WhenToBird

Setophaga castanea · Parulidae

When Do Bay-breasted Warblers Arrive in Illinois?

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

Bay-breasted Warblers mostly pass through Illinois: they arrive in mid August, peak in the second week of September (13% 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 13% of Illinois checklists.

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

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

0%5%10%15%20%Jan 1-7: 0% of 29700 checklistsJan 8-14: 0% of 20189 checklistsJan 15-21: 0% of 19784 checklistsJan 22-31: 0% of 26641 checklistsFeb 1-7: 0% of 20478 checklistsFeb 8-14: 0% of 21967 checklistsFeb 15-21: 0% of 28735 checklistsFeb 22-28: 0% of 24223 checklistsMar 1-7: 0% of 26775 checklistsMar 8-14: 0% of 27579 checklistsMar 15-21: 0% of 27193 checklistsMar 22-31: 0% of 42278 checklistsApr 1-7: 0% of 34579 checklistsApr 8-14: 0% of 38290 checklistsApr 15-21: 0% of 39261 checklistsApr 22-30: 0.1% of 59584 checklistsMay 1-7: 1.0% of 60485 checklistsMay 8-14: 5.9% of 59647 checklistsMay 15-21: 11% of 43173 checklistsMay 22-31: 4.2% of 47913 checklistsJun 1-7: 0.1% of 31151 checklistsJun 8-14: 0.1% of 27692 checklistsJun 15-21: 0% of 23983 checklistsJun 22-30: 0% of 28448 checklistsJul 1-7: 0% of 21273 checklistsJul 8-14: 0% of 19284 checklistsJul 15-21: 0% of 17712 checklistsJul 22-31: 0% of 24500 checklistsAug 1-7: 0.1% of 18498 checklistsAug 8-14: 0.2% of 19331 checklistsAug 15-21: 1.7% of 19983 checklistsAug 22-31: 5.0% of 31892 checklistsSep 1-7: 10% of 26396 checklistsSep 8-14: 14% of 25011 checklistsSep 15-21: 16% of 23597 checklistsSep 22-30: 9.9% of 30638 checklistsOct 1-7: 5.0% of 23949 checklistsOct 8-14: 1.0% of 24412 checklistsOct 15-21: 0.1% of 22359 checklistsOct 22-31: 0.1% of 29794 checklistsNov 1-7: 0.1% of 21877 checklistsNov 8-14: 0.1% of 19742 checklistsNov 15-21: 0.1% of 18989 checklistsNov 22-30: 0.1% of 23905 checklistsDec 1-7: 0% of 16935 checklistsDec 8-14: 0% of 16687 checklistsDec 15-21: 0% of 20931 checklistsDec 22-31: 0% of 29011 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 Illinois 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 Illinois

Best counties

Share of checklists at the peak
  1. Livingston CountyBest the second week of September · 13 checklists that week, 1,092 in all41%
  2. Piatt CountyBest mid September · 58 checklists that week, 4,640 in all41%
  3. Cass CountyBest the second week of September · 15 checklists that week, 1,262 in all36%
  4. Montgomery CountyBest the second week of September · 17 checklists that week, 1,054 in all34%
  5. Whiteside CountyBest the second week of September · 82 checklists that week, 4,111 in all34%
  6. Jasper CountyBest mid September · 17 checklists that week, 1,292 in all33%

Best spots

Share of checklists at the peak
  1. Black Hawk Forest Nature PreserveRock Island County, best the second week of September · 24 checklists that week, 574 in all57%
  2. Douglas Hart Nature CenterColes County, best the second week of September · 32 checklists that week, 823 in all55%
  3. Chicago Women's Park and GardensCook County, best the second week of September · 23 checklists that week, 555 in all55%
  4. Saw Wee Kee ParkKendall County, best the second week of September · 27 checklists that week, 1,327 in all54%
  5. Fox Ridge State ParkColes County, best the second week of September · 28 checklists that week, 1,010 in all51%

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

Best time of day

In Illinois, the Bay-breasted Warbler is most often listed on checklists started between 6 and 8 am (3.6% of those checklists).

0%1%2%3%4%12 am: too few checklists (484) to judge1 am: too few checklists (631) to judge2 am: too few checklists (485) to judge3 am: too few checklists (610) to judge4 am: too few checklists (2321) to judge5 am: too few checklists (23536) to judge6 am: 3.8% of 95511 checklists7 am: 3.4% of 164584 checklists8 am: 2.6% of 163654 checklists9 am: 2.0% of 141804 checklists10 am: 1.6% of 122882 checklists11 am: 1.4% of 100640 checklists12 pm: 1.3% of 89894 checklists1 pm: 1.2% of 82729 checklists2 pm: 1.1% of 79801 checklists3 pm: 1.2% of 82169 checklists4 pm: 1.5% of 75124 checklists5 pm: 1.7% of 57708 checklists6 pm: 1.0% of 41843 checklists7 pm: too few checklists (20943) to judge8 pm: too few checklists (6131) to judge9 pm: too few checklists (1677) to judge10 pm: too few checklists (843) to judge11 pm: too few checklists (448) 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%
May1.0%5.9%11%4.2%
June0.1%0.1%0%0%
July0%0%0%0%
August0.1%0.2%1.7%5.0%
September10%14%16%9.9%
October5.0%1.0%0.1%0.1%
November0.1%0.1%0.1%0.1%
December0%0%0%0%

Neighboring states

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

Common questions

When do Bay-breasted Warblers arrive in Illinois?
Bay-breasted Warblers mostly pass through Illinois: they arrive in mid August, peak in the second week of September (13% of checklists), and most are gone by early October.
When do Bay-breasted Warblers leave Illinois?
Most Bay-breasted Warblers have left Illinois by early October, when reports fall below half their usual rate. Stragglers are still reported until the second week of October.
When is the best time to see a Bay-breasted Warbler in Illinois?
The Bay-breasted Warbler is reported most often in the second week of September, on about 13% of Illinois checklists.
Where in Illinois are Bay-breasted Warblers seen most often?
By county, Livingston County, Piatt County, and Cass County have the highest peak reporting rates for the Bay-breasted Warbler (counties with at least 200 checklists).