In an effort to reduce damage to fruit orchards on the island, the Mauritian Government has just announced (27 October 2018) a further cull of the Endangered Mauritian flying fox Pteropus niger. The cull will aim to reduce the current population by 20%. Half of the original population has already been culled in 2015–2016. A recent study published in OryxThe International Journal of Conservation, by Ryszard Oleksy and colleagues and involving collaborators from Ecosystem Restoration Alliance Indian Ocean, the Durrell Wildlife Conservation Trust, the Universities of Bristol and Exeter and the Mauritian Wildlife Foundation, shows why culling is unnecessary, and how alternatives methods for safeguarding fruit crops are effective.

The Mauritian flying fox is a large fruit-eating bat largely restricted to the island of Mauritius in the Indian Ocean. The bats play a vital role in preserving the island’s disappearing native forests as they disperse the seeds of large trees that form forest canopies. They also feed on cultivated fruit such as mango and lychee, and are hunted because they are perceived to cause large economic losses to commercial fruit farmers. However, information on the scale of damage and the efficacy of mitigation has hitherto been lacking.

Fruit growers estimated economic losses equivalent to at least 5 million US dollars annually at orchards and convinced the Mauritian Government that a cull of flying foxes was necessary. Although accurate numbers of population size and the number of culled bats are difficult to estimate, roughly half the total population of bats may have been culled in 2015–2016. In addition, 5000–6000 bats are probably killed illegally each year.

Given the magnitude of the population decline, the slow reproductive rate of the bats, their vulnerability to cyclones and ongoing habitat loss, the Mauritian flying fox was uplisted as Endangered by the IUCN in its Red List this year. Perhaps only 62,500 bats remained alive in 2016.

It seems bizarre that a species that plays a crucial ecological role and is found nowhere else in the world should be culled to such an extent in the absence of reliable evidence about how much damage it causes and whether culling is an effective form of control. Oleksy et al. measured the extent of damage to commercial fruit farms by the Mauritian flying fox, and determined whether such damage could be managed effectively without the need to cull.

The research showed that bats caused damage to a quarter of all monitored fruits overall, with more damage on taller trees (> 6 m). Significant losses were also caused by birds and by natural fruit fall. Farmers can therefore reduce fruit losses by pruning trees to reduce their height and by harvesting fruit before it is too ripe for selling. By experimentally covering trees with nets, Oleksy and colleagues also showed that fruit damage by bats can be reduced drastically with this methods, even if the nets are placed directly over trees without using a frame. The Mauritian government subsidises the costs of nets by 50–75% at orchards and for backyard growers, respectively. By using these nets, fruit loss by bats can be reduced without the need for culling. Further culling is clearly unnecessary, and hopefully the vital ecological roles played by these remarkable and endangered animals can be encouraged and enhanced in the future.

The paper ‘The impact of the Endangered Mauritian flying fox Pteropus niger on commercial fruit farms and the efficacy of mitigation’ by R.Z. Oleksy, C.L. Ayady, V. Tatayah, C. Jones, J.S.P. Froidevaux, P.A. Racey  & G. Jones is now freely available until November 30.

 

Mauritian flying fox images ©Jacques de Speville.

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