WhenToBird

Mergus merganser · Anatidae

When Do Common Mergansers Arrive in Washington?

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

Common Mergansers are in Washington all year, but most are here in winter: numbers build from early November, peak in the second week of January (14% of checklists), and fall back by mid April. In the quietest week (mid July) they are still on about 2.1% of checklists.

When to look

Numbers buildNov 1-7early November
PeakJan 8-14the second week of January
Fall back byApr 15-21mid April
FewestJul 15-21mid July

Best: the second week of January. Here all year; numbers build from early November and fall back by mid April. Peak: on about 14% of Washington checklists.

  1. Janpeak season
  2. Febpeak season
  3. Marpeak season
  4. Aprpeak season
  5. Maycommon
  6. Jununcommon
  7. Juluncommon
  8. Auguncommon
  9. Sepuncommon
  10. Octcommon
  11. Novpeak season
  12. Decpeak season

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

0%5%10%15%Jan 1-7: 14% of 41928 checklistsJan 8-14: 14% of 31152 checklistsJan 15-21: 14% of 31753 checklistsJan 22-31: 13% of 42530 checklistsFeb 1-7: 13% of 29739 checklistsFeb 8-14: 12% of 32746 checklistsFeb 15-21: 11% of 40328 checklistsFeb 22-28: 14% of 28432 checklistsMar 1-7: 13% of 30758 checklistsMar 8-14: 13% of 29368 checklistsMar 15-21: 12% of 32580 checklistsMar 22-31: 11% of 45614 checklistsApr 1-7: 10% of 33997 checklistsApr 8-14: 9.7% of 34729 checklistsApr 15-21: 8.1% of 38474 checklistsApr 22-30: 6.8% of 52185 checklistsMay 1-7: 5.3% of 44236 checklistsMay 8-14: 4.7% of 48708 checklistsMay 15-21: 4.5% of 41742 checklistsMay 22-31: 3.8% of 57082 checklistsJun 1-7: 3.3% of 39193 checklistsJun 8-14: 3.1% of 36042 checklistsJun 15-21: 2.9% of 34003 checklistsJun 22-30: 2.8% of 39711 checklistsJul 1-7: 2.2% of 31949 checklistsJul 8-14: 2.1% of 29086 checklistsJul 15-21: 2.1% of 28045 checklistsJul 22-31: 2.2% of 38275 checklistsAug 1-7: 2.3% of 28846 checklistsAug 8-14: 2.6% of 28036 checklistsAug 15-21: 3.2% of 27614 checklistsAug 22-31: 3.3% of 40356 checklistsSep 1-7: 3.5% of 31214 checklistsSep 8-14: 4.0% of 27795 checklistsSep 15-21: 4.2% of 29677 checklistsSep 22-30: 4.0% of 35241 checklistsOct 1-7: 4.2% of 28605 checklistsOct 8-14: 4.6% of 28655 checklistsOct 15-21: 5.6% of 24643 checklistsOct 22-31: 7.3% of 34874 checklistsNov 1-7: 7.9% of 25658 checklistsNov 8-14: 9.4% of 25700 checklistsNov 15-21: 10% of 24331 checklistsNov 22-30: 12% of 32784 checklistsDec 1-7: 11% of 24099 checklistsDec 8-14: 12% of 23339 checklistsDec 15-21: 12% of 27666 checklistsDec 22-31: 13% of 42130 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 Washington 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.

Embed this map on your site

Where in Washington

Best counties

Share of checklists at the peak
  1. Skamania CountyBest early February · 177 checklists that week, 10,140 in all44%
  2. Wahkiakum CountyBest the second week of January · 117 checklists that week, 5,618 in all33%
  3. Cowlitz CountyBest mid January · 243 checklists that week, 15,273 in all27%
  4. Garfield CountyBest mid February · 25 checklists that week, 1,130 in all27%
  5. Mason CountyBest mid March · 588 checklists that week, 27,853 in all27%
  6. Adams CountyBest mid November · 20 checklists that week, 4,574 in all25%

Best spots

Share of checklists at the peak
  1. Kitsap Lake ParkKitsap County, best early January · 43 checklists that week, 426 in all97%
  2. Fremont Canal ParkKing County, best early January · 28 checklists that week, 505 in all95%
  3. Vancouver Lake ParkClark County, best early January · 20 checklists that week, 443 in all92%
  4. Foster Island (Wash. Park)King County, best late November · 21 checklists that week, 1,096 in all91%
  5. Tracy Owen Station ParkKing County, best the second week of December · 51 checklists that week, 2,233 in all90%

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

Best time of day

In Washington, the Common Merganser is most often listed on checklists started between 1 and 3 pm (8.5% of those checklists).

0%5%10%12 am: too few checklists (796) to judge1 am: too few checklists (776) to judge2 am: too few checklists (709) to judge3 am: too few checklists (901) to judge4 am: too few checklists (3221) to judge5 am: too few checklists (16576) to judge6 am: 6.2% of 56744 checklists7 am: 7.4% of 133294 checklists8 am: 8.3% of 184196 checklists9 am: 8.1% of 186303 checklists10 am: 8.3% of 177063 checklists11 am: 8.1% of 154936 checklists12 pm: 8.2% of 138061 checklists1 pm: 8.5% of 127449 checklists2 pm: 8.5% of 121511 checklists3 pm: 7.8% of 107793 checklists4 pm: 6.0% of 82862 checklists5 pm: 4.5% of 57183 checklists6 pm: 3.6% of 39886 checklists7 pm: too few checklists (26969) to judge8 pm: too few checklists (12427) to judge9 pm: too few checklists (3658) to judge10 pm: too few checklists (1500) to judge11 pm: too few checklists (834) 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
January14%14%14%13%
February13%12%11%14%
March13%13%12%11%
April10%9.7%8.1%6.8%
May5.3%4.7%4.5%3.8%
June3.3%3.1%2.9%2.8%
July2.2%2.1%2.1%2.2%
August2.3%2.6%3.2%3.3%
September3.5%4.0%4.2%4.0%
October4.2%4.6%5.6%7.3%
November7.9%9.4%10%12%
December11%12%12%13%

Neighboring states

  • Oregon: arrives mid August, 10 weeks earlier than Washington
  • Idaho: arrives mid October, 2 weeks earlier than Washington
  • Montana: arrives the second week of March, 17 weeks later than Washington
  • Nevada: arrives early September, 8 weeks earlier than Washington

Common questions

When do Common Mergansers arrive in Washington?
Common Mergansers are in Washington all year, but most are here in winter: numbers build from early November, peak in the second week of January (14% of checklists), and fall back by mid April. In the quietest week (mid July) they are still on about 2.1% of checklists.
When do Common Mergansers leave Washington?
Common Mergansers never fully leave Washington: numbers fall back below half their usual rate by mid April, but some are still reported in every week, about 2.1% of checklists at the low.
When is the best time to see a Common Merganser in Washington?
The Common Merganser is reported most often in the second week of January, on about 14% of Washington checklists.
Where in Washington are Common Mergansers seen most often?
By county, Skamania County, Wahkiakum County, and Cowlitz County have the highest peak reporting rates for the Common Merganser (counties with at least 200 checklists).