp. Biochem. Physiol. 87A, 1123-l 127. Friedman R. and Mundy P. J. (1983) The use of “restaurants” for the survival of vultures in South Africa. In Vulture Biology and Management (Edited by Wilbur S. R. and Jackson J. A.), pp. 3455354. University of California Press, Berkley. Fry D. M. (1983) Techniques for sexing monomorphic vultures. In Vulture Biology and Management (Edited by Wilbur S. R. and Jackson J. A.), pp. __ 356376. Universitv of California Press, Berkley. C ee G. F.. Caroenter J. W. and Heusler G. L. (1981) Snecies differences in hematological values of captive’ cranes, raptors and quail. J. Wildl. Manage. 45, 463483. C,hebremeskel K., Williams G., Spratt D. and Samour H. J. (1991a) Plasma biochemistry of free-living giant tortoises (Geochelone gigantea) on Curieuse Island (Republic of Seychelles). Comp. Biochem. Physiol. WA, 65-67. Crhebremeskel K., ‘Williams T. D:, Williams G., Gardner D. A. and Crawford M. A. (1991b) . , Plasma metabolites in macaroni penguins (Eudyptes chrysolophus) arriving on land for breeding and molting. Comp. Biochem. Physiol. 99A, 245-250. Ciinn P. J., McIlleron W. G. and Milstein P. (1990) The Complete Book of Southern African Birds. Struik, Cape Town. Ciromadzka-Ostrowska J., Zalewska B., Jakubow K. and Gozlinski H. (1985) Three-year study on trace mineral concentration in the blood plasma of Shetland pony mares. Comp. Biochem. Physibl. 82A, 651660. _ _
plasma
calcium
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Kan K. W. and Cress R. L. (1987) Temporal relationship between fetal bovine skeletal growth and circulating hormone levels. Calc. Tissue Inf. 40, 137-148. LeaMaster B. R., Brock J. A., Fujioka R. S. and Nakamura R. M. (1990) Hematologic and blood Chemistry values for Sarotherodon melanotheron and a red hybrid tilapia in freshwater and seawater. Comp. Biochem. Physiol. WA, 5255529. Lochmiller R. L., Hellgren E. C., Verner L. W., Greene L. W., Amoss M. S., Seager S. W. J. and Grant W. E. (1985) Physiological responses of the adult male collared peccary, Tayassu tajacu (Tayassuidae), to severe dietary restriction. Comp. Biochem. Physiol. 82A, 49-58. Mundy P. J. and Ledger J. A. (1976) Griffon vultures, carnivores and bones. South African J. Sci. 72, 106-l IO. Mundy P. J., Ledger J. A. and Friedman R. (1980) The Cape vulture project in 1977 and 1978. Bokmakierie 32, 2-8. Peinado V., Viscor G. and Palomeque J. (1990) Hematology and blood chemistry in captive Dorcas gazelles and blackbuck. Comp. Biochem. Physiol. 97A, 595-599. Prange H. D., Anderson J. F. and Rahn H. (1979) Scaling of skeletal mass to body mass in birds and mammals. Am. Naturalist 113, 103-122. Rheder N. B. and Bird D. M. (1983) Annual profiles of blood packed cell volumes of captive American kestrels. Can. J. Zool. 61, 255&2555. Siegel H. S. (1980) Physiological stress in birds. Bioscience 30, 529-534. Steyn P. (1985) The Birds of Prey of Southern Africa. David Philip, Cape Town. Sturkie P. D. (1976) Avian Physiology. Springer, New York. Taylor C. W. (1985) Calcium regulation in vertebrates: an overview. Comp. Biochem. Physiol. 82A, 249-255. Vahala J., Kase F. and Pospisil J. (1991) The development of blood picture parameters in the Cape hunting dog (Lycaon pictus). Comp. B&hem. Physiol. 99A, 37-39. Vaughan J. (I 98 1) The Physiology of Bone. Clarendon Press, Oxford. Verdoorn G. H., Becker I. and Branfield A. S. (1992) Annual census of Cape vulture nestlings in the Magaliesberg1990 results. Vulture News 6, 22-29. Verdoorn G. H., Planken H., Welch F., Becker I., Branfield A. and Branfield W. (1989) Report on the activities of the vulture monitoring project. Vulture News 22, 12-20. Vitiuela J., Ferrer M. and Recio F. (1991) Age-related variations in plasma levels of alkaline phosphatase, calcium and inorganic phosphorus in chicks of two species of raptors. Comp. Biochem. Physiol. 99A, 49-54. Williams R. J. P. (1976) Calcium chemistry and its relation to biological function. In Calcium and Biological Systems (Edited bv Duncan D. J.). DD. l-17. Svmnosia of the Society for Experimental B%ogy XXX,* Cambridge University Press, Cambridge. Wolf S. H., Schreiber R. W., Kahana L. and Torres J. J. (1985) Seasonal, sexual and age-related variation in the blood composition of the brown pelican (Pelicanus occidenrales). Comp. Biochem. Physiol. 82A, 837-846.
