Maternity colony

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

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

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

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]

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