WhenToBird

Mergus merganser · Anatidae

When Do Common Mergansers Arrive in Vermont?

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

Common Mergansers reach Vermont in late July, are common by late September, peak in early April (20% of checklists), and most are gone by the second week of May.

When to look

First arrivalsJul 22-31late July
Common bySep 22-30late September
PeakApr 1-7early April
Most gone byMay 8-14the second week of May

Best: early April. First arrivals late July; most are gone by the second week of May. Peak: on about 20% of Vermont checklists.

  1. Jancommon
  2. Febcommon
  3. Marpeak season
  4. Aprpeak season
  5. Maycommon
  6. Junrare
  7. Julrare
  8. Auguncommon
  9. Sepuncommon
  10. Octcommon
  11. Novcommon
  12. Deccommon

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

0%10%20%30%Jan 1-7: 8.3% of 12234 checklistsJan 8-14: 8.5% of 8293 checklistsJan 15-21: 7.9% of 7885 checklistsJan 22-31: 7.9% of 10534 checklistsFeb 1-7: 7.5% of 7212 checklistsFeb 8-14: 7.6% of 8144 checklistsFeb 15-21: 6.7% of 10480 checklistsFeb 22-28: 9.7% of 7932 checklistsMar 1-7: 11% of 8192 checklistsMar 8-14: 15% of 9383 checklistsMar 15-21: 18% of 10620 checklistsMar 22-31: 20% of 16257 checklistsApr 1-7: 20% of 12568 checklistsApr 8-14: 18% of 14677 checklistsApr 15-21: 16% of 14106 checklistsApr 22-30: 12% of 19617 checklistsMay 1-7: 9.2% of 18143 checklistsMay 8-14: 5.1% of 19626 checklistsMay 15-21: 3.8% of 17779 checklistsMay 22-31: 3.0% of 20310 checklistsJun 1-7: 2.3% of 11493 checklistsJun 8-14: 2.1% of 10215 checklistsJun 15-21: 1.9% of 9951 checklistsJun 22-30: 1.9% of 11050 checklistsJul 1-7: 1.3% of 8690 checklistsJul 8-14: 1.5% of 7679 checklistsJul 15-21: 1.7% of 7687 checklistsJul 22-31: 2.1% of 10712 checklistsAug 1-7: 2.8% of 7703 checklistsAug 8-14: 2.9% of 7743 checklistsAug 15-21: 3.2% of 8314 checklistsAug 22-31: 3.5% of 12428 checklistsSep 1-7: 4.4% of 9526 checklistsSep 8-14: 4.7% of 8493 checklistsSep 15-21: 4.9% of 8283 checklistsSep 22-30: 5.1% of 10352 checklistsOct 1-7: 6.2% of 8802 checklistsOct 8-14: 6.5% of 9088 checklistsOct 15-21: 7.2% of 7739 checklistsOct 22-31: 8.8% of 10907 checklistsNov 1-7: 10% of 7868 checklistsNov 8-14: 11% of 7223 checklistsNov 15-21: 11% of 7224 checklistsNov 22-30: 9.3% of 8375 checklistsDec 1-7: 9.8% of 6580 checklistsDec 8-14: 7.4% of 6800 checklistsDec 15-21: 5.4% of 8334 checklistsDec 22-31: 6.3% of 10579 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 Vermont 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 Vermont

Best counties

Share of checklists at the peak
  1. Grand Isle CountyBest the second week of March · 197 checklists that week, 8,507 in all40%
  2. Windsor CountyBest early April · 1974 checklists that week, 73,702 in all27%
  3. Orleans CountyBest the second week of April · 332 checklists that week, 11,785 in all27%
  4. Windham CountyBest early April · 1193 checklists that week, 39,105 in all26%
  5. Bennington CountyBest early April · 567 checklists that week, 21,621 in all21%
  6. Lamoille CountyBest the second week of April · 584 checklists that week, 16,426 in all21%

Best spots

Share of checklists at the peak
  1. Lake ParanBennington County, best early April · 44 checklists that week, 820 in all95%
  2. The GutGrand Isle County, best early December · 22 checklists that week, 185 in all95%
  3. Lake RunnenedeWindsor County, best the second week of April · 90 checklists that week, 2,137 in all93%
  4. Connecticut River ReservoirWindsor County, best the second week of February · 27 checklists that week, 651 in all91%
  5. Chimney PointAddison County, best mid March · 154 checklists that week, 1,924 in all86%

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

Best time of day

In Vermont, the Common Merganser is most often listed on checklists started between 11 am and 1 pm (10% of those checklists).

0%5%10%15%12 am: too few checklists (384) to judge1 am: too few checklists (418) to judge2 am: too few checklists (568) to judge3 am: too few checklists (1183) to judge4 am: too few checklists (3460) to judge5 am: 3.4% of 10340 checklists6 am: 5.9% of 30951 checklists7 am: 6.2% of 64150 checklists8 am: 6.4% of 70252 checklists9 am: 8.3% of 55280 checklists10 am: 9.7% of 47111 checklists11 am: 10% of 37615 checklists12 pm: 9.7% of 32195 checklists1 pm: 9.8% of 30185 checklists2 pm: 10% of 29679 checklists3 pm: 10% of 26483 checklists4 pm: 9.0% of 20110 checklists5 pm: 7.4% of 15993 checklists6 pm: 5.7% of 12110 checklists7 pm: too few checklists (8203) to judge8 pm: too few checklists (4425) to judge9 pm: too few checklists (1829) to judge10 pm: too few checklists (597) to judge11 pm: too few checklists (309) 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
January8.3%8.5%7.9%7.9%
February7.5%7.6%6.7%9.7%
March11%15%18%20%
April20%18%16%12%
May9.2%5.1%3.8%3.0%
June2.3%2.1%1.9%1.9%
July1.3%1.5%1.7%2.1%
August2.8%2.9%3.2%3.5%
September4.4%4.7%4.9%5.1%
October6.2%6.5%7.2%8.8%
November10%11%11%9.3%
December9.8%7.4%5.4%6.3%

Neighboring states

  • New Hampshire: arrives late September, 8 weeks later than Vermont
  • Massachusetts: arrives mid October, 11 weeks later than Vermont
  • Connecticut: arrives mid October, 11 weeks later than Vermont
  • Rhode Island: arrives the second week of November, 14 weeks later than Vermont

Common questions

When do Common Mergansers arrive in Vermont?
Common Mergansers reach Vermont in late July, are common by late September, peak in early April (20% of checklists), and most are gone by the second week of May.
When do Common Mergansers leave Vermont?
Most Common Mergansers have left Vermont by the second week of May, when reports fall below half their usual rate. Stragglers are still reported until early June.
When is the best time to see a Common Merganser in Vermont?
The Common Merganser is reported most often in early April, on about 20% of Vermont checklists.
Where in Vermont are Common Mergansers seen most often?
By county, Grand Isle County, Windsor County, and Orleans County have the highest peak reporting rates for the Common Merganser (counties with at least 200 checklists).