WhenToBird

Mergus serrator · Anatidae

When Do Red-breasted Mergansers Arrive in California?

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

Red-breasted Mergansers are winter birds in California: the first arrive in early November, they are common by the second week of November, peak in early December (3.4% of checklists), and most are gone by early April.

When to look

First arrivalsNov 1-7early November
Common byNov 8-14the second week of November
PeakDec 1-7early December
Most gone byApr 1-7early April

Best: early December. First arrivals early November; most are gone by early April. Peak: on about 3.4% of California checklists.

  1. Janpeak season
  2. Febpeak season
  3. Marpeak season
  4. Aprcommon
  5. Mayuncommon
  6. Junrare
  7. Julrare
  8. Augrare
  9. Seprare
  10. Octrare
  11. Novpeak season
  12. Decpeak season

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

0%1%2%3%4%Jan 1-7: 3.3% of 112336 checklistsJan 8-14: 3.5% of 85518 checklistsJan 15-21: 3.6% of 86488 checklistsJan 22-31: 3.0% of 116174 checklistsFeb 1-7: 2.8% of 75171 checklistsFeb 8-14: 2.6% of 84467 checklistsFeb 15-21: 2.4% of 105683 checklistsFeb 22-28: 3.1% of 83396 checklistsMar 1-7: 2.8% of 77470 checklistsMar 8-14: 2.6% of 75180 checklistsMar 15-21: 2.4% of 80770 checklistsMar 22-31: 2.1% of 114116 checklistsApr 1-7: 1.7% of 84057 checklistsApr 8-14: 1.4% of 83692 checklistsApr 15-21: 1.1% of 89242 checklistsApr 22-30: 1.0% of 114289 checklistsMay 1-7: 0.7% of 85728 checklistsMay 8-14: 0.5% of 91984 checklistsMay 15-21: 0.4% of 75478 checklistsMay 22-31: 0.3% of 106250 checklistsJun 1-7: 0.2% of 70051 checklistsJun 8-14: 0.2% of 67485 checklistsJun 15-21: 0.2% of 66269 checklistsJun 22-30: 0.2% of 79172 checklistsJul 1-7: 0.2% of 62877 checklistsJul 8-14: 0.2% of 60328 checklistsJul 15-21: 0.2% of 59705 checklistsJul 22-31: 0.2% of 83796 checklistsAug 1-7: 0.2% of 60215 checklistsAug 8-14: 0.2% of 60172 checklistsAug 15-21: 0.2% of 59877 checklistsAug 22-31: 0.2% of 89107 checklistsSep 1-7: 0.2% of 72000 checklistsSep 8-14: 0.1% of 71228 checklistsSep 15-21: 0.1% of 76808 checklistsSep 22-30: 0.1% of 100204 checklistsOct 1-7: 0.1% of 76571 checklistsOct 8-14: 0.1% of 80874 checklistsOct 15-21: 0.2% of 74581 checklistsOct 22-31: 0.3% of 97498 checklistsNov 1-7: 1.0% of 70851 checklistsNov 8-14: 2.2% of 72431 checklistsNov 15-21: 2.9% of 66767 checklistsNov 22-30: 3.5% of 94737 checklistsDec 1-7: 3.6% of 65393 checklistsDec 8-14: 3.3% of 67449 checklistsDec 15-21: 2.5% 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. Monterey CountyBest early December · 2617 checklists that week, 132,505 in all20%
  2. Del Norte CountyBest early March · 175 checklists that week, 16,363 in all16%
  3. San Luis Obispo CountyBest mid January · 4602 checklists that week, 124,667 in all9.5%
  4. Orange CountyBest early December · 4345 checklists that week, 244,559 in all6.9%
  5. Humboldt CountyBest the second week of March · 1452 checklists that week, 95,963 in all6.7%
  6. Marin CountyBest late January · 3954 checklists that week, 135,728 in all6.4%

Best spots

Share of checklists at the peak
  1. Golden Gate National Recreation AreaSan Francisco County, best mid January · 140 checklists that week, 5,715 in all82%
  2. Bolsa Chica Ecological ReserveOrange County, best mid February · 171 checklists that week, 7,437 in all80%
  3. Buhne PointHumboldt County, best late March · 28 checklists that week, 1,048 in all79%
  4. Estero Bluffs State Park (Cayucos Point)San Luis Obispo County, best mid January · 81 checklists that week, 1,270 in all77%

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

Best time of day

In California, the Red-breasted Merganser is most often listed on checklists started between 1 and 3 pm (1.8% of those checklists).

0%0.5%1%1.5%2%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: 1.1% of 186053 checklists7 am: 1.4% of 444086 checklists8 am: 1.6% of 535846 checklists9 am: 1.6% of 486061 checklists10 am: 1.7% of 411130 checklists11 am: 1.7% of 325798 checklists12 pm: 1.7% of 269132 checklists1 pm: 1.8% of 244762 checklists2 pm: 1.8% of 235420 checklists3 pm: 1.7% of 232365 checklists4 pm: 1.1% of 208688 checklists5 pm: 0.6% of 146104 checklists6 pm: 0.4% 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
January3.3%3.5%3.6%3.0%
February2.8%2.6%2.4%3.1%
March2.8%2.6%2.4%2.1%
April1.7%1.4%1.1%1.0%
May0.7%0.5%0.4%0.3%
June0.2%0.2%0.2%0.2%
July0.2%0.2%0.2%0.2%
August0.2%0.2%0.2%0.2%
September0.2%0.1%0.1%0.1%
October0.1%0.1%0.2%0.3%
November1.0%2.2%2.9%3.5%
December3.6%3.3%2.5%3.1%

Neighboring states

  • Nevada: arrives early November, in the same week than California
  • Utah: arrives late February, 15 weeks later than California
  • Oregon: arrives late October, 1 week earlier than California
  • Idaho: arrives mid October, 2 weeks earlier than California

Common questions

When do Red-breasted Mergansers arrive in California?
Red-breasted Mergansers are winter birds in California: the first arrive in early November, they are common by the second week of November, peak in early December (3.4% of checklists), and most are gone by early April.
When do Red-breasted Mergansers leave California?
Most Red-breasted Mergansers have left California by early April, when reports fall below half their usual rate. Stragglers are still reported until mid April.
When is the best time to see a Red-breasted Merganser in California?
The Red-breasted Merganser is reported most often in early December, on about 3.4% of California checklists.
Where in California are Red-breasted Mergansers seen most often?
By county, Monterey County, Del Norte County, and San Luis Obispo County have the highest peak reporting rates for the Red-breasted Merganser (counties with at least 200 checklists).