WhenToBird

Geothlypis philadelphia · Parulidae

When Do Mourning Warblers Arrive in Illinois?

Adult Mourning Warbler
Photo: John Rosford, CC BY 4.0 via iNaturalist

Mourning Warblers mostly pass through Illinois: they arrive in the second week of May, peak in late May (4.5% of checklists), and most are gone by early June.

When to look

First arrivalsMay 8-14the second week of May
Common byMay 8-14the second week of May
PeakMay 22-31late May
Most gone byJun 1-7early June

Best: late May. First arrivals the second week of May; most are gone by early June. Peak: on about 4.5% of Illinois checklists.

  1. Jannot usually seen
  2. Febnot usually seen
  3. Marnot usually seen
  4. Aprnot usually seen
  5. Maypeak season
  6. Juncommon
  7. Julnot usually seen
  8. Auguncommon
  9. Sepuncommon
  10. Octrare
  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 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: 0.1% of 60485 checklistsMay 8-14: 1.9% of 59647 checklistsMay 15-21: 6.1% of 43173 checklistsMay 22-31: 5.4% of 47913 checklistsJun 1-7: 0.8% of 31151 checklistsJun 8-14: 0.2% 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: 0.1% of 19284 checklistsJul 15-21: 0% of 17712 checklistsJul 22-31: 0% of 24500 checklistsAug 1-7: 0.1% of 18498 checklistsAug 8-14: 0.1% of 19331 checklistsAug 15-21: 0.4% of 19983 checklistsAug 22-31: 1.0% of 31892 checklistsSep 1-7: 1.0% of 26396 checklistsSep 8-14: 0.9% of 25011 checklistsSep 15-21: 0.6% of 23597 checklistsSep 22-30: 0.4% of 30638 checklistsOct 1-7: 0.1% of 23949 checklistsOct 8-14: 0.1% of 24412 checklistsOct 15-21: 0.1% of 22359 checklistsOct 22-31: 0% 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. Cook CountyBest late May · 16576 checklists that week, 432,644 in all8.4%
  2. Monroe CountyBest late September · 43 checklists that week, 2,547 in all6.6%
  3. Brown CountyBest mid May · 13 checklists that week, 403 in all6.0%
  4. Pike CountyBest late May · 16 checklists that week, 706 in all5.2%
  5. Livingston CountyBest late August · 39 checklists that week, 1,092 in all4.8%
  6. Adams CountyBest mid May · 121 checklists that week, 4,585 in all4.0%

Best spots

Share of checklists at the peak
  1. Lincoln (Abraham)Cook County, best late May · 2053 checklists that week, 40,318 in all39%
  2. Nichols (John Fountain)Cook County, best early June · 30 checklists that week, 492 in all25%
  3. Steward ParkKendall County, best late May · 29 checklists that week, 788 in all24%
  4. West Dupage County Forest PreserveDuPage County, best late May · 210 checklists that week, 3,449 in all24%
  5. La Bagh WoodsCook County, best late May · 330 checklists that week, 6,086 in all23%
  6. Chicago Harbor (Ogden Slip)Cook County, best mid May · 60 checklists that week, 158 in all23%

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

Best time of day

In Illinois, the Mourning Warbler is most often listed on checklists started between 6 and 8 am (1.1% of those checklists).

0%0.5%1%1.5%2%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: 1.5% of 95511 checklists7 am: 0.9% of 164584 checklists8 am: 0.7% of 163654 checklists9 am: 0.5% of 141804 checklists10 am: 0.4% of 122882 checklists11 am: 0.4% of 100640 checklists12 pm: 0.3% of 89894 checklists1 pm: 0.3% of 82729 checklists2 pm: 0.3% of 79801 checklists3 pm: 0.3% of 82169 checklists4 pm: 0.4% of 75124 checklists5 pm: 0.4% of 57708 checklists6 pm: 0.3% 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%
May0.1%1.9%6.1%5.4%
June0.8%0.2%0.1%0.1%
July0.1%0.1%0%0%
August0.1%0.1%0.4%1.0%
September1.0%0.9%0.6%0.4%
October0.1%0.1%0.1%0%
November0%0%0%0%
December0%0%0%0%

Neighboring states

  • Indiana: arrives the second week of May, in the same week than Illinois
  • Wisconsin: arrives the second week of May, in the same week than Illinois
  • Michigan: arrives the second week of May, in the same week than Illinois
  • Iowa: arrives the second week of May, in the same week than Illinois

Common questions

When do Mourning Warblers arrive in Illinois?
Mourning Warblers mostly pass through Illinois: they arrive in the second week of May, peak in late May (4.5% of checklists), and most are gone by early June.
When do Mourning Warblers leave Illinois?
Most Mourning Warblers have left Illinois by early June, when reports fall below half their usual rate.
When is the best time to see a Mourning Warbler in Illinois?
The Mourning Warbler is reported most often in late May, on about 4.5% of Illinois checklists.
Where in Illinois are Mourning Warblers seen most often?
By county, Cook County, Monroe County, and Brown County have the highest peak reporting rates for the Mourning Warbler (counties with at least 200 checklists).