WhenToBird

Setophaga caerulescens · Parulidae

When Do Black-throated Blue Warblers Arrive in Pennsylvania?

Adult male Black-throated Blue Warbler
Photo: Dan Vickers, CC BY 4.0 via iNaturalist

Black-throated Blue Warblers arrive in Pennsylvania in late April, peak in the second week of May (10% of checklists), and most are gone by the second week of July.

When to look

First arrivalsApr 22-30late April
Common byApr 22-30late April
PeakMay 8-14the second week of May
Most gone byJul 8-14the second week of July

Best: the second week of May. First arrivals late April; most are gone by the second week of July. Peak: on about 10% 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. Sepcommon
  10. Octcommon
  11. Novnot usually seen
  12. Decnot usually seen

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

0%5%10%15%Jan 1-7: 0.1% of 47145 checklistsJan 8-14: 0.1% of 35840 checklistsJan 15-21: 0.1% of 35423 checklistsJan 22-31: 0.1% 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: 0.1% of 57252 checklistsApr 22-30: 1.7% of 81727 checklistsMay 1-7: 9.7% of 76472 checklistsMay 8-14: 13% of 79341 checklistsMay 15-21: 7.1% of 61724 checklistsMay 22-31: 2.8% of 70722 checklistsJun 1-7: 2.1% of 45652 checklistsJun 8-14: 2.5% of 41810 checklistsJun 15-21: 2.7% of 38973 checklistsJun 22-30: 2.5% of 44255 checklistsJul 1-7: 2.4% of 34822 checklistsJul 8-14: 1.8% of 31104 checklistsJul 15-21: 1.2% of 29262 checklistsJul 22-31: 0.7% of 41436 checklistsAug 1-7: 0.4% of 29189 checklistsAug 8-14: 0.4% of 28840 checklistsAug 15-21: 0.6% of 29948 checklistsAug 22-31: 1.8% of 48235 checklistsSep 1-7: 3.7% of 37175 checklistsSep 8-14: 4.5% of 36527 checklistsSep 15-21: 5.9% of 37261 checklistsSep 22-30: 5.6% of 43583 checklistsOct 1-7: 5.4% of 35352 checklistsOct 8-14: 3.0% of 35560 checklistsOct 15-21: 1.0% of 33119 checklistsOct 22-31: 0.1% of 44654 checklistsNov 1-7: 0.1% of 32965 checklistsNov 8-14: 0.1% of 31305 checklistsNov 15-21: 0.1% of 29471 checklistsNov 22-30: 0.1% 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.

Embed this map on your site

Where in Pennsylvania

Best counties

Share of checklists at the peak
  1. Warren CountyBest late May · 269 checklists that week, 5,449 in all31%
  2. Philadelphia CountyBest the second week of May · 4389 checklists that week, 96,503 in all27%
  3. Forest CountyBest early June · 133 checklists that week, 5,388 in all21%
  4. Sullivan CountyBest mid June · 160 checklists that week, 4,362 in all21%
  5. Wyoming CountyBest the second week of July · 103 checklists that week, 6,156 in all16%
  6. Potter CountyBest mid June · 250 checklists that week, 9,677 in all16%

Best spots

Share of checklists at the peak
  1. Colton Point State ParkTioga County, best late May · 29 checklists that week, 235 in all96%
  2. Bear Run Nature ReserveFayette County, best late June · 29 checklists that week, 314 in all77%
  3. Forbes State ForestWestmoreland County, best mid May · 27 checklists that week, 380 in all74%
  4. Lower LakeMonroe County, best the second week of May · 28 checklists that week, 1,218 in all66%
  5. Carpenter's Woods ParkPhiladelphia County, best early October · 28 checklists that week, 1,714 in all64%
  6. State Game Land 035Susquehanna County, best mid May · 35 checklists that week, 729 in all62%

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

Best time of day

In Pennsylvania, the Black-throated Blue Warbler is most often listed on checklists started between 6 and 8 am (3.9% of those checklists).

0%2%4%6%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: 4.9% of 92903 checklists7 am: 3.5% of 241233 checklists8 am: 2.8% of 271994 checklists9 am: 2.3% of 236842 checklists10 am: 2.0% of 199508 checklists11 am: 1.6% of 161893 checklists12 pm: 1.5% of 143945 checklists1 pm: 1.3% of 134352 checklists2 pm: 1.1% of 129692 checklists3 pm: 1.1% of 126132 checklists4 pm: 1.1% of 115055 checklists5 pm: 1.2% of 90719 checklists6 pm: 0.9% of 67534 checklists7 pm: 0.6% 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
January0.1%0.1%0.1%0.1%
February0%0%0%0%
March0%0%0%0%
April0%0%0.1%1.7%
May9.7%13%7.1%2.8%
June2.1%2.5%2.7%2.5%
July2.4%1.8%1.2%0.7%
August0.4%0.4%0.6%1.8%
September3.7%4.5%5.9%5.6%
October5.4%3.0%1.0%0.1%
November0.1%0.1%0.1%0.1%
December0.1%0.1%0%0%

Neighboring states

  • Maryland: arrives mid April, 1 week earlier than Pennsylvania
  • District of Columbia: arrives mid April, 1 week earlier than Pennsylvania
  • Delaware: arrives late April, in the same week than Pennsylvania
  • New Jersey: arrives mid April, 1 week earlier than Pennsylvania

Common questions

When do Black-throated Blue Warblers arrive in Pennsylvania?
Black-throated Blue Warblers arrive in Pennsylvania in late April, peak in the second week of May (10% of checklists), and most are gone by the second week of July.
When do Black-throated Blue Warblers leave Pennsylvania?
Most Black-throated Blue Warblers have left Pennsylvania by the second week of July, when reports fall below half their usual rate. Stragglers are still reported until mid July.
When is the best time to see a Black-throated Blue Warbler in Pennsylvania?
The Black-throated Blue Warbler is reported most often in the second week of May, on about 10% of Pennsylvania checklists.
Where in Pennsylvania are Black-throated Blue Warblers seen most often?
By county, Warren County, Philadelphia County, and Forest County have the highest peak reporting rates for the Black-throated Blue Warbler (counties with at least 200 checklists).