WhenToBird

Vireo cassinii · Vireonidae

When Do Cassin's Vireos Arrive in Utah?

Adult Cassin's Vireo
Photo: David Anderson, CC BY 4.0 via iNaturalist

Cassin's Vireos mostly pass through Utah: they arrive in late August, peak in the second week of September (2.6% of checklists), and most are gone by early October.

When to look

First arrivalsAug 22-31late August
Common byAug 22-31late August
PeakSep 8-14the second week of September
Most gone byOct 1-7early October

Best: the second week of September. First arrivals late August; most are gone by early October. Peak: on about 2.6% of Utah checklists.

  1. Jannot usually seen
  2. Febnot usually seen
  3. Marnot usually seen
  4. Aprrare
  5. Mayrare
  6. Junnot usually seen
  7. Julnot usually seen
  8. Augcommon
  9. Seppeak season
  10. Octcommon
  11. Novnot usually seen
  12. Decnot usually seen

Darker months: more checklists report it. Outlined: peak month.

0%1%2%3%Jan 1-7: 0% of 10857 checklistsJan 8-14: 0% of 8333 checklistsJan 15-21: 0% of 8360 checklistsJan 22-31: 0% of 10516 checklistsFeb 1-7: 0.1% of 7416 checklistsFeb 8-14: 0% of 8082 checklistsFeb 15-21: 0% of 9643 checklistsFeb 22-28: 0% of 7960 checklistsMar 1-7: 0% of 7998 checklistsMar 8-14: 0% of 8581 checklistsMar 15-21: 0% of 8637 checklistsMar 22-31: 0.1% of 13006 checklistsApr 1-7: 0.1% of 10562 checklistsApr 8-14: 0.1% of 11694 checklistsApr 15-21: 0.1% of 11382 checklistsApr 22-30: 0.3% of 16626 checklistsMay 1-7: 0.4% of 13523 checklistsMay 8-14: 0.4% of 14714 checklistsMay 15-21: 0.2% of 13711 checklistsMay 22-31: 0.1% of 16546 checklistsJun 1-7: 0.1% of 10284 checklistsJun 8-14: 0% of 9530 checklistsJun 15-21: 0.1% of 8854 checklistsJun 22-30: 0.1% of 10566 checklistsJul 1-7: 0% of 7987 checklistsJul 8-14: 0% of 7471 checklistsJul 15-21: 0.1% of 7240 checklistsJul 22-31: 0.1% of 9329 checklistsAug 1-7: 0.1% of 6521 checklistsAug 8-14: 0.1% of 6423 checklistsAug 15-21: 0.4% of 6208 checklistsAug 22-31: 1.3% of 9089 checklistsSep 1-7: 2.4% of 7081 checklistsSep 8-14: 2.8% of 7306 checklistsSep 15-21: 2.6% of 7208 checklistsSep 22-30: 1.7% of 8876 checklistsOct 1-7: 1.0% of 7265 checklistsOct 8-14: 0.4% of 7226 checklistsOct 15-21: 0.2% of 7007 checklistsOct 22-31: 0.1% of 8443 checklistsNov 1-7: 0% of 6711 checklistsNov 8-14: 0.1% of 6290 checklistsNov 15-21: 0.1% of 6169 checklistsNov 22-30: 0% of 8228 checklistsDec 1-7: 0% of 6011 checklistsDec 8-14: 0% of 6044 checklistsDec 15-21: 0% of 6721 checklistsDec 22-31: 0% of 9982 checklistsJanFebMarAprMayJunJulAugSepOctNovDec
Share of complete checklists reporting it, by week (4 per month). Grey bars: fewer than 10 checklists, not counted.

Frequency is the share of complete checklists in Utah that listed the bird, 2016–2025. It is not a head count, and it follows where and when people go birding. How to read it.

JanFebMarAprMayJunJulAugSepOctNovDec
today
Second week of November

Each county is shaded by the share of complete checklists there that listed the bird, blended with the weeks either side. Darker is more often. It follows where people watch birds, not how many birds there are. How to read it.

