This article was downloaded by: [183.218.64.91] On: 25 March 2014, At: 09:35 Publisher: Taylor & Francis Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK Bird Study Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/tbis20 Nutritional condition of Spanish Imperial Eagle nestlings Aquila adalberti Miguel Ferrer a a Estación Biológica de Doñana, CSIC, Avd. María Luisa, Pabellón del Perú, Sevilla, 41013, Spain Published online: 25 Jun 2009. To cite this article: Miguel Ferrer (1994) Nutritional condition of Spanish Imperial Eagle nestlings Aquila adalberti, Bird Study, 41:2, 120-123 To link to this article: http://dx.doi.org/10.1080/00063659409477207 PLEASE SCROLL DOWN FOR ARTICLE Taylor & Francis makes every effort to ensure the accuracy of all the information (the Content ) contained in the publications on our platform. However, Taylor & Francis, our agents, and our licensors make no representations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of the Content. Any opinions and views expressed in this publication are the opinions and views of the authors, and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon and should be independently verified with primary sources of information. Taylor and Francis shall not be liable for any losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use of the Content. This article may be used for research, teaching, and private study purposes. Any substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form to anyone is expressly forbidden. Terms & Conditions of access and use can be found at http://www.tandfonline.com/ page/terms-and-conditions
Bird Study (1994) 41, 120-123 Nutritional condition of Spanish Imperial Eagle nestlings Aquila adalberti MIGUEL FERRER Estación Biologica de Dorian, CSIC. Avd. Maria Luisa, Pabellón del Peril, 41013 Sevilla, Spain The relationship between clutch-size, brood-size and nutritional condition in Imperial Eagle nestlings in Donana National Park (southwest Spain) was studied during 1986-88. Urea and uric acid level in blood were used to determine nutritional condition. Clutch-size, brood-size and hatching date were closely related to the physiological condition of nestlings, with the largest and earliest broods being better nourished. Sex and size order in the brood had no significant effect on nestling nutritional condition. These results suggest that well nourished females produce more numerous and better nourished nestlings. ome authors have suggested that clutchsize may be adjusted in relation to the quality of the parents or territory. 1'2 In this case, the largest clutch size would be the one with better nourished nestlings because it would tend to be associated with the best parents and/or territories. Others believe, however, that the rearing of a brood may entail a reproductive cost proportional to the size of the brood. In this case, the clutch-size with the better-nourished nestlings might not be the largest one. 3'4 The relationship between offspring number and quality has been viewed as a matter of compromise in models which predict an optimal balance between both traits. These models assume that as offspring number increases, offspring quality must decrease. 5 Large birds of prey, such as the Imperial Eagle, are characterized by long reproductive life and low reproductive rate. 6'7 Offspring quality is especially important in the reproductive strategy of raptors, $'9 since parental investment is very high in each offspring. In most reproductive studies of birds of prey, however, the number of offspring produced has been the variable analysed. lo-1 The aim of this paper is to identify trade-offs between clutch- or brood-size and nestling nutritional condition, thereby influencing fledgling quality, in the Imperial Eagle. MATERIAL AND METHODS The study, carried out in Donana National Park, southwestern Spain, from 1986 to 1988, involved 33 nestlings from 18 nests. Hatching date was known with an accuracy of 2 days. To determine hatching date, periodic visits to the nests were made from the beginning of egglaying. Clutch-size and brood-size were determined during these visits. For analysis Day 1 was considered as the date of the earliest hatch registered during the 3 years. The difference between the earliest and latest hatch was 48 days. To estimate nutritional condition the level of urea and uric acid in the blood was used. As is known for many bird species, including the Imperial Eagle, when tissue protein sources are mobilized actively by starvation, provoking an enhancement of the nitrogenous excretion components into the blood, urea and uric acid values increase. Urea and uric acid levels in blood increase with fasting and decrease slowly with refeeding. They are, therefore, good indicators of nutritional condition in species with poor fat reserves, such as raptors. 13-15 A 2-ml blood sample from the wing radial vein was extracted at the end of the nestling period (between 50 and 67 days old). Blood samples were collected in lithium heparin tubes. Blood centrifugation and se-
Nourishment levels of eaglets 121 ^ 100 80 0 60 N forearm. 20 Size order within the brood was established using forearm length. In total, 11 nestlings from 3-chick nests, 16 from 2-chick nests and 6 from 1-chick nests were analysed. In this sample there were 18 females and 15 males. For brood hierarchy analyses, those broods were considered undernourished whose mean urea value was higher than the nestling population median (median=16 mg/dl). 120-40- 20-0 0 10 20 30 40 50 Hatching date Figure 1. Relation between hatching date (considering as day 1 the day of the earliest hatch recorded during the 3 years of the study) and urea level detected in the chick's blood, using brood means (logarithmic regression r=0.558, P=0.016). paration of plasma (10 min at 3000 rpm) were carried out within 6 hr of the sample being drawn. Blood analyses were carried out in a computer process-controlled autoanalyser (Hitachi 705 multichannel autoanalyser), with the reagents recomrhended by Boehringer-Mannheim Inc. All blood samples were extracted between 11.00 and 15.00 hr to minimize the circadian variations of the biochemical parameters. 