WhenToBird

Mergus merganser · Anatidae

When Do Common Mergansers Arrive in Massachusetts?

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

Common Mergansers are winter birds in Massachusetts: the first arrive in mid October, they are common by the second week of November, peak in the second week of March (13% of checklists), and most are gone by mid April.

When to look

First arrivalsOct 15-21mid October
Common byNov 8-14the second week of November
PeakMar 8-14the second week of March
Most gone byApr 15-21mid April

Best: the second week of March. First arrivals mid October; most are gone by mid April. Peak: on about 13% of Massachusetts checklists.

  1. Jancommon
  2. Febpeak season
  3. Marpeak season
  4. Aprpeak season
  5. Mayuncommon
  6. Junrare
  7. Julnot usually seen
  8. Augrare
  9. Seprare
  10. Octuncommon
  11. Novcommon
  12. Deccommon

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

0%5%10%15%Jan 1-7: 9.3% of 43252 checklistsJan 8-14: 8.9% of 30096 checklistsJan 15-21: 8.3% of 28760 checklistsJan 22-31: 8.1% of 38135 checklistsFeb 1-7: 8.4% of 26442 checklistsFeb 8-14: 8.0% of 29034 checklistsFeb 15-21: 7.3% of 37383 checklistsFeb 22-28: 11% of 29977 checklistsMar 1-7: 13% of 29175 checklistsMar 8-14: 13% of 32399 checklistsMar 15-21: 13% of 34444 checklistsMar 22-31: 12% of 49126 checklistsApr 1-7: 10% of 36456 checklistsApr 8-14: 7.5% of 40908 checklistsApr 15-21: 4.4% of 42078 checklistsApr 22-30: 3.3% of 56465 checklistsMay 1-7: 1.9% of 56994 checklistsMay 8-14: 1.1% of 64079 checklistsMay 15-21: 0.7% of 52020 checklistsMay 22-31: 0.6% of 55402 checklistsJun 1-7: 0.4% of 30682 checklistsJun 8-14: 0.5% of 27557 checklistsJun 15-21: 0.5% of 26163 checklistsJun 22-30: 0.4% of 29576 checklistsJul 1-7: 0.4% of 23931 checklistsJul 8-14: 0.5% of 22389 checklistsJul 15-21: 0.5% of 22365 checklistsJul 22-31: 0.5% of 32631 checklistsAug 1-7: 0.5% of 25133 checklistsAug 8-14: 0.5% of 24610 checklistsAug 15-21: 0.5% of 25350 checklistsAug 22-31: 0.7% of 37198 checklistsSep 1-7: 0.6% of 27402 checklistsSep 8-14: 0.7% of 27700 checklistsSep 15-21: 0.6% of 28398 checklistsSep 22-30: 0.7% of 34646 checklistsOct 1-7: 0.8% of 28620 checklistsOct 8-14: 1.0% of 30144 checklistsOct 15-21: 1.2% of 28893 checklistsOct 22-31: 2.5% of 38869 checklistsNov 1-7: 4.3% of 29782 checklistsNov 8-14: 5.0% of 27582 checklistsNov 15-21: 5.6% of 26642 checklistsNov 22-30: 5.8% of 34390 checklistsDec 1-7: 7.1% of 25164 checklistsDec 8-14: 7.1% of 24892 checklistsDec 15-21: 7.0% of 29022 checklistsDec 22-31: 6.8% 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. Berkshire CountyBest late March · 3506 checklists that week, 92,890 in all31%
  2. Franklin CountyBest mid March · 1144 checklists that week, 41,382 in all27%
  3. Hampden CountyBest the second week of March · 763 checklists that week, 35,410 in all26%
  4. Hampshire CountyBest mid March · 3380 checklists that week, 162,423 in all20%
  5. Middlesex CountyBest early March · 5829 checklists that week, 307,511 in all18%
  6. Worcester CountyBest mid March · 3073 checklists that week, 128,594 in all17%

Best spots

Share of checklists at the peak
  1. Flints PondMiddlesex County, best early December · 23 checklists that week, 383 in all97%
  2. Sandy PondMiddlesex County, best early April · 20 checklists that week, 161 in all97%
  3. Pontoosuc LakeBerkshire County, best late March · 55 checklists that week, 748 in all96%
  4. Mystic LakesMiddlesex County, best mid February · 67 checklists that week, 2,987 in all96%
  5. Nagog PondMiddlesex County, best mid March · 22 checklists that week, 591 in all95%
  6. Chestnut Hill ReservoirSuffolk County, best late December · 76 checklists that week, 3,541 in all94%

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

Best time of day

In Massachusetts, the Common Merganser is most often listed on checklists started between 2 and 4 pm (5.8% of those checklists).

0%2%4%6%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: 3.1% of 108601 checklists7 am: 3.7% of 186104 checklists8 am: 4.3% of 185905 checklists9 am: 4.6% of 166049 checklists10 am: 4.9% of 150508 checklists11 am: 4.9% of 131024 checklists12 pm: 5.0% of 116804 checklists1 pm: 5.2% of 112055 checklists2 pm: 5.7% of 110246 checklists3 pm: 6.0% of 104376 checklists4 pm: 5.3% of 83736 checklists5 pm: 3.6% of 63723 checklists6 pm: 2.5% 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
January9.3%8.9%8.3%8.1%
February8.4%8.0%7.3%11%
March13%13%13%12%
April10%7.5%4.4%3.3%
May1.9%1.1%0.7%0.6%
June0.4%0.5%0.5%0.4%
July0.4%0.5%0.5%0.5%
August0.5%0.5%0.5%0.7%
September0.6%0.7%0.6%0.7%
October0.8%1.0%1.2%2.5%
November4.3%5.0%5.6%5.8%
December7.1%7.1%7.0%6.8%

Neighboring states

  • Rhode Island: arrives the second week of November, 3 weeks later than Massachusetts
  • New Hampshire: arrives late September, 3 weeks earlier than Massachusetts
  • Connecticut: arrives mid October, in the same week than Massachusetts
  • Vermont: arrives late July, 11 weeks earlier than Massachusetts

Common questions

When do Common Mergansers arrive in Massachusetts?
Common Mergansers are winter birds in Massachusetts: the first arrive in mid October, they are common by the second week of November, peak in the second week of March (13% of checklists), and most are gone by mid April.
When do Common Mergansers leave Massachusetts?
Most Common Mergansers have left Massachusetts by mid April, when reports fall below half their usual rate. Stragglers are still reported until the second week of May.
When is the best time to see a Common Merganser in Massachusetts?
The Common Merganser is reported most often in the second week of March, on about 13% of Massachusetts checklists.
Where in Massachusetts are Common Mergansers seen most often?
By county, Berkshire County, Franklin County, and Hampden County have the highest peak reporting rates for the Common Merganser (counties with at least 200 checklists).