WhenToBird

Setophaga pensylvanica · Parulidae

When Do Chestnut-sided Warblers Arrive in Pennsylvania?

Adult male Chestnut-sided Warbler
Photo: Matt Felperin, CC BY 4.0 via iNaturalist

Chestnut-sided Warblers reach Pennsylvania in late April, are common by early May, peak in mid May (11% of checklists), and most are gone by late September.

When to look

First arrivalsApr 22-30late April
Common byMay 1-7early May
PeakMay 15-21mid May
Most gone bySep 22-30late September

Best: mid May. First arrivals late April; most are gone by late September. Peak: on about 11% of Pennsylvania checklists.

  1. Jannot usually seen
  2. Febnot usually seen
  3. Marnot usually seen
  4. Apruncommon
  5. Maypeak season
  6. Juncommon
  7. Julcommon
  8. Augcommon
  9. Seppeak season
  10. Octuncommon
  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% 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: 0.1% of 57252 checklistsApr 22-30: 0.7% of 81727 checklistsMay 1-7: 7.0% of 76472 checklistsMay 8-14: 12% of 79341 checklistsMay 15-21: 12% of 61724 checklistsMay 22-31: 8.1% of 70722 checklistsJun 1-7: 6.0% of 45652 checklistsJun 8-14: 6.0% of 41810 checklistsJun 15-21: 6.0% of 38973 checklistsJun 22-30: 5.2% of 44255 checklistsJul 1-7: 5.0% of 34822 checklistsJul 8-14: 3.5% of 31104 checklistsJul 15-21: 1.7% of 29262 checklistsJul 22-31: 1.1% of 41436 checklistsAug 1-7: 1.0% of 29189 checklistsAug 8-14: 1.5% of 28840 checklistsAug 15-21: 3.0% of 29948 checklistsAug 22-31: 6.8% of 48235 checklistsSep 1-7: 8.1% of 37175 checklistsSep 8-14: 9.0% of 36527 checklistsSep 15-21: 6.9% of 37261 checklistsSep 22-30: 3.6% of 43583 checklistsOct 1-7: 1.2% of 35352 checklistsOct 8-14: 0.3% of 35560 checklistsOct 15-21: 0.1% of 33119 checklistsOct 22-31: 0% of 44654 checklistsNov 1-7: 0% of 32965 checklistsNov 8-14: 0% of 31305 checklistsNov 15-21: 0.1% 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. Warren CountyBest late May · 269 checklists that week, 5,449 in all44%
  2. Sullivan CountyBest late May · 391 checklists that week, 4,362 in all40%
  3. McKean CountyBest the second week of June · 338 checklists that week, 8,592 in all40%
  4. Susquehanna CountyBest late May · 947 checklists that week, 22,573 in all39%
  5. Potter CountyBest late May · 375 checklists that week, 9,677 in all38%
  6. Wayne CountyBest late May · 491 checklists that week, 10,444 in all37%

Best spots

Share of checklists at the peak
  1. State Game Land 176 (south)Centre County, best early June · 34 checklists that week, 790 in all95%
  2. State Game Land 035Susquehanna County, best late May · 59 checklists that week, 729 in all95%
  3. Lake JeanSullivan County, best late May · 24 checklists that week, 334 in all91%
  4. State Game Land 176Centre County, best late May · 219 checklists that week, 2,675 in all84%
  5. Delaware State ForestMonroe County, best mid May · 24 checklists that week, 211 in all79%
  6. Forbes State ForestWestmoreland County, best the second week of June · 21 checklists that week, 380 in all79%

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

Best time of day

In Pennsylvania, the Chestnut-sided Warbler is most often listed on checklists started between 6 and 8 am (5.6% of those checklists).

0%2%4%6%8%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: 7.1% of 92903 checklists7 am: 5.0% of 241233 checklists8 am: 3.7% of 271994 checklists9 am: 2.9% of 236842 checklists10 am: 2.4% of 199508 checklists11 am: 1.9% of 161893 checklists12 pm: 1.6% of 143945 checklists1 pm: 1.5% of 134352 checklists2 pm: 1.3% of 129692 checklists3 pm: 1.3% of 126132 checklists4 pm: 1.3% of 115055 checklists5 pm: 1.7% of 90719 checklists6 pm: 1.7% of 67534 checklists7 pm: 1.5% 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%0.1%0.7%
May7.0%12%12%8.1%
June6.0%6.0%6.0%5.2%
July5.0%3.5%1.7%1.1%
August1.0%1.5%3.0%6.8%
September8.1%9.0%6.9%3.6%
October1.2%0.3%0.1%0%
November0%0%0.1%0%
December0%0%0%0%

Neighboring states

  • Maryland: arrives the second week of August, 14 weeks later than Pennsylvania
  • District of Columbia: arrives the second week of August, 14 weeks later than Pennsylvania
  • Delaware: arrives mid August, 15 weeks later than Pennsylvania
  • New Jersey: arrives late April, in the same week than Pennsylvania

Common questions

When do Chestnut-sided Warblers arrive in Pennsylvania?
Chestnut-sided Warblers reach Pennsylvania in late April, are common by early May, peak in mid May (11% of checklists), and most are gone by late September.
When do Chestnut-sided Warblers leave Pennsylvania?
Most Chestnut-sided Warblers have left Pennsylvania by late September, when reports fall below half their usual rate. Stragglers are still reported until early October.
When is the best time to see a Chestnut-sided Warbler in Pennsylvania?
The Chestnut-sided Warbler is reported most often in mid May, on about 11% of Pennsylvania checklists.
Where in Pennsylvania are Chestnut-sided Warblers seen most often?
By county, Warren County, Sullivan County, and McKean County have the highest peak reporting rates for the Chestnut-sided Warbler (counties with at least 200 checklists).