WhenToBird

Mergus merganser · Anatidae

When Do Common Mergansers Arrive in New Hampshire?

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

Common Mergansers reach New Hampshire in late September, are common by late October, peak in early April (14% of checklists), and most are gone by the second week of May.

When to look

First arrivalsSep 22-30late September
Common byOct 22-31late October
PeakApr 1-7early April
Most gone byMay 8-14the second week of May

Best: early April. First arrivals late September; most are gone by the second week of May. Peak: on about 14% of New Hampshire checklists.

  1. Januncommon
  2. Febcommon
  3. Marpeak season
  4. Aprpeak season
  5. Maycommon
  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: 4.8% of 8253 checklistsJan 8-14: 5.1% of 5998 checklistsJan 15-21: 4.6% of 5734 checklistsJan 22-31: 4.5% of 7776 checklistsFeb 1-7: 5.2% of 5253 checklistsFeb 8-14: 3.9% of 6802 checklistsFeb 15-21: 4.1% of 8852 checklistsFeb 22-28: 6.2% of 5792 checklistsMar 1-7: 7.6% of 6187 checklistsMar 8-14: 10% of 6977 checklistsMar 15-21: 12% of 7863 checklistsMar 22-31: 15% of 11746 checklistsApr 1-7: 15% of 9329 checklistsApr 8-14: 13% of 10499 checklistsApr 15-21: 9.7% of 10376 checklistsApr 22-30: 7.9% of 13086 checklistsMay 1-7: 5.7% of 13198 checklistsMay 8-14: 3.5% of 14980 checklistsMay 15-21: 2.5% of 12487 checklistsMay 22-31: 2.1% of 14294 checklistsJun 1-7: 1.9% of 8974 checklistsJun 8-14: 1.4% of 8395 checklistsJun 15-21: 1.5% of 7670 checklistsJun 22-30: 1.4% of 9188 checklistsJul 1-7: 1.5% of 7707 checklistsJul 8-14: 1.2% of 6554 checklistsJul 15-21: 1.0% of 6636 checklistsJul 22-31: 1.1% of 9599 checklistsAug 1-7: 1.2% of 6436 checklistsAug 8-14: 1.3% of 6477 checklistsAug 15-21: 1.0% of 6510 checklistsAug 22-31: 1.2% of 9762 checklistsSep 1-7: 1.3% of 6700 checklistsSep 8-14: 1.3% of 6012 checklistsSep 15-21: 1.4% of 6238 checklistsSep 22-30: 1.6% of 7619 checklistsOct 1-7: 1.8% of 6702 checklistsOct 8-14: 1.6% of 6863 checklistsOct 15-21: 2.1% of 6284 checklistsOct 22-31: 3.5% of 8287 checklistsNov 1-7: 4.8% of 7584 checklistsNov 8-14: 6.5% of 6056 checklistsNov 15-21: 7.6% of 5597 checklistsNov 22-30: 7.3% of 7140 checklistsDec 1-7: 4.5% of 4623 checklistsDec 8-14: 4.8% of 4920 checklistsDec 15-21: 4.1% of 6416 checklistsDec 22-31: 5.2% of 7659 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 New Hampshire 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 New Hampshire

Best counties

Share of checklists at the peak
  1. Belknap CountyBest early December · 138 checklists that week, 13,295 in all30%
  2. Merrimack CountyBest late March · 1349 checklists that week, 36,980 in all24%
  3. Coos CountyBest mid April · 626 checklists that week, 27,719 in all20%
  4. Sullivan CountyBest early April · 322 checklists that week, 13,105 in all20%
  5. Grafton CountyBest the second week of April · 1396 checklists that week, 45,699 in all19%
  6. Cheshire CountyBest early April · 1087 checklists that week, 39,834 in all19%

Best spots

Share of checklists at the peak
  1. Spofford LakeCheshire County, best late December · 30 checklists that week, 251 in all85%
  2. Keene Forestry ParkCheshire County, best late March · 20 checklists that week, 292 in all85%
  3. Meadow BrookCarroll County, best the second week of April · 42 checklists that week, 648 in all81%
  4. Lake WaukewanBelknap County, best late November · 25 checklists that week, 505 in all80%

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

Best time of day

In New Hampshire, the Common Merganser is most often listed on checklists started between 3 and 5 pm (5.9% of those checklists).

0%2%4%6%12 am: too few checklists (219) to judge1 am: too few checklists (192) to judge2 am: too few checklists (176) to judge3 am: too few checklists (234) to judge4 am: too few checklists (1042) to judge5 am: too few checklists (6352) to judge6 am: 3.9% of 23140 checklists7 am: 3.6% of 43401 checklists8 am: 4.2% of 48039 checklists9 am: 4.7% of 43328 checklists10 am: 5.1% of 37073 checklists11 am: 5.3% of 32028 checklists12 pm: 5.4% of 27396 checklists1 pm: 5.8% of 25182 checklists2 pm: 5.8% of 24318 checklists3 pm: 5.9% of 21974 checklists4 pm: 5.8% of 17958 checklists5 pm: 4.7% of 14528 checklists6 pm: 3.8% of 9144 checklists7 pm: too few checklists (5341) to judge8 pm: too few checklists (1845) to judge9 pm: too few checklists (578) to judge10 pm: too few checklists (346) to judge11 pm: too few checklists (256) 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
January4.8%5.1%4.6%4.5%
February5.2%3.9%4.1%6.2%
March7.6%10%12%15%
April15%13%9.7%7.9%
May5.7%3.5%2.5%2.1%
June1.9%1.4%1.5%1.4%
July1.5%1.2%1.0%1.1%
August1.2%1.3%1.0%1.2%
September1.3%1.3%1.4%1.6%
October1.8%1.6%2.1%3.5%
November4.8%6.5%7.6%7.3%
December4.5%4.8%4.1%5.2%

Neighboring states

  • Massachusetts: arrives mid October, 3 weeks later than New Hampshire
  • Vermont: arrives late July, 8 weeks earlier than New Hampshire
  • Rhode Island: arrives the second week of November, 6 weeks later than New Hampshire
  • Maine: arrives the second week of September, 2 weeks earlier than New Hampshire

Common questions

When do Common Mergansers arrive in New Hampshire?
Common Mergansers reach New Hampshire in late September, are common by late October, peak in early April (14% of checklists), and most are gone by the second week of May.
When do Common Mergansers leave New Hampshire?
Most Common Mergansers have left New Hampshire by the second week of May, when reports fall below half their usual rate. Stragglers are still reported until the second week of June.
When is the best time to see a Common Merganser in New Hampshire?
The Common Merganser is reported most often in early April, on about 14% of New Hampshire checklists.
Where in New Hampshire are Common Mergansers seen most often?
By county, Belknap County, Merrimack County, and Coos County have the highest peak reporting rates for the Common Merganser (counties with at least 200 checklists).