Capacités prédatrices et budgets d'activité chez l'aigle pêcheur, Haliaeetus vocifer

Ten pairs of Fish Eagles Haliaeetus vocifer taken among a dense population in Uganda, were followed at the end of the breeding season to compare the time and energy budgets of breeding and non breeding adults. Fish are usually obtained by diving from a waterside tree. If unsuccessful, the bird searches in flight, an energy-expensive but very rewarding method. The additional food necessary to feed the young is provided m ainly by the male through fishing flights. Another source of increase in energy expenditure related to breeding activities is the more active territorial defense by adults with young than without young. The food consumption of the former is higher than that of the latter ; but the difference is smaller than the increase of the energetic cost of breeding (42 % and 64 % for 1 and 2 fledged young). Thus brood size seems to be limited by the ability of the parents to feed their young and maintain a territory of adequate size or quality, even in the optimal conditions studied. Immature birds suffer he avily from the adults'territorial behaviour, which forces them to make extensive flights and confines them to marginal food sources. This may explain their high mortality rate (83 % during the first four years

Les migrations de rapaces en Afrique Occidentale : adaptations écologiques aux fluctuations saisonnières de production des écosystèmes

Seasonal changes of abundance of diurnal birds of prey have been studied for 50 months in West Africa. Population move ments have been traced through seasonal variations of abundance in adjacent biomes. Relative densities of various species have been estimated by monthly “ road-side counts ”, and correlated with seasonal changes in climate, vegetation structure and availa bility of prey. Five species of West-African Falconiformes perform erratic movements, 13 are partial migrants and 6 undertake regular, long-distance migrations from the rain forest zone to the edge of the desert. Moreover, 17 palearctic birds of prey species occur seasonaly in the area, mostly from September to May. Premigratory fat deposition is uncommon among African migrants, and the moult often takes place during their short range movements. Migrant birds of prey differ in many ways from their sedentary relatives : they are morphologically adapted to hunting in open habitats ; they tend to be very mobile and to exploit locally abundant but transient food sources ; their repro ductive rate is high ; they appear to be very sensitive to the dry heat of the Sahel. On the whole, there is very little ecological overlap between migrant and sedentary birds of prey in the study area. The timing of migratory movements is closely correlated with the onset of the rains, the birds following the seasonal changes of the inter-tropical front : they move northwards with the first rains in spring and southwards at their end in the autumn. This seasonal shift of habitat is also correlated with an increase in the height of the grass cover and sometimes with flooding. The ultimate cause of these seasonal movements appears to be an optimization of the diet of the migrant population. A good correlation has been found between the abundance of migrant birds of prey and that of the grasshopers, their major insect prey. Urban populations of tropical African kites, which benefit from more stable food sources than “ bush ” populations, are also more sedentary. The availability of adequate sources of drinking water in the Sahel zone, is also an important synchronizer for some species. The northern limit of the seasonal movements, as well as the arrival and departure dates of the migrant populations, are on the whole dependent upon the abundance and availability of their major prey species. African migrants generally stay in the southern savannas du ring the dry season when food is abundant and hunting conditions are good. During the rains, they move to the northern grasslands where they take advantage of the seasonal food surplus left unu sed by the sparse populations of resident species. Depending upon the length of the dry season, the proportion of sedentary birds of prey increases from the South to the North of the West African savanna belt. African migrants are the only ones to invade seasonaly the northernmost grasslands. The sou thern ones (the “ guinean savannas ”) are used both by palearctic and african migrants, during the breeding season of the resident species. Palearctic migrants are only found in intermediate latitu des outside the breeding season. Palearctic migrants which have similar diets and hunting methods as african migrants never co-exist with them during the dry season, thus avoiding any competition

Besoins alimentaires quantitatifs de quelques oiseaux tropicaux

The daily consumption of food by some tropical, mostly insectivorous, birds has been studied in Ivory Coast savana-forest mosaic. Different techniques were used : weights of the stomach contents at the end of the activity period, estimates of the quantity of food brought to nestlings at the end of their growth period, estimates of the number of prey items caught by adults during the day, amount of food eaten by captive individuals. For birds whose body weights ranged from 100 to 1,500 g, the daily ration was on average only half of that of their pale- artic or nearctic counterparts. The overall food consumption of the Rollers and Raptors in the Lamto savana averaged 12 g/ha/day - which, on a yearly basis, corresponds to about half of the production of the prey species concerned

Priority areas for vulture conservation in the Horn of Africa largely fall outside the protected area network