0300-9629/93 $6.00 + 0.00 0 1993 Pergamon Press Ltd
BLOOD PLASMA CALCIUM CONCENTRATIONS IN CAPTIVE AND WILD INDIVIDUALS OF THE CAPE GRIFFON VULTURE (GYPS CoPRoTHERES) ERIKA VAN WYK,*
F.
H. VAN DER BANK*and G. H. VERDOORN~
*Sanlam Research Unit for Environmental Conservation, Department of Zoology and tDepartment of Chemistry and Biochemistry, Rand Afrikaans University, P.O. Box 524, Aucklandpark, 2006, Republic of South Africa (Fax 01 I-489-241 1) (Received I June 1992; accepted 1 July 1992) Abstract-l. A calcium deficiency in young Cape vultures manifests as metabolic bone disease or osteodystrophy which is causal to crippling skeletal misformations. 2. Osteodystrophy has only been diagnosed in nestlings showing visible symptoms of the syndrome and when these signs have developed the effects are irreversible. 3. Blood chemistry levels could supply information to facilitate early prognosis of dangerous afflictions. 4. Blood plasma calcium levels of 42 Cape vultures held in captivity and from natural populations were determined. 5. The results were compared to values considered normal for different bird and mammal species. 6. Possible explanations for the fluctuating calcium concentrations are discussed.
1NTRODUCTION
Approximately 98% of the total body calcium concentration is contained within the skeleton (Taylor, 1985) and the net flux of calcium in the plasma is due to bone resorption (Vaughan, 1981). Although the skeletons of birds are well adapted to the demands of flight it is a common fallacy to assume that problems involving calcium regulation in birds are compounded by lightweight bones. In fact bird skeletons weigh almost the same as those of comparably sized mammals (Prange et al., 1979). It has been found that the regulation of plasma calcium in birds is facilitated in a similar manner as in mammals (Taylor, 1985). It can therefore be assumed that occurring complications, resulting from abnormal calcium levels would be experienced in a fashion coinciding between mammals and birds. Exemplary of such a shared phenomenon is metabolic bone disease or osteodystrophy. This condition materializes as excessive cartilage proliferation, retention of cartilage in ossified areas of bones and the absence of orderly alignment of chondrocytes, which are all symptomatic of an individual with rickets (Mundy and Ledger, 1976). Rickets is however caused by a lack of vitamin D which decreases the ability of the body to absorb calcium, whereas osteodystrophy is a syndrome which arises directly from a calcium deficiency (Mundy et al., 1980). Metabolic bone disease has been labeled as a major contributing factor to the decline in numbers experienced by G. coprotheres (Johnson, 1984) and incidence of the affliction have been witnessed in both adult birds and nestlings on various occasions by Cape vulture conservationists (Verdoorn et al., 1989). The Cape griffon vulture is endemic to southern Africa and carries a “threatened and vulnerable”
F ematological values and serum chemistry levels are sensitive indicators of the physiological status of an individual (Siegel, 1980). Biological data acquired fi-om such a physiological assay could provide excelknt indices describing the overall condition of the animal (Peinado et al., 1990) and prove to be beneficial during attempts to detect pathological s.ates in an organism (Ferrer et al., 1987). Many factors, both external and internal, for example food availability and age are known to affect the levels of tlood components (Chaplin et al., 1984). A large catabase is therefore required against