WhenToBird

Mergus merganser · Anatidae

When Do Common Mergansers Arrive in California?

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

Common Mergansers are winter birds in California: the first arrive in mid October, they are common by early November, peak in late January (4.3% of checklists), and most are gone by late May.

When to look

First arrivalsOct 15-21mid October
Common byNov 1-7early November
PeakJan 22-31late January
Most gone byMay 22-31late May

Best: late January. First arrivals mid October; most are gone by late May. Peak: on about 4.3% of California checklists.

  1. Janpeak season
  2. Febpeak season
  3. Marpeak season
  4. Aprcommon
  5. Maycommon
  6. Juncommon
  7. Juluncommon
  8. Auguncommon
  9. Sepcommon
  10. Octcommon
  11. Novcommon
  12. Decpeak season

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

0%2%4%6%Jan 1-7: 3.9% of 112336 checklistsJan 8-14: 3.9% of 85518 checklistsJan 15-21: 4.1% of 86488 checklistsJan 22-31: 4.4% of 116174 checklistsFeb 1-7: 4.2% of 75171 checklistsFeb 8-14: 4.0% of 84467 checklistsFeb 15-21: 3.5% of 105683 checklistsFeb 22-28: 3.8% of 83396 checklistsMar 1-7: 4.0% of 77470 checklistsMar 8-14: 3.6% of 75180 checklistsMar 15-21: 3.4% of 80770 checklistsMar 22-31: 3.1% of 114116 checklistsApr 1-7: 2.8% of 84057 checklistsApr 8-14: 2.8% of 83692 checklistsApr 15-21: 2.5% of 89242 checklistsApr 22-30: 2.3% of 114289 checklistsMay 1-7: 2.1% of 85728 checklistsMay 8-14: 2.0% of 91984 checklistsMay 15-21: 1.9% of 75478 checklistsMay 22-31: 1.9% of 106250 checklistsJun 1-7: 1.6% of 70051 checklistsJun 8-14: 1.7% of 67485 checklistsJun 15-21: 1.8% of 66269 checklistsJun 22-30: 1.7% of 79172 checklistsJul 1-7: 1.7% of 62877 checklistsJul 8-14: 1.5% of 60328 checklistsJul 15-21: 1.5% of 59705 checklistsJul 22-31: 1.5% of 83796 checklistsAug 1-7: 1.6% of 60215 checklistsAug 8-14: 1.6% of 60172 checklistsAug 15-21: 1.5% of 59877 checklistsAug 22-31: 1.7% of 89107 checklistsSep 1-7: 1.7% of 72000 checklistsSep 8-14: 1.8% of 71228 checklistsSep 15-21: 1.8% of 76808 checklistsSep 22-30: 1.6% of 100204 checklistsOct 1-7: 1.4% of 76571 checklistsOct 8-14: 1.5% of 80874 checklistsOct 15-21: 1.6% of 74581 checklistsOct 22-31: 1.7% of 97498 checklistsNov 1-7: 1.9% of 70851 checklistsNov 8-14: 2.1% of 72431 checklistsNov 15-21: 2.2% of 66767 checklistsNov 22-30: 2.6% of 94737 checklistsDec 1-7: 2.8% of 65393 checklistsDec 8-14: 2.7% of 67449 checklistsDec 15-21: 2.9% of 83421 checklistsDec 22-31: 3.1% of 124993 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 California 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 California

Best counties

Share of checklists at the peak
  1. Sierra CountyBest early September · 101 checklists that week, 8,945 in all21%
  2. Modoc CountyBest late January · 51 checklists that week, 6,138 in all20%
  3. Amador CountyBest early November · 40 checklists that week, 4,733 in all20%
  4. El Dorado CountyBest mid August · 473 checklists that week, 25,075 in all20%
  5. Shasta CountyBest the second week of March · 522 checklists that week, 31,369 in all19%
  6. Nevada CountyBest late October · 610 checklists that week, 25,896 in all17%

Best spots

Share of checklists at the peak
  1. American River ParkwaySacramento County, best late January · 39 checklists that week, 1,855 in all99%
  2. OrovilleButte County, best the second week of January · 23 checklists that week, 375 in all95%
  3. American River Parkway (west 2)Sacramento County, best the second week of March · 20 checklists that week, 633 in all92%
  4. Turtle Bay Bird SanctuaryShasta County, best late April · 21 checklists that week, 672 in all90%

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

Best time of day

In California, the Common Merganser is most often listed on checklists started between 1 and 3 pm (2.8% of those checklists).

0%1%2%3%12 am: too few checklists (1688) to judge1 am: too few checklists (1451) to judge2 am: too few checklists (1402) to judge3 am: too few checklists (1743) to judge4 am: too few checklists (4647) to judge5 am: too few checklists (32158) to judge6 am: 2.2% of 186053 checklists7 am: 2.6% of 444086 checklists8 am: 2.7% of 535846 checklists9 am: 2.7% of 486061 checklists10 am: 2.6% of 411130 checklists11 am: 2.6% of 325798 checklists12 pm: 2.6% of 269132 checklists1 pm: 2.8% of 244762 checklists2 pm: 2.8% of 235420 checklists3 pm: 2.6% of 232365 checklists4 pm: 2.3% of 208688 checklists5 pm: 1.7% of 146104 checklists6 pm: 1.5% of 96867 checklists7 pm: too few checklists (50942) to judge8 pm: too few checklists (14803) to judge9 pm: too few checklists (5561) to judge10 pm: too few checklists (3546) to judge11 pm: too few checklists (2092) 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
January3.9%3.9%4.1%4.4%
February4.2%4.0%3.5%3.8%
March4.0%3.6%3.4%3.1%
April2.8%2.8%2.5%2.3%
May2.1%2.0%1.9%1.9%
June1.6%1.7%1.8%1.7%
July1.7%1.5%1.5%1.5%
August1.6%1.6%1.5%1.7%
September1.7%1.8%1.8%1.6%
October1.4%1.5%1.6%1.7%
November1.9%2.1%2.2%2.6%
December2.8%2.7%2.9%3.1%

Neighboring states

  • Nevada: arrives early September, 6 weeks earlier than California
  • Utah: arrives mid September, 4 weeks earlier than California
  • Arizona: arrives late November, 5 weeks later than California
  • Oregon: arrives mid August, 8 weeks earlier than California

Common questions

When do Common Mergansers arrive in California?
Common Mergansers are winter birds in California: the first arrive in mid October, they are common by early November, peak in late January (4.3% of checklists), and most are gone by late May.
When do Common Mergansers leave California?
Most Common Mergansers have left California by late May, when reports fall below half their usual rate. Stragglers are still reported until the second week of July.
When is the best time to see a Common Merganser in California?
The Common Merganser is reported most often in late January, on about 4.3% of California checklists.
Where in California are Common Mergansers seen most often?
By county, Sierra County, Modoc County, and Amador County have the highest peak reporting rates for the Common Merganser (counties with at least 200 checklists).