WhenToBird

Helmitheros vermivorum · Parulidae

When Do Worm-eating Warblers Arrive in Pennsylvania?

Adult Worm-eating Warbler
Photo: kirk gardner, CC BY 4.0 via iNaturalist

Worm-eating Warblers arrive in Pennsylvania in late April, peak in the second week of May (2.5% of checklists), and most are gone by early July.

When to look

First arrivalsApr 22-30late April
Common byApr 22-30late April
PeakMay 8-14the second week of May
Most gone byJul 1-7early July

Best: the second week of May. First arrivals late April; most are gone by early July. Peak: on about 2.5% of Pennsylvania checklists.

  1. Jannot usually seen
  2. Febnot usually seen
  3. Marnot usually seen
  4. Aprcommon
  5. Maypeak season
  6. Juncommon
  7. Julcommon
  8. Auguncommon
  9. Seprare
  10. Octnot usually seen
  11. Novnot usually seen
  12. Decnot usually seen

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

0%1%2%3%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: 0.1% of 54868 checklistsApr 15-21: 0.1% of 57252 checklistsApr 22-30: 0.7% of 81727 checklistsMay 1-7: 2.6% of 76472 checklistsMay 8-14: 2.6% of 79341 checklistsMay 15-21: 2.4% of 61724 checklistsMay 22-31: 1.9% of 70722 checklistsJun 1-7: 1.7% of 45652 checklistsJun 8-14: 2.0% of 41810 checklistsJun 15-21: 1.9% of 38973 checklistsJun 22-30: 1.4% of 44255 checklistsJul 1-7: 1.1% of 34822 checklistsJul 8-14: 0.7% of 31104 checklistsJul 15-21: 0.4% of 29262 checklistsJul 22-31: 0.3% of 41436 checklistsAug 1-7: 0.3% of 29189 checklistsAug 8-14: 0.3% of 28840 checklistsAug 15-21: 0.4% of 29948 checklistsAug 22-31: 0.5% of 48235 checklistsSep 1-7: 0.4% of 37175 checklistsSep 8-14: 0.3% of 36527 checklistsSep 15-21: 0.2% of 37261 checklistsSep 22-30: 0.1% of 43583 checklistsOct 1-7: 0.1% of 35352 checklistsOct 8-14: 0% of 35560 checklistsOct 15-21: 0% of 33119 checklistsOct 22-31: 0% 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% of 28779 checklistsDec 8-14: 0% 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. Perry CountyBest the second week of May · 433 checklists that week, 10,281 in all14%
  2. Blair CountyBest the second week of May · 449 checklists that week, 13,387 in all13%
  3. Huntingdon CountyBest the second week of June · 713 checklists that week, 32,852 in all11%
  4. Mifflin CountyBest the second week of June · 177 checklists that week, 6,998 in all9.3%
  5. Fulton CountyBest early June · 175 checklists that week, 7,004 in all9.1%
  6. Montour CountyBest mid May · 225 checklists that week, 6,082 in all8.6%

Best spots

Share of checklists at the peak
  1. Tuscarora State ForestCumberland County, best the second week of May · 31 checklists that week, 254 in all84%
  2. Sgl 043Chester County, best the second week of May · 60 checklists that week, 593 in all73%
  3. Delaware Water Gap National Recreation AreaMonroe County, best mid May · 34 checklists that week, 287 in all67%
  4. Shenk's Ferry Wildflower PreserveLancaster County, best the second week of May · 36 checklists that week, 433 in all63%
  5. Berks County ParkBerks County, best early June · 22 checklists that week, 249 in all61%
  6. Sgl 217 (northeast)Lehigh County, best the second week of May · 21 checklists that week, 128 in all61%

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

Best time of day

In Pennsylvania, the Worm-eating Warbler is most often listed on checklists started between 6 and 8 am (1.1% 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: 1.6% of 92903 checklists7 am: 1.0% of 241233 checklists8 am: 0.7% of 271994 checklists9 am: 0.7% of 236842 checklists10 am: 0.6% of 199508 checklists11 am: 0.4% of 161893 checklists12 pm: 0.3% of 143945 checklists1 pm: 0.3% of 134352 checklists2 pm: 0.3% of 129692 checklists3 pm: 0.2% of 126132 checklists4 pm: 0.2% of 115055 checklists5 pm: 0.2% 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
January0%0%0%0%
February0%0%0%0%
March0%0%0%0%
April0%0.1%0.1%0.7%
May2.6%2.6%2.4%1.9%
June1.7%2.0%1.9%1.4%
July1.1%0.7%0.4%0.3%
August0.3%0.3%0.4%0.5%
September0.4%0.3%0.2%0.1%
October0.1%0%0%0%
November0%0%0%0%
December0%0%0%0%

Neighboring states

  • Maryland: arrives mid April, 1 week earlier than Pennsylvania
  • District of Columbia: arrives the second week of April, 2 weeks earlier than Pennsylvania
  • Delaware: arrives mid April, 1 week earlier than Pennsylvania
  • New Jersey: arrives mid April, 1 week earlier than Pennsylvania

Common questions

When do Worm-eating Warblers arrive in Pennsylvania?
Worm-eating Warblers arrive in Pennsylvania in late April, peak in the second week of May (2.5% of checklists), and most are gone by early July.
When do Worm-eating Warblers leave Pennsylvania?
Most Worm-eating Warblers have left Pennsylvania by early July, when reports fall below half their usual rate.
When is the best time to see a Worm-eating Warbler in Pennsylvania?
The Worm-eating Warbler is reported most often in the second week of May, on about 2.5% of Pennsylvania checklists.
Where in Pennsylvania are Worm-eating Warblers seen most often?
By county, Perry County, Blair County, and Huntingdon County have the highest peak reporting rates for the Worm-eating Warbler (counties with at least 200 checklists).