WhenToBird

Mergus serrator · Anatidae

When Do Red-breasted Mergansers Arrive in Iowa?

Adult male Red-breasted Merganser
Photo: Peter Chen 2.0, CC BY 4.0 via iNaturalist

Red-breasted Mergansers are winter birds in Iowa: they arrive in late February, peak in late March (6.6% of checklists), and most are gone by late April.

When to look

First arrivalsFeb 22-28late February
Common byFeb 22-28late February
PeakMar 22-31late March
Most gone byApr 22-30late April

Best: late March. First arrivals late February; most are gone by late April. Peak: on about 6.6% of Iowa checklists.

  1. Janrare
  2. Febuncommon
  3. Marpeak season
  4. Aprpeak season
  5. Mayrare
  6. Junnot usually seen
  7. Julnot usually seen
  8. Augnot usually seen
  9. Sepnot usually seen
  10. Octuncommon
  11. Novcommon
  12. Deccommon

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

0%2%4%6%8%Jan 1-7: 0.6% of 5551 checklistsJan 8-14: 0.3% of 3498 checklistsJan 15-21: 0.1% of 3803 checklistsJan 22-31: 0.1% of 4807 checklistsFeb 1-7: 0.1% of 3613 checklistsFeb 8-14: 0.3% of 4173 checklistsFeb 15-21: 0.2% of 5796 checklistsFeb 22-28: 1.3% of 4394 checklistsMar 1-7: 2.6% of 5295 checklistsMar 8-14: 3.8% of 5679 checklistsMar 15-21: 5.9% of 5418 checklistsMar 22-31: 7.3% of 8613 checklistsApr 1-7: 6.3% of 6970 checklistsApr 8-14: 4.1% of 7511 checklistsApr 15-21: 3.9% of 8321 checklistsApr 22-30: 1.8% of 11976 checklistsMay 1-7: 0.4% of 11725 checklistsMay 8-14: 0.3% of 12626 checklistsMay 15-21: 0.2% of 9372 checklistsMay 22-31: 0.1% of 10330 checklistsJun 1-7: 0.1% of 5472 checklistsJun 8-14: 0% of 4568 checklistsJun 15-21: 0% of 3870 checklistsJun 22-30: 0% of 4780 checklistsJul 1-7: 0.1% of 4201 checklistsJul 8-14: 0% of 3605 checklistsJul 15-21: 0% of 3621 checklistsJul 22-31: 0% of 5093 checklistsAug 1-7: 0% of 3931 checklistsAug 8-14: 0% of 3488 checklistsAug 15-21: 0% of 3802 checklistsAug 22-31: 0% of 6293 checklistsSep 1-7: 0% of 5328 checklistsSep 8-14: 0% of 4622 checklistsSep 15-21: 0% of 4367 checklistsSep 22-30: 0% of 6086 checklistsOct 1-7: 0% of 4708 checklistsOct 8-14: 0.1% of 4791 checklistsOct 15-21: 0.1% of 4429 checklistsOct 22-31: 0.6% of 5633 checklistsNov 1-7: 2.8% of 4090 checklistsNov 8-14: 4.1% of 3416 checklistsNov 15-21: 4.7% of 3398 checklistsNov 22-30: 3.4% of 4679 checklistsDec 1-7: 3.5% of 3442 checklistsDec 8-14: 2.0% of 3322 checklistsDec 15-21: 1.1% of 4619 checklistsDec 22-31: 0.8% 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. Jackson CountyBest mid March · 40 checklists that week, 1,765 in all32%
  2. Worth CountyBest early April · 12 checklists that week, 333 in all29%
  3. Marion CountyBest mid March · 81 checklists that week, 3,389 in all21%
  4. Palo Alto CountyBest mid March · 12 checklists that week, 460 in all20%
  5. Clay CountyBest early April · 17 checklists that week, 844 in all18%
  6. Sioux CountyBest late March · 36 checklists that week, 1,159 in all16%

Best spots

Share of checklists at the peak
  1. Pleasant Creek State Recreation AreaLinn County, best the second week of April · 25 checklists that week, 718 in all63%
  2. Big Creek Wildlife Management AreaPolk County, best late March · 34 checklists that week, 500 in all60%
  3. Saylorville Recreation Area (Rock Creek)Polk County, best the second week of November · 73 checklists that week, 1,401 in all55%
  4. Lake MacBrideJohnson County, best early April · 50 checklists that week, 1,067 in all51%
  5. Saylorville Recreation Area (Camp Dodge)Polk County, best mid November · 30 checklists that week, 690 in all48%

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

Best time of day

In Iowa, the Red-breasted Merganser is most often listed on checklists started between 12 and 2 pm (1.7% of those checklists).

0%0.5%1%1.5%2%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: 0.7% of 11313 checklists7 am: 1.1% of 25717 checklists8 am: 1.5% of 29755 checklists9 am: 1.7% of 28897 checklists10 am: 1.5% of 26343 checklists11 am: 1.7% of 21210 checklists12 pm: 1.8% of 17662 checklists1 pm: 1.7% of 16595 checklists2 pm: 1.5% of 16405 checklists3 pm: 1.3% of 17030 checklists4 pm: 1.5% of 17378 checklists5 pm: 1.5% of 14251 checklists6 pm: 1.3% of 10349 checklists7 pm: 0.6% 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
January0.6%0.3%0.1%0.1%
February0.1%0.3%0.2%1.3%
March2.6%3.8%5.9%7.3%
April6.3%4.1%3.9%1.8%
May0.4%0.3%0.2%0.1%
June0.1%0%0%0%
July0.1%0%0%0%
August0%0%0%0%
September0%0%0%0%
October0%0.1%0.1%0.6%
November2.8%4.1%4.7%3.4%
December3.5%2.0%1.1%0.8%

Neighboring states

  • Missouri: arrives early November, 15 weeks earlier than Iowa
  • Wisconsin: arrives mid October, 17 weeks earlier than Iowa
  • Minnesota: arrives the second week of March, 2 weeks later than Iowa
  • Illinois: arrives late October, 16 weeks earlier than Iowa

Common questions

When do Red-breasted Mergansers arrive in Iowa?
Red-breasted Mergansers are winter birds in Iowa: they arrive in late February, peak in late March (6.6% of checklists), and most are gone by late April.
When do Red-breasted Mergansers leave Iowa?
Most Red-breasted Mergansers have left Iowa by late April, when reports fall below half their usual rate.
When is the best time to see a Red-breasted Merganser in Iowa?
The Red-breasted Merganser is reported most often in late March, on about 6.6% of Iowa checklists.
Where in Iowa are Red-breasted Mergansers seen most often?
By county, Jackson County, Worth County, and Marion County have the highest peak reporting rates for the Red-breasted Merganser (counties with at least 200 checklists).