WhenToBird

Mergus serrator · Anatidae

When Do Red-breasted Mergansers Arrive in Wyoming?

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

Red-breasted Mergansers are winter birds in Wyoming: they arrive in early October, peak in the second week of November (2.9% of checklists), and most are gone by the second week of December.

When to look

First arrivalsOct 1-7early October
Common byOct 1-7early October
PeakNov 8-14the second week of November
Most gone byDec 8-14the second week of December

Best: the second week of November. First arrivals early October; most are gone by the second week of December. Peak: on about 2.9% of Wyoming checklists.

  1. Janrare
  2. Febnot usually seen
  3. Marcommon
  4. Aprpeak season
  5. Maycommon
  6. Junnot usually seen
  7. Julnot usually seen
  8. Augnot usually seen
  9. Seprare
  10. Octcommon
  11. Novpeak season
  12. Decuncommon

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

0%1%2%3%4%Jan 1-7: 0.2% of 2543 checklistsJan 8-14: 0.1% of 2114 checklistsJan 15-21: 0.2% of 1984 checklistsJan 22-31: 0% of 2605 checklistsFeb 1-7: 0.1% of 1940 checklistsFeb 8-14: 0% of 1954 checklistsFeb 15-21: 0.1% of 2575 checklistsFeb 22-28: 0% of 1932 checklistsMar 1-7: 0.2% of 2486 checklistsMar 8-14: 0.1% of 2535 checklistsMar 15-21: 0.4% of 2726 checklistsMar 22-31: 0.9% of 4349 checklistsApr 1-7: 2.1% of 3300 checklistsApr 8-14: 2.1% of 3500 checklistsApr 15-21: 2.4% of 3701 checklistsApr 22-30: 2.4% of 5887 checklistsMay 1-7: 0.8% of 5341 checklistsMay 8-14: 0.4% of 6910 checklistsMay 15-21: 0.1% of 6884 checklistsMay 22-31: 0.1% of 10652 checklistsJun 1-7: 0% of 6807 checklistsJun 8-14: 0.1% of 6714 checklistsJun 15-21: 0% of 6708 checklistsJun 22-30: 0% of 8160 checklistsJul 1-7: 0% of 5755 checklistsJul 8-14: 0% of 5379 checklistsJul 15-21: 0% of 5299 checklistsJul 22-31: 0% of 6830 checklistsAug 1-7: 0% of 4581 checklistsAug 8-14: 0% of 4625 checklistsAug 15-21: 0.1% of 4466 checklistsAug 22-31: 0.1% of 6562 checklistsSep 1-7: 0% of 4543 checklistsSep 8-14: 0.1% of 4652 checklistsSep 15-21: 0.1% of 4186 checklistsSep 22-30: 0.2% of 5301 checklistsOct 1-7: 0.2% of 3248 checklistsOct 8-14: 0.6% of 3010 checklistsOct 15-21: 0.6% of 2624 checklistsOct 22-31: 1.8% of 3170 checklistsNov 1-7: 2.8% of 2110 checklistsNov 8-14: 3.3% of 2153 checklistsNov 15-21: 2.3% of 1971 checklistsNov 22-30: 1.1% of 2136 checklistsDec 1-7: 0.8% of 1646 checklistsDec 8-14: 0.3% of 1609 checklistsDec 15-21: 0.2% of 1954 checklistsDec 22-31: 0.1% of 2392 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 Wyoming 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 Wyoming

Best counties

Share of checklists at the peak
  1. Carbon CountyBest the second week of November · 42 checklists that week, 6,429 in all20%
  2. Platte CountyBest mid November · 34 checklists that week, 1,645 in all15%
  3. Natrona CountyBest the second week of November · 74 checklists that week, 5,810 in all10%
  4. Sweetwater CountyBest early November · 23 checklists that week, 5,064 in all7.8%
  5. Lincoln CountyBest early November · 22 checklists that week, 3,169 in all7.2%
  6. Weston CountyBest mid April · 39 checklists that week, 2,297 in all6.7%

Best spots

Share of checklists at the peak
  1. Lake Hattie ReservoirAlbany County, best mid November · 39 checklists that week, 476 in all35%
  2. Alkali LakePark County, best the second week of April · 20 checklists that week, 722 in all35%
  3. State Lands 1111116182Natrona County, best late April · 44 checklists that week, 483 in all34%
  4. Wyoming Hereford Ranch Reservoir Number OneLaramie County, best mid April · 33 checklists that week, 1,242 in all28%
  5. Ray Reservoir (Ray Lake)Fremont County, best the second week of April · 20 checklists that week, 277 in all27%
  6. Dry LakeFremont County, best the second week of November · 22 checklists that week, 276 in all26%

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

Best time of day

In Wyoming, the Red-breasted Merganser is most often listed on checklists started between 1 and 3 pm (0.6% of those checklists).

0%0.5%1%12 am: too few checklists (59) to judge1 am: too few checklists (76) to judge2 am: too few checklists (86) to judge3 am: too few checklists (79) to judge4 am: too few checklists (326) to judge5 am: too few checklists (2271) to judge6 am: 0.3% of 8808 checklists7 am: 0.4% of 18458 checklists8 am: 0.4% of 22143 checklists9 am: 0.4% of 21499 checklists10 am: 0.6% of 19425 checklists11 am: 0.7% of 16017 checklists12 pm: 0.5% of 13868 checklists1 pm: 0.5% of 12984 checklists2 pm: 0.7% of 12605 checklists3 pm: 0.5% of 11821 checklists4 pm: 0.4% of 10571 checklists5 pm: 0.2% of 8746 checklists6 pm: 0.3% of 6707 checklists7 pm: 0.1% of 4890 checklists8 pm: too few checklists (2323) to judge9 pm: too few checklists (554) to judge10 pm: too few checklists (134) to judge11 pm: too few checklists (59) 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
January0.2%0.1%0.2%0%
February0.1%0%0.1%0%
March0.2%0.1%0.4%0.9%
April2.1%2.1%2.4%2.4%
May0.8%0.4%0.1%0.1%
June0%0.1%0%0%
July0%0%0%0%
August0%0%0.1%0.1%
September0%0.1%0.1%0.2%
October0.2%0.6%0.6%1.8%
November2.8%3.3%2.3%1.1%
December0.8%0.3%0.2%0.1%

Neighboring states

  • Colorado: arrives late October, 3 weeks later than Wyoming
  • Utah: arrives late February, 19 weeks later than Wyoming
  • Montana: arrives late February, 19 weeks later than Wyoming
  • Idaho: arrives mid October, 2 weeks later than Wyoming

Common questions

When do Red-breasted Mergansers arrive in Wyoming?
Red-breasted Mergansers are winter birds in Wyoming: they arrive in early October, peak in the second week of November (2.9% of checklists), and most are gone by the second week of December.
When do Red-breasted Mergansers leave Wyoming?
Most Red-breasted Mergansers have left Wyoming by the second week of December, when reports fall below half their usual rate.
When is the best time to see a Red-breasted Merganser in Wyoming?
The Red-breasted Merganser is reported most often in the second week of November, on about 2.9% of Wyoming checklists.
Where in Wyoming are Red-breasted Mergansers seen most often?
By county, Carbon County, Platte County, and Natrona County have the highest peak reporting rates for the Red-breasted Merganser (counties with at least 200 checklists).