WhenToBird

Setophaga castanea · Parulidae

When Do Bay-breasted Warblers Arrive in Pennsylvania?

Adult Bay-breasted Warbler
Photo: Roger A. Morales-Flores, CC BY 4.0 via iNaturalist

Bay-breasted Warblers mostly pass through Pennsylvania: they arrive in late August, peak in mid September (5.7% of checklists), and most are gone by early October.

When to look

First arrivalsAug 22-31late August
Common byAug 22-31late August
PeakSep 15-21mid September
Most gone byOct 1-7early October

Best: mid September. First arrivals late August; most are gone by early October. Peak: on about 5.7% of Pennsylvania checklists.

  1. Jannot usually seen
  2. Febnot usually seen
  3. Marnot usually seen
  4. Aprrare
  5. Maycommon
  6. Junrare
  7. Julnot usually seen
  8. Auguncommon
  9. Seppeak season
  10. Octcommon
  11. Novnot usually seen
  12. Decnot usually seen

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

0%2%4%6%8%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% of 66940 checklistsApr 1-7: 0% of 51147 checklistsApr 8-14: 0% of 54868 checklistsApr 15-21: 0% of 57252 checklistsApr 22-30: 0.1% of 81727 checklistsMay 1-7: 0.9% of 76472 checklistsMay 8-14: 3.6% of 79341 checklistsMay 15-21: 6.8% of 61724 checklistsMay 22-31: 1.4% 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% of 44255 checklistsJul 1-7: 0% of 34822 checklistsJul 8-14: 0% of 31104 checklistsJul 15-21: 0% of 29262 checklistsJul 22-31: 0% of 41436 checklistsAug 1-7: 0% of 29189 checklistsAug 8-14: 0.1% of 28840 checklistsAug 15-21: 0.2% of 29948 checklistsAug 22-31: 1.2% of 48235 checklistsSep 1-7: 3.5% of 37175 checklistsSep 8-14: 6.0% of 36527 checklistsSep 15-21: 6.9% of 37261 checklistsSep 22-30: 4.5% of 43583 checklistsOct 1-7: 1.6% of 35352 checklistsOct 8-14: 0.4% of 35560 checklistsOct 15-21: 0.1% of 33119 checklistsOct 22-31: 0.1% of 44654 checklistsNov 1-7: 0% of 32965 checklistsNov 8-14: 0% of 31305 checklistsNov 15-21: 0% of 29471 checklistsNov 22-30: 0% of 38642 checklistsDec 1-7: 0.1% of 28779 checklistsDec 8-14: 0.1% 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.

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Where in Pennsylvania

Best counties

Share of checklists at the peak
  1. Warren CountyBest mid September · 57 checklists that week, 5,449 in all18%
  2. Erie CountyBest late May · 1859 checklists that week, 49,012 in all16%
  3. Butler CountyBest mid September · 794 checklists that week, 46,093 in all14%
  4. Clarion CountyBest mid September · 131 checklists that week, 9,153 in all14%
  5. Allegheny CountyBest the second week of September · 2883 checklists that week, 152,989 in all14%
  6. Mifflin CountyBest the second week of September · 109 checklists that week, 6,998 in all13%

Best spots

Share of checklists at the peak
  1. Seeickley Heights Borough ParkAllegheny County, best mid September · 69 checklists that week, 1,374 in all57%
  2. Horseshoe PondErie County, best late May · 88 checklists that week, 992 in all57%
  3. Blue Spruce ParkIndiana County, best mid September · 35 checklists that week, 667 in all55%
  4. Woodcock Creek LakeCrawford County, best mid September · 29 checklists that week, 389 in all50%
  5. Frick ParkAllegheny County, best the second week of September · 128 checklists that week, 3,434 in all47%
  6. Deer Lakes ParkAllegheny County, best mid September · 42 checklists that week, 725 in all44%

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

Best time of day

In Pennsylvania, the Bay-breasted Warbler is most often listed on checklists started between 6 and 8 am (1.8% of those checklists).

0%0.5%1%1.5%2%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: 2.0% of 92903 checklists7 am: 1.7% of 241233 checklists8 am: 1.4% of 271994 checklists9 am: 1.0% of 236842 checklists10 am: 0.7% of 199508 checklists11 am: 0.5% of 161893 checklists12 pm: 0.5% of 143945 checklists1 pm: 0.5% of 134352 checklists2 pm: 0.4% of 129692 checklists3 pm: 0.4% of 126132 checklists4 pm: 0.5% of 115055 checklists5 pm: 0.6% of 90719 checklists6 pm: 0.4% 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
January0%0%0%0%
February0%0%0%0%
March0%0%0%0%
April0%0%0%0.1%
May0.9%3.6%6.8%1.4%
June0.1%0.1%0.1%0%
July0%0%0%0%
August0%0.1%0.2%1.2%
September3.5%6.0%6.9%4.5%
October1.6%0.4%0.1%0.1%
November0%0%0%0%
December0.1%0.1%0%0%

Neighboring states

  • Maryland: arrives late August, in the same week than Pennsylvania
  • District of Columbia: arrives late April, 16 weeks earlier than Pennsylvania
  • Delaware: arrives late August, in the same week than Pennsylvania
  • New Jersey: arrives early May, 15 weeks earlier than Pennsylvania

Common questions

When do Bay-breasted Warblers arrive in Pennsylvania?
Bay-breasted Warblers mostly pass through Pennsylvania: they arrive in late August, peak in mid September (5.7% of checklists), and most are gone by early October.
When do Bay-breasted Warblers leave Pennsylvania?
Most Bay-breasted Warblers have left Pennsylvania by early October, when reports fall below half their usual rate.
When is the best time to see a Bay-breasted Warbler in Pennsylvania?
The Bay-breasted Warbler is reported most often in mid September, on about 5.7% of Pennsylvania checklists.
Where in Pennsylvania are Bay-breasted Warblers seen most often?
By county, Warren County, Erie County, and Butler County have the highest peak reporting rates for the Bay-breasted Warbler (counties with at least 200 checklists).