Aldabra Drongo Dicrurus aldabranus Scientific name definitions

Aldabra Atoll, in SW Seychelles.

Recorded mid-Sept to Nov (first nests built) and Mar–May (last fledglings), depending on year; brood-feeding coinciding with main rainy season (Dec–Mar); first laying normally Nov–Dec, clutches in Jan–Feb corresponding to replacements; one successful brood raised per year. Territorial, with stable and very precise territory boundaries throughout breeding season; extremely aggressive, driving out all intruders by mobbing, "dive-bombing", pecking at and pursuing large creatures such as crows (Corvus) or even humans, as well as other animals approaching too close to nest, these ranging from herons (Ardeidae), frigatebirds (Fregata) and boobies (Sula) to coucals (Centropus), turtle-doves (Streptopelia), falcons (Falco), bulbuls (Hypsipetes), terns (Sterna) and fodies (Foudia), and including migrant falcons and rollers (Coracias), and even fruit-bats (Pteropus); one bulbul reported as having been fiercely pecked at and knocked down by the drongo. In courtship, partners face each other, bills held slightly above horizontal, shaking wings vigorously and wagging tail from side to side, while uttering soft high-pitched squeaky sounds; one bird (presumed male) may pick a leaf and offer it to partner. Nest normally built by both sexes within 10–20 days, unfinished nest sometimes abandoned in event of human disturbance; a perfectly rounded cup made from intertwined fine vegetable fibres e.g. casuarina needles, wood-rush (Luzula) or dry monocotyledon grass leaves, bound with cobweb, nest thicker on sides and more thinly constructed at base (through which contents often visible), one nest 13 cm across and 5 cm deep externally, 8 cm across and 2 cm deep internally; generally woven in fork towards end of thin horizontal branch 2–8 m (exceptionally to 13 m) above ground, preferably in taller tree such as casuarina or mangrove tree (e.g. Rhizophora mucronata), also on smaller native tree e.g. fig (Ficus), or in Premna serratifolia, Euphorbia pyrifolia or Mystroxylon aethiopicum in lowland scrub habitat; average territory size 2·25 ha in casuarina woodland (on Picard), 4·5 ha in mixed scrub (Malabar; Passe Hoareau). Clutch 1–3 eggs (average 2·1), decreasing through breeding season, white to pale mauve, with dark red spots more concentrated at larger end, average of two eggs 26·2 x 19·2 mm; if contents lost, up to five replacement clutches laid (normally builds new nest at different site predation, occasionally uses same nest); incubation and chick-feeding by both parents, incubation period 16–18 days, nestling period 15–19 days; juveniles dependent for at least several weeks after fledging, remain with parents until following breeding season, then chased by parents but still tolerated at territory periphery, which they defend against neighbouring conspecifics. Breeding success appears very low owing to extremely high proportion of clutches (73% of eleven clutches in 1999/2000) suffering predation, mainly by Pied Crows (Corvus albus) and rats (Rattus), and probably Madagascar Coucals (Centropus toulou), herons (Ardea, Butorides) and Madagascar Bulbuls (Hypsipetes madagascariensis), as observed or suggested in artificial nest experiments; feral cats and Madagascar Kestrels (Falco newtoni) also suspected of taking chicks; annual productivity low, less than 20% of 14 pairs successful in rearing young on Malabar during 1976/77 season (0·6 fledglings per pair), and on Picard similar values in 1999/2000 (only two of ten pairs successful, 0·4 fledglings per pair) and in 2000/2001, with hatching success 29% and fledging success for hatchlings of 80% over the two seasons; only 23% of eggs laid produced a fledgling; successful nests produce up to three fledglings, but normally only one or two (average 1·6). First breeding not until at least 2 years.