It once flourished in caves all over the southeastern United States, but due to human disturbance, gray bat populations declined severely during the early and mid portion of the 20th century.

[7] Gray bats in the wild may reach ages of at least 13–14 years (based on recapture of banded individuals), although this is considered exceptional.

This reservoir, found in northeastern Alabama, contains the Sauta (formerly Blowing Wind) and Hambrick caves which can accommodate over 200,000 gray bats combined.

[5] Gray bats consume a variety of insects including Coleoptera (beetles), Diptera (flies), Ephemeroptera (mayflies, of which gray bats consume at least six species), Lepidoptera (moths), Neuroptera (net-winged insects), Trichoptera (caddis flies),[7] and Plecoptera (stoneflies).

[13] Juveniles have a tendency to forage more in woodlands and eat more beetles than adults, perhaps they provide a greater energy reward per unit of capture effort.

[13] In captivity, under controlled laboratory conditions, however, insectivorous bats used echolocation to discriminate heavily among potential prey based on shape and texture of a target.

[13] Scientists believe that food moves quickly through the digestive tract of M. grisescens, with feces being purged from the body within 1–2 hours after ingestion.

Gray bats may migrate as far as 500 km (310 mi) from summer caves to reach hibernation caves,[6] although based on band recovery data and the spatial distribution of summer and winter roosts, a migration range below 320 km (200 mi) appears to be the norm.

Gray bats prefer caves located near appropriate foraging sites to reduce the energy costs of flying long distances to find food.

During the peak lactation period, when young are roughly 20–30 days old, females may spend as many as 7 hours a night feeding.

Because of the high energy demands on the females, larger roosts are more beneficial so that all may share the burden of maintaining body temperature.

This increased foraging range will lead to greater energy expenditure, potentially reducing growth in gray bat juveniles.

[6] Because of their high population densities in appropriate habitats, gray bats serve as an important indicator species for conservation efforts.

Because M. grisescens feed on many types of insects with aquatic larval stages, it is believed that this food source may be the root of the chemical concentrations.

After concentration through lactation, a few parts per million in prey of the adult gray bat would cause mortality in these juveniles.

Under conditions of rapid fat utilization, such as migratory stress or initiation of flight by juveniles, residue mobilization of harmful chemicals may occur, causing mortality.

[16] Direct human disturbance and vandalism is the major factor leading to population decline in gray bats.

Many property-owners attempted to exterminate entire colonies due to unsubstantiated fears that the bats may be carrying rabies.

One study showed that caves with ceiling heights greater than 15 metres (49 ft) above the floor were virtually protected from spelunkers.

[17] Even without direct destruction, human visitation to caves can cause adverse effects on gray bat populations.

Each human entry into a cave causes all bats within range of light or sound to at least partially arouse from hibernation.

Continuous surveys since 2009 have indicated that gray bats may be largely resistant to the disease even when sharing roosts with infected individuals of other species.

[18] These contributing factors play an especially important role in determining the internal conditions that foster cave fauna.

[19] Thus, to maximize the gray bat's range, the United States government is funding cave gating programs.

With these limitations in mind, the internal cave gating was placed 5 to 15 meters in advance of historically critical roost areas.

To reduce human impact on gray bat populations, gating, fencing, signposting, and surveillance by law enforcement may be utilized.

Rivers, reservoir shorelines, and forests should be left intact near gray bat caves to allow for adequate foraging.

Finally, the US Fish and Wildlife Service recognized the need for continuing research from the scientific community to further understand human impact on this vulnerable species.

(Before this 2004 discovery, the only known gray bats lived at a site known as Chalk Mine, located in the northeastern portion of the county.

Extensive human disturbance, including the presence of trash, smoke, and graffiti, is believed to have affected the use of the Chalk Mine by bats.