Waarnemingen van roofvogels op de grens van primair regenwoud in Zuidoost-Nigeria

From 31 January through 24 February 2001, the vicinity of Ebbaken (6°38’N, 9°05’E, Boji-Ebok village complex. Cross River State, southeastern Nigeria) was visited to trap and study Barn Swallows Hirundo rustica at the huge roost (1.0-1.5 million birds) in elephant grass Pennisetum in the foothills of Afi Mountain. The area is wedged in between the primary rainforest of Aft Mountain and the high forest with small plantations and fields in the nearby valleys and hills. It is fairly thinly populated, although human impact is increasing (farming, hunting, dear-cuts, selective logging, bush fires). During much of the period, the Harmattan was blowing (steady winds with force 3-4 B), which -together with smoke from bush firesreduced visibility to 800-1500 m in February, Temperatures during daytime ranged between 31 and 40°C in the shade. Raptors were observed from a high vantage point in the foothills about 3 km from Ebbaken during 82 hours between 31 January and 21 February (Table 4); time of the day, species, sex and age, moult, individual plumage characteristics and behaviour were recorded. The area covered from this vantage point encompassed c. 600 ha, measuring some 2x3 km of mainly high forest backed by the primary rainforest of Afi Mountain. During swallow trapping, i.e. the first and last 1-5 hours of daylight each day, systematic observations were kept of avian predator activities and hunting success of species involved (mainly African Hobby Falco cuvieri). At least 12 raptor species showed territorial and/or nesting behaviour in the 600 ha observation area (Table 2). Many pairs had apparently recently finished breeding (end of the dry period) and were seen with fledglings or begging juveniles. Highest densities were reached by African Cuckoo-falcon Aviceda cuculoides, Red-necked Buzzard Buteo auguralis and African Harrier-hawk Polyboroides typus (nearest neighbour distances of 800-1000 m in the latter). The majority of raptor species seen involved local birds, but several Palearctic migrants were also present, i.e. Western Honey-buzzard Pernis apivorus (34 observations, regarding at least 20 individuals among which 7 adult males, 4 adult females, 1 2nd-year female with green-yellow cere and yellow iris and 14 juveniles; a detailed description of this important wintering site is given in Bijlsma in prep ). Western Marsh-harrier Circus aeruginosus (adult male present at swallow roost in early morning hours of 4-18 February, predating on departing swallows and probably roosting in local Pennisetum fields) and Booted Eagle Hieraaetus pennatus (light phase with moult in outermost primaries seen 17, 18 and 20 February, dark phase moulting in primaries, secondaries and rectrices seen on 13 and 20 February; both showing large home ranges and restricted to valleys). The Pennisetum-fields (c. 25 ha surveyed intensively) were also much favoured by other Palearctic migrants like Nightingales Luscinia megarhynchos (full song and calls in early morning of tens of individuals, 1 trapped), Great Reed Warblers Acrocephalus arundinaceus (>5 singing, several trapped), European Reed Warblers A. scirpaceus (4 trapped), Whinchats Saxicola rubetra (>100, of which 26 trapped). Willow Warblers Phylloscopus trochilus (100s present, 24 trapped), Garden Warblers Sylvia borin (1 trapped). Yellow Wagtails Motacilla flava (150-400 roosting in Pennisetum, 3 trapped). Tree Pipits Anthus trivialis (tens present, 2 trapped). Sand Martins Riparia riparia (1 trapped, few among Bam Swallows) and Red-rumped Swallows Hirundo daurica (2 trapped, ditto). Near Camp II in the bushes bordering the Pennisetum-fields, a territorial Spotted Flycatcher Muscicapa striata and ditto Melodious Warbler Hippolais polyglotta were present. For reasons of comparison, the results of a road count from Lagos to Ogoja (densely populated) are presented in Table 1. During this road survey, generalist raptors commensal with human activities dominated the scenery, especially Yellow-billed Kites Milvus migrans parasitus and Hooded Vultures Necrosyrtes monachus. This is very different from the raptor fauna near Afi Mountain in southeastern Nigeria (thinly populated), as shown by the following overview of raptors observed there. African Cuckoo-falcon Aviceda cuculoides: 3 territories located on 600 ha, with persistent calling from each in early morning and late afternoon. Bat Hawk Machaeramphus alcinus: a single observation at dawn on 12 February, when bats were still abundant both at low and high altitudes. The bird was flying high in a southwesterly direction, probably heading for its roost. Yellow-billed Kite Milvus migrans parasitus: one of the commoner species (Table 2, 4), typically associated with human activities (village) and bush fires. The first to show up when the Pennisetum fields caught fire on 7 February, feeding on fleeing insects and small mammals. On later days, one bird was seen with scorched rectrices. At the end of the Harmattan, when the weather changed and cloud formation started, some movements were noticed on 18 and 19 February (for example, 4 heading NNE on 18 February), together with large numbers of Swifts Apus apus and Palm Swifts Cypsirius parvus. Palearctic Black Kites M.m. migrans were not recorded. Palm-nut Vulture Gypohierax angolensis: probably local breeding bird. Two adults, 1 immature and 1 juvenile roosted in the hills nearby. Departure from the roost was well before sunrise (Table 3), the birds passing already at a considerable height using flapping flight and gliding. The birds returned in late afternoon. During daytime, several observations were made of birds of unknown identity (same as roosting birds?) (Table 4). Snake Eagle Circaetus sp.: seen on 16 and 20 February, but specific identity unknown. African Harrier-hawk Polyboroides typus pectoralis: the commonest species observed, with at least 6 pairs on 600 ha of high forest interspersed with small