WhenToBird

Chroicocephalus philadelphia · Laridae

When Do Bonaparte's Gulls Arrive in Wyoming?

Adult Bonaparte's Gull
Photo: Kevin Krebs, CC BY 4.0 via iNaturalist

Bonaparte's Gulls mostly pass through Wyoming: they arrive in early September, peak in early November (2.3% of checklists), and most are gone by early December.

When to look

First arrivalsSep 1-7early September
Common bySep 1-7early September
PeakNov 1-7early November
Most gone byDec 1-7early December

Best: early November. First arrivals early September; most are gone by early December. Peak: on about 2.3% of Wyoming checklists.

  1. Jannot usually seen
  2. Febnot usually seen
  3. Marrare
  4. Aprcommon
  5. Mayuncommon
  6. Junrare
  7. Julnot usually seen
  8. Augnot usually seen
  9. Seprare
  10. Octpeak season
  11. Novpeak season
  12. Decnot usually seen

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

0%1%2%3%Jan 1-7: 0% of 2543 checklistsJan 8-14: 0% of 2114 checklistsJan 15-21: 0% of 1984 checklistsJan 22-31: 0% of 2605 checklistsFeb 1-7: 0% of 1940 checklistsFeb 8-14: 0% of 1954 checklistsFeb 15-21: 0% of 2575 checklistsFeb 22-28: 0% of 1932 checklistsMar 1-7: 0% of 2486 checklistsMar 8-14: 0% of 2535 checklistsMar 15-21: 0% of 2726 checklistsMar 22-31: 0.1% of 4349 checklistsApr 1-7: 0.2% of 3300 checklistsApr 8-14: 0.2% of 3500 checklistsApr 15-21: 0.8% of 3701 checklistsApr 22-30: 1.0% of 5887 checklistsMay 1-7: 0.8% of 5341 checklistsMay 8-14: 0.5% of 6910 checklistsMay 15-21: 0.4% of 6884 checklistsMay 22-31: 0.3% of 10652 checklistsJun 1-7: 0.1% of 6807 checklistsJun 8-14: 0.1% of 6714 checklistsJun 15-21: 0% of 6708 checklistsJun 22-30: 0.1% 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: 0.1% of 4581 checklistsAug 8-14: 0.1% of 4625 checklistsAug 15-21: 0% of 4466 checklistsAug 22-31: 0.1% of 6562 checklistsSep 1-7: 0.1% of 4543 checklistsSep 8-14: 0.1% of 4652 checklistsSep 15-21: 0.2% of 4186 checklistsSep 22-30: 0.2% of 5301 checklistsOct 1-7: 0% of 3248 checklistsOct 8-14: 0.2% of 3010 checklistsOct 15-21: 1.0% of 2624 checklistsOct 22-31: 1.9% of 3170 checklistsNov 1-7: 2.9% of 2110 checklistsNov 8-14: 2.2% of 2153 checklistsNov 15-21: 1.2% of 1971 checklistsNov 22-30: 0.1% of 2136 checklistsDec 1-7: 0.1% of 1646 checklistsDec 8-14: 0% of 1609 checklistsDec 15-21: 0% of 1954 checklistsDec 22-31: 0% 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 all9.4%
  2. Natrona CountyBest the second week of November · 74 checklists that week, 5,810 in all7.0%
  3. Sweetwater CountyBest early November · 23 checklists that week, 5,064 in all6.9%
  4. Weston CountyBest mid November · 12 checklists that week, 2,297 in all6.8%
  5. Johnson CountyBest late October · 159 checklists that week, 5,977 in all6.7%
  6. Uinta CountyBest late October · 35 checklists that week, 1,881 in all6.3%

Best spots

Share of checklists at the peak
  1. State Lands 1111116182Natrona County, best late April · 44 checklists that week, 483 in all30%
  2. Saratoga LakeCarbon County, best late April · 28 checklists that week, 626 in all21%
  3. Lake de SmetJohnson County, best late October · 35 checklists that week, 435 in all21%
  4. Dry LakeFremont County, best the second week of November · 22 checklists that week, 276 in all20%
  5. Ray ReservoirFremont County, best late May · 21 checklists that week, 426 in all13%
  6. Twin Buttes LakeAlbany County, best early November · 41 checklists that week, 405 in all12%

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

Best time of day

In Wyoming, the Bonaparte's Gull is most often listed on checklists started between 4 and 6 pm (0.4% of those checklists).

0%0.5%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: 0.2% of 8808 checklists7 am: 0.2% of 18458 checklists8 am: 0.2% of 22143 checklists9 am: 0.2% of 21499 checklists10 am: 0.3% of 19425 checklists11 am: 0.3% of 16017 checklists12 pm: 0.4% of 13868 checklists1 pm: 0.3% of 12984 checklists2 pm: 0.3% of 12605 checklists3 pm: 0.3% of 11821 checklists4 pm: 0.4% of 10571 checklists5 pm: 0.4% of 8746 checklists6 pm: 0.2% 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%0%0%0%
February0%0%0%0%
March0%0%0%0.1%
April0.2%0.2%0.8%1.0%
May0.8%0.5%0.4%0.3%
June0.1%0.1%0%0.1%
July0%0%0%0%
August0.1%0.1%0%0.1%
September0.1%0.1%0.2%0.2%
October0%0.2%1.0%1.9%
November2.9%2.2%1.2%0.1%
December0.1%0%0%0%

Neighboring states

  • Colorado: arrives late September, 3 weeks later than Wyoming
  • Utah: arrives early October, 4 weeks later than Wyoming
  • Montana: arrives late July, 5 weeks earlier than Wyoming
  • Idaho: arrives early August, 4 weeks earlier than Wyoming

Common questions

When do Bonaparte's Gulls arrive in Wyoming?
Bonaparte's Gulls mostly pass through Wyoming: they arrive in early September, peak in early November (2.3% of checklists), and most are gone by early December.
When do Bonaparte's Gulls leave Wyoming?
Most Bonaparte's Gulls have left Wyoming by early December, when reports fall below half their usual rate.
When is the best time to see a Bonaparte's Gull in Wyoming?
The Bonaparte's Gull is reported most often in early November, on about 2.3% of Wyoming checklists.
Where in Wyoming are Bonaparte's Gulls seen most often?
By county, Carbon County, Natrona County, and Sweetwater County have the highest peak reporting rates for the Bonaparte's Gull (counties with at least 200 checklists).