WhenToBird

Molothrus ater · Icteridae

When Do Brown-headed Cowbirds Arrive in Massachusetts?

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

Brown-headed Cowbirds reach Massachusetts in early March, are common by late March, peak in early May (28% 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 28% of Massachusetts checklists.

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

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

0%10%20%30%Jan 1-7: 0.7% of 43252 checklistsJan 8-14: 0.9% of 30096 checklistsJan 15-21: 0.8% of 28760 checklistsJan 22-31: 0.8% of 38135 checklistsFeb 1-7: 0.7% of 26442 checklistsFeb 8-14: 1.0% of 29034 checklistsFeb 15-21: 1.2% of 37383 checklistsFeb 22-28: 2.0% of 29977 checklistsMar 1-7: 2.6% of 29175 checklistsMar 8-14: 4.6% of 32399 checklistsMar 15-21: 7.4% of 34444 checklistsMar 22-31: 12% of 49126 checklistsApr 1-7: 17% of 36456 checklistsApr 8-14: 23% of 40908 checklistsApr 15-21: 26% of 42078 checklistsApr 22-30: 29% of 56465 checklistsMay 1-7: 30% of 56994 checklistsMay 8-14: 27% of 64079 checklistsMay 15-21: 26% of 52020 checklistsMay 22-31: 23% of 55402 checklistsJun 1-7: 21% of 30682 checklistsJun 8-14: 19% of 27557 checklistsJun 15-21: 18% of 26163 checklistsJun 22-30: 17% of 29576 checklistsJul 1-7: 14% of 23931 checklistsJul 8-14: 11% of 22389 checklistsJul 15-21: 7.1% of 22365 checklistsJul 22-31: 4.8% of 32631 checklistsAug 1-7: 3.9% of 25133 checklistsAug 8-14: 3.7% of 24610 checklistsAug 15-21: 3.0% of 25350 checklistsAug 22-31: 2.4% of 37198 checklistsSep 1-7: 2.0% of 27402 checklistsSep 8-14: 1.9% of 27700 checklistsSep 15-21: 1.7% of 28398 checklistsSep 22-30: 2.0% of 34646 checklistsOct 1-7: 2.2% of 28620 checklistsOct 8-14: 2.1% of 30144 checklistsOct 15-21: 2.3% of 28893 checklistsOct 22-31: 2.0% of 38869 checklistsNov 1-7: 1.5% of 29782 checklistsNov 8-14: 1.2% of 27582 checklistsNov 15-21: 1.0% of 26642 checklistsNov 22-30: 0.9% of 34390 checklistsDec 1-7: 1.2% of 25164 checklistsDec 8-14: 1.1% of 24892 checklistsDec 15-21: 0.9% of 29022 checklistsDec 22-31: 0.7% of 44323 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 Massachusetts 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 Massachusetts

Best counties

Share of checklists at the peak
  1. Bristol CountyBest late April · 2185 checklists that week, 65,262 in all41%
  2. Hampshire CountyBest late April · 5853 checklists that week, 162,423 in all37%
  3. Hampden CountyBest early May · 1213 checklists that week, 35,410 in all36%
  4. Plymouth CountyBest early May · 3126 checklists that week, 89,282 in all33%
  5. Norfolk CountyBest late April · 3973 checklists that week, 114,756 in all33%
  6. Worcester CountyBest early May · 4719 checklists that week, 128,594 in all31%

Best spots

Share of checklists at the peak
  1. Wildwood Conservation AreaHampshire County, best late April · 24 checklists that week, 623 in all84%
  2. Cousins ParkMiddlesex County, best the second week of April · 26 checklists that week, 906 in all80%
  3. Hale ReservationNorfolk County, best early May · 37 checklists that week, 634 in all78%
  4. Memorial Park BeachNorfolk County, best the second week of June · 34 checklists that week, 2,721 in all78%
  5. Poppasguash SwampBristol County, best mid April · 50 checklists that week, 2,031 in all78%

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

Best time of day

In Massachusetts, the Brown-headed Cowbird is most often listed on checklists started between 6 and 8 am (17% of those checklists).

0%10%20%30%12 am: too few checklists (630) to judge1 am: too few checklists (657) to judge2 am: too few checklists (645) to judge3 am: too few checklists (850) to judge4 am: too few checklists (3787) to judge5 am: too few checklists (29743) to judge6 am: 21% of 108601 checklists7 am: 15% of 186104 checklists8 am: 12% of 185905 checklists9 am: 9.7% of 166049 checklists10 am: 7.8% of 150508 checklists11 am: 6.2% of 131024 checklists12 pm: 5.8% of 116804 checklists1 pm: 5.4% of 112055 checklists2 pm: 5.3% of 110246 checklists3 pm: 5.5% of 104376 checklists4 pm: 6.9% of 83736 checklists5 pm: 8.0% of 63723 checklists6 pm: 8.1% of 41435 checklists7 pm: too few checklists (21041) to judge8 pm: too few checklists (5240) to judge9 pm: too few checklists (1722) to judge10 pm: too few checklists (1094) to judge11 pm: too few checklists (704) 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
January0.7%0.9%0.8%0.8%
February0.7%1.0%1.2%2.0%
March2.6%4.6%7.4%12%
April17%23%26%29%
May30%27%26%23%
June21%19%18%17%
July14%11%7.1%4.8%
August3.9%3.7%3.0%2.4%
September2.0%1.9%1.7%2.0%
October2.2%2.1%2.3%2.0%
November1.5%1.2%1.0%0.9%
December1.2%1.1%0.9%0.7%

Neighboring states

  • Rhode Island: arrives late February, 1 week earlier than Massachusetts
  • New Hampshire: arrives early March, in the same week than Massachusetts
  • Connecticut: arrives mid January, 6 weeks earlier than Massachusetts
  • Vermont: arrives early March, in the same week than Massachusetts

Common questions

When do Brown-headed Cowbirds arrive in Massachusetts?
Brown-headed Cowbirds reach Massachusetts in early March, are common by late March, peak in early May (28% of checklists), and most are gone by the second week of July.
When do Brown-headed Cowbirds leave Massachusetts?
Most Brown-headed Cowbirds have left Massachusetts by the second week of 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 Massachusetts?
The Brown-headed Cowbird is reported most often in early May, on about 28% of Massachusetts checklists.
Where in Massachusetts are Brown-headed Cowbirds seen most often?
By county, Bristol County, Hampshire County, and Hampden County have the highest peak reporting rates for the Brown-headed Cowbird (counties with at least 200 checklists).