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A mistery of the highlands of Costa Rica

Scientific name: Aegolius ridgwayi

(Previous Cryptoglaux)

Family: Strigidae

English name: Unspotted Saw-whet Owl

Common names in Spanish: Lechucita Parda, Lechucita de Alfaro, Mochuelo Moreno.

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First collection

The USWO was first collected in 1903 at Cerro La Candelaria - near Escazú - by Costa Rican naturalist Anastasio Alfaro, who was founder and director of the National Museum of Costa Rica (1887) for many years.

The name "unspotted" comes from the fact that its closest relative, the Northern Saw-whet Owl, does have spots.

Head and upper region uniformly brown

Nape golden-brown

Facial disc border, supercilium and chin between white and buff

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External primaries and alula with white  leading edge

Chest between cinnamon and brown

Buff belly

Iris between yellow and greenish yellow

Cere and bill mostly blackish with pale sides

Pinkish-yellow toes

Talons mostly black but some are pale pink


The project

The main objective of our project is to carry out research on the species' natural history and ecology to understand its needs and be capable of proposing conservation guidelines. Most of the information on this website has been generated through the project's efforts.


The USWO is an "umbrella species"; conservation actions to preserve this owl will benefit many other species, both endemic and migratory, that live in the highlands of Central America.

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Their diet is composed mainly of small rodents, shrews and large insects such as beatles and moths.  We have observed them catching rodents both on the ground and on tree trunks, while the insects were captured in mid-air and in all cases they used their talons. 


They tend to hunt from low perches, between 1-3 meters above the ground, from where they observe and listen carefully for their prey.

Part of its diet has been discovered by the finding of pellets.
Pellets are a mass of undigestible food parts that birds of prey regurgitate such as bones, hair and insect exoskeletons.


Pellet dissection
Many skeleton parts of small rodents and beetle exoskeletons were found.




The most commonly heard and recorded vocalizations are those of the males since in the majority of cases they occur in response to playback and it is generally the male who responds more aggressively in territorial defense.

However, we have recorded another nine different vocalizations from both sexes, noting the respective behavior involved with each type of call.

USWO maleSong
00:00 / 00:11
USWO maleAggressive call
00:00 / 00:13
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Male spectrogram

USWO femaleCall
00:00 / 00:06
USWO Canto Hembra.png

Female spectrogram



All known nests except one have been in natural cavities such as knot holes or broken trunks and branches that have rotted out. 


One nest in Guatemala was reported in an old artificial nesting box.  Nest height is anywhere between two and 15 meters above the ground. 

Conservation status


The IUCN lists this species to be of Least Concern but our data shows a strong preference from this species to use paramo and elfin forests which are two habitats at high risk due to rapid climate change.

© Photos & videos by Ernesto Carman, Pablo Siles, Diego Quesada and Marco Molina.

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