WhenToBird

Larus fuscus · Laridae

When Do Lesser Black-backed Gulls Arrive in Pennsylvania?

Adult Lesser Black-backed Gull
Photo: danielarah, CC0 1.0 via iNaturalist

Lesser Black-backed Gulls are winter birds in Pennsylvania: they arrive in late October, peak in mid January (1.9% of checklists), and most are gone by mid March.

When to look

First arrivalsOct 22-31late October
Common byOct 22-31late October
PeakJan 15-21mid January
Most gone byMar 15-21mid March

Best: mid January. First arrivals late October; most are gone by mid March. Peak: on about 1.9% of Pennsylvania checklists.

  1. Janpeak season
  2. Febpeak season
  3. Marpeak season
  4. Apruncommon
  5. Maynot usually seen
  6. Junnot usually seen
  7. Julnot usually seen
  8. Augrare
  9. Sepuncommon
  10. Octuncommon
  11. Novpeak season
  12. Decpeak season

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

0%0.5%1%1.5%2%Jan 1-7: 1.9% of 47145 checklistsJan 8-14: 2.0% of 35840 checklistsJan 15-21: 1.8% of 35423 checklistsJan 22-31: 2.0% of 49126 checklistsFeb 1-7: 1.8% of 36366 checklistsFeb 8-14: 1.6% of 42248 checklistsFeb 15-21: 1.3% of 55888 checklistsFeb 22-28: 2.0% of 42050 checklistsMar 1-7: 1.6% of 42709 checklistsMar 8-14: 1.4% of 43985 checklistsMar 15-21: 1.0% of 44547 checklistsMar 22-31: 0.8% of 66940 checklistsApr 1-7: 0.4% of 51147 checklistsApr 8-14: 0.3% of 54868 checklistsApr 15-21: 0.1% 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: 0.1% of 61724 checklistsMay 22-31: 0.1% 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: 0.1% of 34822 checklistsJul 8-14: 0.1% of 31104 checklistsJul 15-21: 0.1% of 29262 checklistsJul 22-31: 0.1% of 41436 checklistsAug 1-7: 0.1% of 29189 checklistsAug 8-14: 0.1% of 28840 checklistsAug 15-21: 0.1% of 29948 checklistsAug 22-31: 0.2% of 48235 checklistsSep 1-7: 0.4% of 37175 checklistsSep 8-14: 0.5% of 36527 checklistsSep 15-21: 0.6% of 37261 checklistsSep 22-30: 0.6% of 43583 checklistsOct 1-7: 0.5% of 35352 checklistsOct 8-14: 0.6% of 35560 checklistsOct 15-21: 0.6% of 33119 checklistsOct 22-31: 0.6% of 44654 checklistsNov 1-7: 1.0% of 32965 checklistsNov 8-14: 1.5% of 31305 checklistsNov 15-21: 1.4% of 29471 checklistsNov 22-30: 1.7% of 38642 checklistsDec 1-7: 1.8% of 28779 checklistsDec 8-14: 1.4% of 29486 checklistsDec 15-21: 1.3% 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.

Embed this map on your site

Where in Pennsylvania

Best counties

Share of checklists at the peak
  1. Bucks CountyBest early March · 1806 checklists that week, 95,030 in all18%
  2. Lehigh CountyBest late January · 1042 checklists that week, 41,072 in all7.6%
  3. Northampton CountyBest early February · 725 checklists that week, 45,480 in all6.1%
  4. Montgomery CountyBest the second week of January · 3127 checklists that week, 184,237 in all5.6%
  5. Mercer CountyBest late March · 647 checklists that week, 17,853 in all3.8%
  6. Berks CountyBest early January · 1952 checklists that week, 61,798 in all3.6%

Best spots

Share of checklists at the peak
  1. Lake NockamixonBucks County, best mid February · 83 checklists that week, 1,542 in all95%
  2. Williamson ParkBucks County, best mid October · 41 checklists that week, 780 in all80%
  3. Green Lane ReservoirMontgomery County, best late December · 132 checklists that week, 6,265 in all74%
  4. Peace Valley ParkBucks County, best the second week of December · 155 checklists that week, 7,502 in all70%
  5. Nockamixon State ParkBucks County, best late November · 34 checklists that week, 1,645 in all69%

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

Best time of day

In Pennsylvania, the Lesser Black-backed Gull is most often listed on checklists started between 2 and 4 pm (1.1% 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: 0.3% of 92903 checklists7 am: 0.6% of 241233 checklists8 am: 0.6% of 271994 checklists9 am: 0.7% of 236842 checklists10 am: 0.8% of 199508 checklists11 am: 0.9% of 161893 checklists12 pm: 1.0% of 143945 checklists1 pm: 1.1% of 134352 checklists2 pm: 1.1% of 129692 checklists3 pm: 1.1% of 126132 checklists4 pm: 0.7% of 115055 checklists5 pm: 0.3% of 90719 checklists6 pm: 0.2% of 67534 checklists7 pm: 0.1% 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
January1.9%2.0%1.8%2.0%
February1.8%1.6%1.3%2.0%
March1.6%1.4%1.0%0.8%
April0.4%0.3%0.1%0.1%
May0.1%0.1%0.1%0.1%
June0.1%0.1%0.1%0.1%
July0.1%0.1%0.1%0.1%
August0.1%0.1%0.1%0.2%
September0.4%0.5%0.6%0.6%
October0.5%0.6%0.6%0.6%
November1.0%1.5%1.4%1.7%
December1.8%1.4%1.3%1.6%

Neighboring states

  • District of Columbia: arrives mid November, 3 weeks later than Pennsylvania
  • Delaware: arrives mid May, 21 weeks earlier than Pennsylvania
  • New Jersey: arrives late June, 16 weeks earlier than Pennsylvania
  • New York: arrives late May, 20 weeks earlier than Pennsylvania

Common questions

When do Lesser Black-backed Gulls arrive in Pennsylvania?
Lesser Black-backed Gulls are winter birds in Pennsylvania: they arrive in late October, peak in mid January (1.9% of checklists), and most are gone by mid March.
When do Lesser Black-backed Gulls leave Pennsylvania?
Most Lesser Black-backed Gulls have left Pennsylvania by mid March, when reports fall below half their usual rate.
When is the best time to see a Lesser Black-backed Gull in Pennsylvania?
The Lesser Black-backed Gull is reported most often in mid January, on about 1.9% of Pennsylvania checklists.
Where in Pennsylvania are Lesser Black-backed Gulls seen most often?
By county, Bucks County, Lehigh County, and Northampton County have the highest peak reporting rates for the Lesser Black-backed Gull (counties with at least 200 checklists).