which inforrlation obtained can be compared, in order to facilit lte meaningful interpretations of data resulting from analyses (Wolf et al., 1985). Avian hematology has been utilized for some years i 1 ornithological studies, where differences between the blood constituents of taxonomic groups of birds (mainly domestic species) have been described (Gee t t al., 1981). Studies concerning the normal concent rations of blood parameters in wild birds, especially raptors are not very common (Rehder and Bird, 983) and investigations focused on the variability of ! uch parameters with physiological or environmental lactors are even more scarce (Viiiuela et al., 1991). A physiological examination encompasses many parameters, one of which is the level of plasma calcium in the sample (Ghebremeskel et al., 1991a; Vahala et al., 1991). Calcium is a vital macro element rhat has four major biological functions (Hunn, 1985). Regarding the present study, one of the most critical purposes of this mineral is the structural role which involves the skeletal tissue (Williams, 1976). 555
556
ERIKA VAN WYK
status (Brooke, 1984). The birds are specialist feeders (Houston, 1975) and through no fault of their own, the specialization which evolved in order to gain an advantage over competition from other avian scavenger species at a carcass (Gin, et al., 1990), is now detrimental to the survival of the species. Possessing long necks, devoid of feathers and shovel-shaped tongues, Cape vultures are adapted to feed inside a carcass (Butchart, 1989). The birds consume mainly the muscle meat and intestines which contain inadequate calcium concentrations to satisfy the dietary needs of the vultures (Mundy and Ledger, 1976). In addition to supplementing the insufficient calcium levels in their own diet, the adult G. coprotheres rely on bone fragments, left by bonecrushing spotted hyenas (Crocuta crocuta) and other iarge carnivores, to enhance the calcium content of the food provided to nestlings (Butchart, 1990). The ongoing infiltration of man into the natural habitat of the Cape vulture has brought about a change in land-use patterns (Jilbert, 1983). Scavengers and carnivores are not compatible with ruralization or civilization and have been eradicated from these areas. The absence of bone-crushing animals have resulted in a scarcity of bone fragments and thus supplementary calcium, which is essential to normal skeletal development in the rapidly growing vulture nestlings (Coetsee, 1986). Gyps coprotheres nestlings have been reported having paper thin bones which break, bend or fold when the wings are flexed, giving rise to malformations. Many maiden flights attempted by these young birds are therefore also their last as corpses of such deformed nestlings are found at the foot of cliffs and on ledges at breeding colonies (Steyn, 1985). Calcium levels, in conjunction with other minerals such as magnesium offer good indexes as to the mineral dynamics of an individual (Lochmiller et al., 1985) and as most other hematology parameters, should fall within certain limits that could be characteristic for the species or at least for groups of related species (Ferrer et al., 1987). The object of the present study was to determine the calcium values in samples obtained from G. coprotheres individuals and to compare these results to results reported for other raptor species. References to fluctuating calcium levels caused by various factors in different bird and mammal species and the use of calcium values as indicative blood chemistry parameters was examined
et al.
