WhenToBird

Botaurus lentiginosus · Ardeidae

When Do American Bitterns Arrive in Wisconsin?

Adult American Bittern
Photo: Kathy Richardson, CC BY 4.0 via iNaturalist

American Bitterns arrive in Wisconsin in mid April, peak in late May (1.6% of checklists), and most are gone by early September.

When to look

First arrivalsApr 15-21mid April
Common byApr 15-21mid April
PeakMay 22-31late May
Most gone bySep 1-7early September

Best: late May. First arrivals mid April; most are gone by early September. Peak: on about 1.6% of Wisconsin checklists.

  1. Jannot usually seen
  2. Febnot usually seen
  3. Marnot usually seen
  4. Aprcommon
  5. Maypeak season
  6. Junpeak season
  7. Julcommon
  8. Augcommon
  9. Sepuncommon
  10. Octrare
  11. Novnot usually seen
  12. Decnot usually seen

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

0%0.5%1%1.5%2%Jan 1-7: 0% of 27925 checklistsJan 8-14: 0% of 18337 checklistsJan 15-21: 0% of 17370 checklistsJan 22-31: 0% of 23777 checklistsFeb 1-7: 0.1% of 16656 checklistsFeb 8-14: 0.1% of 18286 checklistsFeb 15-21: 0% of 24739 checklistsFeb 22-28: 0.1% of 20113 checklistsMar 1-7: 0% of 24024 checklistsMar 8-14: 0% of 26722 checklistsMar 15-21: 0% of 27238 checklistsMar 22-31: 0.1% of 40171 checklistsApr 1-7: 0.1% of 34961 checklistsApr 8-14: 0.3% of 39128 checklistsApr 15-21: 0.7% of 38887 checklistsApr 22-30: 1.1% of 57231 checklistsMay 1-7: 1.6% of 55115 checklistsMay 8-14: 1.4% of 63098 checklistsMay 15-21: 1.5% of 49821 checklistsMay 22-31: 1.6% of 56796 checklistsJun 1-7: 1.6% of 33621 checklistsJun 8-14: 1.1% of 31282 checklistsJun 15-21: 1.1% of 30186 checklistsJun 22-30: 0.9% of 35128 checklistsJul 1-7: 1.0% of 27088 checklistsJul 8-14: 0.9% of 23293 checklistsJul 15-21: 0.9% of 20933 checklistsJul 22-31: 0.9% of 27595 checklistsAug 1-7: 0.8% of 19147 checklistsAug 8-14: 1.0% of 18286 checklistsAug 15-21: 0.8% of 19195 checklistsAug 22-31: 0.6% of 28229 checklistsSep 1-7: 0.4% of 22408 checklistsSep 8-14: 0.4% of 20857 checklistsSep 15-21: 0.4% of 20707 checklistsSep 22-30: 0.3% of 26469 checklistsOct 1-7: 0.2% of 21069 checklistsOct 8-14: 0.1% of 21011 checklistsOct 15-21: 0.3% of 20006 checklistsOct 22-31: 0.1% of 26362 checklistsNov 1-7: 0.1% of 18928 checklistsNov 8-14: 0.1% of 17052 checklistsNov 15-21: 0% of 16291 checklistsNov 22-30: 0.1% of 20564 checklistsDec 1-7: 0% of 15354 checklistsDec 8-14: 0% of 16294 checklistsDec 15-21: 0% of 21430 checklistsDec 22-31: 0% 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. Dodge CountyBest the second week of June · 1051 checklists that week, 34,980 in all12%
  2. Marquette CountyBest early May · 136 checklists that week, 3,706 in all8.6%
  3. Iron CountyBest the second week of May · 251 checklists that week, 5,981 in all7.8%
  4. Vilas CountyBest the second week of May · 633 checklists that week, 16,082 in all7.8%
  5. Green Lake CountyBest the second week of May · 691 checklists that week, 15,345 in all7.2%
  6. Florence CountyBest early May · 268 checklists that week, 10,179 in all7.1%

Best spots

Share of checklists at the peak
  1. Powell Marsh Wildlife AreaVilas County, best the second week of July · 24 checklists that week, 480 in all70%
  2. White River Marsh Wildlife AreaGreen Lake County, best late May · 22 checklists that week, 174 in all53%
  3. Humboldt ParkMilwaukee County, best mid October · 41 checklists that week, 919 in all46%
  4. Horicon National Wildlife Refuge (Stony Island)Dodge County, best the second week of May · 33 checklists that week, 1,653 in all45%
  5. South Rice LakeMarathon County, best mid July · 20 checklists that week, 534 in all43%
  6. Main FlowageMarathon County, best late May · 26 checklists that week, 276 in all42%

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

Best time of day

In Wisconsin, the American Bittern is most often listed on checklists started between 5 and 7 am (1.5% of those checklists).

0%1%2%3%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: 2.8% of 27016 checklists6 am: 1.1% of 83973 checklists7 am: 0.6% of 160717 checklists8 am: 0.4% of 160531 checklists9 am: 0.5% of 136968 checklists10 am: 0.4% of 119110 checklists11 am: 0.4% of 99116 checklists12 pm: 0.3% of 85078 checklists1 pm: 0.4% of 80688 checklists2 pm: 0.3% of 79140 checklists3 pm: 0.3% of 78599 checklists4 pm: 0.5% of 69767 checklists5 pm: 0.8% of 53229 checklists6 pm: 1.2% 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%0%0%0%
February0.1%0.1%0%0.1%
March0%0%0%0.1%
April0.1%0.3%0.7%1.1%
May1.6%1.4%1.5%1.6%
June1.6%1.1%1.1%0.9%
July1.0%0.9%0.9%0.9%
August0.8%1.0%0.8%0.6%
September0.4%0.4%0.4%0.3%
October0.2%0.1%0.3%0.1%
November0.1%0.1%0%0.1%
December0%0%0%0%

Neighboring states

  • Michigan: arrives mid April, in the same week than Wisconsin
  • Kansas: arrives early April, 2 weeks earlier than Wisconsin
  • South Dakota: arrives mid April, in the same week than Wisconsin
  • North Dakota: arrives early May, 2 weeks later than Wisconsin

Common questions

When do American Bitterns arrive in Wisconsin?
American Bitterns arrive in Wisconsin in mid April, peak in late May (1.6% of checklists), and most are gone by early September.
When do American Bitterns leave Wisconsin?
Most American Bitterns have left Wisconsin by early September, when reports fall below half their usual rate.
When is the best time to see a American Bittern in Wisconsin?
The American Bittern is reported most often in late May, on about 1.6% of Wisconsin checklists.
Where in Wisconsin are American Bitterns seen most often?
By county, Dodge County, Marquette County, and Iron County have the highest peak reporting rates for the American Bittern (counties with at least 200 checklists).