WhenToBird

Nannopterum auritum · Phalacrocoracidae

When Do Double-crested Cormorants Arrive in Illinois?

Adult Double-crested Cormorant
Photo: jubileej, CC0 1.0 via iNaturalist

Double-crested Cormorants reach Illinois in early March, are common by mid March, peak in the second week of August (21% of checklists), and most are gone by the second week of November.

When to look

First arrivalsMar 1-7early March
Common byMar 15-21mid March
PeakAug 8-14the second week of August
Most gone byNov 8-14the second week of November

Best: the second week of August. First arrivals early March; most are gone by the second week of November. Peak: on about 21% of Illinois checklists.

  1. Jannot usually seen
  2. Febrare
  3. Marcommon
  4. Aprpeak season
  5. Maypeak season
  6. Juncommon
  7. Julpeak season
  8. Augpeak season
  9. Seppeak season
  10. Octpeak season
  11. Novcommon
  12. Decrare

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

0%10%20%30%Jan 1-7: 0.8% of 29700 checklistsJan 8-14: 0.6% of 20189 checklistsJan 15-21: 0.5% of 19784 checklistsJan 22-31: 0.6% of 26641 checklistsFeb 1-7: 0.5% of 20478 checklistsFeb 8-14: 0.5% of 21967 checklistsFeb 15-21: 0.5% of 28735 checklistsFeb 22-28: 1.2% of 24223 checklistsMar 1-7: 2.3% of 26775 checklistsMar 8-14: 4.4% of 27579 checklistsMar 15-21: 7.0% of 27193 checklistsMar 22-31: 13% of 42278 checklistsApr 1-7: 17% of 34579 checklistsApr 8-14: 20% of 38290 checklistsApr 15-21: 19% of 39261 checklistsApr 22-30: 19% of 59584 checklistsMay 1-7: 17% of 60485 checklistsMay 8-14: 16% of 59647 checklistsMay 15-21: 17% of 43173 checklistsMay 22-31: 17% of 47913 checklistsJun 1-7: 13% of 31151 checklistsJun 8-14: 13% of 27692 checklistsJun 15-21: 13% of 23983 checklistsJun 22-30: 13% of 28448 checklistsJul 1-7: 14% of 21273 checklistsJul 8-14: 16% of 19284 checklistsJul 15-21: 19% of 17712 checklistsJul 22-31: 21% of 24500 checklistsAug 1-7: 22% of 18498 checklistsAug 8-14: 22% of 19331 checklistsAug 15-21: 21% of 19983 checklistsAug 22-31: 19% of 31892 checklistsSep 1-7: 19% of 26396 checklistsSep 8-14: 19% of 25011 checklistsSep 15-21: 18% of 23597 checklistsSep 22-30: 20% of 30638 checklistsOct 1-7: 18% of 23949 checklistsOct 8-14: 17% of 24412 checklistsOct 15-21: 16% of 22359 checklistsOct 22-31: 14% of 29794 checklistsNov 1-7: 11% of 21877 checklistsNov 8-14: 7.9% of 19742 checklistsNov 15-21: 5.4% of 18989 checklistsNov 22-30: 3.8% of 23905 checklistsDec 1-7: 2.1% of 16935 checklistsDec 8-14: 1.6% of 16687 checklistsDec 15-21: 1.1% of 20931 checklistsDec 22-31: 0.8% 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. Clinton CountyBest late September · 314 checklists that week, 8,606 in all67%
  2. Fulton CountyBest early August · 264 checklists that week, 5,877 in all63%
  3. Moultrie CountyBest early October · 19 checklists that week, 1,367 in all61%
  4. Franklin CountyBest mid September · 41 checklists that week, 1,745 in all59%
  5. Marion CountyBest mid August · 25 checklists that week, 2,946 in all57%
  6. Putnam CountyBest the second week of April · 63 checklists that week, 3,333 in all55%

Best spots

Share of checklists at the peak
  1. Bensenville Ditch Forest PreserveDuPage County, best late May · 34 checklists that week, 1,826 in all100%
  2. Twin LakesLake County, best the second week of April · 28 checklists that week, 850 in all99%
  3. Baker LakeCook County, best late April · 27 checklists that week, 539 in all99%
  4. Ben Butterworth Memorial ParkwayRock Island County, best early October · 22 checklists that week, 700 in all99%
  5. Ron Beese ParkCook County, best late March · 55 checklists that week, 632 in all98%

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

Best time of day

In Illinois, the Double-crested Cormorant is most often listed on checklists started between 6 and 8 am (17% of those checklists).

0%5%10%15%20%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: 19% of 95511 checklists7 am: 15% of 164584 checklists8 am: 13% of 163654 checklists9 am: 12% of 141804 checklists10 am: 11% of 122882 checklists11 am: 11% of 100640 checklists12 pm: 11% of 89894 checklists1 pm: 10% of 82729 checklists2 pm: 10% of 79801 checklists3 pm: 10% of 82169 checklists4 pm: 11% of 75124 checklists5 pm: 12% of 57708 checklists6 pm: 10% 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
January0.8%0.6%0.5%0.6%
February0.5%0.5%0.5%1.2%
March2.3%4.4%7.0%13%
April17%20%19%19%
May17%16%17%17%
June13%13%13%13%
July14%16%19%21%
August22%22%21%19%
September19%19%18%20%
October18%17%16%14%
November11%7.9%5.4%3.8%
December2.1%1.6%1.1%0.8%

Neighboring states

  • Indiana: arrives late February, 1 week earlier than Illinois
  • Wisconsin: arrives late March, 3 weeks later than Illinois
  • Michigan: arrives mid March, 2 weeks later than Illinois
  • Iowa: arrives the second week of March, 1 week later than Illinois

Common questions

When do Double-crested Cormorants arrive in Illinois?
Double-crested Cormorants reach Illinois in early March, are common by mid March, peak in the second week of August (21% of checklists), and most are gone by the second week of November.
When do Double-crested Cormorants leave Illinois?
Most Double-crested Cormorants have left Illinois by the second week of November, when reports fall below half their usual rate. Stragglers are still reported until early December.
When is the best time to see a Double-crested Cormorant in Illinois?
The Double-crested Cormorant is reported most often in the second week of August, on about 21% of Illinois checklists.
Where in Illinois are Double-crested Cormorants seen most often?
By county, Clinton County, Fulton County, and Moultrie County have the highest peak reporting rates for the Double-crested Cormorant (counties with at least 200 checklists).