Vulture populations are in severe decline across Africa and prioritization of geographic areas for their conservation is urgently needed. To do so, we compiled three independent datasets on vulture occurrence from road-surveys, GPS-tracking, and citizen science (eBird), and used maximum entropy to build ensemble species distribution models (SDMs). We then identified spatial vulture conservation priorities in Ethiopia, a stronghold for vultures in Africa, while accounting for uncertainty in our predictions. We were able to build robust distribution models for five vulture species across the entirety of Ethiopia, including three Critically Endangered, one Endangered, and one Near Threatened species. We show that priorities occur in the highlands of Ethiopia, which provide particularly important habitat for Bearded Gypaetus barbatus, Hooded Necrosyrtes monachus, Ruppell's Gyps ruppelli and White-backed Gyps africanus Vultures, as well as the lowlands of north-eastern Ethiopia, which are particularly valuable for the Egyptian Vulture Neophron percnopterus. One-third of the core distribution of the Egyptian Vulture was protected, followed by the White-backed Vulture at one-sixth, and all other species at one-tenth. Overall, only about one-fifth of vulture priority areas were protected. Given that there is limited protection of priority areas and that vultures range widely, we argue that measures of broad spatial and legislative scope will be necessary to address drivers of vulture declines, including poisoning, energy infrastructure, and climate change, while considering the local social context and aiding sustainable development.Peer reviewe

Exemple de prédation naturelle sur une population nicheuse de Quelea Q. quelea (L.) au Mali

The predation pressure upon nine breeding colonies of Red billed Quelea (Quelea q. quelea ) has been estimated in September 1973 in Eastern Mali, Western Africa. Large numbers of predatory birds (Kites, Hawks, Ruzzards, Eagles, Falcons, Storks, Herons, Ibises, Hornbills, Crows, etc.) were found to feed upon young queleas : up to 763 predators in a colony of 28,000 nests. Details are given on feeding techniques, food preferences and average daily consumption of the most important predators. In this particular case, 32 % of the nests were destroyed between laying and hatching times. Furthermore 25 % of the nestlings appear to have been subsequently destroyed by predators. On the whole, each adult breeding pair did not produce more than 1,7 fledglings. The causes of this unusually high mortality rate are discussed

Organisation et fonctionnement du peuplement d’oiseaux en forêt guyanaise application à la conservation

Ornithological surveys were carried out, from 1981 to 1986, in the hinterland of French Guiana, in order to find out the best possible location, and estimate the optimal size, of a national park in this rain forest area. The structure of the bird community, together with the structure of the assemblages of small foliage gleaners and of diurnal raptors, were studied in ten sites within the unbroken primary forest. The main results of these studies are briefly summarized : local and regional species richness, diversity, trophic guilds, population density, vertical and horizontal distribution, etc. In mature undisturbed rain forest, about 1% of the species are abundant, and up to 80% and more may be considered as rare. Any kind of large scale perturbation (either logging or hunting) leads to an increase of common species, and to a decrease of the rare ones, eventually leading to a reduction of richness, diversity, and equitability, as well as of the density and biomass of the bird community as a whole. Al least along the habitat axis, species niches are densely packed and often widely overlapping. There is a roughly equal trend among species toward specialization and generalism. Competition is likely to be reduced at least as much by low densities, uneven distribution and interspecific territoriality or avoidance, than by ecological segregation. Apparent coexistence is thus limited by low spatial overlap, whatever the similarity of the niches, and rarity of many species is a major condition of community richness. There are different ecological correlates of rarity according to specific responses to the strong constraints of this ecosystem (habitat heterogeneity, food seasonality, interspecific competition, predation pressure). The relatively low level of food availability for insectivores is investigated. The numerous tree fall gaps and other disturbances (flooding, army ants, ...), randomly distributed, and colonized by fugitive species, are other important factors maintaining species diversity. Rain forest bird communities are very sensitive to human disturbance. Any kind of logging or hunting must be excluded from reserves designed for the conservation of «pristine» bird communities. From our estimates in Guiana, the minimum critical area of such reserves, including long term viable populations of every species (when isolated), may probably be over 10 000 km2.Thiollay Jean-Marc. Organisation et fonctionnement du peuplement d’oiseaux en forêt guyanaise application à la conservation . In: Revue d'Écologie. Supplément n°4, 1987. pp. 149-160

