WhenToBird

Setophaga virens · Parulidae

When Do Black-throated Green Warblers Arrive in Illinois?

Adult Black-throated Green Warbler
Photo: Ken Clark, CC BY 4.0 via iNaturalist

Black-throated Green Warblers arrive in Illinois in mid April, peak in the second week of May (13% of checklists), and most are gone by early June.

When to look

First arrivalsApr 15-21mid April
Common byApr 15-21mid April
PeakMay 8-14the second week of May
Most gone byJun 1-7early June

Best: the second week of May. First arrivals mid April; most are gone by early June. Peak: on about 13% of Illinois checklists.

  1. Jannot usually seen
  2. Febnot usually seen
  3. Marnot usually seen
  4. Aprcommon
  5. Maypeak season
  6. Junrare
  7. Julnot usually seen
  8. Auguncommon
  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: 0.1% of 42278 checklistsApr 1-7: 0.1% of 34579 checklistsApr 8-14: 0.1% of 38290 checklistsApr 15-21: 0.5% of 39261 checklistsApr 22-30: 3.7% of 59584 checklistsMay 1-7: 12% of 60485 checklistsMay 8-14: 16% of 59647 checklistsMay 15-21: 13% of 43173 checklistsMay 22-31: 4.1% of 47913 checklistsJun 1-7: 0.2% of 31151 checklistsJun 8-14: 0.1% of 27692 checklistsJun 15-21: 0.1% of 23983 checklistsJun 22-30: 0.1% of 28448 checklistsJul 1-7: 0.1% of 21273 checklistsJul 8-14: 0% of 19284 checklistsJul 15-21: 0% of 17712 checklistsJul 22-31: 0.1% of 24500 checklistsAug 1-7: 0.1% of 18498 checklistsAug 8-14: 0.1% of 19331 checklistsAug 15-21: 0.3% of 19983 checklistsAug 22-31: 2.7% of 31892 checklistsSep 1-7: 6.7% of 26396 checklistsSep 8-14: 9.8% of 25011 checklistsSep 15-21: 12% of 23597 checklistsSep 22-30: 13% of 30638 checklistsOct 1-7: 9.0% of 23949 checklistsOct 8-14: 3.4% of 24412 checklistsOct 15-21: 0.7% of 22359 checklistsOct 22-31: 0.2% of 29794 checklistsNov 1-7: 0.1% of 21877 checklistsNov 8-14: 0.1% 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. Wayne CountyBest late September · 12 checklists that week, 394 in all50%
  2. Richland CountyBest late September · 11 checklists that week, 580 in all44%
  3. Brown CountyBest mid September · 10 checklists that week, 403 in all38%
  4. Perry CountyBest late September · 20 checklists that week, 783 in all37%
  5. Piatt CountyBest late September · 77 checklists that week, 4,640 in all35%
  6. Livingston CountyBest late September · 18 checklists that week, 1,092 in all34%

Best spots

Share of checklists at the peak
  1. Bowen ParkLake County, best the second week of May · 47 checklists that week, 565 in all65%
  2. Cunliff ParkCook County, best the second week of May · 22 checklists that week, 354 in all64%
  3. Sedge Meadow Forest PreserveLake County, best the second week of May · 74 checklists that week, 504 in all59%
  4. Dam Number 4 South WoodsCook County, best the second week of May · 47 checklists that week, 492 in all58%
  5. Bemis Woods NorthCook County, best the second week of May · 54 checklists that week, 803 in all57%
  6. Skokie Lagoons (Crow Island)Cook County, best the second week of May · 309 checklists that week, 3,351 in all56%

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

Best time of day

In Illinois, the Black-throated Green Warbler is most often listed on checklists started between 6 and 8 am (5.4% 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: 5.8% of 95511 checklists7 am: 5.1% of 164584 checklists8 am: 4.0% of 163654 checklists9 am: 3.2% of 141804 checklists10 am: 2.6% of 122882 checklists11 am: 2.2% of 100640 checklists12 pm: 1.9% of 89894 checklists1 pm: 1.8% of 82729 checklists2 pm: 1.7% of 79801 checklists3 pm: 1.8% of 82169 checklists4 pm: 2.2% of 75124 checklists5 pm: 2.4% 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%0.1%
April0.1%0.1%0.5%3.7%
May12%16%13%4.1%
June0.2%0.1%0.1%0.1%
July0.1%0%0%0.1%
August0.1%0.1%0.3%2.7%
September6.7%9.8%12%13%
October9.0%3.4%0.7%0.2%
November0.1%0.1%0%0%
December0%0%0%0%

Neighboring states

  • Indiana: arrives late August, 17 weeks later than Illinois
  • Wisconsin: arrives late April, 1 week later than Illinois
  • Michigan: arrives late April, 1 week later than Illinois
  • Iowa: arrives late August, 17 weeks later than Illinois

Common questions

When do Black-throated Green Warblers arrive in Illinois?
Black-throated Green Warblers arrive in Illinois in mid April, peak in the second week of May (13% of checklists), and most are gone by early June.
When do Black-throated Green Warblers leave Illinois?
Most Black-throated Green Warblers have left Illinois by early June, when reports fall below half their usual rate.
When is the best time to see a Black-throated Green Warbler in Illinois?
The Black-throated Green Warbler is reported most often in the second week of May, on about 13% of Illinois checklists.
Where in Illinois are Black-throated Green Warblers seen most often?
By county, Wayne County, Richland County, and Brown County have the highest peak reporting rates for the Black-throated Green Warbler (counties with at least 200 checklists).