WhenToBird

Chroicocephalus philadelphia · Laridae

When Do Bonaparte's Gulls Arrive in Wisconsin?

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

Bonaparte's Gulls mostly pass through Wisconsin: they arrive in late March, peak in mid April (6.0% of checklists), and most are gone by late November.

When to look

First arrivalsMar 22-31late March
Common byMar 22-31late March
PeakApr 15-21mid April
Most gone byNov 22-30late November

Best: mid April. First arrivals late March; most are gone by late November. Peak: on about 6.0% of Wisconsin checklists.

  1. Jannot usually seen
  2. Febnot usually seen
  3. Maruncommon
  4. Aprpeak season
  5. Maycommon
  6. Jununcommon
  7. Julrare
  8. Augrare
  9. Sepuncommon
  10. Octuncommon
  11. Novcommon
  12. Decrare

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

0%2%4%6%8%Jan 1-7: 0.1% of 27925 checklistsJan 8-14: 0.1% of 18337 checklistsJan 15-21: 0% of 17370 checklistsJan 22-31: 0% of 23777 checklistsFeb 1-7: 0% of 16656 checklistsFeb 8-14: 0% of 18286 checklistsFeb 15-21: 0% of 24739 checklistsFeb 22-28: 0% of 20113 checklistsMar 1-7: 0.1% of 24024 checklistsMar 8-14: 0.1% of 26722 checklistsMar 15-21: 0.1% of 27238 checklistsMar 22-31: 1.0% of 40171 checklistsApr 1-7: 3.0% of 34961 checklistsApr 8-14: 5.3% of 39128 checklistsApr 15-21: 6.9% of 38887 checklistsApr 22-30: 5.9% of 57231 checklistsMay 1-7: 3.0% of 55115 checklistsMay 8-14: 1.2% of 63098 checklistsMay 15-21: 1.4% of 49821 checklistsMay 22-31: 1.7% of 56796 checklistsJun 1-7: 1.1% of 33621 checklistsJun 8-14: 0.8% of 31282 checklistsJun 15-21: 0.7% of 30186 checklistsJun 22-30: 0.8% of 35128 checklistsJul 1-7: 0.6% of 27088 checklistsJul 8-14: 0.7% of 23293 checklistsJul 15-21: 0.6% of 20933 checklistsJul 22-31: 0.6% of 27595 checklistsAug 1-7: 0.7% of 19147 checklistsAug 8-14: 0.6% of 18286 checklistsAug 15-21: 0.8% of 19195 checklistsAug 22-31: 0.7% of 28229 checklistsSep 1-7: 0.5% of 22408 checklistsSep 8-14: 0.7% of 20857 checklistsSep 15-21: 1.4% of 20707 checklistsSep 22-30: 1.2% of 26469 checklistsOct 1-7: 0.9% of 21069 checklistsOct 8-14: 1.1% of 21011 checklistsOct 15-21: 1.9% of 20006 checklistsOct 22-31: 2.5% of 26362 checklistsNov 1-7: 2.7% of 18928 checklistsNov 8-14: 2.3% of 17052 checklistsNov 15-21: 1.4% of 16291 checklistsNov 22-30: 0.7% of 20564 checklistsDec 1-7: 0.3% of 15354 checklistsDec 8-14: 0.2% of 16294 checklistsDec 15-21: 0.1% of 21430 checklistsDec 22-31: 0.1% of 26314 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 Wisconsin 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 Wisconsin

Best counties

Share of checklists at the peak
  1. Columbia CountyBest mid April · 631 checklists that week, 15,761 in all23%
  2. Douglas CountyBest mid September · 816 checklists that week, 14,015 in all20%
  3. Kewaunee CountyBest mid April · 309 checklists that week, 9,747 in all18%
  4. Manitowoc CountyBest late May · 1357 checklists that week, 26,017 in all17%
  5. Ashland CountyBest late October · 464 checklists that week, 16,576 in all16%
  6. Sheboygan CountyBest early June · 706 checklists that week, 25,419 in all14%

Best spots

Share of checklists at the peak
  1. South Side Memorial BeachSheboygan County, best the second week of June · 35 checklists that week, 231 in all85%
  2. Manitowoc Small Boat HarborManitowoc County, best late May · 240 checklists that week, 2,200 in all81%
  3. North Point ParkSheboygan County, best mid June · 32 checklists that week, 1,755 in all79%

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

Best time of day

In Wisconsin, the Bonaparte's Gull is most often listed on checklists started between 1 and 3 pm (1.7% of those checklists).

0%0.5%1%1.5%2%12 am: too few checklists (993) to judge1 am: too few checklists (844) to judge2 am: too few checklists (839) to judge3 am: too few checklists (1488) to judge4 am: too few checklists (5344) to judge5 am: 0.9% of 27016 checklists6 am: 1.5% of 83973 checklists7 am: 1.3% of 160717 checklists8 am: 1.3% of 160531 checklists9 am: 1.5% of 136968 checklists10 am: 1.5% of 119110 checklists11 am: 1.6% of 99116 checklists12 pm: 1.7% of 85078 checklists1 pm: 1.7% of 80688 checklists2 pm: 1.8% of 79140 checklists3 pm: 1.7% of 78599 checklists4 pm: 1.7% of 69767 checklists5 pm: 1.7% of 53229 checklists6 pm: 1.7% of 38769 checklists7 pm: too few checklists (24396) to judge8 pm: too few checklists (10155) to judge9 pm: too few checklists (4990) to judge10 pm: too few checklists (2463) to judge11 pm: too few checklists (1281) 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
January0.1%0.1%0%0%
February0%0%0%0%
March0.1%0.1%0.1%1.0%
April3.0%5.3%6.9%5.9%
May3.0%1.2%1.4%1.7%
June1.1%0.8%0.7%0.8%
July0.6%0.7%0.6%0.6%
August0.7%0.6%0.8%0.7%
September0.5%0.7%1.4%1.2%
October0.9%1.1%1.9%2.5%
November2.7%2.3%1.4%0.7%
December0.3%0.2%0.1%0.1%

Neighboring states

  • Illinois: arrives early October, 23 weeks earlier than Wisconsin
  • Iowa: arrives mid September, 23 weeks later than Wisconsin
  • Michigan: arrives late July, 16 weeks later than Wisconsin
  • Minnesota: arrives early April, 1 week later than Wisconsin

Common questions

When do Bonaparte's Gulls arrive in Wisconsin?
Bonaparte's Gulls mostly pass through Wisconsin: they arrive in late March, peak in mid April (6.0% of checklists), and most are gone by late November.
When do Bonaparte's Gulls leave Wisconsin?
Most Bonaparte's Gulls have left Wisconsin by late November, when reports fall below half their usual rate.
When is the best time to see a Bonaparte's Gull in Wisconsin?
The Bonaparte's Gull is reported most often in mid April, on about 6.0% of Wisconsin checklists.
Where in Wisconsin are Bonaparte's Gulls seen most often?
By county, Columbia County, Douglas County, and Kewaunee County have the highest peak reporting rates for the Bonaparte's Gull (counties with at least 200 checklists).