WhenToBird

Molothrus ater · Icteridae

When Do Brown-headed Cowbirds Arrive in Michigan?

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

Brown-headed Cowbirds reach Michigan in early March, are common by late March, peak in early May (36% of checklists), and most are gone by the second week of July.

When to look

First arrivalsMar 1-7early March
Common byMar 22-31late March
PeakMay 1-7early May
Most gone byJul 8-14the second week of July

Best: early May. First arrivals early March; most are gone by the second week of July. Peak: on about 36% of Michigan checklists.

  1. Jannot usually seen
  2. Febrare
  3. Maruncommon
  4. Aprpeak season
  5. Maypeak season
  6. Juncommon
  7. Julcommon
  8. Augrare
  9. Seprare
  10. Octrare
  11. Novnot usually seen
  12. Decnot usually seen

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

0%10%20%30%40%Jan 1-7: 0.5% of 38160 checklistsJan 8-14: 0.6% of 24696 checklistsJan 15-21: 0.9% of 23771 checklistsJan 22-31: 0.8% of 31347 checklistsFeb 1-7: 1.0% of 23225 checklistsFeb 8-14: 1.1% of 27398 checklistsFeb 15-21: 1.2% of 36606 checklistsFeb 22-28: 2.4% of 27127 checklistsMar 1-7: 3.2% of 29700 checklistsMar 8-14: 5.0% of 31587 checklistsMar 15-21: 8.1% of 32118 checklistsMar 22-31: 12% of 47777 checklistsApr 1-7: 19% of 38557 checklistsApr 8-14: 27% of 42207 checklistsApr 15-21: 30% of 42759 checklistsApr 22-30: 35% of 64458 checklistsMay 1-7: 38% of 60998 checklistsMay 8-14: 36% of 72091 checklistsMay 15-21: 33% of 59058 checklistsMay 22-31: 28% of 64724 checklistsJun 1-7: 25% of 35990 checklistsJun 8-14: 24% of 32595 checklistsJun 15-21: 23% of 30017 checklistsJun 22-30: 23% of 33988 checklistsJul 1-7: 20% of 28708 checklistsJul 8-14: 15% of 25175 checklistsJul 15-21: 9.7% of 24084 checklistsJul 22-31: 5.4% of 33522 checklistsAug 1-7: 4.1% of 25098 checklistsAug 8-14: 3.4% of 24353 checklistsAug 15-21: 3.3% of 25059 checklistsAug 22-31: 2.4% of 37489 checklistsSep 1-7: 1.5% of 28410 checklistsSep 8-14: 1.2% of 27887 checklistsSep 15-21: 1.4% of 26614 checklistsSep 22-30: 1.6% of 32557 checklistsOct 1-7: 2.4% of 25844 checklistsOct 8-14: 2.4% of 27741 checklistsOct 15-21: 2.0% of 24693 checklistsOct 22-31: 1.6% of 32460 checklistsNov 1-7: 1.0% of 23660 checklistsNov 8-14: 1.1% of 21542 checklistsNov 15-21: 0.8% of 19922 checklistsNov 22-30: 0.6% of 25069 checklistsDec 1-7: 0.8% of 18272 checklistsDec 8-14: 0.7% of 18961 checklistsDec 15-21: 0.7% of 24171 checklistsDec 22-31: 0.6% of 30908 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 Michigan 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 Michigan

Best counties

Share of checklists at the peak
  1. Ionia CountyBest the second week of May · 237 checklists that week, 5,509 in all58%
  2. Lenawee CountyBest early May · 423 checklists that week, 11,588 in all57%
  3. Ogemaw CountyBest early May · 143 checklists that week, 4,675 in all53%
  4. Saginaw CountyBest the second week of May · 331 checklists that week, 8,573 in all50%
  5. Genesee CountyBest early May · 1120 checklists that week, 29,698 in all49%
  6. Isabella CountyBest early May · 1106 checklists that week, 23,321 in all47%

Best spots

Share of checklists at the peak
  1. Upper Macatawa Natural Area - East (northeast)Ottawa County, best late May · 30 checklists that week, 764 in all91%
  2. Flushing Township ParkGenesee County, best the second week of May · 83 checklists that week, 1,247 in all86%
  3. Long Lake (Fish Lake)Lapeer County, best late April · 28 checklists that week, 280 in all86%
  4. Inter-City Bike TrailJackson County, best mid May · 34 checklists that week, 125 in all85%
  5. Eliza HowellWayne County, best the second week of May · 23 checklists that week, 479 in all85%

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

Best time of day

In Michigan, the Brown-headed Cowbird is most often listed on checklists started between 6 and 8 am (26% of those checklists).

0%10%20%30%40%12 am: too few checklists (712) to judge1 am: too few checklists (592) to judge2 am: too few checklists (532) to judge3 am: too few checklists (516) to judge4 am: too few checklists (1592) to judge5 am: too few checklists (6849) to judge6 am: 33% of 39298 checklists7 am: 24% of 120344 checklists8 am: 18% of 180109 checklists9 am: 15% of 171966 checklists10 am: 13% of 156332 checklists11 am: 11% of 134964 checklists12 pm: 9.9% of 120967 checklists1 pm: 9.0% of 113852 checklists2 pm: 8.4% of 110773 checklists3 pm: 8.2% of 105530 checklists4 pm: 8.6% of 100958 checklists5 pm: 11% of 80085 checklists6 pm: 12% of 62883 checklists7 pm: 12% of 44912 checklists8 pm: too few checklists (21062) to judge9 pm: too few checklists (5920) to judge10 pm: too few checklists (1629) to judge11 pm: too few checklists (775) 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%0.9%0.8%
February1.0%1.1%1.2%2.4%
March3.2%5.0%8.1%12%
April19%27%30%35%
May38%36%33%28%
June25%24%23%23%
July20%15%9.7%5.4%
August4.1%3.4%3.3%2.4%
September1.5%1.2%1.4%1.6%
October2.4%2.4%2.0%1.6%
November1.0%1.1%0.8%0.6%
December0.8%0.7%0.7%0.6%

Neighboring states

  • Ohio: arrives the second week of February, 3 weeks earlier than Michigan
  • Indiana: arrives mid February, 2 weeks earlier than Michigan
  • Illinois: arrives mid February, 2 weeks earlier than Michigan
  • Wisconsin: arrives the second week of March, 1 week later than Michigan

Common questions

When do Brown-headed Cowbirds arrive in Michigan?
Brown-headed Cowbirds reach Michigan in early March, are common by late March, peak in early May (36% of checklists), and most are gone by the second week of July.
When do Brown-headed Cowbirds leave Michigan?
Most Brown-headed Cowbirds have left Michigan 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 Michigan?
The Brown-headed Cowbird is reported most often in early May, on about 36% of Michigan checklists.
Where in Michigan are Brown-headed Cowbirds seen most often?
By county, Ionia County, Lenawee County, and Ogemaw County have the highest peak reporting rates for the Brown-headed Cowbird (counties with at least 200 checklists).