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Where in Utah

Best counties

Share of checklists at the peak
  1. Davis CountyBest the second week of September · 863 checklists that week, 39,952 in all10%
  2. Juab CountyBest the second week of September · 38 checklists that week, 2,572 in all3.4%
  3. Sanpete CountyBest early September · 143 checklists that week, 6,190 in all3.2%
  4. Weber CountyBest the second week of September · 179 checklists that week, 13,172 in all2.9%
  5. Garfield CountyBest the second week of September · 291 checklists that week, 10,367 in all2.9%
  6. Utah CountyBest mid September · 989 checklists that week, 70,971 in all2.8%

Best spots

Share of checklists at the peak
  1. Antelope Island State ParkDavis County, best the second week of September · 147 checklists that week, 2,493 in all42%
  2. Utah Lake WetlandsUtah County, best mid September · 35 checklists that week, 1,189 in all13%
  3. International Peace GardensSalt Lake County, best mid September · 23 checklists that week, 211 in all13%
  4. Willard Bay State ParkBox Elder County, best the second week of September · 34 checklists that week, 800 in all12%
  5. Indian CanyonWashington County, best early May · 112 checklists that week, 1,539 in all12%

Busy spots report more of everything; compare the checklist counts before you drive anywhere.

Best time of day

In Utah, the Cassin's Vireo is most often listed on checklists started between 6 and 8 am (0.5% of those checklists).

0%0.5%1%12 am: too few checklists (242) to judge1 am: too few checklists (178) to judge2 am: too few checklists (169) to judge3 am: too few checklists (162) to judge4 am: too few checklists (284) to judge5 am: too few checklists (1984) to judge6 am: 0.4% of 11714 checklists7 am: 0.5% of 33209 checklists8 am: 0.4% of 46944 checklists9 am: 0.4% of 46290 checklists10 am: 0.3% of 43144 checklists11 am: 0.3% of 36893 checklists12 pm: 0.2% of 32758 checklists1 pm: 0.2% of 30142 checklists2 pm: 0.2% of 29414 checklists3 pm: 0.1% of 29491 checklists4 pm: 0.1% of 29154 checklists5 pm: 0.2% of 22256 checklists6 pm: 0.1% of 17383 checklists7 pm: 0.1% of 13099 checklists8 pm: too few checklists (6647) to judge9 pm: too few checklists (1753) to judge10 pm: too few checklists (599) to judge11 pm: too few checklists (307) to judge12a3a6a9a12p3p6p9p
Share of checklists started in each local hour that reported it. It reflects when people go birding as well as when birds are active. Grey hours have too few checklists (under 2% of the state’s, or under 200) to judge.
Week-by-week table
MonthDays 1-78-1415-2122-end
January0%0%0%0%
February0.1%0%0%0%
March0%0%0%0.1%
April0.1%0.1%0.1%0.3%
May0.4%0.4%0.2%0.1%
June0.1%0%0.1%0.1%
July0%0%0.1%0.1%
August0.1%0.1%0.4%1.3%
September2.4%2.8%2.6%1.7%
October1.0%0.4%0.2%0.1%
November0%0.1%0.1%0%
December0%0%0%0%

Neighboring states

  • Nevada: arrives the second week of April, 18 weeks earlier than Utah
  • Colorado: arrives late August, in the same week than Utah
  • Idaho: arrives late April, 16 weeks earlier than Utah
  • New Mexico: arrives mid August, 1 week earlier than Utah

Common questions

When do Cassin's Vireos arrive in Utah?
Cassin's Vireos mostly pass through Utah: they arrive in late August, peak in the second week of September (2.6% of checklists), and most are gone by early October.
When do Cassin's Vireos leave Utah?
Most Cassin's Vireos have left Utah by early October, when reports fall below half their usual rate.
When is the best time to see a Cassin's Vireo in Utah?
The Cassin's Vireo is reported most often in the second week of September, on about 2.6% of Utah checklists.
Where in Utah are Cassin's Vireos seen most often?
By county, Davis County, Juab County, and Sanpete County have the highest peak reporting rates for the Cassin's Vireo (counties with at least 200 checklists).