WhenToBird

Mergus merganser · Anatidae

When Do Common Mergansers Arrive in South Dakota?

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

Common Mergansers are winter birds in South Dakota: the first arrive in the second week of October, they are common by the second week of November, peak in early December (14% of checklists), and most are gone by the second week of April.

When to look

First arrivalsOct 8-14the second week of October
Common byNov 8-14the second week of November
PeakDec 1-7early December
Most gone byApr 8-14the second week of April

Best: early December. First arrivals the second week of October; most are gone by the second week of April. Peak: on about 14% of South Dakota checklists.

  1. Janpeak season
  2. Febpeak season
  3. Marpeak season
  4. Aprcommon
  5. Mayuncommon
  6. Junrare
  7. Juluncommon
  8. Auguncommon
  9. Sepuncommon
  10. Octuncommon
  11. Novpeak season
  12. Decpeak season

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

0%5%10%15%20%Jan 1-7: 9.3% of 1699 checklistsJan 8-14: 14% of 967 checklistsJan 15-21: 14% of 893 checklistsJan 22-31: 12% of 1338 checklistsFeb 1-7: 12% of 898 checklistsFeb 8-14: 9.0% of 1013 checklistsFeb 15-21: 8.0% of 1650 checklistsFeb 22-28: 11% of 1011 checklistsMar 1-7: 13% of 1304 checklistsMar 8-14: 14% of 1447 checklistsMar 15-21: 12% of 1524 checklistsMar 22-31: 12% of 2850 checklistsApr 1-7: 9.7% of 2170 checklistsApr 8-14: 8.4% of 2259 checklistsApr 15-21: 6.3% of 2578 checklistsApr 22-30: 3.7% of 3858 checklistsMay 1-7: 2.1% of 3532 checklistsMay 8-14: 1.7% of 4498 checklistsMay 15-21: 1.5% of 4211 checklistsMay 22-31: 1.4% of 5094 checklistsJun 1-7: 1.3% of 3279 checklistsJun 8-14: 1.5% of 3503 checklistsJun 15-21: 2.0% of 2861 checklistsJun 22-30: 1.6% of 3893 checklistsJul 1-7: 1.0% of 2666 checklistsJul 8-14: 1.5% of 2554 checklistsJul 15-21: 2.2% of 2412 checklistsJul 22-31: 2.1% of 2746 checklistsAug 1-7: 2.2% of 1842 checklistsAug 8-14: 1.6% of 1899 checklistsAug 15-21: 2.6% of 1757 checklistsAug 22-31: 2.6% of 2464 checklistsSep 1-7: 1.9% of 1894 checklistsSep 8-14: 3.5% of 1794 checklistsSep 15-21: 2.3% of 1671 checklistsSep 22-30: 1.9% of 2085 checklistsOct 1-7: 2.8% of 1429 checklistsOct 8-14: 2.2% of 1441 checklistsOct 15-21: 2.7% of 1330 checklistsOct 22-31: 4.8% of 1471 checklistsNov 1-7: 4.0% of 1168 checklistsNov 8-14: 8.7% of 1068 checklistsNov 15-21: 9.9% of 985 checklistsNov 22-30: 13% of 1108 checklistsDec 1-7: 13% of 890 checklistsDec 8-14: 16% of 957 checklistsDec 15-21: 11% of 1246 checklistsDec 22-31: 9.4% of 1514 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 South Dakota 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 South Dakota

Best counties

Share of checklists at the peak
  1. Charles Mix CountyBest mid January · 28 checklists that week, 2,198 in all43%
  2. Edmunds CountyBest early April · 11 checklists that week, 466 in all41%
  3. Hughes CountyBest the second week of March · 63 checklists that week, 3,765 in all39%
  4. Lyman CountyBest mid January · 15 checklists that week, 878 in all38%
  5. Sully CountyBest late March · 12 checklists that week, 632 in all38%
  6. Pennington CountyBest the second week of January · 144 checklists that week, 12,603 in all36%

Best spots

Share of checklists at the peak
  1. Canyon Lake ParkPennington County, best the second week of January · 59 checklists that week, 2,659 in all91%
  2. Oahe Downstream Recreation AreaStanley County, best the second week of December · 23 checklists that week, 509 in all63%
  3. Farm IslandHughes County, best mid March · 24 checklists that week, 825 in all43%
  4. Lake YanktonYankton County, best late January · 22 checklists that week, 250 in all35%
  5. Oaha Recreation AreaStanley County, best late April · 23 checklists that week, 247 in all29%
  6. Cow Creek Recreation AreaSully County, best late October · 23 checklists that week, 140 in all8.2%

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

Best time of day

In South Dakota, the Common Merganser is most often listed on checklists started between 6 and 8 am (9.4% of those checklists).

0%5%10%15%12 am: too few checklists (49) to judge1 am: too few checklists (44) to judge2 am: too few checklists (33) to judge3 am: too few checklists (59) to judge4 am: too few checklists (227) to judge5 am: too few checklists (1080) to judge6 am: 4.9% of 3387 checklists7 am: 11% of 7718 checklists8 am: 4.9% of 10342 checklists9 am: 4.7% of 10758 checklists10 am: 4.2% of 9123 checklists11 am: 4.5% of 7814 checklists12 pm: 3.7% of 6876 checklists1 pm: 4.6% of 6801 checklists2 pm: 4.6% of 6673 checklists3 pm: 4.7% of 6344 checklists4 pm: 4.1% of 6412 checklists5 pm: 5.0% of 5570 checklists6 pm: 3.7% of 4276 checklists7 pm: 1.8% of 3183 checklists8 pm: too few checklists (1499) to judge9 pm: too few checklists (329) to judge10 pm: too few checklists (82) to judge11 pm: too few checklists (42) 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%14%14%12%
February12%9.0%8.0%11%
March13%14%12%12%
April9.7%8.4%6.3%3.7%
May2.1%1.7%1.5%1.4%
June1.3%1.5%2.0%1.6%
July1.0%1.5%2.2%2.1%
August2.2%1.6%2.6%2.6%
September1.9%3.5%2.3%1.9%
October2.8%2.2%2.7%4.8%
November4.0%8.7%9.9%13%
December13%16%11%9.4%

Neighboring states

  • Nebraska: arrives early November, 3 weeks later than South Dakota
  • North Dakota: arrives late October, 2 weeks later than South Dakota
  • Minnesota: arrives mid July, 11 weeks earlier than South Dakota
  • Iowa: arrives early November, 3 weeks later than South Dakota

Common questions

When do Common Mergansers arrive in South Dakota?
Common Mergansers are winter birds in South Dakota: the first arrive in the second week of October, they are common by the second week of November, peak in early December (14% of checklists), and most are gone by the second week of April.
When do Common Mergansers leave South Dakota?
Most Common Mergansers have left South Dakota by the second week of April, when reports fall below half their usual rate. Stragglers are still reported until early May.
When is the best time to see a Common Merganser in South Dakota?
The Common Merganser is reported most often in early December, on about 14% of South Dakota checklists.
Where in South Dakota are Common Mergansers seen most often?
By county, Charles Mix County, Edmunds County, and Hughes County have the highest peak reporting rates for the Common Merganser (counties with at least 200 checklists).