THE UNSPOTTED
SAW-WHET OWL
PROJECT
Scientific name: Aegolius ridgwayi
Name in English: Unspotted Saw-whet Owl
Common names in Spanish: Lechucita Parda, Lechucita de Alfaro, Mochuelo Moreno
Global distribution: from Mexico southern mountains to western Panama
Distribution in Costa Rica: highlands of Talamanca Mountain Range and Turrialba and Irazú Volcanoes (from 2.500 m.s.n.m.)
GENERAL INFORMATION
HISTORY
Description
The species was described in 1905 on the Washington Biological Society academic journal under the name of Cryptoglaux ridgwayi. This genus, which means "little hidden owl," was given to species that are now within the Aegolius genus.
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.
Alfaro named the species ridgwayi in honor to Robert Ridgway, an American ornithologist and secretary of the Smithsonian Institute who made great contributions to the natural history of Costa Rica.
Photo of the specimen collected by Alfaro property of the Smithsonian Museum of Natural History collection.
Table 1
Records of the subspecies of Aegolius ridgwayi made for the first time in chronological order
MEASUREMENTS
Height: 18 cm
Wing: ♂ 140 mm, ♀ 151 mm
Wingspan: ♀ 514 mm
Weight: ♂ 85 g, ♀ 115-126 g
Since this species has never been studied before we did not know what size bands should be used, but with the measurements we have made we were able to order the correct size bands for this species.
The bands have an email adress (uswocr@gmail.com) and a numeral series. The series for the males is M001-M100 and for the females H001-H100.
PLUMAGE
Head and upper region uniformly brown
Nape golden-brown
Facial disc border, supercilium and chin between white and buff
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
AGE
Age is determined by studying the molt cycle of the individual (the relative age of its flight feathers) and one of the techniques we use is to determine this is by looking at the feathers under ultraviolet light.
New feathers have porphyrines which reflect UV light and makes them glow pink. In older feathers the porphyrines have degraded due to exposition to sunlight and when UV light is cast upon them they look dark and opaque. Immature individuals are the only ones going to have one generation of feathers and they will all appear an even pink under UV light. Adults can have up to three generations of flight feathers.
DIET
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
Pellet dissection | Many skeleton parts of small rodents and beetle exoskeletons were found.
VOCALIZATION
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.
Male spectrogram
