Camp. Biochem. Physid Vol. 87A, NO. 2, pp. 381.-386, 1987 0300-9629/87 $3.00 + 0.00 Printed in Great Britain 0 1987Pergamon Journals Ltd METABOLIC RESPONSES OF BUT,?30 BUTEO TO LONG-TERM FASTING AND REFEEDING TOMAS GARCIA-RODRIGUEZ, MIGUEL FERRER, JUAN C. CARRILLO and JAVIER CASTROVIEJO Estacibn Biol6gica de Dofiana, CSIC, 41013~&villa, Spain. Telephone: (954)232340 (Recej~e~ 1 August 1986) Abstract-l. The effects of long-term fasting (13 days) and refeeding (15 days) on body mass and eight blood parameters were determined in the buzzard (Buteo buteo). 2. Body mass decreased linearly during the first IO days of fasting. By day 13, the buzzards had lost 26% of their initial mass. 3. Urea and uric acid were significantly increased by the starvation. Blood glucose and cholesterol increased during fasting. The other blood parameters were not affected by food deprivation. 4. Increase in plasma globulins at the beginning of refeeding may have produced hemodilution. 5. The results suggest that tissue catabolism of proteins was strongly increased in food-deprived buzzards. INTRODUCTION ~ematological studies carried out on birds of prey have, until now, been mainly concerned with deter- minations of normal values for several blood par- ameters (Cooper, 1972, 1975, 1978; Balash et al., 1976; Smith and Bush, 1978; Gee et al., 1981; Rehder ef al., 1982; Rehder and Bird, 1983). Investigations performed with raptors into the variability of the blood parameters in relation to certain physiological or ambient factors are scant (Migliorini et al., 1973; Shapiro and Weathers, 1981; Rehder et al., 1982; Rehder and Bird, 1983; Chaplin et al., 1984). A special interest of fasting studies is not only the increased physiological knowledge of a bird, but also the possibility of obtaining data of ecological im- portance. Thus, many birds of prey, such a buzzards (Buteo buteo) must undergo phases of prey scarcity at some periods of the year, because of their irregular feeding. In this way, the available biomass can be greatly affected during the winter, when the raptors must frequently endure long periods of food de- privation, since the low temperatures, snow, rain and reduced daylight hours make prey less available (Kendeigh, 1945; Ivacic and Labisky, 1973). More- over, it is interesting to compare the fasting charac- teristics of these birds, with a strict diet, since they are carnivorous, with other groups of birds with quite different diets, in which starvation has been more widely studied (Okumura and Tasaki, 1969; Bello et al., 1976; Sturkie, 1976; Groscolas and Rodriguez, 1981; Dewasmes et al., 1984; Cherel and Le Maho, 1985). In this paper, we carry out a study of the influence of long-term fasting on body mass and basal blood rates of several hematological values (hematocrit, hemoglobin, glucose, urea, uric acid, cholesterol, total protein, albumin and globulin) in captive buz- zards (Buteo buteo). The change of these blood parameters in the raptors after a refeeding phase was also investigated. The object of this study was to acquire greater knowledge of the physiology of this bird of prey. Moreover, this can serve to establish the basis for similar investigations in other raptors, such as vul- tures or black and red kites, which may provide taxonomic and ecological data, through the com- parisons between their respective behavior as a result of fasting or determined ambient factors. Likewise, these studies of starvation augment the data that we have about the general hematology of birds of prey and help us to follow the pathological or nutritional states of the birds that are brought into our Center. Buzzards were maintained in captivity and in- vestigated in the Raptor Recuperation Center of Doiiana Biological Station. MATERIAL AND METHODS Seven buzzards (Buteo buteo) were used, which had been in captivity for 2 months. This species is found in the area of study, with a great increase in winter. Birds were kept in individual cages specially made for this purpose during April 1986, in the Raptor Recuperation Center of Doiiana Biological Station, at air temperature and natural photo- period. Before fasting and after refeeding, raptors were fed daily ad libitum, with rabbit and chicken carcasses (approx 17.4% protein, 24.8% fat, 0.9% ash and 56.9% moisture; Walt and Merril, 1975). Buzzards were previously selected in order to avoid using diseased or injured birds, which would be a serious disad- vantage for the objectives of this work. Sex differences were not considered in the data treatment. Measurements on the first day of starvation (which could be considered as normal basal levels in al! parameters) began 12 h after food had been removed. Birds were de- prived of nourishment for 13 days, weighed and bled periodically; after this time, raptors were refed daily for 15 days until the last sample was obtained. In this refeeding period, blood was always collected 12 hr after the last feed, in order to avoid metabolic interferences with the basal levels of the hematological parameters. Blood samples were always obtained from the brachial vein of the wing, at the same time each day (120&1300 hr) to eliminate diurnal fluctuations caused by the circadian rhythm (Twiest and Smith, 1970; Chaplin et al., 1984). Blood testing procedures Plasma was consistently used, because of the handling facilities it offered. Heparin was used as an anticoagulant. 381