WhenToBird

Setophaga castanea · Parulidae

When Do Bay-breasted Warblers Arrive in Wisconsin?

Adult Bay-breasted Warbler
Photo: Roger A. Morales-Flores, CC BY 4.0 via iNaturalist

Bay-breasted Warblers mostly pass through Wisconsin: they arrive in mid August, peak in the second week of September (7.0% of checklists), and most are gone by early October.

When to look

First arrivalsAug 15-21mid August
Common byAug 15-21mid August
PeakSep 8-14the second week of September
Most gone byOct 1-7early October

Best: the second week of September. First arrivals mid August; most are gone by early October. Peak: on about 7.0% of Wisconsin checklists.

  1. Jannot usually seen
  2. Febnot usually seen
  3. Marnot usually seen
  4. Aprnot usually seen
  5. Maycommon
  6. Jununcommon
  7. Julnot usually seen
  8. Augcommon
  9. Seppeak season
  10. Octuncommon
  11. Novnot usually seen
  12. Decnot usually seen

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

0%2%4%6%8%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% of 16656 checklistsFeb 8-14: 0% of 18286 checklistsFeb 15-21: 0% of 24739 checklistsFeb 22-28: 0% of 20113 checklistsMar 1-7: 0% of 24024 checklistsMar 8-14: 0% of 26722 checklistsMar 15-21: 0% of 27238 checklistsMar 22-31: 0% of 40171 checklistsApr 1-7: 0% of 34961 checklistsApr 8-14: 0% of 39128 checklistsApr 15-21: 0% of 38887 checklistsApr 22-30: 0.1% of 57231 checklistsMay 1-7: 0.3% of 55115 checklistsMay 8-14: 3.7% of 63098 checklistsMay 15-21: 6.8% of 49821 checklistsMay 22-31: 2.5% of 56796 checklistsJun 1-7: 0.1% of 33621 checklistsJun 8-14: 0.1% of 31282 checklistsJun 15-21: 0% of 30186 checklistsJun 22-30: 0% of 35128 checklistsJul 1-7: 0% of 27088 checklistsJul 8-14: 0% of 23293 checklistsJul 15-21: 0.1% of 20933 checklistsJul 22-31: 0.1% of 27595 checklistsAug 1-7: 0.1% of 19147 checklistsAug 8-14: 0.2% of 18286 checklistsAug 15-21: 1.3% of 19195 checklistsAug 22-31: 4.4% of 28229 checklistsSep 1-7: 7.1% of 22408 checklistsSep 8-14: 7.4% of 20857 checklistsSep 15-21: 6.6% of 20707 checklistsSep 22-30: 2.9% of 26469 checklistsOct 1-7: 0.7% of 21069 checklistsOct 8-14: 0.1% of 21011 checklistsOct 15-21: 0.1% of 20006 checklistsOct 22-31: 0.1% of 26362 checklistsNov 1-7: 0.1% of 18928 checklistsNov 8-14: 0% of 17052 checklistsNov 15-21: 0% of 16291 checklistsNov 22-30: 0% 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. Marquette CountyBest the second week of September · 66 checklists that week, 3,706 in all17%
  2. Dunn CountyBest the second week of September · 107 checklists that week, 8,247 in all14%
  3. Waushara CountyBest the second week of September · 70 checklists that week, 5,880 in all13%
  4. Milwaukee CountyBest the second week of September · 2082 checklists that week, 114,667 in all13%
  5. Green CountyBest early September · 61 checklists that week, 4,387 in all13%
  6. Calumet CountyBest mid May · 645 checklists that week, 12,359 in all13%

Best spots

Share of checklists at the peak
  1. Sheridan Park (south)Milwaukee County, best early September · 29 checklists that week, 349 in all65%
  2. Warnimont ParkMilwaukee County, best early September · 107 checklists that week, 2,226 in all55%
  3. Warnimont Park (south)Milwaukee County, best late August · 25 checklists that week, 300 in all53%
  4. Lake Kegonsa State ParkDane County, best the second week of September · 143 checklists that week, 3,030 in all53%
  5. Lakeshore PreserveDane County, best the second week of September · 85 checklists that week, 3,146 in all50%
  6. Weborg PointDoor County, best late May · 107 checklists that week, 868 in all48%

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

Best time of day

In Wisconsin, the Bay-breasted Warbler is most often listed on checklists started between 5 and 7 am (2.1% 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: 1.4% of 27016 checklists6 am: 2.3% of 83973 checklists7 am: 1.7% of 160717 checklists8 am: 1.5% of 160531 checklists9 am: 1.1% of 136968 checklists10 am: 0.9% of 119110 checklists11 am: 0.8% of 99116 checklists12 pm: 0.7% of 85078 checklists1 pm: 0.6% of 80688 checklists2 pm: 0.6% of 79140 checklists3 pm: 0.6% of 78599 checklists4 pm: 0.9% of 69767 checklists5 pm: 1.0% of 53229 checklists6 pm: 0.6% 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%0%0%0%
March0%0%0%0%
April0%0%0%0.1%
May0.3%3.7%6.8%2.5%
June0.1%0.1%0%0%
July0%0%0.1%0.1%
August0.1%0.2%1.3%4.4%
September7.1%7.4%6.6%2.9%
October0.7%0.1%0.1%0.1%
November0.1%0%0%0%
December0%0%0%0%

Neighboring states

  • Illinois: arrives mid August, in the same week than Wisconsin
  • Iowa: arrives mid August, in the same week than Wisconsin
  • Michigan: arrives the second week of August, 1 week earlier than Wisconsin
  • Minnesota: arrives mid August, in the same week than Wisconsin

Common questions

When do Bay-breasted Warblers arrive in Wisconsin?
Bay-breasted Warblers mostly pass through Wisconsin: they arrive in mid August, peak in the second week of September (7.0% of checklists), and most are gone by early October.
When do Bay-breasted Warblers leave Wisconsin?
Most Bay-breasted Warblers have left Wisconsin by early October, when reports fall below half their usual rate.
When is the best time to see a Bay-breasted Warbler in Wisconsin?
The Bay-breasted Warbler is reported most often in the second week of September, on about 7.0% of Wisconsin checklists.
Where in Wisconsin are Bay-breasted Warblers seen most often?
By county, Marquette County, Dunn County, and Waushara County have the highest peak reporting rates for the Bay-breasted Warbler (counties with at least 200 checklists).