WhenToBird

Molothrus ater · Icteridae

When Do Brown-headed Cowbirds Arrive in Missouri?

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

Brown-headed Cowbirds reach Missouri in mid February, are common by late March, peak in early May (47% of checklists), and most are gone by the second week of July.

When to look

First arrivalsFeb 15-21mid February
Common byMar 22-31late March
PeakMay 1-7early May
Most gone byJul 8-14the second week of July

Best: early May. First arrivals mid February; most are gone by the second week of July. Peak: on about 47% of Missouri checklists.

  1. Janrare
  2. Febrare
  3. Marcommon
  4. Aprpeak season
  5. Maypeak season
  6. Junpeak season
  7. Julcommon
  8. Augrare
  9. Seprare
  10. Octrare
  11. Novrare
  12. Decrare

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

0%20%40%60%Jan 1-7: 2.2% of 12628 checklistsJan 8-14: 3.2% of 9076 checklistsJan 15-21: 3.7% of 8790 checklistsJan 22-31: 2.9% of 11986 checklistsFeb 1-7: 3.4% of 8987 checklistsFeb 8-14: 3.5% of 10394 checklistsFeb 15-21: 4.1% of 15472 checklistsFeb 22-28: 4.8% of 9917 checklistsMar 1-7: 7.1% of 9877 checklistsMar 8-14: 11% of 9570 checklistsMar 15-21: 15% of 10274 checklistsMar 22-31: 25% of 16156 checklistsApr 1-7: 34% of 12774 checklistsApr 8-14: 42% of 14048 checklistsApr 15-21: 45% of 14894 checklistsApr 22-30: 48% of 23288 checklistsMay 1-7: 47% of 22645 checklistsMay 8-14: 46% of 21384 checklistsMay 15-21: 45% of 13989 checklistsMay 22-31: 42% of 15784 checklistsJun 1-7: 41% of 9691 checklistsJun 8-14: 40% of 9036 checklistsJun 15-21: 39% of 7907 checklistsJun 22-30: 36% of 9831 checklistsJul 1-7: 33% of 8008 checklistsJul 8-14: 27% of 7202 checklistsJul 15-21: 18% of 7151 checklistsJul 22-31: 9.4% of 9833 checklistsAug 1-7: 5.6% of 7639 checklistsAug 8-14: 5.0% of 7507 checklistsAug 15-21: 4.8% of 7429 checklistsAug 22-31: 3.0% of 11182 checklistsSep 1-7: 1.9% of 9471 checklistsSep 8-14: 1.6% of 8501 checklistsSep 15-21: 1.3% of 8169 checklistsSep 22-30: 1.9% of 11572 checklistsOct 1-7: 3.3% of 9028 checklistsOct 8-14: 3.7% of 9413 checklistsOct 15-21: 3.3% of 8656 checklistsOct 22-31: 2.8% of 11625 checklistsNov 1-7: 2.9% of 8627 checklistsNov 8-14: 2.2% of 8284 checklistsNov 15-21: 1.9% of 8075 checklistsNov 22-30: 1.8% of 10430 checklistsDec 1-7: 2.3% of 7870 checklistsDec 8-14: 1.6% of 7567 checklistsDec 15-21: 1.6% of 9696 checklistsDec 22-31: 1.9% of 13142 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 Missouri 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 Missouri

Best counties

Share of checklists at the peak
  1. Randolph CountyBest late May · 20 checklists that week, 838 in all79%
  2. Wright CountyBest late April · 37 checklists that week, 638 in all75%
  3. Moniteau CountyBest the second week of April · 13 checklists that week, 614 in all74%
  4. Miller CountyBest late April · 56 checklists that week, 1,190 in all72%
  5. Lewis CountyBest late April · 34 checklists that week, 1,047 in all71%
  6. Daviess CountyBest mid May · 24 checklists that week, 1,354 in all70%

Best spots

Share of checklists at the peak
  1. Bee Tree County ParkSt. Louis County, best late April · 40 checklists that week, 562 in all94%
  2. Line Creek GreenwayPlatte County, best the second week of May · 37 checklists that week, 588 in all90%
  3. Wolf Bayou Conservation AreaPemiscot County, best early May · 21 checklists that week, 203 in all88%
  4. Jefferson Barracks County ParkSt. Louis County, best late April · 26 checklists that week, 1,157 in all87%
  5. Platte Landing Park (Future)Platte County, best late April · 30 checklists that week, 300 in all85%

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

Best time of day

In Missouri, the Brown-headed Cowbird is most often listed on checklists started between 6 and 8 am (28% of those checklists).

0%10%20%30%40%12 am: too few checklists (205) to judge1 am: too few checklists (179) to judge2 am: too few checklists (204) to judge3 am: too few checklists (216) to judge4 am: too few checklists (630) to judge5 am: too few checklists (5072) to judge6 am: 34% of 27231 checklists7 am: 25% of 64162 checklists8 am: 22% of 67854 checklists9 am: 20% of 56515 checklists10 am: 17% of 47496 checklists11 am: 15% of 38845 checklists12 pm: 14% of 33383 checklists1 pm: 13% of 32503 checklists2 pm: 13% of 32615 checklists3 pm: 12% of 32514 checklists4 pm: 14% of 30274 checklists5 pm: 17% of 23446 checklists6 pm: 18% of 16374 checklists7 pm: too few checklists (10236) to judge8 pm: too few checklists (3133) to judge9 pm: too few checklists (722) to judge10 pm: too few checklists (405) to judge11 pm: too few checklists (261) 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
January2.2%3.2%3.7%2.9%
February3.4%3.5%4.1%4.8%
March7.1%11%15%25%
April34%42%45%48%
May47%46%45%42%
June41%40%39%36%
July33%27%18%9.4%
August5.6%5.0%4.8%3.0%
September1.9%1.6%1.3%1.9%
October3.3%3.7%3.3%2.8%
November2.9%2.2%1.9%1.8%
December2.3%1.6%1.6%1.9%

Neighboring states

  • Arkansas: arrives mid March, 4 weeks later than Missouri
  • Iowa: arrives the second week of March, 3 weeks later than Missouri
  • Kansas: arrives early March, 2 weeks later than Missouri
  • Illinois: arrives mid February, in the same week than Missouri

Common questions

When do Brown-headed Cowbirds arrive in Missouri?
Brown-headed Cowbirds reach Missouri in mid February, are common by late March, peak in early May (47% of checklists), and most are gone by the second week of July.
When do Brown-headed Cowbirds leave Missouri?
Most Brown-headed Cowbirds have left Missouri by the second week of July, when reports fall below half their usual rate. Stragglers are still reported until mid August.
When is the best time to see a Brown-headed Cowbird in Missouri?
The Brown-headed Cowbird is reported most often in early May, on about 47% of Missouri checklists.
Where in Missouri are Brown-headed Cowbirds seen most often?
By county, Randolph County, Wright County, and Moniteau County have the highest peak reporting rates for the Brown-headed Cowbird (counties with at least 200 checklists).