WhenToBird

Circus hudsonius · Accipitridae

When Do Northern Harriers Arrive in California?

Northern Harriers are in California all year, but most are here in winter: numbers build from the second week of October, peak in mid November (9.6% of checklists), and fall back by the second week of March. In the quietest week (mid May) they are still on about 2.1% of checklists.

When to look

Numbers buildOct 8-14the second week of October
PeakNov 15-21mid November
Fall back byMar 8-14the second week of March
FewestMay 15-21mid May

Best: mid November. Here all year; numbers build from the second week of October and fall back by the second week of March. Peak: on about 9.6% of California checklists.

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

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

0%5%10%Jan 1-7: 8.4% of 112336 checklistsJan 8-14: 8.3% of 85518 checklistsJan 15-21: 8.3% of 86488 checklistsJan 22-31: 7.9% of 116174 checklistsFeb 1-7: 7.6% of 75171 checklistsFeb 8-14: 7.3% of 84467 checklistsFeb 15-21: 6.3% of 105683 checklistsFeb 22-28: 7.2% of 83396 checklistsMar 1-7: 6.6% of 77470 checklistsMar 8-14: 6.3% of 75180 checklistsMar 15-21: 5.9% of 80770 checklistsMar 22-31: 5.3% of 114116 checklistsApr 1-7: 4.4% of 84057 checklistsApr 8-14: 3.9% of 83692 checklistsApr 15-21: 3.3% of 89242 checklistsApr 22-30: 2.7% of 114289 checklistsMay 1-7: 2.4% of 85728 checklistsMay 8-14: 2.1% of 91984 checklistsMay 15-21: 2.0% of 75478 checklistsMay 22-31: 2.1% of 106250 checklistsJun 1-7: 2.2% of 70051 checklistsJun 8-14: 2.2% of 67485 checklistsJun 15-21: 2.1% of 66269 checklistsJun 22-30: 2.0% of 79172 checklistsJul 1-7: 2.3% of 62877 checklistsJul 8-14: 2.1% of 60328 checklistsJul 15-21: 2.3% of 59705 checklistsJul 22-31: 2.4% of 83796 checklistsAug 1-7: 2.4% of 60215 checklistsAug 8-14: 2.8% of 60172 checklistsAug 15-21: 2.9% of 59877 checklistsAug 22-31: 3.2% of 89107 checklistsSep 1-7: 3.6% of 72000 checklistsSep 8-14: 3.6% of 71228 checklistsSep 15-21: 4.3% of 76808 checklistsSep 22-30: 4.9% of 100204 checklistsOct 1-7: 5.5% of 76571 checklistsOct 8-14: 6.3% of 80874 checklistsOct 15-21: 6.8% of 74581 checklistsOct 22-31: 7.6% of 97498 checklistsNov 1-7: 8.6% of 70851 checklistsNov 8-14: 9.4% of 72431 checklistsNov 15-21: 9.9% of 66767 checklistsNov 22-30: 9.5% of 94737 checklistsDec 1-7: 9.2% of 65393 checklistsDec 8-14: 8.6% of 67449 checklistsDec 15-21: 8.3% of 83421 checklistsDec 22-31: 8.1% of 124993 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 California 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 California

Best counties

Share of checklists at the peak
  1. Colusa CountyBest late February · 218 checklists that week, 7,653 in all42%
  2. Modoc CountyBest early December · 54 checklists that week, 6,138 in all40%
  3. Glenn CountyBest the second week of January · 145 checklists that week, 5,189 in all39%
  4. Merced CountyBest early December · 282 checklists that week, 13,095 in all37%
  5. Imperial CountyBest mid November · 455 checklists that week, 24,551 in all36%
  6. Napa CountyBest the second week of November · 324 checklists that week, 18,976 in all29%

Best spots

Share of checklists at the peak
  1. Piute PondsLos Angeles County, best mid February · 26 checklists that week, 1,269 in all97%
  2. Harmony Headlands State ParkSan Luis Obispo County, best late March · 29 checklists that week, 681 in all96%
  3. RamalSonoma County, best late November · 20 checklists that week, 701 in all95%
  4. Fly BayNapa County, best mid November · 22 checklists that week, 1,284 in all94%
  5. Long PondHumboldt County, best mid December · 20 checklists that week, 487 in all93%

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

Best time of day

In California, the Northern Harrier is most often listed on checklists started between 1 and 3 pm (6.3% of those checklists).

0%2%4%6%8%12 am: too few checklists (1688) to judge1 am: too few checklists (1451) to judge2 am: too few checklists (1402) to judge3 am: too few checklists (1743) to judge4 am: too few checklists (4647) to judge5 am: too few checklists (32158) to judge6 am: 3.5% of 186053 checklists7 am: 4.9% of 444086 checklists8 am: 5.6% of 535846 checklists9 am: 5.9% of 486061 checklists10 am: 6.0% of 411130 checklists11 am: 5.8% of 325798 checklists12 pm: 5.8% of 269132 checklists1 pm: 6.3% of 244762 checklists2 pm: 6.3% of 235420 checklists3 pm: 5.9% of 232365 checklists4 pm: 5.0% of 208688 checklists5 pm: 3.7% of 146104 checklists6 pm: 2.6% of 96867 checklists7 pm: too few checklists (50942) to judge8 pm: too few checklists (14803) to judge9 pm: too few checklists (5561) to judge10 pm: too few checklists (3546) to judge11 pm: too few checklists (2092) 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
January8.4%8.3%8.3%7.9%
February7.6%7.3%6.3%7.2%
March6.6%6.3%5.9%5.3%
April4.4%3.9%3.3%2.7%
May2.4%2.1%2.0%2.1%
June2.2%2.2%2.1%2.0%
July2.3%2.1%2.3%2.4%
August2.4%2.8%2.9%3.2%
September3.6%3.6%4.3%4.9%
October5.5%6.3%6.8%7.6%
November8.6%9.4%9.9%9.5%
December9.2%8.6%8.3%8.1%

Neighboring states

  • Nevada: arrives the second week of October, in the same week than California
  • Utah: arrives the second week of August, 8 weeks earlier than California
  • Arizona: arrives late August, 6 weeks earlier than California
  • Oregon: arrives the second week of September, 4 weeks earlier than California

Common questions

When do Northern Harriers arrive in California?
Northern Harriers are in California all year, but most are here in winter: numbers build from the second week of October, peak in mid November (9.6% of checklists), and fall back by the second week of March. In the quietest week (mid May) they are still on about 2.1% of checklists.
When do Northern Harriers leave California?
Northern Harriers never fully leave California: numbers fall back below half their usual rate by the second week of March, but some are still reported in every week, about 2.1% of checklists at the low.
When is the best time to see a Northern Harrier in California?
The Northern Harrier is reported most often in mid November, on about 9.6% of California checklists.
Where in California are Northern Harriers seen most often?
By county, Colusa County, Modoc County, and Glenn County have the highest peak reporting rates for the Northern Harrier (counties with at least 200 checklists).