Fruit Bats & Farmers: A Smarter Approach to Crop Protection in Mauritius

Original Article by:

Geetika Bhanda, Tropical Island Biodiversity, Ecology and Conservation Pole of Research, Faculty of Science, University of Mauritius

Ryszard Z. Oleksy, Ecosystem Restoration Alliance Indian Ocean, St. Pierre, Mauritius; School of Biological Sciences, University of Bristol, Bristol, United Kingdom

Raphaël D. Reinegger, School of Biological Sciences, University of Bristol, Bristol, United Kingdom

Cláudia Baider, The Mauritius Herbarium, Ministry of Agro-Industry,Food Security, Blue Economy and Fisheries

F.B. Vincent Florens, Tropical Island Biodiversity, Ecology and Conservation Pole of Research, Faculty of Science, University of Mauritius

Summary

New research on fruit damage in Mauritian lychee orchards reveals that effective crop protection requires understanding animal behaviour. Here are the main findings:

• Of the damaged fruits, Endangered flying foxes cause most damage (78%) but aren’t the only ones responsible: alien birds account for 16% of fruit loss.

• Protection should start much earlier: bats begin eating fruit in week 6-7 after fruit set, when fruits are still unripe, not when they start ripening.

• Timing-based deterrence has limited benefits: the difference between early and late night bat feeding is only 1-3 fruits per tree per night, protection day and night is preferable.

• Netting outperforms noise and smoke: physical barriers work against both nocturnal bats and diurnal birds, while active deterrents show limited effectiveness.

In Mauritius, an ongoing challenge exists between fruit farmers and one of the island’s most important native species. The Mauritian flying fox (Pteropus niger), a large fruit bat endemic to the Mascarenes, with original populations that have already been driven extinct in Rodrigues and Réunion, has become central to discussions about crop protection and conservation. In response to farmers’ concerns about fruit damage, the government implemented culling campaigns that have contributed to the species’ declining population while failing to achieve their intended objectives (Florens, 2016; Vincenot, Florens & Kingston, 2017).

But what if there was a better way? This research suggests that understanding when and how these bats feed could offer farmers more effective protection strategies without decimating a species already threatened with extinction and crucial to the island’s native vegetation ecosystems and biodiversity.

The Problem: When Conservation Meets Agriculture

The Mauritian flying fox isn’t just another frugivore fond of commercial fruits like lychee, it’s an ecological keystone species that plays a vital role in plant reproduction, hence forest regeneration, by dispersing seeds across the island’s forests (Florens et al., 2017) and possibly pollinating some species (Nyhagen et al., 2005). As the only remaining native frugivore capable of eating larger fruits following centuries of human-driven extinctions (Heinen et al., 2023), these bats are essential for maintaining Mauritius’s unique biodiversity, as they are the last survivors capable of helping large-seeded trees reproduce.

Yet farmers have increasingly complained about damage to their lychee and mango crops. Claims of fruit loss escalated dramatically from 30-40% in 2012 to include exaggerations as high as 75 to100% in orchards by 2015 (Government of Mauritius, 2010; Anonymous, 2013; Anonymous, 2015a; Anonymous, 2015b). Frustrated by mounting losses, the Mauritian government weakened the country’s biodiversity protection laws in 2015 to allow mass culling of flying foxes (Florens, 2015; Florens, 2016).

Repeated culling campaigns not only failed to increase fruit production, as scientists had predicted (Olival, 2016; Florens & Baider, 2019), but also contributed to the species’ deteriorating conservation status. The International Union for Conservation of Nature upgraded the Mauritian flying fox from “Vulnerable” to “Endangered” on its Red List of threatened species (Kingston et al., 2018).

When human-wildlife tensions arise, there are serious and growing challenges to wildlife (Madden, 2004; Frank, Glikman & Marchini, 2019).

