WhenToBird

Vireo cassinii · Vireonidae

When Do Cassin's Vireos Arrive in Oregon?

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

Cassin's Vireos reach Oregon in the second week of April, are common by mid April, peak in late May (4.0% of checklists), and most are gone by early September.

When to look

First arrivalsApr 8-14the second week of April
Common byApr 15-21mid April
PeakMay 22-31late May
Most gone bySep 1-7early September

Best: late May. First arrivals the second week of April; most are gone by early September. Peak: on about 4.0% of Oregon checklists.

  1. Jannot usually seen
  2. Febnot usually seen
  3. Marnot usually seen
  4. Aprpeak season
  5. Maypeak season
  6. Junpeak season
  7. Julcommon
  8. Auguncommon
  9. Sepuncommon
  10. Octrare
  11. Novnot usually seen
  12. Decnot usually seen

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

0%2%4%6%Jan 1-7: 0% of 34973 checklistsJan 8-14: 0% of 26807 checklistsJan 15-21: 0% of 26567 checklistsJan 22-31: 0.1% of 36019 checklistsFeb 1-7: 0% of 24020 checklistsFeb 8-14: 0% of 25765 checklistsFeb 15-21: 0% of 31019 checklistsFeb 22-28: 0% of 24582 checklistsMar 1-7: 0% of 24834 checklistsMar 8-14: 0.1% of 24642 checklistsMar 15-21: 0% of 27420 checklistsMar 22-31: 0.1% of 39913 checklistsApr 1-7: 0.1% of 28817 checklistsApr 8-14: 0.6% of 31221 checklistsApr 15-21: 2.2% of 34402 checklistsApr 22-30: 3.7% of 47144 checklistsMay 1-7: 3.8% of 37716 checklistsMay 8-14: 3.7% of 39651 checklistsMay 15-21: 4.2% of 37496 checklistsMay 22-31: 4.0% of 56967 checklistsJun 1-7: 3.8% of 35893 checklistsJun 8-14: 3.3% of 31880 checklistsJun 15-21: 3.6% of 30942 checklistsJun 22-30: 3.5% of 38478 checklistsJul 1-7: 2.5% of 27409 checklistsJul 8-14: 2.0% of 25161 checklistsJul 15-21: 1.7% of 25473 checklistsJul 22-31: 1.5% of 33920 checklistsAug 1-7: 1.2% of 24310 checklistsAug 8-14: 1.2% of 23675 checklistsAug 15-21: 1.3% of 23623 checklistsAug 22-31: 1.5% of 33762 checklistsSep 1-7: 1.5% of 25120 checklistsSep 8-14: 1.0% of 24458 checklistsSep 15-21: 0.6% of 25528 checklistsSep 22-30: 0.3% of 31631 checklistsOct 1-7: 0.1% of 25498 checklistsOct 8-14: 0.1% of 25161 checklistsOct 15-21: 0.1% of 23701 checklistsOct 22-31: 0.1% of 30996 checklistsNov 1-7: 0.1% of 21089 checklistsNov 8-14: 0% of 21880 checklistsNov 15-21: 0.1% of 21501 checklistsNov 22-30: 0% of 28930 checklistsDec 1-7: 0% of 19807 checklistsDec 8-14: 0.1% of 21022 checklistsDec 15-21: 0.1% of 24817 checklistsDec 22-31: 0.1% of 37592 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 Oregon 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 Oregon

Best counties

Share of checklists at the peak
  1. Wasco CountyBest the second week of June · 497 checklists that week, 13,127 in all13%
  2. Jackson CountyBest late May · 2009 checklists that week, 60,428 in all12%
  3. Wallowa CountyBest late June · 393 checklists that week, 9,170 in all12%
  4. Jefferson CountyBest early June · 544 checklists that week, 11,014 in all11%
  5. Douglas CountyBest the second week of May · 491 checklists that week, 17,976 in all11%
  6. Union CountyBest the second week of June · 706 checklists that week, 33,301 in all9.5%

Best spots

Share of checklists at the peak
  1. Camas PrairieWasco County, best late May · 29 checklists that week, 124 in all65%
  2. Whiskey SpringJefferson County, best late August · 25 checklists that week, 435 in all55%
  3. Deschutes River Segment C (northwest)Deschutes County, best late August · 25 checklists that week, 441 in all53%
  4. Glaze MeadowDeschutes County, best the second week of June · 36 checklists that week, 250 in all48%
  5. Skinner Butte ParkLane County, best late April · 384 checklists that week, 2,638 in all46%

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

Best time of day

In Oregon, the Cassin's Vireo is most often listed on checklists started between 6 and 8 am (2.8% of those checklists).

0%1%2%3%4%12 am: too few checklists (1505) to judge1 am: too few checklists (675) to judge2 am: too few checklists (626) to judge3 am: too few checklists (1641) to judge4 am: too few checklists (3696) to judge5 am: too few checklists (14524) to judge6 am: 3.4% of 50677 checklists7 am: 2.6% of 125347 checklists8 am: 2.0% of 163668 checklists9 am: 1.6% of 160351 checklists10 am: 1.2% of 148940 checklists11 am: 1.0% of 124743 checklists12 pm: 0.8% of 112537 checklists1 pm: 0.8% of 98999 checklists2 pm: 0.7% of 94690 checklists3 pm: 0.6% of 87923 checklists4 pm: 0.6% of 75235 checklists5 pm: 0.7% of 54504 checklists6 pm: 0.6% of 40469 checklists7 pm: 0.4% of 33675 checklists8 pm: too few checklists (18715) to judge9 pm: too few checklists (5839) to judge10 pm: too few checklists (2704) to judge11 pm: too few checklists (1549) 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%0.1%
February0%0%0%0%
March0%0.1%0%0.1%
April0.1%0.6%2.2%3.7%
May3.8%3.7%4.2%4.0%
June3.8%3.3%3.6%3.5%
July2.5%2.0%1.7%1.5%
August1.2%1.2%1.3%1.5%
September1.5%1.0%0.6%0.3%
October0.1%0.1%0.1%0.1%
November0.1%0%0.1%0%
December0%0.1%0.1%0.1%

Neighboring states

  • Washington: arrives mid April, 1 week later than Oregon
  • Idaho: arrives late April, 2 weeks later than Oregon
  • Nevada: arrives the second week of April, in the same week than Oregon
  • California: arrives the second week of April, in the same week than Oregon

Common questions

When do Cassin's Vireos arrive in Oregon?
Cassin's Vireos reach Oregon in the second week of April, are common by mid April, peak in late May (4.0% of checklists), and most are gone by early September.
When do Cassin's Vireos leave Oregon?
Most Cassin's Vireos have left Oregon by early September, when reports fall below half their usual rate. Stragglers are still reported until the second week of September.
When is the best time to see a Cassin's Vireo in Oregon?
The Cassin's Vireo is reported most often in late May, on about 4.0% of Oregon checklists.
Where in Oregon are Cassin's Vireos seen most often?
By county, Wasco County, Jackson County, and Wallowa County have the highest peak reporting rates for the Cassin's Vireo (counties with at least 200 checklists).