Mauritius Kestrel – The world’s Rarest Bird of Prey
Despite intensive efforts to help this little falcon Mauritius Kestrel, the tiny remnant population in the native evergreen forests of south-west Mauritius remains at only about 15—25 birds in the best years.
In 1966, there were just 20—25 individual Mauritius kestrels (Falco punctatus) and they had declined to only six in 1973 when for the first time a pair was trapped and mated for propagation. The wild birds hung on in the Black River gorges and similar environs rugged country which miraculously escaped the wholesale forest destruction brought about by pressure from one of the densest human populations in the world.
The species, slightly shorter and heavier than the common kestrel (Falco tinnunculus), appears never to have been common. Consideration of present territory requirements suggests that even when most of the island was covered with forest in the mid-18th century (estimated suitable habitat then 1,644 sq km / 630 sq miles) there were only Unusually among kestrels, the male and female punctatus have identical plumage, but they exhibit marked sexual dimorphism, the males weighing just 178 g (6 oz) and the females 231 g (8 oz).
Mauritius Kestrel Habitat and Nesting
The short, rounded wings are not very good for hovering so hunting concentrates on searching for prey from a perch or slowly quartering the forest canopy. Arboreal prey, such as the main food item geckos (Phelsuma), is stalked by rapid hops along branches. Small insects, dragonflies, locusts, small birds and rodents are also taken.
Rather confiding birds, sitting Mauritius kestrels sometimes allow approach to within a few metres of the nest, usually in a tree cavity. Unlike all other kestrels, the young remain with their parents near the nest-site until the next breeding season.
Nests in tree cavities tend to be depredated by introduced macaque monkeys, which have become a great menace to all arboreal-nesting birds on the island. Fortunately, when the kestrel’s population was at its very lowest in 1974, one pair chose to nest out of the monkeys’ reach on the sheer face of a tall cliff. They fledged three young and thereby increased the population by a third! The progeny of this pair continued to nest in such inaccessible places, and by 1976 there were 12 birds. Sadly, the tree-nesters continued to be unsuccessful.
Reasons and Research about the extinction of Mauritius Kestrel
Intensive research really began during the 1981/82 breeding season, but by 1983/84 only six or seven pairs were known, eight or nine in 1984/85 and seven or eight in 1985/86. Despite all the efforts, the number of Mauritius Kestrel birds has not increased much since the 1960s. But although breeding success is on the whole poor, there is considerable variation from year to year: in the 1984/85 season 11 young fledged but in 1985/86 just five. Also, the number of breeding pairs is limited by the number of breeding territories holding adequate food.
In addition to habitat destruction, human persecution aided the decline and when the population was critically low the monkeys kept it down. This inevitably led to considerable inbreeding and it has been suggested that as a result there has been a genetic deterioration, resulting in reduced reproductive capacity and increased susceptibility to disease and other stresses.
The remaining habitat of just 3,035 ha (7,500 acres) will never support many more pairs, even without the monkeys. Unlike other species in the sub-genus, such as the Seychelles kestrel (Falco araea), punctatus has shown no adaptability to its changed environment, including utilization of man-made structures or exotic stands of trees as nest-sites.
It seems tied to the native evergreen forest and the greatest hope for species survival might be in transferring some birds to islands such as Reunion where sizeable native forests remain.
In the meantime, active management has been stepped up and the productivity of a pair that had supplementary feeding has improved. During the 1985/86 breeding season, 14 Mauritius Kestrel birds were bred in captivity and four of them were released in January 1986 in an area of rather suitable lowland forest that did not already have kestrels. Release techniques had been perfected on other falcons and the young birds were being fed daily on white mice, gradually gaining their independence.
Among the world’s other rarest birds of prey are the Madagascar serpent eagle (Eutriorchis astur) and the Madagascar fish eagle (Haliaeetus vociferoides), both of which struggle on in very small but unknown numbers in isolated reserves and remote areas. Before the coming of man 3,000 years ago, Madagascar was mostly forested but since then settlement by many peoples with varieties of agriculture has robbed this great island (larger than France) of much of its richness and diversity of wildlife.