Investigating the agents of fruit damage

Flying foxes (Chiroptera: Pteropodidae) are mainly frugivorous bats that often forage on commercial crops, leading to human-wildlife conflicts and frequently resulting in persecution, illegal killing and government-led culling (Aziz et al., 2016; Bumrungsri et al., 2009; Epstein et al., 2009). While non-lethal alternatives like netting (Korine, Izhaki & Arad, 1999; Oleksy et al., 2021), or deterrent systems (Ullio,2002; Chakravarthy & Girish, 2003) exist, certain difficulties may impede their implementation, such as high costs and labour requirements (Gough, 2002; Ullio,2002; Tollington et al., 2019).

To develop better solutions, the research needed to understand what was actually happening in the orchards. Were flying foxes really the main drivers of fruit losses? When were they most active? And were there patterns in their feeding behaviour that could inform more targeted protection strategies?

The authors conducted detailed observations in two lychee orchards and several backyard gardens, monitoring fruit damage around the clock throughout the fruiting season. They meticulously recorded which animals were eating the fruit, when they were most active, and how many fruits and how much of each fruit they consumed at different times of day and night.

The approach was both comprehensive and practical. Rather than relying on farmers’ reports alone, the research directly observed and measured damage patterns. It examined individual fruits to determine which species had caused the damage, tracked the timing of feeding events, and even assessed how fruit ripeness affected consumption patterns.

The Findings

The results revealed a more nuanced picture than the simple narrative of “bats eating all the fruit.” While flying foxes were indeed the primary cause of damage, accounting for 78% of fruit loss, they weren’t the only players in this drama.

Birds, particularly invasive species like ring-necked parakeets (Alexandrinus krameri), red-whiskered bulbuls (Pycnonotus jocosus), village weavers (Ploceus cucullatus), and common mynas (Acridotheres tristis) were responsible for another 16% of damage. Long-tailed macaques (Macaca fascicularis) have also been reported to extensively damage crops on backyard lychee trees, but this could not be confirmed at the specific sites studied (Tollington et al.,2019).

Timing Matters

Flying foxes demonstrated seasonal movement patterns depending on food availability (Oleksy et al., 2019), with more flying foxes foraging outside natural forest areas during commercial fruiting seasons (Seegobin, Oleksy & Florens, 2022). Studies on other bat species have shown similar patterns, with bats flying directly towards known foraging sites at nightfall (Markus & Hall, 2004) and timing their visits based on understanding of tree phenology (Harten et al., 2024).

The research uncovered important patterns in the feeding times of different species. Flying foxes were most active during the early part of the night, consuming 59% of their nightly lychee intake before midnight, with this early-night preference being statistically significant at one orchard and in backyard gardens. However, the practical difference was modest: just one to three more fruits eaten per tree per night in the early night compared to late night in the three orchards. Also noteworthy, non-netted orchard lychee trees sustained high fruit losses to flying foxes despite being subjected to some degree of sound and smoke deterrence.

Birds, predictably, caused most of their damage during daylight hours, with nearly half of the overall 16% damage that they contribute to, occurring in the first half of the day. This suggests that any protection strategy focused solely on deterring nocturnal flying foxes would miss a significant portion of the problem.

Ripeness and Seasonality

The study found that flying foxes began damaging fruit much earlier in the season than farmers typically expected. Damage occurred when fruits were still unripe, starting around the seventh week after fruit set. However, as fruits ripened, the bats consumed 39-42% more pulp per fruit, suggesting they preferred ripe fruit when available but would settle for unripe fruit when hungry. This resulted in greater damage during the unripe stage, as they consumed less pulp per fruit.

This behavior is consistent with optimal foraging theory, where animals become more choosy during high fruit availability when the probability of obtaining higher quality fruits increases (Pyke, 1984; Janson, 1996).

This finding challenges the common assumption that protection efforts should begin only when fruits start ripening. The bats were already there, eating the unripe fruit, weeks before farmers typically noticed the damage.

Practical Recommendations

Based on these findings, the researchers developed several practical recommendations that could help farmers protect their crops more effectively while reducing pressure on the flying fox population.