in order to supplement the existing information bank of avian physiology, as data regarding threatened species are very uncommon. MATERIAL
AND METHODS
Sample collection Gyps copratheres individuals were sampled at six localities in South Africa during the period February 1990-January 1991 (Table 1). A total of 42 blood samples were obtained of which 21 were from birds held in captivity and the remaining samples from birds located in two geographically separated breeding colonies. Both colonies are situated in the Transvaal and with the exception of one adult bird, samples were taken from nestlings more than 40 days old. The captive vultures were sampied at four different institutions and ranged in age from immature to adult. Due to the extensive techniques required to positively identify the gender of monomorphic vultures (Fry, 1983) no differentiation based on sex was included in the study. Blood samples were taken from the underwing by means of a brachial venipuncture. Aliquots of 2 ml were directly transferred to polypropylene test tubes which contained heparin as anticoagulant. The test tubes were in turn placed in liquid nitrogen and transported to the laboratory. The blood samples were centrifuged at 2000g for 10 min to facilitate plasma separation and the plasma was stored at -20°C to await further analysis. Analytical methods
Chemical analyses were preformed using a Corning 940 Calcium Analyzing Instrument following the procedure and using the reagent systems as described by the manufacturers (Corning Scientific Instruments, Medfield, MA). The total plasma calcium levels are expressed as mg% (mg/dl). Each individual sample was subjected to three consecutive runs through the calcium analyzer in order to ensure maximum accuracy of values measured. Ranges, mean values (Z), and standard errors (SE) per location were obtained from levels detected in each individual. information regarding the concentrations detected in each Cape vulture is available on request from the authors. Upper and lower extremes were excluded from calculations of mean calcium concentrations for each location in order to obtain a more realistic index.
Table I. Blood plasma calcium levels of Gyps coprorheres sampled at six localities Localities Captive individuals De Witdt Johannesburg Tygerberg World of Birds Natural populations Manoutsa Scheerpoort
Coordinates
iv
Range
Mean f SE
25’41’S,27’56’E 26‘ IO’S, 27’47% 3Y 46’5,18’: 48’E 34“ 03’5.18” 20’E
9 3 7 2
6.99-10.67 10.0~10.58 7.89-10.32 9.92-9.95
9.52 i 0.959 10.30 *0.217 9.41 i 0.800 9.94 i 0.0 IS
24’ 26’s, 30” 41’E 25” 45’S, 27’45’E
1 14
8.76-10.44 6.22-l I .06
9.18 k0.561 8.82 k 1.391
Griffon vulture blood plasma calcium RESULTS
The lowest calcium concentration (6.22 mg%) was recorded in a Cape vulture from the Scheerpoort colony followed by 6.98 mg% in an individual located at De Wildt Cheetah Research and Breeding Station. The highest calcium level (11.06 mg%) was detected at Scheerpoort and is well above the upper range values calculated for the remaining locations (Table 1). The arithmetic means calculated for the four locations where the vultures are held in captivity are higher than the means determined for the two natural plrpulations. The highest average blood plasma calci urn concentrations were found for vultures from the Jrrhannesburg Zoo and World of Birds. Individuals from Scheerpoort, which include representatives of the upper and lower limits of the range for all samples a ialysed, have the lowest average value (8.82 mg%).
DISCUSSION
The dispersion of the values around their means aopear to coincide with data obtained by other authors who have studied raptor species (Balash e’ al., 1976; Ferrer et al., 1987) and the maximum r:tnge values are within limits reported for other birds of prey. Calcium concentrations for nine captive raptor species were published by Ferrer et al. (1987) where tie lowest minimum range value was 7.2 mg% (calcukited for 13 individuals of the black kite, Miluus migruns). Three Cape vulture individuals were found t,) have levels below 7.2 mg% and the mean value of 8.82 mg% determined for Scheerpoort birds (Table 1) i:. lower than averages obtained for