WhenToBird

Molothrus ater · Icteridae

When Do Brown-headed Cowbirds Arrive in Washington?

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

Brown-headed Cowbirds reach Washington in the second week of April, are common by mid April, peak in mid May (25% of checklists), and most are gone by mid July.

When to look

First arrivalsApr 8-14the second week of April
Common byApr 15-21mid April
PeakMay 15-21mid May
Most gone byJul 15-21mid July

Best: mid May. First arrivals the second week of April; most are gone by mid July. Peak: on about 25% of Washington checklists.

  1. Jannot usually seen
  2. Febnot usually seen
  3. Marnot usually seen
  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: 0.5% of 41928 checklistsJan 8-14: 0.6% of 31152 checklistsJan 15-21: 0.5% of 31753 checklistsJan 22-31: 0.6% of 42530 checklistsFeb 1-7: 0.4% of 29739 checklistsFeb 8-14: 0.4% of 32746 checklistsFeb 15-21: 0.4% of 40328 checklistsFeb 22-28: 0.4% of 28432 checklistsMar 1-7: 0.5% of 30758 checklistsMar 8-14: 0.4% of 29368 checklistsMar 15-21: 0.5% of 32580 checklistsMar 22-31: 0.9% of 45614 checklistsApr 1-7: 1.5% of 33997 checklistsApr 8-14: 3.4% of 34729 checklistsApr 15-21: 8.3% of 38474 checklistsApr 22-30: 16% of 52185 checklistsMay 1-7: 22% of 44236 checklistsMay 8-14: 25% of 48708 checklistsMay 15-21: 26% of 41742 checklistsMay 22-31: 25% of 57082 checklistsJun 1-7: 24% of 39193 checklistsJun 8-14: 22% of 36042 checklistsJun 15-21: 21% of 34003 checklistsJun 22-30: 20% of 39711 checklistsJul 1-7: 18% of 31949 checklistsJul 8-14: 16% of 29086 checklistsJul 15-21: 11% of 28045 checklistsJul 22-31: 7.0% of 38275 checklistsAug 1-7: 6.3% of 28846 checklistsAug 8-14: 5.9% of 28036 checklistsAug 15-21: 5.5% of 27614 checklistsAug 22-31: 4.1% of 40356 checklistsSep 1-7: 2.2% of 31214 checklistsSep 8-14: 1.0% of 27795 checklistsSep 15-21: 0.6% of 29677 checklistsSep 22-30: 0.5% of 35241 checklistsOct 1-7: 0.4% of 28605 checklistsOct 8-14: 0.4% of 28655 checklistsOct 15-21: 0.5% of 24643 checklistsOct 22-31: 0.4% of 34874 checklistsNov 1-7: 0.4% of 25658 checklistsNov 8-14: 0.5% of 25700 checklistsNov 15-21: 0.5% of 24331 checklistsNov 22-30: 0.3% of 32784 checklistsDec 1-7: 0.4% of 24099 checklistsDec 8-14: 0.5% of 23339 checklistsDec 15-21: 0.4% of 27666 checklistsDec 22-31: 0.4% of 42130 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 Washington 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 Washington

Best counties

Share of checklists at the peak
  1. Wahkiakum CountyBest late May · 209 checklists that week, 5,618 in all43%
  2. Clark CountyBest the second week of May · 1444 checklists that week, 53,250 in all38%
  3. Spokane CountyBest late May · 1741 checklists that week, 43,379 in all36%
  4. Jefferson CountyBest mid May · 1263 checklists that week, 59,663 in all36%
  5. San Juan CountyBest the second week of May · 1058 checklists that week, 35,337 in all36%
  6. Walla Walla CountyBest early June · 991 checklists that week, 35,829 in all35%

Best spots

Share of checklists at the peak
  1. Sportsmans LakeSan Juan County, best early May · 33 checklists that week, 609 in all94%
  2. Bateman IslandBenton County, best late May · 54 checklists that week, 1,967 in all90%
  3. Hamilton IslandSkamania County, best late April · 23 checklists that week, 794 in all85%

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

Best time of day

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

0%10%20%30%12 am: too few checklists (796) to judge1 am: too few checklists (776) to judge2 am: too few checklists (709) to judge3 am: too few checklists (901) to judge4 am: too few checklists (3221) to judge5 am: too few checklists (16576) to judge6 am: 22% of 56744 checklists7 am: 13% of 133294 checklists8 am: 9.8% of 184196 checklists9 am: 7.6% of 186303 checklists10 am: 6.3% of 177063 checklists11 am: 5.1% of 154936 checklists12 pm: 4.6% of 138061 checklists1 pm: 4.2% of 127449 checklists2 pm: 4.0% of 121511 checklists3 pm: 4.0% of 107793 checklists4 pm: 4.8% of 82862 checklists5 pm: 6.4% of 57183 checklists6 pm: 7.2% of 39886 checklists7 pm: too few checklists (26969) to judge8 pm: too few checklists (12427) to judge9 pm: too few checklists (3658) to judge10 pm: too few checklists (1500) to judge11 pm: too few checklists (834) 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
January0.5%0.6%0.5%0.6%
February0.4%0.4%0.4%0.4%
March0.5%0.4%0.5%0.9%
April1.5%3.4%8.3%16%
May22%25%26%25%
June24%22%21%20%
July18%16%11%7.0%
August6.3%5.9%5.5%4.1%
September2.2%1.0%0.6%0.5%
October0.4%0.4%0.5%0.4%
November0.4%0.5%0.5%0.3%
December0.4%0.5%0.4%0.4%

Neighboring states

  • Oregon: arrives early April, 1 week earlier than Washington
  • Idaho: arrives mid April, 1 week later than Washington
  • Montana: arrives late April, 2 weeks later than Washington
  • Nevada: arrives late March, 2 weeks earlier than Washington

Common questions

When do Brown-headed Cowbirds arrive in Washington?
Brown-headed Cowbirds reach Washington in the second week of April, are common by mid April, peak in mid May (25% of checklists), and most are gone by mid July.
When do Brown-headed Cowbirds leave Washington?
Most Brown-headed Cowbirds have left Washington 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 Washington?
The Brown-headed Cowbird is reported most often in mid May, on about 25% of Washington checklists.
Where in Washington are Brown-headed Cowbirds seen most often?
By county, Wahkiakum County, Clark County, and Spokane County have the highest peak reporting rates for the Brown-headed Cowbird (counties with at least 200 checklists).