Earlier Protection Timeline

The most important recommendation is to begin protecting fruit trees no later than the sixth week after fruit set, typically between early October and early November in Mauritius. This is weeks earlier than most farmers currently start their protection efforts, but it’s when the bats actually begin feeding. This implies that the bird nets should be made available on the market at an earlier date than they usually are, and so also for the deployment of the government’s bird net subsidy programme.

Netting Over Noise

While many farmers rely on active deterrence methods like noise, smoke, and lights, the research suggests these have limited effectiveness. Similar deterrent practices have been reported in Australia and India (Srinivasulu & Srinivasulu, 2001; Bicknell, 2002), though their effectiveness has rarely been scientifically evaluated. The difference in bat damage between early and late night was so small that concentrating deterrent efforts during early evening hours would save only about 1 kg of fruit per tree per night.

Instead, netting emerged as the most effective protection method, offering several advantages:

• It works against both nocturnal bats and diurnal birds, and for at least 3-5 years when properly used.

• It provides consistent protection without requiring constant human presence.

• It doesn’t habituate animals to deterrent methods over time.

Comprehensive Approach

Since birds cause significant damage during daylight hours, protection strategies must address both nocturnal and diurnal threats. A bat-only approach will leave crops vulnerable to bird damage, while bird-only deterrents ignore the larger threat from flying foxes. Successful active deterrence of flying foxes at night may even merely result in more fruits being available to be damaged by birds the next day.

Policy Solutions

There are systemic issues that discourage farmers from adopting more effective protection methods. Net supplies are sometimes limited during the fruiting season, and the cost of netting can be a deterrent for small-scale farmers. This is especially true when nets are not used properly, resulting in single-season use instead of the intended lifespan of three to five successive fruiting seasons. Ensuring adequate and affordable supplies of protective netting and the use of best practice in their deployment using supporting frames, could significantly reduce reliance on less effective deterrent methods.

A Path Forward

This research demonstrates that effective wildlife management requires understanding animal behaviour. By studying when and how flying foxes actually feed, scientists have identified protection strategies that could be effective where lethal control has so far consistently failed the fruit growers. Replacing lethal control with judicious crop protection would also preserve both a threatened Mascarene endemic species essential to Mauritius’s native vegetation ecosystems, and the image of the fruit production industry.

The research was also able to highlight the importance of evidence-based approaches to human-wildlife conflict. The story of Mauritius’s flying foxes serves as both a cautionary tale and a source of optimism. It demonstrates that simplistic quick fix management often backfires and that with careful research and practical solutions, it is possible to find approaches that work for both farmers and wildlife.

For other regions facing similar conflicts, the lesson is clear: instead of reaching for lethal control measures, it pays to invest in understanding the problem.

Full reference original article:

Bhanda G, Oleksy RZ, Reinegger RD, Baider C, Florens FBV. 2025. A study of diel and seasonal patterns of loss of commercial lychee fruits to vertebrate frugivores: implications for mitigating a human-wildlife conflict. PeerJ 13:e19269, http://doi.org/10.7717/peerj.19269

Other publications by authors on fruit bat-related publications only :

Seegobin V. O., R. Z. Oleksy,F. B. V. Florens (2024). Foraging habitat quality of an Endangered mass-culled flying fox is reduced by alien plant invasion and improved by alien plant control. Journal for Nature Conservation 78: 126569 https://doi.org/10.1016/j.jnc.2024.126569

Kingston T., F. B. V. Florens, C. E. Vincenot (2023) Large old world fruit bats on the brink of extinction: causes and consequences. Annual Review of Ecology Evolution and Systematics 54: 237-257. https://doi.org/10.1146/annurev-ecolsys-110321-055122

Seegobin V. O., R. Z. Oleksy,F. B. V. Florens (2022). Foraging and roosting patterns of a repeatedly mass-culled island flying fox offers avenues to mitigate human-wildlife conflict. Biodiversity 23(2): 49-60. https://doi.org/10.1080/14888386.2022.2107569

