Impacts of Pressure on Bat Populations

Dear Colleagues,

Although several studies have highlighted their value in terms of providing ecosystem services (e.g., pest control, seed dispersal, and pollination), and although legally protected in many countries through national or supranational laws, bat populations are declining around the globe—largely as a result of human activity. Of the 1296 bat species that have been assessed by the International Union for the Conservation of Nature (IUCN), almost a third are considered either threatened (critically endangered (23), endangered (56), vulnerable (107)) and 82 are considered near-threatened, highlighting the need for more conservation attention to these species. In addition, bats also are among the most under-studied of mammals: 231 bat species are listed by the IUCN lists as Data Deficient, meaning there is not enough information available to determine their conservation status, underlining the need for more surveys and research.

Numerous causes of this situation have been identified, and include:

1) The loss of natural habitat, which remains the most widespread peril worldwide for bats. This is especially critical in the tropical rainforests, which tend to have high species diversity and experience drastic clearance for the settlement of farm crops, mining operations, cattle pastures, or cities.

2) Agricultural intensification, which is particularly an established threat for bats. In some areas, bats are considered as an agricultural pest due to the damage they cause to fruit production and are directly regulated. At least half of the global population of the Mauritian flying fox (Pteropus niger) was destroyed due to the two successive mass culls planned by the Mauritian government. Using the best available evidence, the IUCN moved the Mauritian flying fox to a higher threat category, from Vulnerable to Endangered. However, in addition to this direct destruction of bats, agricultural intensification also involves (i) the replacement of natural and semi-natural habitat with annual crops, (ii) the fragmentation of natural habitats, (iii) the homogenization of the farming landscape over space and time, and (iv) and increased use of fertilizers and pesticides. A major issue is therefore the reconciliation of agricultural production with biodiversity, and the identification of practices that contribute to maintaining viable bats populations.

3) Emerging infectious diseases such as white-nose syndrome have drastically impacted North American bats: 6 million bats have been killed by a cold-loving fungus called Pseudogymnoascus destructans. This disease continues its spread across the continent, causing mortality rates that approach 100% at some sites.

4) Roost destruction and disturbance. In many countries, bats regularly use artificial above-ground structures as breeding colonies or for hibernacula. However, houses, historical monuments, and public buildings can be subject to rehabilitation works, and in addition cohabiting with bats can lead to disagreements, underlining the need of efficient mitigation strategies for bats in buildings.

5) Destruction due to harmful myths. Unfortunately, bats are still casually killed because of misplaced fears. In Latin America, whole colonies are routinely destroyed in the mistaken belief that all bats are vampires, stressing the need of public awareness.

6) Hunting. In regions such as Southeast Asia and the Pacific islands, bats are hunted, both as bush meat for local consumption and commercially for markets and restaurants.

6) Light pollution. This new emerging human pressure is a major threat to biodiversity worldwide, decreasing habitat quality and landscape connectivity for nocturnal species. The impact of artificial light is poorly accounted for, in a large part due to the lack of quantitative information and relevant guidelines to limit its negative effects.

7) Wind farm development. Hundreds of thousands of bats are killed each year in the United States by collisions with the spinning blades of wind turbines or rapid pressure changes at turbines that can result in barotrauma. According to the low growth rate of bat populations, fatalities at wind turbines may threaten population viability. Another research gap in wind turbines is the loss of habitat use resulting from the potential negative impact of wind turbines. The European recommendations (wind turbines at least 200 m from any wooded edge) set to limit mortality events likely strongly underestimate the loss of bat activity. The current situation is particularly worrying, because few turbines comply with recommendations, which themselves are far from sufficient to limit the loss of habitat use.

8) The development of transportation infrastructure, which involve direct mortality and indirect impact though a road-zone effect (up to five kilometers) where a significant negative effect of major roads on bat activity has been detected. No assessment of these two impacts of road on bat population viability and few offsetting actions are carried out during road construction. It seems urgent to consider these road effects with the cumulative effects of other roads by improving habitat connectivity and foraging areas in land use policies.

Dr. Christian Kerbiriou
Guest Editor

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• conservation biology
• biodiversity monitoring
• anthropogenic pressure on bats
• conservation status of bats
• research priorities in conservation of bats
• conservation action plan for bats
• bats population trends
• house bat management
• bat fatalities
• bat mortality