Vireo cassinii
Silhouette: Caleb Gordon · PhyloPic
In 3 days ~40% in a week ~70%
Cassin's vireo (Vireo cassinii) is a small North American songbird, ranging from southern British Columbia in Canada through the western coastal states of the United States, including California, Oregon, and Washington. The Cassin's Vireo moves down Western United States forests in its migration. During its migration in early spring and late fall, it spends the winter in regions from southern Arizona (the Sonoran Desert) to southern Mexico, including parts of Baja California and the Pacific coast of Mexico.
The vireo is 11–14 cm (4–6 inches) long. It has a grayish olive head, back, and flanks, with whitish underparts. One of its distinctive features is the solid white "spectacles" around its eyes, along with white wing bars. These markings set it apart from other similar species like the plumbeous vireo and the blue-headed vireo.
Cassin's vireo is known for its persistent song, which consists of short, rough-whistled phrases of several notes.These phrases are 2 seconds apart and often alternate between ending on high and low notes, creating a "question-and-answer" pattern. The Cassin's Vireo is known to sing for an extensive duration of time. Hearing... Wikipedia →
| # | Park | Country | Daily sighting probability |
|---|---|---|---|
| 1 | Yosemite National Park | 🇺🇸 United States | |
| 2 | Glacier National Park | 🇺🇸 United States | |
| 3 | Jasper National Park | 🇨🇦 Canada | |
| 4 | Sequoia and Kings Canyon National Parks | 🇺🇸 United States | |
| 5 | Banff National Park | 🇨🇦 Canada | |
| 6 | Death Valley National Park | 🇺🇸 United States | |
| 7 | Zion National Park | 🇺🇸 United States | |
| 8 | Big Bend National Park | 🇺🇸 United States | |
| 9 | Cumbres de Monterrey National Park | 🇲🇽 Mexico | |
| 10 | Saguaro National Park | 🇺🇸 United States | |
| 11 | Guadalupe Mountains National Park | 🇺🇸 United States | |
| 12 | Redwood National Park | 🇺🇸 United States | |
| 13 | Grand Canyon National Park | 🇺🇸 United States | |
| 14 | Joshua Tree National Park | 🇺🇸 United States | |
| 15 | Great Bear Rainforest | 🇨🇦 Canada | |
| 16 | Olympic National Park | 🇺🇸 United States | |
| 17 | Grand Teton National Park | 🇺🇸 United States | |
| 18 | Rocky Mountain National Park | 🇺🇸 United States | |
| 19 | Channel Islands National Park | 🇺🇸 United States |
| # | City | Country | Daily sighting probability |
|---|---|---|---|
| 1 | Toluca | 🇲🇽 México | |
| 2 | Mexico City | 🇲🇽 México | |
| 3 | Guadalajara | 🇲🇽 México | |
| 4 | Puebla | 🇲🇽 México | |
| 5 | Sacramento | 🇺🇸 United States | |
| 6 | Monterrey | 🇲🇽 México | |
| 7 | Portland | 🇺🇸 United States | |
| 8 | Las Vegas | 🇺🇸 United States | |
| 9 | Mesa | 🇺🇸 United States | |
| 10 | Los Angeles | 🇺🇸 United States |
Possible
About 20% of wildlife watchers report a Cassin's Vireo sighting in Glacier National Park on a given day, based on 448 verified sightings from GBIF citizen-science data from 2019 to 2026. It is the 47th most-seen of the 174 birds we can rate there. Over three days the chance rises to about 40%, and over a week to about 70%, if each day is a fresh chance.
May
In that month about 30% of wildlife watchers report a Cassin's Vireo in Glacier National Park on a given day, against under 5% in January–February and October–November, the lowest months.
Between 9 am and noon
Across all the parks we cover, that three-hour window holds the most Cassin's Vireo sightings with a recorded time, and about 9 in 10 of them come between 6 am and 6 pm: it is a daytime animal.
2nd of 19
Of the 19 parks where we can rate Cassin's Vireo sightings, Glacier National Park ranks 2nd at about 20%. The best odds are in Yosemite National Park (United States, about 30%).
Same genus: Vireo
The closest relatives of the Cassin's Vireo that you can see in Glacier National Park (genus Vireo, Vireos) are Warbling Vireo (about 40%) and Red-eyed Vireo (about 10%), with each one's daily chance of a sighting.
GBIF citizen-science records
It is estimated from how often the Cassin's Vireo is recorded against all the birds logged in Glacier National Park (448 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.
