WhenToBird

Molothrus ater · Icteridae

When Do Brown-headed Cowbirds Arrive in Maine?

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

Brown-headed Cowbirds reach Maine in the second week of March, are common by late March, peak in early May (12% of checklists), and most are gone by late June.

When to look

First arrivalsMar 8-14the second week of March
Common byMar 22-31late March
PeakMay 1-7early May
Most gone byJun 22-30late June

Best: early May. First arrivals the second week of March; most are gone by late June. Peak: on about 12% of Maine checklists.

  1. Jannot usually seen
  2. Febnot usually seen
  3. Maruncommon
  4. Aprpeak season
  5. Maypeak season
  6. Juncommon
  7. Juluncommon
  8. Augrare
  9. Sepnot usually seen
  10. Octnot usually seen
  11. Novnot usually seen
  12. Decnot usually seen

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

0%5%10%15%Jan 1-7: 0.1% of 15499 checklistsJan 8-14: 0.2% of 11141 checklistsJan 15-21: 0.2% of 10729 checklistsJan 22-31: 0.2% of 15084 checklistsFeb 1-7: 0.1% of 9403 checklistsFeb 8-14: 0.1% of 11268 checklistsFeb 15-21: 0.1% of 14061 checklistsFeb 22-28: 0.3% of 9977 checklistsMar 1-7: 0.4% of 9649 checklistsMar 8-14: 0.9% of 11781 checklistsMar 15-21: 2.3% of 11613 checklistsMar 22-31: 4.1% of 17798 checklistsApr 1-7: 7.1% of 14638 checklistsApr 8-14: 11% of 16511 checklistsApr 15-21: 12% of 17164 checklistsApr 22-30: 12% of 22602 checklistsMay 1-7: 13% of 22556 checklistsMay 8-14: 13% of 27842 checklistsMay 15-21: 10% of 27748 checklistsMay 22-31: 7.4% of 38715 checklistsJun 1-7: 5.5% of 26916 checklistsJun 8-14: 5.1% of 23737 checklistsJun 15-21: 4.6% of 22733 checklistsJun 22-30: 4.1% of 28248 checklistsJul 1-7: 3.6% of 20290 checklistsJul 8-14: 3.2% of 18534 checklistsJul 15-21: 2.2% of 17319 checklistsJul 22-31: 1.3% of 22815 checklistsAug 1-7: 1.0% of 15004 checklistsAug 8-14: 1.0% of 14603 checklistsAug 15-21: 0.6% of 14972 checklistsAug 22-31: 0.6% of 19813 checklistsSep 1-7: 0.6% of 14567 checklistsSep 8-14: 0.3% of 14520 checklistsSep 15-21: 0.3% of 14339 checklistsSep 22-30: 0.4% of 16879 checklistsOct 1-7: 0.3% of 12959 checklistsOct 8-14: 0.2% of 13168 checklistsOct 15-21: 0.4% of 11184 checklistsOct 22-31: 0.3% of 13717 checklistsNov 1-7: 0.2% of 9823 checklistsNov 8-14: 0.1% of 9007 checklistsNov 15-21: 0.2% of 8528 checklistsNov 22-30: 0.1% of 10228 checklistsDec 1-7: 0.1% of 7505 checklistsDec 8-14: 0.1% of 7982 checklistsDec 15-21: 0.2% of 10455 checklistsDec 22-31: 0.1% of 14285 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 Maine 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.

Embed this map on your site

Where in Maine

Best counties

Share of checklists at the peak
  1. York CountyBest early May · 3100 checklists that week, 101,844 in all20%
  2. Androscoggin CountyBest late April · 650 checklists that week, 16,955 in all17%
  3. Lincoln CountyBest early May · 1452 checklists that week, 59,429 in all16%
  4. Cumberland CountyBest the second week of May · 8112 checklists that week, 169,501 in all16%
  5. Sagadahoc CountyBest mid April · 486 checklists that week, 21,736 in all14%
  6. Kennebec CountyBest the second week of May · 1947 checklists that week, 48,185 in all14%

Best spots

Share of checklists at the peak
  1. Fort Foster ParkYork County, best late April · 76 checklists that week, 2,318 in all52%
  2. River Point Conservation AreaCumberland County, best early May · 62 checklists that week, 1,146 in all46%
  3. Timber PointYork County, best late April · 128 checklists that week, 3,561 in all44%
  4. Town of Cape ElizabethCumberland County, best mid May · 49 checklists that week, 367 in all41%
  5. Great Pond (Libbyshears)York County, best early May · 56 checklists that week, 1,215 in all41%
  6. Hickley ParkCumberland County, best late May · 328 checklists that week, 2,519 in all39%

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

Best time of day

In Maine, the Brown-headed Cowbird is most often listed on checklists started between 5 and 7 am (8.2% of those checklists).

0%5%10%12 am: too few checklists (510) to judge1 am: too few checklists (517) to judge2 am: too few checklists (581) to judge3 am: too few checklists (3242) to judge4 am: too few checklists (7221) to judge5 am: 8.8% of 19895 checklists6 am: 8.0% of 54578 checklists7 am: 6.3% of 92775 checklists8 am: 4.6% of 86962 checklists9 am: 3.4% of 78989 checklists10 am: 2.7% of 70954 checklists11 am: 2.3% of 59331 checklists12 pm: 2.1% of 50943 checklists1 pm: 2.0% of 49775 checklists2 pm: 1.9% of 49001 checklists3 pm: 2.1% of 43252 checklists4 pm: 2.8% of 33413 checklists5 pm: 3.3% of 25547 checklists6 pm: 3.5% of 18309 checklists7 pm: too few checklists (14287) to judge8 pm: too few checklists (5336) to judge9 pm: too few checklists (2253) to judge10 pm: too few checklists (1518) to judge11 pm: too few checklists (720) 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
January0.1%0.2%0.2%0.2%
February0.1%0.1%0.1%0.3%
March0.4%0.9%2.3%4.1%
April7.1%11%12%12%
May13%13%10%7.4%
June5.5%5.1%4.6%4.1%
July3.6%3.2%2.2%1.3%
August1.0%1.0%0.6%0.6%
September0.6%0.3%0.3%0.4%
October0.3%0.2%0.4%0.3%
November0.2%0.1%0.2%0.1%
December0.1%0.1%0.2%0.1%

Neighboring states

  • New Hampshire: arrives early March, 1 week earlier than Maine
  • Massachusetts: arrives early March, 1 week earlier than Maine
  • Vermont: arrives early March, 1 week earlier than Maine
  • Rhode Island: arrives late February, 2 weeks earlier than Maine

Common questions

When do Brown-headed Cowbirds arrive in Maine?
Brown-headed Cowbirds reach Maine in the second week of March, are common by late March, peak in early May (12% of checklists), and most are gone by late June.
When do Brown-headed Cowbirds leave Maine?
Most Brown-headed Cowbirds have left Maine by late June, when reports fall below half their usual rate. Stragglers are still reported until early August.
When is the best time to see a Brown-headed Cowbird in Maine?
The Brown-headed Cowbird is reported most often in early May, on about 12% of Maine checklists.
Where in Maine are Brown-headed Cowbirds seen most often?
By county, York County, Androscoggin County, and Lincoln County have the highest peak reporting rates for the Brown-headed Cowbird (counties with at least 200 checklists).