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Zoological Society of London

9 July 2021

New study provides insight to success of ground-breaking reintroduction project 

A new study by conservation experts in the UK and Mauritius will guide the next steps in the recovery of a tropical bird of prey, once regarded ‘the rarest bird in the world’. 
After it was discovered that only a handful remained in the wild in the early 1970s, the Mauritius Kestrel became the focus of an ongoing restoration programme. The project saw scientists and conservation biologists from around the world come together to reintroduce the threatened species, in a bid to bring it back from the brink of extinction. 
Now in new research published this week, scientists have analysed decades of monitoring data from the programme, which has provided a comprehensive insight into the kestrels’ survival and breeding rates – revealing how successful the reintroduction has been on the Indian Ocean island.  
Conducted by a team of scientists from ZSL (Zoological Society of London), Mauritian Wildlife Foundation, Durrell Wildlife Conservation Trust, Durrell Institute of Conservation and Ecology, The Peregrine Fund, and supported by the National Parks and Conservation Service (Government of Mauritius), the research’s findings provide valuable evidence which can be used to guide the next steps in the recovery of the native predator, once widely distributed across the country.

A kestrel sitting between two tree branches
© Malcolm Nicholl/ZSL

Mauritian kestrel numbers originally declined due to extensive habitat loss and the widespread application of insecticides to control malarial mosquitos and pests in agricultural systems; by the late 1950’s, it was restricted to the remote Black River Gorges. By 1974, numbers had fallen to just four known birds in the wild. 
The original restorative programme involved captive-bred birds which were reintroduced into four mountain ranges across the island. Following long-term management of the newcomers which included help with feeding and nest sites, the Mauritius Kestrel population grew to an estimated 350-400 individuals by 2000, and was down-listed to Vulnerable on the IUCN Red List of Threatened Species. However, recent evidence has shown that the species is once again in decline, and it was re-graded to Endangered in 2014.

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Senior Research Fellow at ZSL’s Institute of Zoology and project lead, Malcolm Nicoll said:  

“The Mauritius Kestrel Restoration Programme has long been seen as one of the most successful bird recoveries in the world. Reintroducing a species is a complex, long-term process, and the evidence the team have collected here will be instrumental in helping us to understand what has worked, and just as importantly, what hasn’t worked for these birds.”

A Mauritius kestrel sitting at the top of a tree branch
© Malcolm Nicholl/ZSL

For more than 20 years, researchers studied the four reintroduced populations, with their results revealing that each population had varied success. 
The population of kestrels on the Eastern side of the island, for example were found to be thriving with more than 50 monitored pairs, while the population in the North had declined and eventually completely disappeared by 2007. 

Dr Vikash Tatayah, Conservation Director for the Mauritian Wildlife Foundation who runs the kestrel recovery programme said:

“The Mauritius Kestrel is one of several species of birds that we have saved from extinction, and our proudest bird rescue success.  However, it is still far from easy.  We are battling with over four centuries of human colonisation, development, habitat loss and degradation, and invasive species.   
“Thanks to very close monitoring spanning over four decades undertaken by ourselves and our partners - including ZSL- we are able to tease apart overall population trends from trajectories at more local levels.  This allows us to understand localised population declines and to take corrective measures at both these regional scales, and to further improve the kestrel population management overall.”

Three Mauritius kestrel chicks huddled together
© Malcolm Nicholl/ZSL

Nest sites in each population were also regularly monitored as part of the programme. Kestrels nest in cavities in cliffs and trees, but there is a shortage of natural nest sites in some areas of Mauritius, due to habitat loss. Artificial nest boxes designed specifically for the kestrels were set up, and the teams found that in some cases, the birds bred more successfully where boxes were provided. 
Professor Carl Jones, Chief Scientist at Durrell Wildlife Conservation Trust and Scientific Director at the Mauritian Wildlife Foundation, set up the species recovery programme in the late 1970s.

Professor Jones said:

“Conservation work for the Mauritius Kestrel involved a whole range of innovative techniques to breed the species in captivity and to reintroduce them into the wild.  Once reintroduced the birds were carefully cared for, provided with nest-boxes, given extra food, predators were controlled, and the breeding pairs were nurtured to ensure they raised the maximum number of young. This work was continued until the birds had become re-established.  
“We now know from this study that we should have continued this care for longer, to ensure the populations continued to flourish.  It clearly demonstrates the importance of managing free-living populations of an endangered species and provides an important example of how we need to look after and monitor the most vulnerable species.”    

In recent years, the reintroduction programme has been revived to help alleviate a declining population of kestrels in the Western region. A team of expert bird keepers from ZSL London and Whipsnade Zoos were sent to Mauritius to help with the rearing and release of the birds. 

Curator of birds at ZSL and head of the ZSL zoo team who helped to rear and release the young birds, Gary Ward said:

“ZSL’s zoo bird keeping teams provided their unique animal care expertise and skills to this programme - both caring for the birds at the breeding facility and assisting with their release. Their invaluable knowledge and experience - learned from years of looking after birds at London and Whipsnade Zoos - proved to be a vital asset for this iconic project. It’s important that we continue to evaluate all steps along the way, so that we can ensure a bright future for these kestrels – and other animals we may help to reintroduce in the future.”

Dr Nicoll concluded: 

“This project is a great example of conservation scientists in Mauritius and elsewhere, working with zoo experts to help reverse species decline. This combination of expertise has been invaluable, and we hope that the research findings will help us understand how to best support the recovery of the Mauritius Kestrel for years to come.”

The team will continue to closely monitor the progress of the kestrel populations, and the findings of this study will be used to inform the next stages in the long running programme of bringing the rare Mauritius kestrel back from the brink. You can support ZSL's world-leading conservation work by donating to us online. 

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