WhenToBird

Setophaga virens · Parulidae

When Do Black-throated Green Warblers Arrive in Pennsylvania?

Adult Black-throated Green Warbler
Photo: Ken Clark, CC BY 4.0 via iNaturalist

Black-throated Green Warblers arrive in Pennsylvania in mid April, peak in mid September (14% of checklists), and most are gone by the second week of October.

When to look

First arrivalsApr 15-21mid April
Common byApr 15-21mid April
PeakSep 15-21mid September
Most gone byOct 8-14the second week of October

Best: mid September. First arrivals mid April; most are gone by the second week of October. Peak: on about 14% of Pennsylvania checklists.

  1. Jannot usually seen
  2. Febnot usually seen
  3. Marnot usually seen
  4. Aprcommon
  5. Maypeak season
  6. Jununcommon
  7. Juluncommon
  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%5%10%15%20%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: 0.1% of 51147 checklistsApr 8-14: 0.1% of 54868 checklistsApr 15-21: 1.1% of 57252 checklistsApr 22-30: 5.7% of 81727 checklistsMay 1-7: 13% of 76472 checklistsMay 8-14: 14% of 79341 checklistsMay 15-21: 9.3% of 61724 checklistsMay 22-31: 5.6% of 70722 checklistsJun 1-7: 4.4% of 45652 checklistsJun 8-14: 5.0% of 41810 checklistsJun 15-21: 5.4% of 38973 checklistsJun 22-30: 5.2% of 44255 checklistsJul 1-7: 5.2% of 34822 checklistsJul 8-14: 4.3% of 31104 checklistsJul 15-21: 3.0% of 29262 checklistsJul 22-31: 2.0% of 41436 checklistsAug 1-7: 1.0% of 29189 checklistsAug 8-14: 0.8% of 28840 checklistsAug 15-21: 1.2% of 29948 checklistsAug 22-31: 3.6% of 48235 checklistsSep 1-7: 8.4% of 37175 checklistsSep 8-14: 12% of 36527 checklistsSep 15-21: 14% of 37261 checklistsSep 22-30: 15% of 43583 checklistsOct 1-7: 10% of 35352 checklistsOct 8-14: 4.3% of 35560 checklistsOct 15-21: 1.1% of 33119 checklistsOct 22-31: 0.2% of 44654 checklistsNov 1-7: 0.1% of 32965 checklistsNov 8-14: 0.1% of 31305 checklistsNov 15-21: 0% of 29471 checklistsNov 22-30: 0.1% of 38642 checklistsDec 1-7: 0.1% of 28779 checklistsDec 8-14: 0% of 29486 checklistsDec 15-21: 0.1% of 37465 checklistsDec 22-31: 0.1% 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. Sullivan CountyBest late June · 168 checklists that week, 4,362 in all48%
  2. Elk CountyBest late May · 292 checklists that week, 6,751 in all44%
  3. Warren CountyBest the second week of July · 142 checklists that week, 5,449 in all35%
  4. Forest CountyBest mid June · 135 checklists that week, 5,388 in all34%
  5. Cameron CountyBest mid May · 128 checklists that week, 5,057 in all31%
  6. Jefferson CountyBest the second week of May · 242 checklists that week, 5,956 in all30%

Best spots

Share of checklists at the peak
  1. Tumbling Run Reservoir Number TwoSchuylkill County, best early May · 20 checklists that week, 190 in all81%
  2. Colton Point State ParkTioga County, best late May · 29 checklists that week, 235 in all77%
  3. Sgl 217 (northeast)Lehigh County, best the second week of May · 21 checklists that week, 128 in all76%
  4. Redbank Valley TrailClarion County, best late May · 23 checklists that week, 112 in all73%
  5. Bear Run Nature ReserveFayette County, best late June · 29 checklists that week, 314 in all70%
  6. Tuscarora State ForestCumberland County, best early May · 40 checklists that week, 254 in all68%

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

Best time of day

In Pennsylvania, the Black-throated Green Warbler is most often listed on checklists started between 6 and 8 am (6.9% of those checklists).

0%5%10%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: 8.1% of 92903 checklists7 am: 6.4% of 241233 checklists8 am: 5.0% of 271994 checklists9 am: 4.1% of 236842 checklists10 am: 3.4% of 199508 checklists11 am: 2.7% of 161893 checklists12 pm: 2.4% of 143945 checklists1 pm: 2.2% of 134352 checklists2 pm: 2.0% of 129692 checklists3 pm: 1.8% of 126132 checklists4 pm: 2.0% of 115055 checklists5 pm: 2.4% of 90719 checklists6 pm: 2.1% of 67534 checklists7 pm: 1.4% 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%
April0.1%0.1%1.1%5.7%
May13%14%9.3%5.6%
June4.4%5.0%5.4%5.2%
July5.2%4.3%3.0%2.0%
August1.0%0.8%1.2%3.6%
September8.4%12%14%15%
October10%4.3%1.1%0.2%
November0.1%0.1%0%0.1%
December0.1%0%0.1%0.1%

Neighboring states

  • Maryland: arrives mid August, 16 weeks later than Pennsylvania
  • District of Columbia: arrives mid August, 16 weeks later than Pennsylvania
  • Delaware: arrives late August, 17 weeks later than Pennsylvania
  • New Jersey: arrives mid April, in the same week than Pennsylvania

Common questions

When do Black-throated Green Warblers arrive in Pennsylvania?
Black-throated Green Warblers arrive in Pennsylvania in mid April, peak in mid September (14% of checklists), and most are gone by the second week of October.
When do Black-throated Green Warblers leave Pennsylvania?
Most Black-throated Green Warblers have left Pennsylvania by the second week of October, when reports fall below half their usual rate. Stragglers are still reported until mid October.
When is the best time to see a Black-throated Green Warbler in Pennsylvania?
The Black-throated Green Warbler is reported most often in mid September, on about 14% of Pennsylvania checklists.
Where in Pennsylvania are Black-throated Green Warblers seen most often?
By county, Sullivan County, Elk County, and Warren County have the highest peak reporting rates for the Black-throated Green Warbler (counties with at least 200 checklists).