WhenToBird

Molothrus ater · Icteridae

When Do Brown-headed Cowbirds Arrive in Oregon?

Adult female Brown-headed Cowbird
Photo: Nicole, CC BY 4.0 via iNaturalist

Brown-headed Cowbirds reach Oregon in early April, are common by mid April, peak in mid May (24% of checklists), and most are gone by mid July.

When to look

First arrivalsApr 1-7early April
Common byApr 15-21mid April
PeakMay 15-21mid May
Most gone byJul 15-21mid July

Best: mid May. First arrivals early April; most are gone by mid July. Peak: on about 24% of Oregon checklists.

  1. Jannot usually seen
  2. Febnot usually seen
  3. Marrare
  4. Aprcommon
  5. Maypeak season
  6. Junpeak season
  7. Julcommon
  8. Auguncommon
  9. Seprare
  10. Octnot usually seen
  11. Novnot usually seen
  12. Decnot usually seen

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

0%10%20%30%Jan 1-7: 0.8% of 34973 checklistsJan 8-14: 0.8% of 26807 checklistsJan 15-21: 0.8% of 26567 checklistsJan 22-31: 0.7% of 36019 checklistsFeb 1-7: 0.5% of 24020 checklistsFeb 8-14: 0.5% of 25765 checklistsFeb 15-21: 0.6% of 31019 checklistsFeb 22-28: 0.8% of 24582 checklistsMar 1-7: 0.8% of 24834 checklistsMar 8-14: 0.8% of 24642 checklistsMar 15-21: 1.1% of 27420 checklistsMar 22-31: 1.4% of 39913 checklistsApr 1-7: 2.7% of 28817 checklistsApr 8-14: 4.9% of 31221 checklistsApr 15-21: 9.5% of 34402 checklistsApr 22-30: 17% of 47144 checklistsMay 1-7: 22% of 37716 checklistsMay 8-14: 24% of 39651 checklistsMay 15-21: 25% of 37496 checklistsMay 22-31: 24% of 56967 checklistsJun 1-7: 22% of 35893 checklistsJun 8-14: 20% of 31880 checklistsJun 15-21: 19% of 30942 checklistsJun 22-30: 17% of 38478 checklistsJul 1-7: 17% of 27409 checklistsJul 8-14: 15% of 25161 checklistsJul 15-21: 11% of 25473 checklistsJul 22-31: 5.7% of 33920 checklistsAug 1-7: 4.2% of 24310 checklistsAug 8-14: 4.5% of 23675 checklistsAug 15-21: 3.6% of 23623 checklistsAug 22-31: 2.8% of 33762 checklistsSep 1-7: 1.7% of 25120 checklistsSep 8-14: 1.1% of 24458 checklistsSep 15-21: 0.8% of 25528 checklistsSep 22-30: 0.6% of 31631 checklistsOct 1-7: 0.5% of 25498 checklistsOct 8-14: 0.5% of 25161 checklistsOct 15-21: 0.5% of 23701 checklistsOct 22-31: 0.5% of 30996 checklistsNov 1-7: 0.5% of 21089 checklistsNov 8-14: 0.6% of 21880 checklistsNov 15-21: 0.5% of 21501 checklistsNov 22-30: 0.8% of 28930 checklistsDec 1-7: 0.7% of 19807 checklistsDec 8-14: 0.7% of 21022 checklistsDec 15-21: 0.7% of 24817 checklistsDec 22-31: 0.8% 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. Columbia CountyBest the second week of May · 556 checklists that week, 27,750 in all44%
  2. Klamath CountyBest mid May · 752 checklists that week, 26,875 in all37%
  3. Washington CountyBest mid May · 2629 checklists that week, 110,376 in all35%
  4. Deschutes CountyBest mid May · 2617 checklists that week, 86,260 in all32%
  5. Harney CountyBest late May · 6713 checklists that week, 40,943 in all28%
  6. Multnomah CountyBest the second week of May · 4941 checklists that week, 182,088 in all27%

Best spots

Share of checklists at the peak
  1. Kelley Point ParkMultnomah County, best late May · 21 checklists that week, 992 in all89%
  2. Company LakeMultnomah County, best early June · 21 checklists that week, 750 in all85%
  3. Bybee LakeMultnomah County, best the second week of May · 26 checklists that week, 1,688 in all84%
  4. Klamath FallsKlamath County, best mid May · 26 checklists that week, 720 in all84%
  5. Fern Ridge Wildlife Area (Coyote Creek)Lane County, best mid June · 22 checklists that week, 981 in all83%
  6. Malheur National Wildlife RefugeHarney County, best early June · 392 checklists that week, 4,410 in all83%

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

Best time of day

In Oregon, the Brown-headed Cowbird is most often listed on checklists started between 6 and 8 am (16% of those checklists).

0%5%10%15%20%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: 20% of 50677 checklists7 am: 14% of 125347 checklists8 am: 11% of 163668 checklists9 am: 8.7% of 160351 checklists10 am: 6.6% of 148940 checklists11 am: 5.3% of 124743 checklists12 pm: 4.6% of 112537 checklists1 pm: 4.0% of 98999 checklists2 pm: 3.7% of 94690 checklists3 pm: 3.5% of 87923 checklists4 pm: 3.8% of 75235 checklists5 pm: 4.9% of 54504 checklists6 pm: 5.6% of 40469 checklists7 pm: 4.3% 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
January0.8%0.8%0.8%0.7%
February0.5%0.5%0.6%0.8%
March0.8%0.8%1.1%1.4%
April2.7%4.9%9.5%17%
May22%24%25%24%
June22%20%19%17%
July17%15%11%5.7%
August4.2%4.5%3.6%2.8%
September1.7%1.1%0.8%0.6%
October0.5%0.5%0.5%0.5%
November0.5%0.6%0.5%0.8%
December0.7%0.7%0.7%0.8%

Neighboring states

  • Washington: arrives the second week of April, 1 week later than Oregon
  • Idaho: arrives mid April, 2 weeks later than Oregon
  • Nevada: arrives late March, 1 week earlier than Oregon
  • California: arrives mid February, 6 weeks earlier than Oregon

Common questions

When do Brown-headed Cowbirds arrive in Oregon?
Brown-headed Cowbirds reach Oregon in early April, are common by mid April, peak in mid May (24% of checklists), and most are gone by mid July.
When do Brown-headed Cowbirds leave Oregon?
Most Brown-headed Cowbirds have left Oregon by mid July, when reports fall below half their usual rate. Stragglers are still reported until early September.
When is the best time to see a Brown-headed Cowbird in Oregon?
The Brown-headed Cowbird is reported most often in mid May, on about 24% of Oregon checklists.
Where in Oregon are Brown-headed Cowbirds seen most often?
By county, Columbia County, Klamath County, and Washington County have the highest peak reporting rates for the Brown-headed Cowbird (counties with at least 200 checklists).