cultivated fields. Two pairs were accompanied by a juvenile and a begging juvenile, respectively. Between 11 and 13 hrs local time, most pairs intensively displayed, showing elaborate undulating and meandering flights at medium and great heights. Wings were partly contracted during steep dives and upward swoops (sometimes followed by a sideways roll or looping at its zenith), with the hand performing 4-6 fast and shallow wing beats. Display flights were highly visible, even with the naked eye at long distance. Sometimes, displays were accompanied by a repeated high, bisyllabic ‘he-heeee’. The begging call of the recently fled youngster was also twotoned, but with a throaty first part and a high, short-pitched second part: ‘gjuuu-le’. Red-chested Goshawk Accipiter toussenelii: more Sparrowhawk- than Goshawklike. A second calender-year male was caught during swallow trapping on 11 February 2001. Measurements, mass and colouration of soft parts are detailed in Table 5. The differences in tail-banding between a first- and second-year bird can clearly be seen from Photographs 4 and 5; see also moult scores in Table 6. An adult female was seen still-hunting from cover bordering cultivated fields, using perch heights of 3-6 m, on 17 February. Black Sparrowhawk Accipiter melanoleucus: distinctly Goshawk-like in appearance and behaviour, not Sparrowhawk-like. Two pairs and solitary birds were seen soaring in late morning (Table 4), the pairs displaying exclusive territories. A juvenile focused on chickens during hunts at Ebbaken, making dashes from the forest at the edge of the village. Presumably this juvenile was captured and eaten by villagers on 7 February. An adult female showed moult in the centre of her left secondaries on 19 February. Shikra Accipiter badius: a male was caught during swallow trapping on 18 February, almost having completed its moult from first- to second-year plumage (compare old outermost rectrices with fresh other tail-feathers; Photographs 6 and 7). Measurements, mass and colouration of soft parts are given in Table 7. Lizard Buzzard Kaupifalco monogrammicus: almost entirely restricted to edges of high forest on hill sides near Ebbaken, with only a single pair in the study plot of 600 ha. Most recordings refer to calling individuals. Red-necked Buzzard Buteo auguralis: highly territorial within 200 m from nest sites. One pair was tending a nestling of 16-17 days old (16 February: primaries just emerging from blood shafts) on an old Yellow-billed Kite nest in a huge cotton wood. Feeding times were 8.59, 10.45, 12.08 and 14.47 hr (6 February: between 8.00 and 16 00 hrs), 9.32, 10.10, 11.41 and 13.49 hr (16 February, between 8.00 and 15.00 hrs) and 11.12, 11.22 and 13.08 hr (19 February, between 10.00 and 14.00 hrs). Identified prey items were lizards (2x) and cane rat (lx). Other pairs were present with begging fledged juveniles. Wahlberg’s Eagle Aquila wahlbergi: two pairs resided in the 600 ha plot, activities above tree-level being confined to the few hours around noun (Table 4). Parallel flights of both pairs were frequently seen, indicating exclusive home ranges. Display, seen on 1 February, is reminiscent of that of Lesser Spotted Eagle Aquila pomarina, with steep undulations at great heights accompanied by a high-pitched, hoarse ‘cheee-cheeeeee’. African Hobby Falco cuvieri: the swallow roost attracted many African Hobbies (up to 7 seen simultaneously), but numbers declined after bush fires had destroyed large sections of Pennisetum on 7 February and the swallows started to switch to another site near Enyi. In late February, when only 100 s of Bam Swallows were still using the Ebbaken-site, the local breeding pair with one juvenile was still in attendance. Activities of African Hobbies peaked from just before swallow departure/arrival till the majority of swallows had left the roost or had settled. The birds used several hunting strategies: low quartering, very low speeding, cruising at medium heights and diving, hot pursuits at low level or in mid-air, and cooperative hunting. During daytime, observations were less frequent, involving birds soaring at great heights. Once an African Hobby was observed while catching insects in mid-air (2 successful catches in 4 minutes, 20 February, 11.13 hr), suggesting a mainly vertebrate diet. Despite careful observations, European Hobbies Falco subbuteo were not recorded. Lanner Falcon Falco biarmicus: an adult was recorded on 21 February near Enyi, a village close to Ebbaken, with extensive Pennisetum areas to which the swallow roost had switched after fires had raked important sections of the roost near Ebbaken. The raptor fauna near Aft Mountain shows distinct characteristics of high forest in transition from primary to secondary forest. Typical raptor species of primary rainforest were not recorded (probably partly because of biased method of recording. with insufficient attention and inadequate census methods for primary rainforest), whereas species typical of secondary rainforest abounded (Tables 2 and 4). With an increasing pressure from human settlement, including increase in number of farms, frequency and extent of bush fires, logging and hunting, the raptor fauna will continue to change. The high density and species composition of the raptor fauna lend further support to the need of active protection of the Afi River Forest Reserve and its surroundings. The importance of this area, as shown by the presence of populations of Mountain Gorilla Gorilla gorilla, Drill Mandrillus leucophaeus, Chimpansee Pan troglodytes, Grey-necked Picathartes Picathartes oreas and many turaco species (including the Great Blue Turaco Corythaeola cristata), is also clearly shown by the diverse raptor fauna. The high density of Honey Buzzards Pernis apivorus associated with high forest also has serious consequences for our conception of its habitat requirements in Africa, and the possible impact of rainforest destruction on its winter survival and population dynamics.