SUMMARY The diet of African buffalo Syncerus coffer (Sparrman) was studied in Lake Manyara National Park, northern Tanzania, in conjunction with production, consumption and protein concentration of the major food plants. Production and relative growth rates of leaves of Cynodon dactylon (L.) Pers., Cynodon plectostachyus (K. Schum.) Pilg. and Sporobolus spicatus (Vahl) Kunth were generally highest during the short rains, lower during the long rains and negligible during the long dry season. The grass Chloris gayana Kunth showed its peak in production and consumption in the dry season. The concentration of crude protein in the green leaves reflected this pattern of growth and was highest during periods of vigorous growth. Green leaves always had a higher crude protein concentration than green stalk, and green parts than dead parts. Cyperus laevigatus L. did not show marked seasonality in its production pattern or in the crude protein concentration in its green parts. The diet, as determined through faecal analyses, reflected grass species high in protein, except during the dry season when the buffalo concentrated on the sedge, which had a low protein concentration but which offered a dense sward enabling them to collect sufficient food. The concentration of crude protein in the diet was determined through faecal nitrogen determination. The quality of the diet showed a clear seasonality, at the end of the dry season approaching the minimum requirements for maintenance. The crude protein concentration showed that the buffalo consumed a combination of species and species parts, so that they ingested a balanced diet with regard to their requirements for protein and energy. Résumé On a étudié le régime alimentaire du buffle africain Syncerus coffer au Pre National du Lac Manyara, en Tanzanie du Nord, en rapport avec la production, la consommation et la concentration en protéines des principales plantes alimentaires. La production et le taux de croissance relatif des feuilles de Cynodon dactylon, C. plectostachyus et Sporobolus spicatus sont généralement les plus élevés durant la petite saison des pluies, plus faibles durant la grande saison des pluies et négligeables durant la grande saison sèche. La production et la consommation de la graminée Chloris gayana sont maximales durant la saison sèche. La concentration de protéines brutes dans les feuilles vertes reflète ce mode de croissance et est la plus élevée durant les périodes de croissance vigoureuse. Les feuilles vertes ont toujours une concentration de protéines brutes plus élevée que la tige, et les parties vertes plus élevée que les parties mortes. On n'a pas relevé de saisonnalité marquée dans le mode de production ou la concentration en protéines brutes dans les parties vertes de Cyprus laevigatus. Le régime alimentaire, établi par analyses fécales, reflète la présence d'espèces de graminées riches en protéines, sauf durant la saison séche lorsque le buffle se concentre sur les laîches; celles‐ci ont une concentration faible en protéines mais constituent une p...

A comparison of the feeding strategy of four large herbivores-buffalo, wildebeest, Burchell's zebra and elephant-was carried out in Lake Manyara National Park, Tanzania. It appears that, especially during the dry season, elephant are timelimited and, presumably to alleviate a shortage in energy intake, switch from grazing to browsing. Zebra and wildebeest show very high grazing times during the day and have very little resting time during the dry season. If these two species are time-limited at that time of the year, it appears to be due to predation risk at night. Buffalo are not time-limited, and show two foraging strategies; namely, an option in which they emphasize bulk feeding, and one in which selection is stressed. They appear to be resource-limited. All four species show a remarkable correspondence in the proportion of time they spend on food collection. On a yearly basis, the amount of time spent on foraging plus moving approximates to 80% of their (day) time. Nevertheless, the feeding strategies of these species are different although they inhabit the same environment and face the same sort of shortages. R6SWlliiOn a compark les stratkgies alimentaires de quatre grands herbivores-buffle, gnou, ztbre de Burchell et klkphant-au Parc National du Lac Manyara, en Tanzanie. I1 semble que, specialement durant la saison stche, les klephants manquent de temps et, sans doute pour compenser une insuffisance en apport knergktique, passent a la consommation de feuilles. Les ztbres et les gnous passent un temms considkrable a brouter durant le jour et ont trts peu de temps de repos durant la saison &he. Si ces deux esptces manquent de temps a cette kpoque de l'annee, cela semble Stre A cause du rique de prkdation nocturne. Les buffles ne manquent pas de temps et prksentent deux stratkgies alimentaires: une premitre option favorise l'alimentation de masse, et une autre ou la sklection est manifeste. 11s semblent &tre limites par les ressources. Ces quatre esptces prksentent une remarquable correspondance dans la proportion de temps passt a la recherche de nourriture. Sur un base annuelle, la proportion de temps passk a se nourrir et se dkplacer est d'environ 80% du temps diurne. Neanmoins, les stratkgies alimentaires de ces esptces diffkrent alors qu'ils vivent dans le mSme environnement et subissent les mkmes contraintes.

Because energy reserves limit flight range, wind assistance may be of crucial importance for migratory birds. We tracked eight Bewick's swans Cygnus columbianus bewickii, using 95-g satellite transmitters with altimeters and activity sensors, during their spring migration from Denmark to northern Russia in 1996. During the 82 occasions where a swan's location was recorded in flight, average flight altitude was 165 m a.s.l. with a maximum of 759 m a.s.l., despite winds often being more favourable at higher altitudes. We also counted Bewick's swans departing from the Gulf of Finland and subsequently passing an observatory in the next major stop-over area 800 km further north in the White Sea, northern Russia, during the springs of 1994, 1995 and 1996. A comparison of these counts with wind data provided evidence for Bewick's swans using favourable changes in wind conditions to embark on migration. Changes in the numbers of birds arriving in the White Sea correlated best with favourable changes in winds in the Gulf of Finland 1 day earlier. Again, migratory volume showed a correlation with winds at low altitudes only, despite wind conditions for the swans being more favourable at high altitudes. We conclude that the relatively large Bewick's swan tends to gear its migration to wind conditions at low altitude only. We argue that Bewick's swans do not climb to high altitudes because of mechanical and physiological limitations with respect to the generation of power for flight and to avoid rapid dehydration.