WhenToBird

Mergus merganser · Anatidae

When Do Common Mergansers Arrive in Oregon?

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

Common Mergansers are winter birds in Oregon: the first arrive in mid August, they are common by the second week of October, peak in mid January (11% of checklists), and most are gone by the second week of April.

When to look

First arrivalsAug 15-21mid August
Common byOct 8-14the second week of October
PeakJan 15-21mid January
Most gone byApr 8-14the second week of April

Best: mid January. First arrivals mid August; most are gone by the second week of April. Peak: on about 11% of Oregon checklists.

  1. Janpeak season
  2. Febpeak season
  3. Marpeak season
  4. Aprcommon
  5. Mayuncommon
  6. Jununcommon
  7. Juluncommon
  8. Auguncommon
  9. Sepcommon
  10. Octcommon
  11. Novpeak season
  12. Decpeak season

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

0%5%10%15%Jan 1-7: 11% of 34973 checklistsJan 8-14: 11% of 26807 checklistsJan 15-21: 11% of 26567 checklistsJan 22-31: 11% of 36019 checklistsFeb 1-7: 10% of 24020 checklistsFeb 8-14: 9.2% of 25765 checklistsFeb 15-21: 9.1% of 31019 checklistsFeb 22-28: 8.5% of 24582 checklistsMar 1-7: 9.1% of 24834 checklistsMar 8-14: 8.7% of 24642 checklistsMar 15-21: 7.9% of 27420 checklistsMar 22-31: 7.3% of 39913 checklistsApr 1-7: 6.1% of 28817 checklistsApr 8-14: 5.6% of 31221 checklistsApr 15-21: 4.7% of 34402 checklistsApr 22-30: 4.3% of 47144 checklistsMay 1-7: 3.5% of 37716 checklistsMay 8-14: 2.9% of 39651 checklistsMay 15-21: 2.8% of 37496 checklistsMay 22-31: 2.5% of 56967 checklistsJun 1-7: 2.1% of 35893 checklistsJun 8-14: 2.2% of 31880 checklistsJun 15-21: 2.1% of 30942 checklistsJun 22-30: 1.9% of 38478 checklistsJul 1-7: 1.9% of 27409 checklistsJul 8-14: 1.7% of 25161 checklistsJul 15-21: 1.9% of 25473 checklistsJul 22-31: 1.9% of 33920 checklistsAug 1-7: 2.0% of 24310 checklistsAug 8-14: 2.1% of 23675 checklistsAug 15-21: 2.6% of 23623 checklistsAug 22-31: 2.9% of 33762 checklistsSep 1-7: 3.4% of 25120 checklistsSep 8-14: 3.7% of 24458 checklistsSep 15-21: 4.3% of 25528 checklistsSep 22-30: 4.4% of 31631 checklistsOct 1-7: 5.2% of 25498 checklistsOct 8-14: 5.3% of 25161 checklistsOct 15-21: 6.1% of 23701 checklistsOct 22-31: 7.8% of 30996 checklistsNov 1-7: 9.0% of 21089 checklistsNov 8-14: 9.5% of 21880 checklistsNov 15-21: 9.3% of 21501 checklistsNov 22-30: 9.4% of 28930 checklistsDec 1-7: 9.5% of 19807 checklistsDec 8-14: 8.8% of 21022 checklistsDec 15-21: 8.9% of 24817 checklistsDec 22-31: 9.8% of 37592 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 Oregon 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 Oregon

Best counties

Share of checklists at the peak
  1. Sherman CountyBest the second week of November · 238 checklists that week, 4,629 in all49%
  2. Jefferson CountyBest late November · 195 checklists that week, 11,014 in all32%
  3. Hood River CountyBest early January · 122 checklists that week, 9,695 in all31%
  4. Morrow CountyBest mid January · 50 checklists that week, 3,484 in all30%
  5. Klamath CountyBest late March · 619 checklists that week, 26,875 in all30%
  6. Wasco CountyBest early November · 142 checklists that week, 13,127 in all26%

Best spots

Share of checklists at the peak
  1. Clackamette CoveClackamas County, best late January · 25 checklists that week, 541 in all97%
  2. Klamath FallsKlamath County, best late March · 23 checklists that week, 720 in all96%
  3. Rogue River (east)Jackson County, best late January · 25 checklists that week, 321 in all96%
  4. Hellroaring CanyonSherman County, best the second week of November · 92 checklists that week, 344 in all96%
  5. Suttle LakeJefferson County, best late November · 30 checklists that week, 441 in all95%

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

Best time of day

In Oregon, the Common Merganser is most often listed on checklists started between 1 and 3 pm (7.1% of those checklists).

0%2%4%6%8%12 am: too few checklists (1505) to judge1 am: too few checklists (675) to judge2 am: too few checklists (626) to judge3 am: too few checklists (1641) to judge4 am: too few checklists (3696) to judge5 am: too few checklists (14524) to judge6 am: 3.1% of 50677 checklists7 am: 4.9% of 125347 checklists8 am: 6.1% of 163668 checklists9 am: 6.6% of 160351 checklists10 am: 6.6% of 148940 checklists11 am: 6.8% of 124743 checklists12 pm: 6.5% of 112537 checklists1 pm: 7.1% of 98999 checklists2 pm: 7.1% of 94690 checklists3 pm: 6.8% of 87923 checklists4 pm: 5.0% of 75235 checklists5 pm: 3.4% of 54504 checklists6 pm: 2.6% of 40469 checklists7 pm: 1.5% of 33675 checklists8 pm: too few checklists (18715) to judge9 pm: too few checklists (5839) to judge10 pm: too few checklists (2704) to judge11 pm: too few checklists (1549) 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
January11%11%11%11%
February10%9.2%9.1%8.5%
March9.1%8.7%7.9%7.3%
April6.1%5.6%4.7%4.3%
May3.5%2.9%2.8%2.5%
June2.1%2.2%2.1%1.9%
July1.9%1.7%1.9%1.9%
August2.0%2.1%2.6%2.9%
September3.4%3.7%4.3%4.4%
October5.2%5.3%6.1%7.8%
November9.0%9.5%9.3%9.4%
December9.5%8.8%8.9%9.8%

Neighboring states

  • Washington: arrives early November, 10 weeks later than Oregon
  • Idaho: arrives mid October, 8 weeks later than Oregon
  • Nevada: arrives early September, 2 weeks later than Oregon
  • California: arrives mid October, 8 weeks later than Oregon

Common questions

When do Common Mergansers arrive in Oregon?
Common Mergansers are winter birds in Oregon: the first arrive in mid August, they are common by the second week of October, peak in mid January (11% of checklists), and most are gone by the second week of April.
When do Common Mergansers leave Oregon?
Most Common Mergansers have left Oregon by the second week of April, when reports fall below half their usual rate. Stragglers are still reported until mid May.
When is the best time to see a Common Merganser in Oregon?
The Common Merganser is reported most often in mid January, on about 11% of Oregon checklists.
Where in Oregon are Common Mergansers seen most often?
By county, Sherman County, Jefferson County, and Hood River County have the highest peak reporting rates for the Common Merganser (counties with at least 200 checklists).