WhenToBird

Larus marinus · Laridae

When Do Great Black-backed Gulls Arrive in Pennsylvania?

Adult Great Black-backed Gull
Photo: Rob Wadsworth, CC0 1.0 via iNaturalist

Great Black-backed Gulls are winter birds in Pennsylvania: they arrive in early October, peak in the second week of January (2.3% of checklists), and most are gone by early April.

When to look

First arrivalsOct 1-7early October
Common byOct 1-7early October
PeakJan 8-14the second week of January
Most gone byApr 1-7early April

Best: the second week of January. First arrivals early October; most are gone by early April. Peak: on about 2.3% of Pennsylvania checklists.

  1. Janpeak season
  2. Febpeak season
  3. Marcommon
  4. Apruncommon
  5. Mayrare
  6. Junrare
  7. Juluncommon
  8. Auguncommon
  9. Sepuncommon
  10. Octuncommon
  11. Novcommon
  12. Decpeak season

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

0%1%2%3%Jan 1-7: 2.2% of 47145 checklistsJan 8-14: 2.5% of 35840 checklistsJan 15-21: 2.1% of 35423 checklistsJan 22-31: 2.1% of 49126 checklistsFeb 1-7: 1.8% of 36366 checklistsFeb 8-14: 1.5% of 42248 checklistsFeb 15-21: 1.3% of 55888 checklistsFeb 22-28: 1.3% of 42050 checklistsMar 1-7: 1.0% of 42709 checklistsMar 8-14: 0.8% of 43985 checklistsMar 15-21: 0.7% of 44547 checklistsMar 22-31: 0.6% of 66940 checklistsApr 1-7: 0.5% of 51147 checklistsApr 8-14: 0.3% of 54868 checklistsApr 15-21: 0.2% of 57252 checklistsApr 22-30: 0.1% of 81727 checklistsMay 1-7: 0.1% of 76472 checklistsMay 8-14: 0.1% of 79341 checklistsMay 15-21: 0.2% of 61724 checklistsMay 22-31: 0.2% of 70722 checklistsJun 1-7: 0.1% of 45652 checklistsJun 8-14: 0.1% of 41810 checklistsJun 15-21: 0.1% of 38973 checklistsJun 22-30: 0.1% of 44255 checklistsJul 1-7: 0.2% of 34822 checklistsJul 8-14: 0.2% of 31104 checklistsJul 15-21: 0.3% of 29262 checklistsJul 22-31: 0.3% of 41436 checklistsAug 1-7: 0.6% of 29189 checklistsAug 8-14: 0.7% of 28840 checklistsAug 15-21: 0.7% of 29948 checklistsAug 22-31: 0.6% of 48235 checklistsSep 1-7: 0.6% of 37175 checklistsSep 8-14: 0.4% of 36527 checklistsSep 15-21: 0.4% of 37261 checklistsSep 22-30: 0.5% of 43583 checklistsOct 1-7: 0.5% of 35352 checklistsOct 8-14: 0.5% of 35560 checklistsOct 15-21: 0.5% of 33119 checklistsOct 22-31: 0.8% of 44654 checklistsNov 1-7: 0.7% of 32965 checklistsNov 8-14: 1.0% of 31305 checklistsNov 15-21: 1.1% of 29471 checklistsNov 22-30: 1.3% of 38642 checklistsDec 1-7: 1.5% of 28779 checklistsDec 8-14: 1.4% of 29486 checklistsDec 15-21: 1.5% of 37465 checklistsDec 22-31: 1.9% 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. Philadelphia CountyBest early January · 2586 checklists that week, 96,503 in all17%
  2. Erie CountyBest mid December · 849 checklists that week, 49,012 in all15%
  3. Delaware CountyBest mid January · 1431 checklists that week, 76,406 in all8.3%
  4. Bucks CountyBest early January · 2454 checklists that week, 95,030 in all8.1%
  5. Lancaster CountyBest mid January · 1680 checklists that week, 97,892 in all3.5%
  6. Northampton CountyBest late January · 1073 checklists that week, 45,480 in all2.6%

Best spots

Share of checklists at the peak
  1. McClure ParkDelaware County, best late January · 35 checklists that week, 541 in all96%
  2. Williamson ParkBucks County, best mid December · 31 checklists that week, 780 in all83%
  3. Citizens Bank AcquisitionPhiladelphia County, best the second week of January · 25 checklists that week, 701 in all82%
  4. Schuylkill Rowing BasinPhiladelphia County, best the second week of December · 20 checklists that week, 1,027 in all80%
  5. Glen FoerdPhiladelphia County, best early February · 33 checklists that week, 1,031 in all77%

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

Best time of day

In Pennsylvania, the Great Black-backed Gull is most often listed on checklists started between 1 and 3 pm (0.9% of those checklists).

0%0.5%1%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: 0.7% of 92903 checklists7 am: 0.8% of 241233 checklists8 am: 0.6% of 271994 checklists9 am: 0.7% of 236842 checklists10 am: 0.8% of 199508 checklists11 am: 0.8% of 161893 checklists12 pm: 0.9% of 143945 checklists1 pm: 0.9% of 134352 checklists2 pm: 0.9% of 129692 checklists3 pm: 0.9% of 126132 checklists4 pm: 0.8% of 115055 checklists5 pm: 0.4% of 90719 checklists6 pm: 0.3% of 67534 checklists7 pm: 0.2% 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
January2.2%2.5%2.1%2.1%
February1.8%1.5%1.3%1.3%
March1.0%0.8%0.7%0.6%
April0.5%0.3%0.2%0.1%
May0.1%0.1%0.2%0.2%
June0.1%0.1%0.1%0.1%
July0.2%0.2%0.3%0.3%
August0.6%0.7%0.7%0.6%
September0.6%0.4%0.4%0.5%
October0.5%0.5%0.5%0.8%
November0.7%1.0%1.1%1.3%
December1.5%1.4%1.5%1.9%

Neighboring states

  • Maryland: arrives late May, 17 weeks earlier than Pennsylvania
  • District of Columbia: arrives late October, 3 weeks later than Pennsylvania
  • Delaware: arrives early November, 4 weeks later than Pennsylvania
  • New Jersey: year-round, peaks mid January

Common questions

When do Great Black-backed Gulls arrive in Pennsylvania?
Great Black-backed Gulls are winter birds in Pennsylvania: they arrive in early October, peak in the second week of January (2.3% of checklists), and most are gone by early April.
When do Great Black-backed Gulls leave Pennsylvania?
Most Great Black-backed Gulls have left Pennsylvania by early April, when reports fall below half their usual rate.
When is the best time to see a Great Black-backed Gull in Pennsylvania?
The Great Black-backed Gull is reported most often in the second week of January, on about 2.3% of Pennsylvania checklists.
Where in Pennsylvania are Great Black-backed Gulls seen most often?
By county, Philadelphia County, Erie County, and Delaware County have the highest peak reporting rates for the Great Black-backed Gull (counties with at least 200 checklists).