Cormura brevirostris
Silhouette: T. Michael Keesey · PhyloPic
In 3 days ~30% in a week ~50%
The chestnut sac-winged bat, or Wagner's sac-winged bat (Cormura brevirostris) is a species of sac-winged bat native to South and Central America. It is the only species within its genus. The chestnut sac-winged bat is a relatively small member of its family, with adults usually measuring 7 cm (2.8 in) in length, and weighing 7 to 11 g (0.25 to 0.39 oz). Soft, dense fur covers the body, and the inner parts of the wings, reaching as far as the mid-humerus and mid-femur on both the upper and lower surfaces. The fur is brown-black or red-brown in colour, being darker above, and paler on the underside of the animal. The wings are black, with the membranes extending as far as the ankles.
The tail projects from the middle of the membrane between the legs, but does not extend beyond it, so is not visible in silhouette. The tail measures about 1.5 cm (0.59 in) in length, although only 1 to 3 mm (0.039 to 0.118 in) of the tip is visible above the membrane. Males of the species have sacs in the centre of the membranes on the forward surfaces of the wings, which reach from the edge of the membrane almost to the elbow. This distinguishes it from all other sac-winged bats, in which... Wikipedia →
| # | Park | Country | Daily sighting probability |
|---|---|---|---|
| 1 | Corcovado National Park | 🇨🇷 Costa Rica |
More parks will be added in future updates.
With luck
About 10% of wildlife watchers report a Chestnut Sac-winged Bat sighting in Corcovado National Park on a given day, based on 10 verified sightings from GBIF citizen-science data from 2019 to 2026. It is the 20th most-seen of the 31 mammals we can rate there. Over three days the chance rises to about 30%, and over a week to about 50%, if each day is a fresh chance.
May and September
In those months about 20% of wildlife watchers report a Chestnut Sac-winged Bat in Corcovado National Park on a given day, against under 5% in June, August and October–December, the lowest months.
Between 9 am and noon
Across all the parks we cover, that three-hour window holds the most Chestnut Sac-winged Bat sightings with a recorded time, and about 6 in 10 of them come between 6 am and 6 pm: it is seen both by day and at night.
Only Corcovado National Park, in our data
Corcovado National Park is the only park on Wallace's Line with enough records to rate Chestnut Sac-winged Bat sightings: about 10% of wildlife watchers there report one on a given day.
Same family: Emballonuridae
The closest relatives of the Chestnut Sac-winged Bat that you can see in Corcovado National Park (family Emballonuridae, Sheath-tailed Bats) are Thomas's Shaggy Bat (about 10%), Proboscis Bat (about 10%) and Greater Sac-winged Bat (about 10%), with each one's daily chance of a sighting.
GBIF citizen-science records
It is estimated from how often the Chestnut Sac-winged Bat is recorded against all the mammals logged in Corcovado National Park (10 verified sightings from 2019 to 2026), calibrated against known sighting rates. Figures are rounded to the nearest 10% because citizen-science data supports honest approximations, not decimals, and months with records from fewer than five people show "—". How it works.