eight out of rine raptor species studied by Ferrer et al. (1987). The latter authors obtained blood calcium values fJr the griffon vulture (Gyps fuluus), which ranged f-om 7.5 mg% to 10.9 mg%. The De Wildt and 5,cheerpoort birds have lower-limit range values less than 7.5 mg% and only samples from Scheerpoort contained levels higher than the upper-limit range 1alue of 10.9 mg% (Table 1). Blood physiology parameters, as mentioned pre\ iously, can be affected by numerous factors of which several will be discussed in order to supply possible zxplanations regarding the fluctuations detected in the present study. Stress has been labeled as an influencing factor on blood physiology parameters, c,specially when caused by handling and transport of animals. Calcium concentrations however, do not :eem to vary significantly when animals are subjected to these circumstances. In research conducted on the channel catfish (Icmlurus punctatus) pre-stress plasma calcium levels were 0.2 mg% higher than lfalues obtained after the fish had been subjected to severe handling and transport related tension (Ellsaesser and Clem, 1987). When the latter is taken into consideration with the fact that care was taken
557
to minimize stress during the sampling procedure of Cape vulture individuals, it can be disregarded as being causal to the variation in calcium levels in this study. It is a well documented fact that sexually mature females of a species in general display higher calcium levels than male individuals (LeaMaster et al., 1990). Female macaroni penguins (Eudyptes chrysoiophus) showed mean levels of 5.4mg% compared to the 2.4mg% measured in males (Ghebremeskel et al., 1991b). Levels within the female birds may as much as double, as the female accumulates adequate body reserves before the onset of egglaying (Sturkie, 1976). This can be demonstrated by calcium concentrations of 9.3 mg% (range 7.4-10.5 mg%) measured in nonbreeding females of the brown pelican (Pelicanus occident&) whereas levels of 15.5 mg% (range 10.8-22.5 mg%) were detected in breeding individuals (Wolf et al., 1985). Gender is a factor that should be considered as far as the captive individuals are concerned due to the fact that the birds varied in age from immature to mature. It can however be disregarded for the natural samples as samples were only taken from nestlings. The exceeding 10.0 mg% recorded for two birds from De Wildt and two from Tygerberg Zoo respectively in this study (Table I), may thus be indicative of female Cape vultures sampled. The age of the animal is yet another important factor which determines the calcium levels present in the body. Active bone formation takes place during the first few months of a young bird and therefore levels measured in such individuals are higher than blood plasma calcium levels for adult birds (Kan and Cress, 1987). Viriuela et al. (1991) examined nestlings, sub-adults and adults of red kites (Miluus milvus) and found the calcium levels of the nestlings to be 10.76 mg% compared to the 9.54 mg% detected in the sub-adult and adult samples. Wolf et al. (1985) reported that calcium concentrations decrease with age in the brown pelican. Definite distinctions could be made between fledglings and immature to adult groups as far as calcium levels were concerned where mean values were calculated as 11.5 mg% and 9.0mg% respectively (Wolf et al., 1985). Variation in values from the Cape vultures in captivity (Table 1) may be due to age fluctuations of birds within and between sampling areas. Although the average values obtained for the nestlings from the natural populations are lower than the mean values obtained for the individuals in captivity, it should be noted that the highest level (11.06 mg%) was measured in an individual from natural colonies. A bird from Manoutsa and one from Scheerpoort contained calcium levels higher than 10.0 mg% (Table 1). Food availability is not a factor the captive Cape vultures have to contend with due to the fact that calcium supplements are added to the food the birds receive. It has been reported that the calcium levels in individuals should not fluctuate greatly, even over
558
ERIKA VAN WYK et al.