Densités estivales d’oiseaux dans quelques milieux herbacés de Vendée

Counts of breeding birds have been made, during early June 1967, on five quadrats in various open habitats, North of the Anse de l’Aiguillon, Vendée. Only two species breed regularly in open meadows : the Lapwing and the Sky lark. The 51 other species, although they find most of their food there, nest in habitats with more varied vegetation

Stratégies adaptatives comparées des rolliers (Coracias SP.) Sédentaires et migrateurs dans une savane guinéenne

The Blue-bellied Roller, Coracias cyanogaster, was studied in the southern guinean savanna of Lamto (Ivory Coast). Its social behaviour (this bird lives in promiscuous territorial groups) facilitates the exploitation of patchily available food sources. The frequency of moves between perches and other features of its perch hunting method are generally consistent with the optimal foraging theory, except when a group following behaviour is involved. Hunting success increases and movements are reduced when both the abundance of grasshoppers (its staple food) increases and the vegetation cover decreases. Prey detectability plays an important role in habitat selection. Capture rates markedly decrease at the beginning of the rainy season, which is a difficult period for both the sedentary and the migratory species. The frequency of attacks is maximum in mid-morning and end of afternoon. On average a roller spends 85 % of the day perch hunting, 7 % resting, 1.8 % flying and handling prey and 6.2 % in social interactions. The average capture rate is of 33 preys per day (7-10 g, fresh weight), following 40 capture attempts. This predation pressure represents a little more than 1 per cent of the available prey biomass. The migratory rollers, Coracias naevia and C. abyssinica, which breed in Ivory Coast in March-April like C. cyanogaster, occur in more open grasslands. They hunt from lower perches where they stay for longer periods than the Blue-bellied Roller. The two migrant species have larger individual hunting territories, a narrower diet and use less diversified capture techniques. They are not adapted to rainy season’s conditions in the southern savannas (where the height of grass cover and the density of the vegetation hinder prey capture), and this may explain their northward migration at that time of the year.Le Rollier à ventre bleu, Coracias cyanogaster, a été étudié en détail en savane préforestière de Lamto (Côte-d’Ivoire). Son comportement social favorise l’exploitation des ressources localisées. Sa chasse à l’affût, et notamment la fréquence des changements de perchoirs, est généralement conforme aux prévisions de la théorie de l'optimal foraging, à l’exception de l’entraînement social du groupe qui augmente la fréquence des déplacements. Plus les proies sont visibles (savane claire), plus le succès de chasse est élevé et plus les déplacements sont réduits (éléments déterminant le choix du milieu). Les circuits de chasse s’effectuent par étapes et décrivent des boucles. Le taux de succès de la chasse diminue en saison des pluies, laquelle est donc aussi pour le sédentaire, la période limitante. La fréquence des attaques est maximale en milieu de matinée et en fin d’après-midi. Un Rollier moyen passe 85 % de la journée (12 h 30) en affût, 7 % au repos, 1,8 % en vols de chasse et captures et 6,2 % en interactions sociales. Il effectue par jour 40 attaques, dont 33 captures pesant au total 7 à 10 g et représentant par mois plus de 1 % de la biomasse disponible des proies exploitées. Les migrateurs, C. naevia et C. abyssinica, habitent en Côte-d’Ivoire des milieux plus ouverts, à sol plus dégagé que le précédent. Ils chassent sur des perchoirs en moyenne plus bas, qu’ils occupent pendant des périodes plus longues. Ils ont des terrains de chasse individuels plus vastes, un régime alimentaire plus spécialisé et des techniques de capture moins diversifiées que le sédentaire. Ils sont moins bien adaptés que ce dernier aux conditions de la saison des pluies (hauteur et densité de la végétation), ce qui explique alors leur remontée vers le nord où les conditions correspondent mieux à leurs aptitudes.Thiollay Jean-Marc. Stratégies adaptatives comparées des rolliers (Coracias SP.) Sédentaires et migrateurs dans une savane guinéenne. In: Revue d'Écologie (La Terre et La Vie), tome 40, n°3, 1985. pp. 355-378

Migot, P. & Stahl, Ph. (Eds). — Actes du Colloque « Prédation et gestion des prédateurs ». ONC-UNFDC, 48 rue d’Alésia, 75014 Paris, 1993

Thiollay Jean-Marc. Migot, P. & Stahl, Ph. (Eds). — Actes du Colloque « Prédation et gestion des prédateurs ». ONC-UNFDC, 48 rue d’Alésia, 75014 Paris, 1993. In: Revue d'Écologie (La Terre et La Vie), tome 50, n°1, 1995. pp. 95-96