17 '19 Sex was determined by measuring the RESULTS There was no relationship between urea or uric acid levels and the age of nestlings (urea: r=0.133, df=32, P=0.416; uric acid: r=0.162, df=32, P=0.339). Hatching date proved to be closely related to the nutritional condition of the nestlings. Urea and uric acid levels increased with the hatching date (using brood means, urea: r=0.558, df=17, P=0.016; uric acid: r=0.595, df=17, P=0.009, Fig. 1). Variance analysis (4-way ANOVA) of the 18 nests using the residual from the regression of urea and uric acid levels on the hatching date showed no significant differences between the 3 years of the study (Table 1), nor were significant differences between sexes detected (Table 1). Clutch size was closely correlated with nestling nutritional condition. Nestlings from clutches of 4 eggs were better nourished than nestlings from clutches of 2 eggs (Table 1). Brood size had a significant effect on urea and Table 1. Variance analysis (4-way ANOVA) of the 18 nests using the residual from the regression of urea and uric acid levels on the hatching date in Spanish Imperial Eagle chick's blood Urea residuals Uric acid residuals n Average F P Average F P Clutch-size 2 10 0.008 0.191 3 20 0.016 3.882 0.032-0.048 3.731 0.038 4 3-0.015-0.317 Brood-size 1 6 0.016 0.191 2 16-0.010 4.201 0.021-0.048 5.282 0.012 3 11-0.214-0.317 Year 1986 8 0.001 0.069 1987 11-0.015 0.679 0.426-0.012 0.094 0.400 1988 14 0.012 0.097 Sex Male 8 0.003 1.868 0.118 0.064 2.723 0.324 Female 11-0.003-0.054
122 M. Ferrer uric acid residual values (Table 1). Size order did not have a significant effect on nutritional condition using urea and uric acid residuals (urea: F=0.170, df=32, P=0.909; uric acid: F=0.181, df=32, P=0.908), not even if we include in the analysis only those nests whose urea means were higher than the median of the population (urea: F=0.589, df=14, P=0.570; uric acid: F=1.465, df=32, P=0.269). DISCUSSION These results demonstrate significant differences in nutritional condition of nestlings. These differences were related to clutch-size, brood-size, and hatching date; the largest and earliest broods were the ones with betternourished nestlings, as predicted by Perrins & Moss. 1 The data revealed no negative trade-off between offspring number and nutritional level. Models that predict an optimal offspring number assume that the amount of energy devoted to reproduction is limited, and hence the existence of an optimum investment level per unit of offspring, but this is not universal. Interestingly, the correlation between broodsize and nutritional level was positive, which would invalidate the assumption of these models. This same conclusion was found by other authors in birds 21,22 and amphibians2 324 For many birds, productivity decreases as laying dates become later. 25'26 In the case of the Spanish Imperial Eagle, late breeding pairs produced not only fewer nestlings 2 2 but also more poorly nourished ones than earlier nesters. If, as is true for other species of raptors, 6' 12 the laying date and clutch-size are determined to a great extent by physical condition of the female during the pre-laying period, it should also follow that undernourished females would produce fewer and undernourished offspring. Several studies on other species have shown that juvenile survival increases with fledgling weight. 28'29 Thus, one might expect that undernourished Spanish Imperial Eagle juveniles suffer higher mortality. Furthermore, the poor feeding conditions faced by young eagles late in the season appear to be aggravated by a shorter period of parental care after fledging. 30 If so, a small fraction of the breeding pairs may be making a disproportionate contribution to the recruitment of the population. ACKNOWLEDGEMENTS I am indebted to F. Recio for helping in the laboratory and L. Garcia and R. Cadenas, for helping in the field. I thank A.G. Gosler, M. Marquiss and I. Newton for suggestions on the manuscript. This study was supported by DGICYT, project number PB87-0405. REFERENCES 1. Perrins, C.M. & Moss, D. (1975) Reproductive rates in the great tit, Parus major. J. Anim. Ecol. 44, 695-706. 2. Hiigstedt, G. (1980) Evolution of clutch size in birds: adaptive variation in relation to territory quality. Science, 210, 1148-1150. 3. Charnov, E.L. & Krebs, J.R. (1974) On clutch-size and fitness. Ibis, 116, 217-219 4. Smith, H.G., Kallander, H. & Nilsson, J.A. (1989). The trade-off between offspring number and quality in the great tit Parus major. J. Anim. Ecol. 58, 383-401. 5. Smith, C.C. & Fretwell, S.D. (1974) The optimal balance between size and number of offspring. Am. Nat. 108, 499-506. 6. Newton, I. (1979) Population Ecology of Raptors. T Sr AD Poyser Ltd. Berkhamsted. 7. Ferrer, M. & Calder6n, J. (1990) The Spanish Imperial Eagle in Donana National Park: a study of population dynamics. Biol. Conserv. 51, 151-161. 8. Amadon, D. (1963) The evolution of low reproductive rates in birds. Evolution, 18, 105-110. 9. Simmons, R. (1988) Offspring quality and the evolution of cainism. Ibis, 130, 339-357. 10. Newton, I. & Marquiss, M. (1981) Effect of additional food on laying dates and clutch sizes of Sparrowhawks. Ornis Scand. 12, 224-229. 11. Korpimiiki, E. (1987) Clutch size, breeding success and brood size experiments in Tengmalm's Owl Aegolius funereus: a test of hypotheses. Ornis Scand. 18, 277-284. 12. H&rnfeldt, B. & Eklund, U. (1990) The effect of food on laying date and clutch size in Tengmalm's Owl Aegolius funereus. Ibis, 132, 395-406. 13. Okumura, J. & Tasaki, I. (1969) Effect of fasting, refeeding and dietary protein levels on uric acid and ammonia content of blood, liver and kidney in chickens. J. Nutr. 97, 316-320. 14. Jeffrey, D.A., Peakall, D.B., Miller, D.S. & Herzberg G.R. (1985) Blood chemistry changes in food-deprived Herring Gulls. Comp. Biochem. Physiol. 81A, 911-913. 15. Ferrer, M., Garcia-Rodriguez, T., Carrillo, J.C. & Castroviejo, J. (1987): Hematocrit and blood chemistry values in captive raptors. Comp. Biochem. Physiol. 87A, 1123-1127.
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