Mammals have conquered virtually all media, and have spread throughout the entire planet. They populate the oceans, are natively present on every continent except Antarctica, and some have attained the ability to fly .
The largest known animal species in the history of evolution is a mammal: the blue whale. And thanks to the great variety that mammals present, they also have extraordinarily small species .
The title of the smallest mammal is disputed by two species; the adult specimens of both can weigh less than two grams, although one of the cases presents greater variability within the species and can weigh up to three. This detail makes the bumblebee bat the winning species.
the bumblebee bat
Its common name leaves no room for doubt. This animal, with the scientific name Craseonycteris thonglongyai , is extraordinarily small, measuring between 29 and 33 millimeters in length, and weighing between 1.5 and 2 grams . So small and so elusive that it was unknown until 1974. It lives in two specific regions of forests and caves in Myanmar (Burma) and Thailand, always associated with outcrops of limestone near rivers.
It rests inside limestone caves, forming numerous groups that can exceed 100 individuals, and even reach 500. Individuals sleep hanging from the walls or ceiling of the cavity. They have been observed to make seasonal migrations from one cave to another .
It is insectivorous, and its feeding area extends up to a kilometer around the resting cave. The flights are short, less than an hour, at twilight times —dusk and dawn—. It hunts flying insects using echolocation, like many other bat species.
During the dry season, populations reproduce. Each female gives birth to a single calf , which remains attached to the mother, hooked to one of the two nipples that it presents in the pubic region.
This bat is subject to various threats from humans. On the one hand, its resting caves are used as tourist places or to carry out religious activities . The burning of incense by monks in the region has a significant impact on these little bats. In some places bat guano is also extracted as a source of fertilizer, or limestone directly . These disturbances are considered the main anthropic threats to bumblebee bats.
The population of these little bats is very difficult to quantify; their size makes them very difficult to census, so we only have estimates. Eight caves have been located in the Myanmar population with an estimated population of less than 4,000 individuals . On the other hand, in Thailand they have been observed distributed in a total of 44 caves, with a population of less than 6500 individuals in total . The constant threats are causing both populations to be in decline, which is why the IUCN catalogs it, since 2008, as a vulnerable species.
The Etruscan shrew, tied for weight
Much more common and numerous is the Etruscan shrew ( Suncus etruscus ) , rival of the bumblebee bat in the category of lightest known mammal. With a weight between 1.7 and 3 grams , in general this animal would receive the silver medal, although occasionally, some adult individuals weigh less than some bumblebee bat specimens. However, it is undoubtedly a larger animal; Without counting the tail, the Etruscan shrew measures between 35 and 50 millimeters .
It extends from the area of Myanmar and Thailand, where it shares habitat with the bumblebee bat, to a large part of the Mediterranean basin, including the Italian and Iberian peninsulas, except for the northwestern quadrant. It inhabits temperate, Mediterranean, and tropical forests , and readily associates with rural human populations, where it takes advantage of abandoned crops.
They are solitary animals that do not tolerate the presence of their congeners, except for reproductive purposes. The female has a very long gestation, between 26 and 28 days, and between 2 and 7 pups weighing just 0.2 grams are born , which the mother cares for and feeds for three weeks. A week after weaning, the offspring are already forced independent, hated by the mother, who begins to consider them her competitors.
REFERENCES:
Francis, C. et al. 2018. Craseonycteris thonglongyai. IUCN Red List of Threatened Species.
Libois, R. et al. 1999. Suncus atruscus. En A. J. Mitchell-Jones et al. (Eds.), The Atlas of european mammals. Academic Press.
Pereira, M. J. R. et al. 2006. Status of the world’s smallest mammal, the bumble-bee bat Craseonycteris thonglongyai, in Myanmar. Oryx, 40(4), 456-463. DOI: 10.1017/S0030605306001268
Puechmaille, S. et al. 2009. Population size, distribution, threats and conservation status of two endangered bat species Craseonycteris thonglongyai and Hipposideros turpis. Endangered Species Research, 8, 15-23. DOI: 10.3354/esr00157
