Bat
Predators, parasites, and diseases

Bats are subject to predation from birds of prey, such as owls, hawks, and falcons, and at roosts from terrestrial predators able to climb, such as cats. Low-flying bats are vulnerable to crocodiles. Twenty species of tropical New World snakes are known to capture bats, often waiting at the entrances of refuges, such as caves, for bats to fly past. J. Rydell and J. R. Speakman argue that bats evolved nocturnality during the early and middle Eocene period to avoid predators. The evidence is thought by some zoologists to be equivocal so far.

As are most mammals, bats are hosts to a number of internal and external parasites. Among ectoparasites, bats carry fleas and mites, as well as specific parasites such as bat bugs and bat flies (Nycteribiidae and Streblidae). Bats are among the few non-aquatic mammalian orders that do not host lice, possibly due to competition from more specialised parasites that occupy the same niche.

White nose syndrome is a condition associated with the deaths of millions of bats in the Eastern United States and Canada. The disease is named after a white fungus, Pseudogymnoascus destructans, found growing on the muzzles, ears, and wings of affected bats. The fungus is mostly spread from bat to bat, and causes the disease. The fungus was first discovered in central New York State in 2006 and spread quickly to the entire Eastern US north of Florida; mortality rates of 90–100% have been observed in most affected caves. New England and the mid-Atlantic states have, since 2006, witnessed entire species completely extirpated and others with numbers that have gone from the hundreds of thousands, even millions, to a few hundred or less. Nova Scotia, Quebec, Ontario, and New Brunswick have witnessed identical die offs, with the Canadian government making preparations to protect all remaining bat populations in its territory. Scientific evidence suggests that longer winters where the fungus has a longer period to infect bats result in greater mortality. In 2014, the infection crossed the Mississippi River, and in 2017, it was found on bats in Texas.

Bats are natural reservoirs for a large number of zoonotic pathogens, including rabies, endemic in many bat populations, histoplasmosis both directly and in guano, Nipah and Hendra viruses, and possibly the ebola virus, whose natural reservoir is yet unknown. Their high mobility, broad distribution, long life spans, substantial sympatry (range overlap) of species, and social behaviour make bats favourable hosts and vectors of disease. Reviews have found different answers as to whether bats have more zoonotic viruses than other mammal groups. One 2015 review found that bats, rodents, and primates all harbored significantly more zoonotic viruses (which can be transmitted to humans) than other mammal groups, though the differences among the aforementioned three groups were not significant (bats have no more zoonotic viruses than rodents and primates). Another 2020 review of mammals and birds found that the identity of the taxonomic groups did not have any impact on the probability of harboring zoonotic viruses. Instead, more diverse groups had greater viral diversity.

They seem to be highly resistant to many of the pathogens they carry, suggesting a degree of adaptation to their immune systems. Their interactions with livestock and pets, including predation by vampire bats, accidental encounters, and the scavenging of bat carcasses, compound the risk of zoonotic transmission. Bats are implicated in the emergence of severe acute respiratory syndrome (SARS) in China, since they serve as natural hosts for coronaviruses, several from a single cave in Yunnan, one of which developed into the SARS virus. However, they neither cause nor spread COVID-19.
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