WhenToBird

Hydroprogne caspia · Laridae

When Do Caspian Terns Arrive in Pennsylvania?

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

Caspian Terns arrive in Pennsylvania in the second week of July, peak in mid August (2.3% of checklists), and most are gone by the second week of October.

When to look

First arrivalsJul 8-14the second week of July
Common byJul 8-14the second week of July
PeakAug 15-21mid August
Most gone byOct 8-14the second week of October

Best: mid August. First arrivals the second week of July; most are gone by the second week of October. Peak: on about 2.3% of Pennsylvania checklists.

  1. Jannot usually seen
  2. Febnot usually seen
  3. Marrare
  4. Aprcommon
  5. Mayuncommon
  6. Junrare
  7. Julcommon
  8. Augpeak season
  9. Seppeak season
  10. Octuncommon
  11. Novnot usually seen
  12. Decnot usually seen

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

0%1%2%3%Jan 1-7: 0% of 47145 checklistsJan 8-14: 0% of 35840 checklistsJan 15-21: 0% of 35423 checklistsJan 22-31: 0% of 49126 checklistsFeb 1-7: 0% of 36366 checklistsFeb 8-14: 0% of 42248 checklistsFeb 15-21: 0% of 55888 checklistsFeb 22-28: 0% of 42050 checklistsMar 1-7: 0% of 42709 checklistsMar 8-14: 0% of 43985 checklistsMar 15-21: 0% of 44547 checklistsMar 22-31: 0.1% of 66940 checklistsApr 1-7: 0.3% of 51147 checklistsApr 8-14: 0.9% of 54868 checklistsApr 15-21: 1.6% of 57252 checklistsApr 22-30: 1.2% of 81727 checklistsMay 1-7: 0.7% of 76472 checklistsMay 8-14: 0.6% of 79341 checklistsMay 15-21: 0.5% of 61724 checklistsMay 22-31: 0.3% of 70722 checklistsJun 1-7: 0.2% of 45652 checklistsJun 8-14: 0.2% of 41810 checklistsJun 15-21: 0.3% of 38973 checklistsJun 22-30: 0.2% of 44255 checklistsJul 1-7: 0.5% of 34822 checklistsJul 8-14: 0.6% of 31104 checklistsJul 15-21: 0.8% of 29262 checklistsJul 22-31: 1.2% of 41436 checklistsAug 1-7: 1.8% of 29189 checklistsAug 8-14: 2.5% of 28840 checklistsAug 15-21: 2.4% of 29948 checklistsAug 22-31: 2.1% of 48235 checklistsSep 1-7: 2.0% of 37175 checklistsSep 8-14: 1.1% of 36527 checklistsSep 15-21: 0.9% of 37261 checklistsSep 22-30: 0.9% of 43583 checklistsOct 1-7: 0.8% of 35352 checklistsOct 8-14: 0.5% of 35560 checklistsOct 15-21: 0.1% of 33119 checklistsOct 22-31: 0.1% of 44654 checklistsNov 1-7: 0.1% of 32965 checklistsNov 8-14: 0% of 31305 checklistsNov 15-21: 0% of 29471 checklistsNov 22-30: 0.1% of 38642 checklistsDec 1-7: 0% of 28779 checklistsDec 8-14: 0% of 29486 checklistsDec 15-21: 0% of 37465 checklistsDec 22-31: 0% of 50651 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 Pennsylvania 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.

Embed this map on your site

Where in Pennsylvania

Best counties

Share of checklists at the peak
  1. Erie CountyBest mid August · 657 checklists that week, 49,012 in all18%
  2. Philadelphia CountyBest the second week of August · 1241 checklists that week, 96,503 in all15%
  3. Delaware CountyBest the second week of August · 1046 checklists that week, 76,406 in all10%
  4. Crawford CountyBest mid August · 331 checklists that week, 23,552 in all7.9%
  5. Lancaster CountyBest mid August · 1431 checklists that week, 97,892 in all6.1%
  6. Clearfield CountyBest late September · 166 checklists that week, 9,768 in all3.5%

Best spots

Share of checklists at the peak
  1. Pymatuning State ParkCrawford County, best late August · 24 checklists that week, 1,001 in all76%
  2. Presque Isle State ParkErie County, best late August · 41 checklists that week, 1,465 in all61%
  3. Horseshoe Pond (Mill Creek)Erie County, best early May · 20 checklists that week, 531 in all60%

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

Best time of day

In Pennsylvania, the Caspian Tern is most often listed on checklists started between 6 and 8 am (0.7% of those checklists).

0%0.5%1%1.5%12 am: too few checklists (1558) to judge1 am: too few checklists (1136) to judge2 am: too few checklists (839) to judge3 am: too few checklists (842) to judge4 am: too few checklists (2550) to judge5 am: too few checklists (18294) to judge6 am: 1.0% of 92903 checklists7 am: 0.5% of 241233 checklists8 am: 0.5% of 271994 checklists9 am: 0.5% of 236842 checklists10 am: 0.5% of 199508 checklists11 am: 0.5% of 161893 checklists12 pm: 0.4% of 143945 checklists1 pm: 0.4% of 134352 checklists2 pm: 0.5% of 129692 checklists3 pm: 0.5% of 126132 checklists4 pm: 0.5% of 115055 checklists5 pm: 0.7% of 90719 checklists6 pm: 0.7% of 67534 checklists7 pm: 0.5% of 43004 checklists8 pm: too few checklists (13966) to judge9 pm: too few checklists (3913) to judge10 pm: too few checklists (1989) to judge11 pm: too few checklists (1146) 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%
April0.3%0.9%1.6%1.2%
May0.7%0.6%0.5%0.3%
June0.2%0.2%0.3%0.2%
July0.5%0.6%0.8%1.2%
August1.8%2.5%2.4%2.1%
September2.0%1.1%0.9%0.9%
October0.8%0.5%0.1%0.1%
November0.1%0%0%0.1%
December0%0%0%0%

Neighboring states

  • Maryland: arrives mid July, 1 week later than Pennsylvania
  • District of Columbia: arrives mid July, 1 week later than Pennsylvania
  • Delaware: arrives early April, 13 weeks earlier than Pennsylvania
  • New Jersey: arrives mid July, 1 week later than Pennsylvania

Common questions

When do Caspian Terns arrive in Pennsylvania?
Caspian Terns arrive in Pennsylvania in the second week of July, peak in mid August (2.3% of checklists), and most are gone by the second week of October.
When do Caspian Terns leave Pennsylvania?
Most Caspian Terns have left Pennsylvania by the second week of October, when reports fall below half their usual rate.
When is the best time to see a Caspian Tern in Pennsylvania?
The Caspian Tern is reported most often in mid August, on about 2.3% of Pennsylvania checklists.
Where in Pennsylvania are Caspian Terns seen most often?
By county, Erie County, Philadelphia County, and Delaware County have the highest peak reporting rates for the Caspian Tern (counties with at least 200 checklists).