WhenToBird

Circus hudsonius · Accipitridae

When Do Northern Harriers Arrive in Pennsylvania?

Northern Harriers are winter birds in Pennsylvania: the first arrive in the second week of September, they are common by mid September, peak in early November (2.7% of checklists), and most are gone by the second week of April.

When to look

First arrivalsSep 8-14the second week of September
Common bySep 15-21mid September
PeakNov 1-7early November
Most gone byApr 8-14the second week of April

Best: early November. First arrivals the second week of September; most are gone by the second week of April. Peak: on about 2.7% of Pennsylvania checklists.

  1. Janpeak season
  2. Febpeak season
  3. Marcommon
  4. Aprcommon
  5. Mayuncommon
  6. Junrare
  7. Julnot usually seen
  8. Auguncommon
  9. Sepcommon
  10. Octpeak season
  11. Novpeak season
  12. Decpeak season

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

0%1%2%3%Jan 1-7: 2.4% of 47145 checklistsJan 8-14: 2.2% of 35840 checklistsJan 15-21: 2.3% of 35423 checklistsJan 22-31: 2.5% of 49126 checklistsFeb 1-7: 2.2% of 36366 checklistsFeb 8-14: 1.8% of 42248 checklistsFeb 15-21: 1.2% of 55888 checklistsFeb 22-28: 1.6% of 42050 checklistsMar 1-7: 1.8% of 42709 checklistsMar 8-14: 1.6% of 43985 checklistsMar 15-21: 1.4% of 44547 checklistsMar 22-31: 1.4% of 66940 checklistsApr 1-7: 1.4% of 51147 checklistsApr 8-14: 1.3% of 54868 checklistsApr 15-21: 1.0% of 57252 checklistsApr 22-30: 0.6% of 81727 checklistsMay 1-7: 0.5% of 76472 checklistsMay 8-14: 0.4% of 79341 checklistsMay 15-21: 0.3% of 61724 checklistsMay 22-31: 0.2% of 70722 checklistsJun 1-7: 0.2% of 45652 checklistsJun 8-14: 0.1% of 41810 checklistsJun 15-21: 0.1% of 38973 checklistsJun 22-30: 0.1% of 44255 checklistsJul 1-7: 0.1% of 34822 checklistsJul 8-14: 0.1% of 31104 checklistsJul 15-21: 0.1% of 29262 checklistsJul 22-31: 0.1% of 41436 checklistsAug 1-7: 0.1% of 29189 checklistsAug 8-14: 0.1% of 28840 checklistsAug 15-21: 0.3% of 29948 checklistsAug 22-31: 0.4% of 48235 checklistsSep 1-7: 0.6% of 37175 checklistsSep 8-14: 0.9% of 36527 checklistsSep 15-21: 1.6% of 37261 checklistsSep 22-30: 1.6% of 43583 checklistsOct 1-7: 2.0% of 35352 checklistsOct 8-14: 2.2% of 35560 checklistsOct 15-21: 2.6% of 33119 checklistsOct 22-31: 2.5% of 44654 checklistsNov 1-7: 2.8% of 32965 checklistsNov 8-14: 2.8% of 31305 checklistsNov 15-21: 2.4% of 29471 checklistsNov 22-30: 2.5% of 38642 checklistsDec 1-7: 2.3% of 28779 checklistsDec 8-14: 2.4% of 29486 checklistsDec 15-21: 2.3% of 37465 checklistsDec 22-31: 2.6% 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. Montour CountyBest early February · 103 checklists that week, 6,082 in all19%
  2. Mifflin CountyBest late November · 152 checklists that week, 6,998 in all17%
  3. Perry CountyBest late October · 228 checklists that week, 10,281 in all14%
  4. Wyoming CountyBest early January · 60 checklists that week, 6,156 in all14%
  5. Schuylkill CountyBest late October · 636 checklists that week, 22,261 in all10%
  6. Crawford CountyBest early December · 272 checklists that week, 23,552 in all9.8%

Best spots

Share of checklists at the peak
  1. Panhandle TrailWashington County, best late November · 20 checklists that week, 328 in all79%
  2. Bryn Coed PreserveChester County, best late February · 37 checklists that week, 1,440 in all75%
  3. Valley Forge National Historical ParkMontgomery County, best the second week of December · 49 checklists that week, 2,587 in all68%
  4. State Game Land 290Dauphin County, best late November · 27 checklists that week, 890 in all63%

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

Best time of day

In Pennsylvania, the Northern Harrier is most often listed on checklists started between 3 and 5 pm (1.9% of those checklists).

0%1%2%3%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: 0.7% of 92903 checklists7 am: 0.9% of 241233 checklists8 am: 1.1% of 271994 checklists9 am: 1.2% of 236842 checklists10 am: 1.3% of 199508 checklists11 am: 1.5% of 161893 checklists12 pm: 1.5% of 143945 checklists1 pm: 1.5% of 134352 checklists2 pm: 1.7% of 129692 checklists3 pm: 1.9% of 126132 checklists4 pm: 2.1% of 115055 checklists5 pm: 1.2% of 90719 checklists6 pm: 0.7% of 67534 checklists7 pm: 0.4% 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
January2.4%2.2%2.3%2.5%
February2.2%1.8%1.2%1.6%
March1.8%1.6%1.4%1.4%
April1.4%1.3%1.0%0.6%
May0.5%0.4%0.3%0.2%
June0.2%0.1%0.1%0.1%
July0.1%0.1%0.1%0.1%
August0.1%0.1%0.3%0.4%
September0.6%0.9%1.6%1.6%
October2.0%2.2%2.6%2.5%
November2.8%2.8%2.4%2.5%
December2.3%2.4%2.3%2.6%

Neighboring states

  • Maryland: arrives the second week of September, in the same week than Pennsylvania
  • Delaware: arrives mid August, 3 weeks earlier than Pennsylvania
  • New Jersey: arrives late August, 2 weeks earlier than Pennsylvania
  • New York: arrives mid August, 3 weeks earlier than Pennsylvania

Common questions

When do Northern Harriers arrive in Pennsylvania?
Northern Harriers are winter birds in Pennsylvania: the first arrive in the second week of September, they are common by mid September, peak in early November (2.7% of checklists), and most are gone by the second week of April.
When do Northern Harriers leave Pennsylvania?
Most Northern Harriers have left Pennsylvania by the second week of April, when reports fall below half their usual rate.
When is the best time to see a Northern Harrier in Pennsylvania?
The Northern Harrier is reported most often in early November, on about 2.7% of Pennsylvania checklists.
Where in Pennsylvania are Northern Harriers seen most often?
By county, Montour County, Mifflin County, and Perry County have the highest peak reporting rates for the Northern Harrier (counties with at least 200 checklists).