WhenToBird

Setophaga pensylvanica · Parulidae

When Do Chestnut-sided Warblers Arrive in Illinois?

Adult male Chestnut-sided Warbler
Photo: Matt Felperin, CC BY 4.0 via iNaturalist

Chestnut-sided Warblers mostly pass through Illinois: the first show up in late April, they are common by early May, peak in mid May (15% of checklists), and most are gone by early June.

When to look

First arrivalsApr 22-30late April
Common byMay 1-7early May
PeakMay 15-21mid May
Most gone byJun 1-7early June

Best: mid May. First arrivals late April; most are gone by early June. Peak: on about 15% of Illinois checklists.

  1. Jannot usually seen
  2. Febnot usually seen
  3. Marnot usually seen
  4. Aprrare
  5. Maypeak season
  6. Jununcommon
  7. Julnot usually seen
  8. Auguncommon
  9. Sepcommon
  10. Octuncommon
  11. Novnot usually seen
  12. Decnot usually seen

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

0%10%20%30%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: 0.1% of 39261 checklistsApr 22-30: 0.3% of 59584 checklistsMay 1-7: 4.6% of 60485 checklistsMay 8-14: 16% of 59647 checklistsMay 15-21: 21% of 43173 checklistsMay 22-31: 8.5% of 47913 checklistsJun 1-7: 0.8% of 31151 checklistsJun 8-14: 0.4% of 27692 checklistsJun 15-21: 0.3% of 23983 checklistsJun 22-30: 0.2% of 28448 checklistsJul 1-7: 0.2% of 21273 checklistsJul 8-14: 0.1% of 19284 checklistsJul 15-21: 0.1% of 17712 checklistsJul 22-31: 0.1% of 24500 checklistsAug 1-7: 0.1% of 18498 checklistsAug 8-14: 0.2% of 19331 checklistsAug 15-21: 1.1% of 19983 checklistsAug 22-31: 6.1% of 31892 checklistsSep 1-7: 9.3% of 26396 checklistsSep 8-14: 11% of 25011 checklistsSep 15-21: 9.7% of 23597 checklistsSep 22-30: 7.3% of 30638 checklistsOct 1-7: 2.5% of 23949 checklistsOct 8-14: 0.2% of 24412 checklistsOct 15-21: 0.1% of 22359 checklistsOct 22-31: 0.1% of 29794 checklistsNov 1-7: 0% of 21877 checklistsNov 8-14: 0% of 19742 checklistsNov 15-21: 0% of 18989 checklistsNov 22-30: 0% 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. Richland CountyBest late September · 11 checklists that week, 580 in all48%
  2. Edwards CountyBest the second week of September · 25 checklists that week, 797 in all43%
  3. Montgomery CountyBest the second week of September · 17 checklists that week, 1,054 in all39%
  4. Wayne CountyBest early September · 22 checklists that week, 394 in all38%
  5. Wabash CountyBest the second week of September · 15 checklists that week, 602 in all37%
  6. Logan CountyBest the second week of September · 25 checklists that week, 1,522 in all37%

Best spots

Share of checklists at the peak
  1. Black Hawk Forest Nature PreserveRock Island County, best late August · 28 checklists that week, 574 in all74%
  2. Ewing IiiMcLean County, best early September · 74 checklists that week, 2,378 in all62%
  3. Steward ParkKendall County, best late August · 33 checklists that week, 788 in all59%
  4. Dead LakeLake County, best late May · 112 checklists that week, 1,516 in all57%
  5. La Bagh WoodsCook County, best mid May · 571 checklists that week, 6,086 in all54%
  6. Skokie Lagoons (Crow Island)Cook County, best mid May · 238 checklists that week, 3,351 in all52%

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

Best time of day

In Illinois, the Chestnut-sided Warbler is most often listed on checklists started between 6 and 8 am (5.0% of those checklists).

0%2%4%6%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: 5.7% of 95511 checklists7 am: 4.7% of 164584 checklists8 am: 3.5% of 163654 checklists9 am: 2.8% of 141804 checklists10 am: 2.3% of 122882 checklists11 am: 1.9% of 100640 checklists12 pm: 1.8% of 89894 checklists1 pm: 1.6% of 82729 checklists2 pm: 1.5% of 79801 checklists3 pm: 1.6% of 82169 checklists4 pm: 2.0% of 75124 checklists5 pm: 2.3% of 57708 checklists6 pm: 1.5% 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%0.1%0.3%
May4.6%16%21%8.5%
June0.8%0.4%0.3%0.2%
July0.2%0.1%0.1%0.1%
August0.1%0.2%1.1%6.1%
September9.3%11%9.7%7.3%
October2.5%0.2%0.1%0.1%
November0%0%0%0%
December0%0%0%0%

Neighboring states

  • Indiana: arrives mid August, 15 weeks later than Illinois
  • Wisconsin: arrives early May, 1 week later than Illinois
  • Michigan: arrives early May, 1 week later than Illinois
  • Iowa: arrives the second week of August, 14 weeks later than Illinois

Common questions

When do Chestnut-sided Warblers arrive in Illinois?
Chestnut-sided Warblers mostly pass through Illinois: the first show up in late April, they are common by early May, peak in mid May (15% of checklists), and most are gone by early June.
When do Chestnut-sided Warblers leave Illinois?
Most Chestnut-sided Warblers have left Illinois by early June, when reports fall below half their usual rate.
When is the best time to see a Chestnut-sided Warbler in Illinois?
The Chestnut-sided Warbler is reported most often in mid May, on about 15% of Illinois checklists.
Where in Illinois are Chestnut-sided Warblers seen most often?
By county, Richland County, Edwards County, and Montgomery County have the highest peak reporting rates for the Chestnut-sided Warbler (counties with at least 200 checklists).