A maternity colony refers to a temporary association of reproductive female bats for giving birth to, nursing, and weaning their pups. The colonies are initiated by pregnant bats. After giving birth, the colony consists of the lactating females and their offspring. After weaning, juveniles will leave the maternity colony, and the colony itself will break apart. The size of a maternity colony is highly variable by species, with some species forming colonies consisting of ten or fewer individuals, while the largest maternity colony in the world in Bracken Cave is estimated to have over 15 million bats.

Townsend's big-eared bats exiting a maternity colony in a mine

Benefits of a maternity colony

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Maternity colonies are especially prevalent in temperate regions due to the thermal benefits of roosting with other individuals.[1] Outside of the winter months, non-reproductive females and male bats enter torpor for short periods to conserve energy when temperatures are below an optimum threshold. However, torpor is detrimental to reproductive females because it delays the development of the fetus and slows milk production.[1] Therefore, female bats are highly incentivized to maintain a constant body temperature. Roosting in a large group allows females to share body heat, lowering the energetic costs for individuals.

Risks of a maternity colony

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Roosting in large groups brings risks to the members of a maternity colony. Predators such as hawks and owls can learn to anticipate the emergence of bats from a specific roost at sunset.[2] Smaller colonies are thought to be less risky than larger colonies, because the nightly emergence of bats would attract less attention.[3]

Species that form maternity colonies

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Incomplete list
Common name Scientific name Range Maternity colony size
Family: Vespertilionidae
Little brown bat Myotis lucifugus U.S., Canada 107-349[4]
Southeastern myotis Myotis austroriparius Southeastern U.S. 1000 [5]
Fringed myotis Myotis thysanodes Canada, Western U.S., Mexico 40-200[6]
Indiana bat Myotis sodalis Midwestern U.S. 30-300[7][8]
Northern long-eared bat Myotis septentrionalis Eastern U.S., Canada 11-65[9]
Bechstein's bat Myotis bechsteinii Europe, Asia 15-40[10]
Geoffroy's bat Myotis emarginatus Europe <10-985[11]
Gray bat Myotis grisescens Southeastern U.S. 100,000 [12]
Hodgson's bat Myotis formosus Asia 82-200[13]
Eastern small-footed bat Myotis leibii Eastern U.S., Canada ≤22[14]
Greater mouse-eared bat Myotis myotis Europe 50-800[15]
Cave myotis Myotis velifer Southwest U.S., Mexico 100-3,000[16]
Yuma myotis Myotis yumanensis Western U.S. 100-1,000 [16]
Arizona myotis Myotis occultus Southwestern U.S. 67[17]
Daubenton's bat Myotis daubentonii Europe, Asia 6-144[18]
Long-eared myotis Myotis evotis Canada, Western U.S. 4[19]
Tricolored bat Perimyotis subflavus Eastern U.S. 9-40[20][21]
Parti-coloured bat Vespertilio murinus Europe, Asia >30[22]
Big brown bat Eptesicus fuscus North America, Central America, the Caribbean 20-100[23]
Serotine bat Eptesicus serotinus Europe, Asia 5-200[24]
Northern bat Eptesicus nilsonii Europe, Asia 10-70[25]
Silver-haired bat Lasionycteris noctivagans Bermuda, Canada, Mexico, U.S. 8[26]
Townsend's big-eared bat Corynorhinus townsendii Canada, Mexico, U.S. 40-55[27]
Virginia big-eared bat Corynorhinus townsendii virginianus Appalachian U.S. 100-6335[28]
Ozark big-eared bat Corynorhinus townsendii ingens AR, OK, MO 55-309[29]
Rafinesque's big-eared bat Corynorhinus rafinesquii Southeastern U.S. ≤118[30]
Common noctule Nyctalus noctula Europe, Asia, North Africa 20-50[31]
Common pipistrelle Pipistrellus pipistrellus Europe, North Africa, Asia 92-262[32]
Nathusius's pipistrelle Pipistrellus nathusii Europe 5-150[33]
Evening bat Nycticeius humeralis Eastern U.S. ≤492[34]
Gould's wattled bat Chalinolobus gouldii Australia 20-30[35]
Southern forest bat Vespadelus regulus Australia <25[36]
Lesser long-eared bat Nyctophilus geoffroyi Australia 3-23 [36]
Pallid bat Antrozous pallidus Canada, Western U.S., Mexico 10-150[16]
Barbastelle Barbastella barbastellus Europe 10[37]
Allen's big-eared bat Plecotus phyllotis Southwestern U.S., Mexico 18-97[38]
Family: Rhinolophidae
Mehely's horseshoe bat Rhinolophus mehelyi Europe, Middle East <60[39]
Lesser horseshoe bat Rhinolophus hipposideros Europe, North Africa, Asia 2-750[40][41]
Rufous horseshoe bat Rhinolophus rouxii Asia, Southeast Asia 50-60[42]
Family: Molossidae
Mexican free-tailed bat Tadarida brasiliensis U.S., Central America, South America ≤15 million[43]
Big free-tailed bat Nyctinomops macrotis North America, Central America, South America ≤2,000[44]
Family: Phyllostomatidae
Geoffroy's tailless bat Anoura geoffroyi Central America, South America <150[45]
Family:Miniopteridae
Common bent-wing bat Miniopterus schreibersii Europe, Asia, Australia 2,500-5,000[46]
Family: Pteripodidae
Bornean large flying fox Pteropus vampyrus Borneo <15,000[47]

References

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  31. ^ Csorba, G.; Hutson, A.M. (2016). "Nyctalus noctula". IUCN Red List of Threatened Species. 2016: e.T14920A22015682. doi:10.2305/IUCN.UK.2016-2.RLTS.T14920A22015682.en. Retrieved 12 November 2021.
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  38. ^ Cockrum, E. L., & Musgrove, B. F. (1964). Additional records of the Mexican big-eared bat, Plecotus phyllotis (Allen), from Arizona. Journal of Mammalogy, 45(3), 472-474.
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  47. ^ Gumal, M. T. (2004). Diurnal home range and roosting trees of a maternity colony of Pteropus vampyrus natunae (Chiroptera: Pteropodidae) in Sedilu, Sarawak. Journal of Tropical Ecology, 20(03), 247-258.