WhenToBird

Nannopterum auritum · Phalacrocoracidae

When Do Double-crested Cormorants Arrive in Pennsylvania?

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

Double-crested Cormorants reach Pennsylvania in the second week of March, are common by mid March, peak in the second week of April (12% of checklists), and most are gone by late November.

When to look

First arrivalsMar 8-14the second week of March
Common byMar 15-21mid March
PeakApr 8-14the second week of April
Most gone byNov 22-30late November

Best: the second week of April. First arrivals the second week of March; most are gone by late November. Peak: on about 12% of Pennsylvania checklists.

  1. Januncommon
  2. Febrare
  3. Marcommon
  4. Aprpeak season
  5. Maycommon
  6. Jununcommon
  7. Julcommon
  8. Augpeak season
  9. Seppeak season
  10. Octpeak season
  11. Novcommon
  12. Decuncommon

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

0%5%10%15%Jan 1-7: 2.0% of 47145 checklistsJan 8-14: 1.9% of 35840 checklistsJan 15-21: 1.7% of 35423 checklistsJan 22-31: 1.3% of 49126 checklistsFeb 1-7: 1.3% of 36366 checklistsFeb 8-14: 1.2% of 42248 checklistsFeb 15-21: 1.0% of 55888 checklistsFeb 22-28: 1.3% of 42050 checklistsMar 1-7: 1.5% of 42709 checklistsMar 8-14: 2.2% of 43985 checklistsMar 15-21: 4.3% of 44547 checklistsMar 22-31: 8.4% of 66940 checklistsApr 1-7: 11% of 51147 checklistsApr 8-14: 12% of 54868 checklistsApr 15-21: 12% of 57252 checklistsApr 22-30: 8.7% of 81727 checklistsMay 1-7: 6.8% of 76472 checklistsMay 8-14: 6.2% of 79341 checklistsMay 15-21: 5.5% of 61724 checklistsMay 22-31: 4.9% of 70722 checklistsJun 1-7: 4.0% of 45652 checklistsJun 8-14: 3.4% of 41810 checklistsJun 15-21: 3.3% of 38973 checklistsJun 22-30: 3.1% of 44255 checklistsJul 1-7: 3.4% of 34822 checklistsJul 8-14: 4.4% of 31104 checklistsJul 15-21: 5.3% of 29262 checklistsJul 22-31: 5.6% of 41436 checklistsAug 1-7: 7.1% of 29189 checklistsAug 8-14: 9.4% of 28840 checklistsAug 15-21: 9.5% of 29948 checklistsAug 22-31: 9.6% of 48235 checklistsSep 1-7: 9.9% of 37175 checklistsSep 8-14: 8.9% of 36527 checklistsSep 15-21: 8.7% of 37261 checklistsSep 22-30: 9.4% of 43583 checklistsOct 1-7: 8.7% of 35352 checklistsOct 8-14: 8.7% of 35560 checklistsOct 15-21: 7.6% of 33119 checklistsOct 22-31: 8.6% of 44654 checklistsNov 1-7: 7.6% of 32965 checklistsNov 8-14: 7.3% of 31305 checklistsNov 15-21: 5.1% of 29471 checklistsNov 22-30: 4.5% of 38642 checklistsDec 1-7: 3.3% of 28779 checklistsDec 8-14: 2.3% of 29486 checklistsDec 15-21: 1.7% of 37465 checklistsDec 22-31: 1.6% 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.

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Where in Pennsylvania

Best counties

Share of checklists at the peak
  1. Mercer CountyBest mid August · 257 checklists that week, 17,853 in all30%
  2. Bucks CountyBest early October · 1720 checklists that week, 95,030 in all30%
  3. Erie CountyBest early September · 793 checklists that week, 49,012 in all30%
  4. Philadelphia CountyBest early November · 1589 checklists that week, 96,503 in all29%
  5. Snyder CountyBest early April · 114 checklists that week, 5,676 in all28%
  6. Lancaster CountyBest mid August · 1431 checklists that week, 97,892 in all27%

Best spots

Share of checklists at the peak
  1. Lake AugustaNorthumberland County, best late August · 28 checklists that week, 811 in all100%
  2. McClure ParkDelaware County, best mid February · 26 checklists that week, 541 in all98%
  3. Schuylkill River Open SpaceMontgomery County, best the second week of September · 35 checklists that week, 2,272 in all98%
  4. Nockamixon State Park (Lake Nockamixon)Bucks County, best the second week of April · 44 checklists that week, 1,554 in all97%

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

Best time of day

In Pennsylvania, the Double-crested Cormorant is most often listed on checklists started between 6 and 8 am (6.7% of those checklists).

0%2%4%6%8%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: 7.5% of 92903 checklists7 am: 6.4% of 241233 checklists8 am: 5.6% of 271994 checklists9 am: 5.6% of 236842 checklists10 am: 5.6% of 199508 checklists11 am: 5.7% of 161893 checklists12 pm: 5.9% of 143945 checklists1 pm: 5.7% of 134352 checklists2 pm: 5.6% of 129692 checklists3 pm: 5.4% of 126132 checklists4 pm: 5.4% of 115055 checklists5 pm: 6.1% of 90719 checklists6 pm: 5.7% of 67534 checklists7 pm: 3.2% 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
January2.0%1.9%1.7%1.3%
February1.3%1.2%1.0%1.3%
March1.5%2.2%4.3%8.4%
April11%12%12%8.7%
May6.8%6.2%5.5%4.9%
June4.0%3.4%3.3%3.1%
July3.4%4.4%5.3%5.6%
August7.1%9.4%9.5%9.6%
September9.9%8.9%8.7%9.4%
October8.7%8.7%7.6%8.6%
November7.6%7.3%5.1%4.5%
December3.3%2.3%1.7%1.6%

Neighboring states

  • Maryland: arrives mid March, 1 week later than Pennsylvania
  • District of Columbia: year-round, peaks early December
  • Delaware: arrives mid July, 17 weeks later than Pennsylvania
  • New Jersey: arrives mid July, 17 weeks later than Pennsylvania

Common questions

When do Double-crested Cormorants arrive in Pennsylvania?
Double-crested Cormorants reach Pennsylvania in the second week of March, are common by mid March, peak in the second week of April (12% of checklists), and most are gone by late November.
When do Double-crested Cormorants leave Pennsylvania?
Most Double-crested Cormorants have left Pennsylvania by late November, when reports fall below half their usual rate. Stragglers are still reported until mid December.
When is the best time to see a Double-crested Cormorant in Pennsylvania?
The Double-crested Cormorant is reported most often in the second week of April, on about 12% of Pennsylvania checklists.
Where in Pennsylvania are Double-crested Cormorants seen most often?
By county, Mercer County, Bucks County, and Erie County have the highest peak reporting rates for the Double-crested Cormorant (counties with at least 200 checklists).