WhenToBird

Mergus merganser · Anatidae

When Do Common Mergansers Arrive in Connecticut?

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

Common Mergansers are winter birds in Connecticut: the first arrive in mid October, they are common by the second week of November, peak in the second week of March (10% 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 10% of Connecticut checklists.

  1. Janpeak season
  2. Febpeak season
  3. Marpeak season
  4. Aprpeak season
  5. Mayuncommon
  6. Junrare
  7. Julrare
  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: 8.5% of 18950 checklistsJan 8-14: 8.2% of 13676 checklistsJan 15-21: 7.8% of 13377 checklistsJan 22-31: 8.1% of 17004 checklistsFeb 1-7: 8.0% of 10218 checklistsFeb 8-14: 7.6% of 11568 checklistsFeb 15-21: 6.9% of 15916 checklistsFeb 22-28: 8.8% of 11413 checklistsMar 1-7: 9.8% of 10754 checklistsMar 8-14: 10% of 12051 checklistsMar 15-21: 10% of 12616 checklistsMar 22-31: 9.3% of 17801 checklistsApr 1-7: 7.8% of 13186 checklistsApr 8-14: 6.5% of 14428 checklistsApr 15-21: 4.6% of 14738 checklistsApr 22-30: 3.9% of 21753 checklistsMay 1-7: 2.6% of 22494 checklistsMay 8-14: 2.2% of 23363 checklistsMay 15-21: 2.2% of 20219 checklistsMay 22-31: 1.7% of 20778 checklistsJun 1-7: 1.5% of 12234 checklistsJun 8-14: 1.2% of 12491 checklistsJun 15-21: 1.3% of 10856 checklistsJun 22-30: 1.1% of 11964 checklistsJul 1-7: 0.8% of 9437 checklistsJul 8-14: 0.9% of 8599 checklistsJul 15-21: 0.8% of 8252 checklistsJul 22-31: 0.9% of 11329 checklistsAug 1-7: 1.2% of 8116 checklistsAug 8-14: 0.8% of 8051 checklistsAug 15-21: 0.9% of 8502 checklistsAug 22-31: 1.2% of 13673 checklistsSep 1-7: 1.0% of 9873 checklistsSep 8-14: 1.0% of 9735 checklistsSep 15-21: 0.9% of 10120 checklistsSep 22-30: 1.0% of 12543 checklistsOct 1-7: 0.7% of 10735 checklistsOct 8-14: 0.7% of 10869 checklistsOct 15-21: 1.0% of 10436 checklistsOct 22-31: 2.1% of 13808 checklistsNov 1-7: 3.4% of 10507 checklistsNov 8-14: 6.0% of 9827 checklistsNov 15-21: 6.7% of 9904 checklistsNov 22-30: 7.4% of 13396 checklistsDec 1-7: 7.2% of 8974 checklistsDec 8-14: 6.6% of 9468 checklistsDec 15-21: 6.2% of 11614 checklistsDec 22-31: 6.6% of 16616 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 Connecticut 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 Connecticut

Best counties

Share of checklists at the peak
  1. Litchfield CountyBest late March · 2141 checklists that week, 69,766 in all27%
  2. Hartford CountyBest the second week of January · 2785 checklists that week, 105,735 in all19%
  3. Windham CountyBest mid March · 382 checklists that week, 19,034 in all16%
  4. Tolland CountyBest late November · 920 checklists that week, 39,004 in all12%
  5. Middlesex CountyBest the second week of February · 786 checklists that week, 39,919 in all12%
  6. New Haven CountyBest early February · 2540 checklists that week, 139,721 in all7.2%

Best spots

Share of checklists at the peak
  1. Bantam LakeLitchfield County, best mid March · 92 checklists that week, 2,470 in all99%
  2. Camp CourantHartford County, best early December · 39 checklists that week, 903 in all97%
  3. Wangumbaug LakeTolland County, best mid December · 21 checklists that week, 431 in all96%
  4. Point Folly CampgroundLitchfield County, best mid March · 49 checklists that week, 1,650 in all95%
  5. Columbia LakeTolland County, best the second week of November · 23 checklists that week, 278 in all95%
  6. Hockanum River Reservoir (Burnside)Hartford County, best early January · 30 checklists that week, 279 in all92%

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

Best time of day

In Connecticut, the Common Merganser is most often listed on checklists started between 2 and 4 pm (5.6% of those checklists).

0%2%4%6%12 am: too few checklists (325) to judge1 am: too few checklists (367) to judge2 am: too few checklists (488) to judge3 am: too few checklists (792) to judge4 am: too few checklists (2722) to judge5 am: too few checklists (9489) to judge6 am: 5.0% of 33657 checklists7 am: 4.1% of 62964 checklists8 am: 3.9% of 70645 checklists9 am: 4.3% of 64870 checklists10 am: 4.5% of 58827 checklists11 am: 4.8% of 51689 checklists12 pm: 4.8% of 45288 checklists1 pm: 5.3% of 44765 checklists2 pm: 5.4% of 44173 checklists3 pm: 5.8% of 41979 checklists4 pm: 4.8% of 33219 checklists5 pm: 3.1% of 24828 checklists6 pm: 2.6% of 15856 checklists7 pm: too few checklists (8126) to judge8 pm: too few checklists (1994) to judge9 pm: too few checklists (533) to judge10 pm: too few checklists (349) to judge11 pm: too few checklists (286) 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
January8.5%8.2%7.8%8.1%
February8.0%7.6%6.9%8.8%
March9.8%10%10%9.3%
April7.8%6.5%4.6%3.9%
May2.6%2.2%2.2%1.7%
June1.5%1.2%1.3%1.1%
July0.8%0.9%0.8%0.9%
August1.2%0.8%0.9%1.2%
September1.0%1.0%0.9%1.0%
October0.7%0.7%1.0%2.1%
November3.4%6.0%6.7%7.4%
December7.2%6.6%6.2%6.6%

Neighboring states

  • Rhode Island: arrives the second week of November, 3 weeks later than Connecticut
  • Massachusetts: arrives mid October, in the same week than Connecticut
  • New Jersey: arrives early November, 2 weeks later than Connecticut
  • New York: arrives mid August, 8 weeks earlier than Connecticut

Common questions

When do Common Mergansers arrive in Connecticut?
Common Mergansers are winter birds in Connecticut: the first arrive in mid October, they are common by the second week of November, peak in the second week of March (10% of checklists), and most are gone by mid April.
When do Common Mergansers leave Connecticut?
Most Common Mergansers have left Connecticut by mid April, when reports fall below half their usual rate. Stragglers are still reported until late June.
When is the best time to see a Common Merganser in Connecticut?
The Common Merganser is reported most often in the second week of March, on about 10% of Connecticut checklists.
Where in Connecticut are Common Mergansers seen most often?
By county, Litchfield County, Hartford County, and Windham County have the highest peak reporting rates for the Common Merganser (counties with at least 200 checklists).