WhenToBird

Hydroprogne caspia · Laridae

When Do Caspian Terns Arrive in Illinois?

Adult Caspian Tern
Photo: Daughter Dad, CC BY 4.0 via iNaturalist

Caspian Terns reach Illinois in late March, are common by the second week of April, peak in late July (16% of checklists), and most are gone by late August.

When to look

First arrivalsMar 22-31late March
Common byApr 8-14the second week of April
PeakJul 22-31late July
Most gone byAug 22-31late August

Best: late July. First arrivals late March; most are gone by late August. Peak: on about 16% of Illinois checklists.

  1. Jannot usually seen
  2. Febnot usually seen
  3. Marrare
  4. Aprcommon
  5. Maycommon
  6. Juncommon
  7. Julpeak season
  8. Augpeak season
  9. Sepuncommon
  10. Octnot usually seen
  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: 0.1% of 27579 checklistsMar 15-21: 0.1% of 27193 checklistsMar 22-31: 0.8% of 42278 checklistsApr 1-7: 3.6% of 34579 checklistsApr 8-14: 7.2% of 38290 checklistsApr 15-21: 9.8% of 39261 checklistsApr 22-30: 12% of 59584 checklistsMay 1-7: 9.6% of 60485 checklistsMay 8-14: 9.0% of 59647 checklistsMay 15-21: 10% of 43173 checklistsMay 22-31: 8.5% of 47913 checklistsJun 1-7: 6.6% of 31151 checklistsJun 8-14: 6.2% of 27692 checklistsJun 15-21: 7.3% of 23983 checklistsJun 22-30: 8.4% of 28448 checklistsJul 1-7: 11% of 21273 checklistsJul 8-14: 13% of 19284 checklistsJul 15-21: 15% of 17712 checklistsJul 22-31: 16% of 24500 checklistsAug 1-7: 16% of 18498 checklistsAug 8-14: 14% of 19331 checklistsAug 15-21: 11% of 19983 checklistsAug 22-31: 6.9% of 31892 checklistsSep 1-7: 4.0% of 26396 checklistsSep 8-14: 3.2% of 25011 checklistsSep 15-21: 2.1% of 23597 checklistsSep 22-30: 1.1% of 30638 checklistsOct 1-7: 0.4% of 23949 checklistsOct 8-14: 0.1% 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. Clinton CountyBest the second week of August · 209 checklists that week, 8,606 in all47%
  2. Fulton CountyBest late July · 166 checklists that week, 5,877 in all43%
  3. Franklin CountyBest early September · 45 checklists that week, 1,745 in all37%
  4. Mason CountyBest mid August · 240 checklists that week, 5,020 in all34%
  5. Putnam CountyBest the second week of August · 61 checklists that week, 3,333 in all32%
  6. Cook CountyBest late July · 7146 checklists that week, 432,644 in all29%

Best spots

Share of checklists at the peak
  1. North Salt Creek County Forest PreserveDuPage County, best early August · 87 checklists that week, 3,304 in all96%
  2. Des Plaines State Fish and Wildlife AreaWill County, best late July · 20 checklists that week, 1,300 in all95%
  3. Jackson (Andrew) (Jackson Park Beach)Cook County, best the second week of May · 25 checklists that week, 754 in all94%
  4. Center ParkSangamon County, best mid July · 22 checklists that week, 715 in all89%

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

Best time of day

In Illinois, the Caspian Tern is most often listed on checklists started between 6 and 8 am (7.2% of those checklists).

0%5%10%15%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: 10% of 95511 checklists7 am: 5.5% of 164584 checklists8 am: 4.4% of 163654 checklists9 am: 4.2% of 141804 checklists10 am: 4.1% of 122882 checklists11 am: 3.9% of 100640 checklists12 pm: 3.6% of 89894 checklists1 pm: 3.4% of 82729 checklists2 pm: 3.6% of 79801 checklists3 pm: 3.5% of 82169 checklists4 pm: 4.5% of 75124 checklists5 pm: 5.6% of 57708 checklists6 pm: 5.6% 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%0.1%0.1%0.8%
April3.6%7.2%9.8%12%
May9.6%9.0%10%8.5%
June6.6%6.2%7.3%8.4%
July11%13%15%16%
August16%14%11%6.9%
September4.0%3.2%2.1%1.1%
October0.4%0.1%0.1%0.1%
November0%0%0%0%
December0%0%0%0%

Neighboring states

  • Indiana: arrives late March, in the same week than Illinois
  • Wisconsin: arrives the second week of April, 2 weeks later than Illinois
  • Michigan: arrives the second week of April, 2 weeks later than Illinois
  • Iowa: arrives late July, 16 weeks later than Illinois

Common questions

When do Caspian Terns arrive in Illinois?
Caspian Terns reach Illinois in late March, are common by the second week of April, peak in late July (16% of checklists), and most are gone by late August.
When do Caspian Terns leave Illinois?
Most Caspian Terns have left Illinois by late August, when reports fall below half their usual rate. Stragglers are still reported until late September.
When is the best time to see a Caspian Tern in Illinois?
The Caspian Tern is reported most often in late July, on about 16% of Illinois checklists.
Where in Illinois are Caspian Terns seen most often?
By county, Clinton County, Fulton County, and Franklin County have the highest peak reporting rates for the Caspian Tern (counties with at least 200 checklists).