Have you ever heard of the Mauritius kestrel? At one point, these small falcons were renowned as the rarest birds in the world, with only four known individuals still alive in the wild. The road to recovery for Mauritius kestrels has been a long one requiring the cooperation of many groups and many people, but the story of this modern conservation icon is still teaching us new lessons. As we engage in international conservation projects with local partners around the globe, we never stop learning from our peers.
Mauritius is a small island nation in the Indian Ocean, about 700 miles from Madagascar. It is famous in the annals of conservation as the setting for perhaps the most famous animal extinction since the end of the Pleistocene: the loss of the dodo. There are no more dodos on Mauritius, and in 1974, the Mauritius kestrel appeared poised to follow suit. These small falcons hunt lizards and small birds in the tangled canopies of Mauritius’ forests, but centuries of deforestation, introduced predators preying on eggs and chicks, and widespread use of the pesticide DDT reduced their numbers. How could the population possibly be rescued with only four birds still known to exist?
The answer was a carefully-executed program of captive breeding, hand-rearing, supplemental feeding of wild birds, control of introduced rats and macaques, and reintroduction undertaken by a slew of nonprofit organizations as well as the Mauritius government. By the 1990s, birds hatched in captivity and then “hacked” (a sort of soft-release where birds hunt wild prey but receive supplemental food at a safe site) into the wild had bolstered the population to 800 birds. From a known total of 4, this was a huge accomplishment. The Mauritius kestrel was downgraded from “Critically Endangered” to “Vulnerable” by the IUCN. This success was widely and rightly hailed as a model for conservation of rare species going forward.
This year, however, new research is reminding us that conservation is not a “one and done” deal. A recent paper published in Ibis (the international journal of avian science) reveals that some kestrel populations on Mauritius are consistently declining or even locally extinct. A team of researchers from the Durrell Wildlife Conservation Trust (Zoo New England partners with Durrell to help conserve the critically endangered Cuban Solenodon) and Durrell Institute of Conservation and Ecology, the UK Institute of Zoology, the Mauritian Wildlife Foundation, and the Mauritian Government analyzed the trends among four different populations of Mauritius kestrel since management was scaled back in the 1990s, after the bird’s conservation status was revised.
Simply put, the researchers discovered that while the population on the eastern part of the island had fared well, the northern population had disappeared, and the western population was in a steady decline. The reason, they said, was that reproduction in these populations was lower than in the eastern group due to lower availability of nest sites. Kestrels readily use human-made nest boxes, and these boxes consistently produce larger and more successful broods than natural cavities, on average. Unfortunately, once the kestrel was down-listed, interest from donors and funding agencies shrank, and the birds could not be monitored or assisted as they had been before. Had the work been able to continue uninterrupted, monitoring and timely intervention could have provided more nest sites to struggling populations and avoided another crash. Now, the population is back down to ~250 individuals, and the kestrels have been up-listed to Endangered by IUCN.
As we continue our own work, it’s a useful reminder that nature is always changing and natural systems are complex. Any recovery plan or intervention that does not include monitoring after the fact is in danger of failing even with the most encouraging short-term results. When working with long-lived animals like turtles, this lesson is even more salient. Zoo New England’s Field Conservation Department is therefore committed to working on our projects for the long-term; some of our staff have worked with Blanding’s turtles at Great Meadows in Concord, for example, every year since 2003!