Albert S., O. Flores, C. Baider, F. B. V. Florens, D. Strasberg (2021). Differing severity of frugivore loss contrasts the fate of native forests on the land of the Dodo (Mascarene archipelago). Biological Conservation 257: 109131 https://doi.org/10.1016/j.biocon.2021.109131

Oleksy, R. Z., Ayady, C. L., Tatayah, V., Jones, C., Froidevaux, J. S. P., Racey, P. A., Jones, G. (2021). The impact of the Endangered Mauritian flying fox Pteropus niger on commercial fruit farms and the efficacy of mitigation. Oryx 55: 114–121. https://doi.org/10.1017/S0030605318001138

Reinegger, D. R., Ryszard, Z. O., Bissessur, P., Naujeer, H., Gareth, J. (2021). First come, first served: Fruit availability to keystone bat species is potentially reduced by invasive macaques. Journal of Mammalogy 102: 428–439. https://doi.org/10.1093/jmammal/gyaa182

Krivek G., F. B. V. Florens, C. Baider, V. O. Seegobin, T. Haugaasen (2020). Invasive alien plant control improves foraging habitat quality of a threatened island flying fox. Journal for Nature Conservation 54: Article 125805 https://doi.org/10.1016/j.jnc.2020.125805

Florens F. B. V., Baider C. (2019). Mass-culling of a threatened island flying fox species failed to increase fruit growers’ profits and revealed gaps to be addressed for effective conservation. Journal for Nature Conservation 47: 58-64. https://doi.org/10.1016/j.jnc.2018.11.008

Oleksy, R. Z., Ayady, C. L., Tatayah, V., Jones, C., Howey, P. W., Froidevaux, J. S. P., Racey, P. A., Jones, G. (2019). The movement ecology of the Mauritian flying fox (Pteropus niger): A long-term study using solar-powered GSM/GPS tags. Movement Ecology 7: 12. https://doi.org/10.1186/s40462-019-0156-6

Florens F. B. V., C. E. Vincenot (2018). Broader conservation strategies needed. Science 362 (6413): 409. https://www.science.org/doi/10.1126/science.aav5161

Kingston T., F. B. V. Florens, R. Oleksy, K. Ruhomaun, V. Tatayah (2018). Pteropus niger. The IUCN Red List of Threatened Species 2018. https://www.iucnredlist.org/species/18743/86475525

Florens F. B. V., C. Baider, V. Marday, G.M.N. Martin, Z. Zmanay, R. Oleksy, G. Krivek, C. Vincenot, D. Strasberg, T. Kingston (2017). Disproportionately large ecological role of a flying fox species in native forests of an oceanic island. Journal for Nature Conservation, 40: 85-93. https://doi.org/10.1016/j.jnc.2017.10.002

Baider C., F. B. V. Florens, Vincenot C., T. Kingston (2017). These bats need a break. Biosphere 25: 18-27.

Vincenot C., F. B. V. Florens , T. Kingston (2017). Can we protect island flying foxes?  Science 355(6332): 1368-1370. https://doi.org/10.1126/science.aam7582

Florens F. B. V. (2016). Biodiversity law: Mauritius culls threatened fruit bats. Nature 530: 33. https://doi.org/10.1038/530033a

Florens F. B. V. (2015). Flying foxes face cull despite evidence. Science 350 (6266): 1325-1326. https://doi.org/10.1126/science.350.6266.1325-a

Oleksy, R., Racey, P. A., Jones, G. (2015). High-resolution GPS tracking reveals habitat selection and the potential for long-distance seed dispersal by Madagascan flying foxes Pteropus rufus. Global Ecology and Conservation 3: 678-692. https://doi.org/10.1016/j.gecco.2015.02.012

Florens F. B. V. (2012). Going to bat for an Endangered species. Science 336 (6085): 1101. https://www.science.org/doi/10.1126/science.336.6085.1102-a

Main photo from Jacques de Speville.

Charles Telfair Centre is an independent, nonpartisan not for profit organisation and does not take specific positions. All views, positions, and conclusions expressed in our publications are solely those of the author(s).