“Mauritius kestrel” copyright © Diane L. Schirf

The Mauritius kestrel (Falco punctatus), endemic to Mauritius in the Indian Ocean and the island’s only bird of prey, is the world’s rarest falcon. Its known population had been reduced to two breeding pairs by the early 1970s, when it became the world’s rarest bird. It has been studied since 1973, when conservation efforts began to prevent its extinction.

The Mauritius kestrel is a distinct island form, with males averaging 130–140g and females 160–170g. Adult females and immatures are indistinguishable by plumage. The kestrel occupies a niche similar to that of accipiters in its natural habitat of mature evergreen subtropical forests. With short, rounded wings and a dashing hunting technique, its morphology and behavior also demonstrate convergence with accipiters. Diet appears to be partly variable, depending on interrelated factors such as habitat, availability of prey, and season, as well as the ability, experience, preference, age, and sex of the individual. Its nickname, “mangeur des poules,” is inaccurate. Intensive studies in the 1970s revealed that prey includes lizards (primarily Phelsuma geckos), birds (primarily grey white-eyes, Zosterops borbonicus, and introduced common waxbills, Estrilda astrild), and insects (primarily dragonflies and cicadas, along with cockroaches and crickets). Although grey white-eyes were considered the single most important prey, geckos were thought to form 50 percent of the diet, and, during October/November 1981, 94 percent of 218 identified prey items brought to one nest were geckos.

Pairs appear to require a territory of up to 150 ha. Courtship activity begins in September and October, with eggs (usually three) being laid between October and January in a cliff hole. Most first clutches occur in late October. The female is the primary incubator, and the eggs hatch after about 30 days. The young remain in the nest until about five and a half weeks old and are partly dependent on their parents for several months, longer than is typical in temperate-zone kestrels. Parents tolerate young birds until the next breeding season, when they are driven away. Both sexes are mature at one year old, but do not necessarily breed.

The Mauritius kestrel was never abundant, although it was reported in the 1850s that it was “plentiful wherever the indigenous woods exist.” Before Mauritius was discovered, it probably occurred throughout the island. Between 1820 and 1840, it was found mainly in the extensive forests of the island’s center as well as in southwestern coastal areas. Its range continued to contract and, by the 1950s, it was restricted to the remote forests of the southwestern plateau. They are now restricted to an area no greater than 50 square kilometers in the southwest, which features cliffs and ravines.

There are many causes for the kestrel’s decline, including chronic loss of native forest habitat and the degeneration of remaining forests as introduced plants invade them, their seeds spread by native and nonnative frugivorous birds and mammals. The kestrel’s favored prey items, including insects, geckos, and passerines, all have declined; the density of Phelsuma geckos depends largely on the density of native trees and shrubs. Grey white-eyes, an ecologically generalized species, are less common in the remaining native forest than in more disturbed areas of mixed vegetation. Introduced diseases, predation by introduced species, human persecution, pesticide contamination and natural disasters such as cyclones have probably taken their toll as well. Inbreeding in such a small population is also a concern.

Exhibit and Collection History

Mauritius kestrels can be found at the North of England Zoological Society’s Zoological Gardens, Upton-by-Chester, U.K. (one male, one female); Paradise Park at Cornwall’s Conservation Park, Cornwall, U.K. (one female); Durrell Wildlife Preservation Trust, Jersey, U.K. (five males, four females, and one offspring); and Paignton Zoological & Botanical Garden, Devon, U.K. (one female), and The Hawk Conservancy, Hampshire, U.K. (one female), for a total of six males, eight females, and one unsexed offspring.

The Mauritius kestrel has not always done well in captivity. As an island species, it is susceptible to alien pathogens. Necropsies performed on captive individuals have revealed problems such as sinus infections, hepatic lesions, respiratory infections, oviduct conditions and infections, and the presence of DDE, a metabolite of DDT. Genetic deterioration may also be a factor.

Conservation Organizations and Partnerships

In 1973, a World Wildlife Fund (WWF) project, managed by the International Council for Bird Preservation (ICBP) and with the financial support of the New York Zoological Society (NYZS), was begun to study the kestrel and to attempt to save it from what must have seemed like certain extinction. The project has operated in conjunction with the Jersey Wildlife Preservation Trust (JWPT) and with the active participation of the Government of Mauritius. In 1984, the project became part of the Mauritius Wildlife Research and Conservation Programme (MWRCP). The Peregrine Fund also plays an active role in conservation of the kestrel.

Conservation measures have included captive breeding and reintroduction, legal protection, public education and awareness programs, and habitat preservation in the form of the Macabé/Bel Ombre Nature Reserve, created in 1974 and covering 3,594 ha. The Mauritius kestrel is listed on Appendix I of CITES, to which Mauritius is a party.

Techniques used to promote the kestrel’s survival have included removing fertile eggs from the wild, substituting plastic dummies, and returning the hatchlings to the mother; supplementary feedings of mice to maximize egg production; and double clutching (removing the first clutch to encourage production of a second, a strategy that proved to work well with American kestrels).

In 1994 on the Ile Aux Aigrettes off the coast of Mauritius, in what must have been a frustrating moment of irony for conservationists, a Mauritius kestrel ate a newly hatched offspring of a recently reintroduced pair of Mauritius pink pigeons, the world’s rarest pigeon. The kestrel was captured and removed to a forest site on Mauritius.

From a low of two breeding pairs in the 1970s, the Mauritius kestrel now numbers a wild population of 350 individuals. Releases of captive birds have ended, thanks to the program’s success and the dedicated efforts of many organizations and individuals. The population is monitored carefully during the summer breeding season, and monkeyproof, cycloneproof artificial nesting boxes are placed in selected areas. Young are tagged and measured. The kestrel is still a highly endangered species; to ensure its survival, its population will have to be managed carefully for the foreseeable future.

Further reading:

Collar, N. J. and S. N. Stuart. Threatened Birds of Africa and Related Islands: The ICBP/IUCN Red Data Book, Part 1, third edition. Cambridge, U.K. and Gland, Switzerland, 1985.

Newton, I. and R. D. Chancellor, Conservation Studies on Raptors, based on the proceedings of the Second World Conference on Birds of Prey, April 1982, ICBP Technical Publication No. 5. Norwich, England, 1985.

The Mauritius Wildlife Foundation. http://www.maurinet.com/wildlife.html.

ISIS Abstract. September 1999.

Chicago Tribune. “Botanists Battle to Avert Repeat of Dodo’s Demise,” 2 December 1988, and “Rare Falcon Likes His Pigeon Rare, Too,” 10 October 1994.

2000
An edited version of this article was published in Encyclopedia of the World’s Zoos, April, 1, 2001,  winner of the Outstanding Reference Source award for 2001 from the American Library Association.