WhenToBird

Mergus merganser · Anatidae

When Do Common Mergansers Arrive in Maine?

Adult female Common Merganser
Photo: Christoph Moning, CC BY 4.0 via iNaturalist

Common Mergansers are winter birds in Maine: the first arrive in the second week of September, they are common by late October, peak in late March (9.2% of checklists), and most are gone by early May.

When to look

First arrivalsSep 8-14the second week of September
Common byOct 22-31late October
PeakMar 22-31late March
Most gone byMay 1-7early May

Best: late March. First arrivals the second week of September; most are gone by early May. Peak: on about 9.2% of Maine checklists.

  1. Jancommon
  2. Febcommon
  3. Marpeak season
  4. Aprpeak season
  5. Mayuncommon
  6. Junrare
  7. Julrare
  8. Augrare
  9. Sepuncommon
  10. Octuncommon
  11. Novcommon
  12. Decuncommon

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

0%5%10%Jan 1-7: 4.0% of 15499 checklistsJan 8-14: 4.2% of 11141 checklistsJan 15-21: 4.1% of 10729 checklistsJan 22-31: 4.2% of 15084 checklistsFeb 1-7: 4.5% of 9403 checklistsFeb 8-14: 4.6% of 11268 checklistsFeb 15-21: 4.1% of 14061 checklistsFeb 22-28: 4.8% of 9977 checklistsMar 1-7: 5.6% of 9649 checklistsMar 8-14: 6.5% of 11781 checklistsMar 15-21: 7.9% of 11613 checklistsMar 22-31: 9.5% of 17798 checklistsApr 1-7: 9.9% of 14638 checklistsApr 8-14: 8.2% of 16511 checklistsApr 15-21: 6.0% of 17164 checklistsApr 22-30: 4.3% of 22602 checklistsMay 1-7: 2.6% of 22556 checklistsMay 8-14: 1.6% of 27842 checklistsMay 15-21: 1.5% of 27748 checklistsMay 22-31: 1.3% of 38715 checklistsJun 1-7: 1.2% of 26916 checklistsJun 8-14: 1.3% of 23737 checklistsJun 15-21: 1.1% of 22733 checklistsJun 22-30: 1.2% of 28248 checklistsJul 1-7: 1.1% of 20290 checklistsJul 8-14: 1.1% of 18534 checklistsJul 15-21: 1.3% of 17319 checklistsJul 22-31: 1.2% of 22815 checklistsAug 1-7: 1.4% of 15004 checklistsAug 8-14: 1.3% of 14603 checklistsAug 15-21: 1.1% of 14972 checklistsAug 22-31: 1.3% of 19813 checklistsSep 1-7: 1.5% of 14567 checklistsSep 8-14: 1.4% of 14520 checklistsSep 15-21: 1.5% of 14339 checklistsSep 22-30: 1.4% of 16879 checklistsOct 1-7: 1.7% of 12959 checklistsOct 8-14: 1.7% of 13168 checklistsOct 15-21: 2.1% of 11184 checklistsOct 22-31: 3.2% of 13717 checklistsNov 1-7: 3.9% of 9823 checklistsNov 8-14: 4.4% of 9007 checklistsNov 15-21: 4.1% of 8528 checklistsNov 22-30: 3.6% of 10228 checklistsDec 1-7: 3.1% of 7505 checklistsDec 8-14: 3.4% of 7982 checklistsDec 15-21: 3.3% of 10455 checklistsDec 22-31: 3.3% 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.

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Where in Maine

Best counties

Share of checklists at the peak
  1. Aroostook CountyBest early November · 138 checklists that week, 16,817 in all28%
  2. Sagadahoc CountyBest late March · 593 checklists that week, 21,736 in all22%
  3. Androscoggin CountyBest the second week of November · 313 checklists that week, 16,955 in all22%
  4. Kennebec CountyBest late March · 1524 checklists that week, 48,185 in all19%
  5. Penobscot CountyBest early April · 1452 checklists that week, 56,895 in all17%
  6. Piscataquis CountyBest early May · 133 checklists that week, 14,837 in all17%

Best spots

Share of checklists at the peak
  1. Bay Bridge Landing Wetland ParkCumberland County, best late March · 62 checklists that week, 1,493 in all94%
  2. Abagadasset RiverSagadahoc County, best late March · 33 checklists that week, 167 in all92%
  3. Black PointHancock County, best late December · 22 checklists that week, 471 in all92%
  4. Dismal SwampKennebec County, best the second week of April · 27 checklists that week, 562 in all88%
  5. Jagger PondYork County, best late March · 74 checklists that week, 1,870 in all88%
  6. Hallowell Waterfront ParkKennebec County, best late March · 27 checklists that week, 266 in all86%

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

Best time of day

In Maine, the Common Merganser is most often listed on checklists started between 1 and 3 pm (3.5% of those checklists).

0%1%2%3%4%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: 2.5% of 19895 checklists6 am: 2.7% of 54578 checklists7 am: 2.7% of 92775 checklists8 am: 2.9% of 86962 checklists9 am: 3.3% of 78989 checklists10 am: 3.3% of 70954 checklists11 am: 3.3% of 59331 checklists12 pm: 3.3% of 50943 checklists1 pm: 3.6% of 49775 checklists2 pm: 3.4% of 49001 checklists3 pm: 3.4% of 43252 checklists4 pm: 2.9% of 33413 checklists5 pm: 2.3% of 25547 checklists6 pm: 1.7% 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
January4.0%4.2%4.1%4.2%
February4.5%4.6%4.1%4.8%
March5.6%6.5%7.9%9.5%
April9.9%8.2%6.0%4.3%
May2.6%1.6%1.5%1.3%
June1.2%1.3%1.1%1.2%
July1.1%1.1%1.3%1.2%
August1.4%1.3%1.1%1.3%
September1.5%1.4%1.5%1.4%
October1.7%1.7%2.1%3.2%
November3.9%4.4%4.1%3.6%
December3.1%3.4%3.3%3.3%

Neighboring states

  • New Hampshire: arrives late September, 2 weeks later than Maine
  • Massachusetts: arrives mid October, 5 weeks later than Maine
  • Vermont: arrives late July, 6 weeks earlier than Maine
  • Rhode Island: arrives the second week of November, 8 weeks later than Maine

Common questions

When do Common Mergansers arrive in Maine?
Common Mergansers are winter birds in Maine: the first arrive in the second week of September, they are common by late October, peak in late March (9.2% of checklists), and most are gone by early May.
When do Common Mergansers leave Maine?
Most Common Mergansers have left Maine by early May, when reports fall below half their usual rate. Stragglers are still reported until mid May.
When is the best time to see a Common Merganser in Maine?
The Common Merganser is reported most often in late March, on about 9.2% of Maine checklists.
Where in Maine are Common Mergansers seen most often?
By county, Aroostook County, Sagadahoc County, and Androscoggin County have the highest peak reporting rates for the Common Merganser (counties with at least 200 checklists).