a period of years, when they are maintained on a stable diet (Gromadzka-Ostrowska et al., 1985). A restricted food intake could definitely influence total plasma calcium levels (Lochmiller et al., 1985). The latter authors detected significantly lower values of calcium in adult male collared peccaries (Tayussu tajucu) after they had been fed on a restricted diet for three weeks. Under natural conditions Cape vultures are subjected to numerous environmental variables of which food availability is one of the greatest. The nestling is dependent on the adult bird not only for the required quantity of food but also for a certain quality of food (Brown et al., 1982). When carcasses and bone fragments are in low supply, the stronger, more aggressive parents will acquire larger portions of the quarry and therefore the nestlings of these birds will be in better condition. The reason why the wide calcium level range was detected in the Scheerpoort colony (Table 1) is not clear as the food supplied for these vultures at vulture feeding sites include fragmented bones. In reports for Cape vulture monitoring projects in 1977 and 1978 Mundy et al. (1980) noted that thirteen young birds with osteodystrophy were found at the Scheerpoort and Robert’s Farm colonies in the Magaliesberg. During their 1990 report of the two colonies Verdoorn et al. (1992) observed no immediate signs of the affliction. This positive phenomenon is a result of a direct step towards the conservation strategy being devised for this endemic vulture species. Vulture restaurants were set up at various points within the vicinity of the colonies, providing not only carcasses but also bone fragments for the Cape vultures to feed on (Friedman and Mundy, 1983; Verdoorn et al., 1992). It could be speculated that certain parent birds do have a great diligence and capacity to locate bone chips before other birds do, which would explain the fluctuations in calcium levels within nestlings of similar age groups. Data concerning normal blood plasma calcium values for G. coprotheres are absent from the literature surveyed. It was therefore not possible to assess whether the values obtained in this study are characteristic for this species or perhaps an indication of specifically in the breeding serious problems, colonies. Birds with higher serum mineral values are not a cause for concern but the low levels experienced by individuals could be indicative of pathological states which may lead to the development of osteodystrophy. Whatever the case may be, evidence suggests that a decreased immunity and increased susceptibility to infection may result from mineral deficiencies during malnutrition (Chandra and Dayton, 1982) and that young birds are less able to recover from severe calcium fluctuations (Brown et al., 1970). It could therefore be asked why low calcium concentrations were detected in the Scheerpoort colony which is known to have hosted nestlings with meta-
bolic bone disease and not in the Manoutsa colony where the incidence of this syndrome is very uncommon, and why do values obtained from the latter colony not fluctuate to the extent of the values detected in the Scheerpoort colony? In order to provide definite answers to questions such as these, further blood chemistry data for this species is required and it is essential to obtain normal values for specific parameters. The detection of blood calcium levels which could give rise to complications resulting from malnutrition is extremely important. The calcium levels in plasma for instance, normally vary between 9.0 and 10.0 mg% in humans. Tetany ordinarily occurs when blood concentrations of calcium fall from natural levels of 9.4 to approx. 6.0 mg% and it is usually lethal when levels are about 4.0 mg%. When the levels rise above approximately 12 mg%, the nervous system is depressed and reflex activities of the central nervous system become sluggish. This effect becomes marked as the blood level of calcium rises above 15.0 mg% and when concentrations exceed around 17.0 mg% in the body fluids. The effect could be rapidly lethal as calcium phosphate is likely to precipitate throughout the blood and soft tissue (Guyton, 1987). There are few pristine places left on planet earth thus vulture populations need to be managed (Eitniear, 1989). In order to devise a successful conservation strategy the maximum knowledge regarding the species involved should be obtained. It is therefore recommended that physiological data be added to such knowledge to strengthen the current strategy and ensure the success of a long term management programme. Acknowledgemenw-The authors wish to thank the Sanlam Research Unit for Environmental Conservation for financial assistance during this study. We would also like to thank Dr Lynn Golly, Mr John Spence, Dr Richard Burroughs, MS Ann van Dyk, Mr Koos Meyer, Mr Walter Mangold, Mr Walter Neser, Mr Heiner Meyer, Mr Danie Terblanche, Mr Albert Froneman, MS Ingrid Becker, Mr Richard Anker-Simmons and Mr Willie Boshoff for their cooperation and assistance during the collection of blood samples from Cape vultures. My gratitude is extended toward Mr Victor Wepener for his assistance during the analysis of the samples. REFERENCES Balash J., Musquera S., Palacios L., Jiminiz M. and Palomeque J. (1976) Comparative hematology of some falconiformes. Condor 78, 258-259. Brooke R. K. (1984) South African Red Data Book-Birds. Foundation for Research Development, CSIR, Pretoria. Brown D. M., Perey D. Y. E. and Jowsey J. (1970) Effects of ultimobranchialectomy on bone decomposition and mineral metabolism of the chicken. Endocrinology 87, 1282-1291. Brown L. H., Urban E. K. and Newman K. (1982) The Birds of Prey of Southern Africa, Vol. 1. Academic Press, London. Butchart D. (1989) Vultures a dying symbol of Africa. Getaway (October), 51-55.
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