WhenToBird

Mergus serrator · Anatidae

When Do Red-breasted Mergansers Arrive in Illinois?

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

Red-breasted Mergansers are winter birds in Illinois: the first arrive in late October, they are common by the second week of November, peak in mid March (16% of checklists), and most are gone by mid April.

When to look

First arrivalsOct 22-31late October
Common byNov 8-14the second week of November
PeakMar 15-21mid March
Most gone byApr 15-21mid April

Best: mid March. First arrivals late October; most are gone by mid April. Peak: on about 16% of Illinois checklists.

  1. Jancommon
  2. Febcommon
  3. Marpeak season
  4. Aprpeak season
  5. Mayuncommon
  6. Junnot usually seen
  7. Julnot usually seen
  8. Augnot usually seen
  9. Sepnot usually seen
  10. Octrare
  11. Novcommon
  12. Deccommon

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

0%5%10%15%20%Jan 1-7: 9.7% of 29700 checklistsJan 8-14: 9.3% of 20189 checklistsJan 15-21: 8.5% of 19784 checklistsJan 22-31: 8.6% of 26641 checklistsFeb 1-7: 8.7% of 20478 checklistsFeb 8-14: 8.6% of 21967 checklistsFeb 15-21: 7.4% of 28735 checklistsFeb 22-28: 12% of 24223 checklistsMar 1-7: 13% of 26775 checklistsMar 8-14: 15% of 27579 checklistsMar 15-21: 16% of 27193 checklistsMar 22-31: 17% of 42278 checklistsApr 1-7: 14% of 34579 checklistsApr 8-14: 11% of 38290 checklistsApr 15-21: 8.3% of 39261 checklistsApr 22-30: 5.0% of 59584 checklistsMay 1-7: 2.6% of 60485 checklistsMay 8-14: 1.2% of 59647 checklistsMay 15-21: 0.8% of 43173 checklistsMay 22-31: 0.4% of 47913 checklistsJun 1-7: 0.3% of 31151 checklistsJun 8-14: 0.1% of 27692 checklistsJun 15-21: 0.1% of 23983 checklistsJun 22-30: 0.1% of 28448 checklistsJul 1-7: 0.1% of 21273 checklistsJul 8-14: 0.1% of 19284 checklistsJul 15-21: 0.2% of 17712 checklistsJul 22-31: 0.2% of 24500 checklistsAug 1-7: 0.1% of 18498 checklistsAug 8-14: 0.1% of 19331 checklistsAug 15-21: 0.1% of 19983 checklistsAug 22-31: 0.1% of 31892 checklistsSep 1-7: 0.1% of 26396 checklistsSep 8-14: 0.1% of 25011 checklistsSep 15-21: 0.1% of 23597 checklistsSep 22-30: 0.2% of 30638 checklistsOct 1-7: 0.2% of 23949 checklistsOct 8-14: 0.3% of 24412 checklistsOct 15-21: 0.7% of 22359 checklistsOct 22-31: 1.7% of 29794 checklistsNov 1-7: 3.9% of 21877 checklistsNov 8-14: 7.2% of 19742 checklistsNov 15-21: 9.9% of 18989 checklistsNov 22-30: 13% of 23905 checklistsDec 1-7: 12% of 16935 checklistsDec 8-14: 11% of 16687 checklistsDec 15-21: 7.8% of 20931 checklistsDec 22-31: 11% of 29011 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 Illinois 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 Illinois

Best counties

Share of checklists at the peak
  1. Lake CountyBest the second week of December · 1410 checklists that week, 113,940 in all32%
  2. Cook CountyBest mid March · 8417 checklists that week, 432,644 in all31%
  3. Clinton CountyBest late March · 315 checklists that week, 8,606 in all24%
  4. Richland CountyBest mid March · 11 checklists that week, 580 in all23%
  5. Shelby CountyBest late March · 30 checklists that week, 1,001 in all22%
  6. Putnam CountyBest late March · 82 checklists that week, 3,333 in all22%

Best spots

Share of checklists at the peak
  1. Jackson (Andrew) (Yacht Harbor)Cook County, best late March · 31 checklists that week, 940 in all99%
  2. Outer HarborCook County, best late December · 23 checklists that week, 353 in all98%
  3. Bensenville Ditch Forest PreserveDuPage County, best late March · 178 checklists that week, 1,826 in all98%
  4. Big Bend LakeCook County, best late March · 62 checklists that week, 511 in all98%
  5. Lincoln (Abraham) (Belmont Harbor)Cook County, best mid December · 34 checklists that week, 1,176 in all97%
  6. Park No. 566Cook County, best early December · 85 checklists that week, 3,444 in all96%

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

Best time of day

In Illinois, the Red-breasted Merganser is most often listed on checklists started between 11 am and 1 pm (6.6% of those checklists).

0%2%4%6%8%12 am: too few checklists (484) to judge1 am: too few checklists (631) to judge2 am: too few checklists (485) to judge3 am: too few checklists (610) to judge4 am: too few checklists (2321) to judge5 am: too few checklists (23536) to judge6 am: 4.9% of 95511 checklists7 am: 5.4% of 164584 checklists8 am: 5.0% of 163654 checklists9 am: 5.5% of 141804 checklists10 am: 6.0% of 122882 checklists11 am: 6.6% of 100640 checklists12 pm: 6.7% of 89894 checklists1 pm: 6.2% of 82729 checklists2 pm: 6.5% of 79801 checklists3 pm: 5.9% of 82169 checklists4 pm: 4.4% of 75124 checklists5 pm: 3.2% of 57708 checklists6 pm: 2.0% of 41843 checklists7 pm: too few checklists (20943) to judge8 pm: too few checklists (6131) to judge9 pm: too few checklists (1677) to judge10 pm: too few checklists (843) to judge11 pm: too few checklists (448) 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
January9.7%9.3%8.5%8.6%
February8.7%8.6%7.4%12%
March13%15%16%17%
April14%11%8.3%5.0%
May2.6%1.2%0.8%0.4%
June0.3%0.1%0.1%0.1%
July0.1%0.1%0.2%0.2%
August0.1%0.1%0.1%0.1%
September0.1%0.1%0.1%0.2%
October0.2%0.3%0.7%1.7%
November3.9%7.2%9.9%13%
December12%11%7.8%11%

Neighboring states

  • Indiana: arrives early November, 1 week later than Illinois
  • Wisconsin: arrives mid October, 1 week earlier than Illinois
  • Michigan: arrives late September, 4 weeks earlier than Illinois
  • Iowa: arrives late February, 16 weeks later than Illinois

Common questions

When do Red-breasted Mergansers arrive in Illinois?
Red-breasted Mergansers are winter birds in Illinois: the first arrive in late October, they are common by the second week of November, peak in mid March (16% of checklists), and most are gone by mid April.
When do Red-breasted Mergansers leave Illinois?
Most Red-breasted Mergansers have left Illinois by mid April, when reports fall below half their usual rate. Stragglers are still reported until the second week of May.
When is the best time to see a Red-breasted Merganser in Illinois?
The Red-breasted Merganser is reported most often in mid March, on about 16% of Illinois checklists.
Where in Illinois are Red-breasted Mergansers seen most often?
By county, Lake County, Cook County, and Clinton County have the highest peak reporting rates for the Red-breasted Merganser (counties with at least 200 checklists).