WhenToBird

Mergus merganser · Anatidae

When Do Common Mergansers Arrive in Iowa?

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

Common Mergansers are winter birds in Iowa: the first arrive in early November, they are common by mid November, peak in the second week of March (12% of checklists), and most are gone by early April.

When to look

First arrivalsNov 1-7early November
Common byNov 15-21mid November
PeakMar 8-14the second week of March
Most gone byApr 1-7early April

Best: the second week of March. First arrivals early November; most are gone by early April. Peak: on about 12% of Iowa checklists.

  1. Jancommon
  2. Febpeak season
  3. Marpeak season
  4. Apruncommon
  5. Maynot usually seen
  6. Junnot usually seen
  7. Julnot usually seen
  8. Augnot usually seen
  9. Sepnot usually seen
  10. Octnot usually seen
  11. Novcommon
  12. Decpeak season

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

0%5%10%15%Jan 1-7: 6.2% of 5551 checklistsJan 8-14: 4.7% of 3498 checklistsJan 15-21: 3.9% of 3803 checklistsJan 22-31: 4.5% of 4807 checklistsFeb 1-7: 4.7% of 3613 checklistsFeb 8-14: 5.7% of 4173 checklistsFeb 15-21: 6.1% of 5796 checklistsFeb 22-28: 9.2% of 4394 checklistsMar 1-7: 13% of 5295 checklistsMar 8-14: 12% of 5679 checklistsMar 15-21: 9.9% of 5418 checklistsMar 22-31: 7.1% of 8613 checklistsApr 1-7: 3.7% of 6970 checklistsApr 8-14: 1.8% of 7511 checklistsApr 15-21: 0.9% of 8321 checklistsApr 22-30: 0.3% of 11976 checklistsMay 1-7: 0.1% of 11725 checklistsMay 8-14: 0.1% of 12626 checklistsMay 15-21: 0.1% of 9372 checklistsMay 22-31: 0.1% of 10330 checklistsJun 1-7: 0.1% of 5472 checklistsJun 8-14: 0.1% of 4568 checklistsJun 15-21: 0.1% of 3870 checklistsJun 22-30: 0.1% of 4780 checklistsJul 1-7: 0.1% of 4201 checklistsJul 8-14: 0.1% of 3605 checklistsJul 15-21: 0.1% of 3621 checklistsJul 22-31: 0.1% of 5093 checklistsAug 1-7: 0.1% of 3931 checklistsAug 8-14: 0% of 3488 checklistsAug 15-21: 0.1% of 3802 checklistsAug 22-31: 0% of 6293 checklistsSep 1-7: 0.1% of 5328 checklistsSep 8-14: 0% of 4622 checklistsSep 15-21: 0.1% of 4367 checklistsSep 22-30: 0% of 6086 checklistsOct 1-7: 0.1% of 4708 checklistsOct 8-14: 0.1% of 4791 checklistsOct 15-21: 0.1% of 4429 checklistsOct 22-31: 0.2% of 5633 checklistsNov 1-7: 1.0% of 4090 checklistsNov 8-14: 3.5% of 3416 checklistsNov 15-21: 4.4% of 3398 checklistsNov 22-30: 6.9% of 4679 checklistsDec 1-7: 9.7% of 3442 checklistsDec 8-14: 10% of 3322 checklistsDec 15-21: 7.1% of 4619 checklistsDec 22-31: 6.7% of 5113 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 Iowa 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 Iowa

Best counties

Share of checklists at the peak
  1. Marion CountyBest early March · 97 checklists that week, 3,389 in all48%
  2. Jackson CountyBest early March · 46 checklists that week, 1,765 in all48%
  3. Worth CountyBest late March · 10 checklists that week, 333 in all43%
  4. Hancock CountyBest the second week of March · 12 checklists that week, 449 in all41%
  5. Harrison CountyBest early March · 32 checklists that week, 1,977 in all40%
  6. Hamilton CountyBest the second week of March · 25 checklists that week, 965 in all36%

Best spots

Share of checklists at the peak
  1. Saylorville Recreation Area (Camp Dodge)Polk County, best the second week of December · 47 checklists that week, 690 in all91%
  2. Saylorville Recreation Area (Rock Creek)Polk County, best the second week of December · 68 checklists that week, 1,401 in all86%
  3. Saylorville Recreation Area (northwest)Polk County, best early March · 23 checklists that week, 1,546 in all76%
  4. Storm LakeBuena Vista County, best the second week of March · 22 checklists that week, 836 in all66%
  5. Lake Manawa State ParkPottawattamie County, best the second week of March · 37 checklists that week, 599 in all66%
  6. Saylorville Recreation Area (Big Creek)Polk County, best early December · 24 checklists that week, 999 in all61%

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

Best time of day

In Iowa, the Common Merganser is most often listed on checklists started between 12 and 2 pm (3.7% of those checklists).

0%1%2%3%4%12 am: too few checklists (96) to judge1 am: too few checklists (99) to judge2 am: too few checklists (67) to judge3 am: too few checklists (82) to judge4 am: too few checklists (201) to judge5 am: too few checklists (1888) to judge6 am: 0.6% of 11313 checklists7 am: 1.8% of 25717 checklists8 am: 2.7% of 29755 checklists9 am: 3.1% of 28897 checklists10 am: 3.3% of 26343 checklists11 am: 3.3% of 21210 checklists12 pm: 3.8% of 17662 checklists1 pm: 3.7% of 16595 checklists2 pm: 3.2% of 16405 checklists3 pm: 3.2% of 17030 checklists4 pm: 2.8% of 17378 checklists5 pm: 1.9% of 14251 checklists6 pm: 1.1% of 10349 checklists7 pm: 0.4% of 6233 checklists8 pm: too few checklists (2002) to judge9 pm: too few checklists (392) to judge10 pm: too few checklists (186) to judge11 pm: too few checklists (87) 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
January6.2%4.7%3.9%4.5%
February4.7%5.7%6.1%9.2%
March13%12%9.9%7.1%
April3.7%1.8%0.9%0.3%
May0.1%0.1%0.1%0.1%
June0.1%0.1%0.1%0.1%
July0.1%0.1%0.1%0.1%
August0.1%0%0.1%0%
September0.1%0%0.1%0%
October0.1%0.1%0.1%0.2%
November1.0%3.5%4.4%6.9%
December9.7%10%7.1%6.7%

Neighboring states

  • Missouri: arrives mid November, 2 weeks later than Iowa
  • Wisconsin: arrives mid September, 6 weeks earlier than Iowa
  • Minnesota: arrives mid July, 14 weeks earlier than Iowa
  • Illinois: arrives the second week of November, 1 week later than Iowa

Common questions

When do Common Mergansers arrive in Iowa?
Common Mergansers are winter birds in Iowa: the first arrive in early November, they are common by mid November, peak in the second week of March (12% of checklists), and most are gone by early April.
When do Common Mergansers leave Iowa?
Most Common Mergansers have left Iowa by early April, when reports fall below half their usual rate. Stragglers are still reported until the second week of April.
When is the best time to see a Common Merganser in Iowa?
The Common Merganser is reported most often in the second week of March, on about 12% of Iowa checklists.
Where in Iowa are Common Mergansers seen most often?
By county, Marion County, Jackson County, and Worth County have the highest peak reporting rates for the Common Merganser (counties with at least 200 checklists).