WhenToBird

Molothrus ater · Icteridae

When Do Brown-headed Cowbirds Arrive in New Hampshire?

Adult female Brown-headed Cowbird
Photo: Nicole, CC BY 4.0 via iNaturalist

Brown-headed Cowbirds reach New Hampshire in early March, are common by late March, peak in early May (17% of checklists), and most are gone by the second week of July.

When to look

First arrivalsMar 1-7early March
Common byMar 22-31late March
PeakMay 1-7early May
Most gone byJul 8-14the second week of July

Best: early May. First arrivals early March; most are gone by the second week of July. Peak: on about 17% of New Hampshire checklists.

  1. Jannot usually seen
  2. Febnot usually seen
  3. Marcommon
  4. Aprpeak season
  5. Maypeak season
  6. Juncommon
  7. Juluncommon
  8. Augrare
  9. Sepnot usually seen
  10. Octnot usually seen
  11. Novnot usually seen
  12. Decnot usually seen

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

0%5%10%15%20%Jan 1-7: 0.1% of 8253 checklistsJan 8-14: 0.2% of 5998 checklistsJan 15-21: 0.2% of 5734 checklistsJan 22-31: 0.1% of 7776 checklistsFeb 1-7: 0.1% of 5253 checklistsFeb 8-14: 0.1% of 6802 checklistsFeb 15-21: 0.2% of 8852 checklistsFeb 22-28: 0.8% of 5792 checklistsMar 1-7: 0.7% of 6187 checklistsMar 8-14: 2.3% of 6977 checklistsMar 15-21: 4.0% of 7863 checklistsMar 22-31: 7.1% of 11746 checklistsApr 1-7: 9.9% of 9329 checklistsApr 8-14: 13% of 10499 checklistsApr 15-21: 15% of 10376 checklistsApr 22-30: 17% of 13086 checklistsMay 1-7: 18% of 13198 checklistsMay 8-14: 17% of 14980 checklistsMay 15-21: 15% of 12487 checklistsMay 22-31: 11% of 14294 checklistsJun 1-7: 9.7% of 8974 checklistsJun 8-14: 8.3% of 8395 checklistsJun 15-21: 8.9% of 7670 checklistsJun 22-30: 7.3% of 9188 checklistsJul 1-7: 7.1% of 7707 checklistsJul 8-14: 5.6% of 6554 checklistsJul 15-21: 3.4% of 6636 checklistsJul 22-31: 2.1% of 9599 checklistsAug 1-7: 1.8% of 6436 checklistsAug 8-14: 1.4% of 6477 checklistsAug 15-21: 1.1% of 6510 checklistsAug 22-31: 0.8% of 9762 checklistsSep 1-7: 0.5% of 6700 checklistsSep 8-14: 0.4% of 6012 checklistsSep 15-21: 0.5% of 6238 checklistsSep 22-30: 0.6% of 7619 checklistsOct 1-7: 0.6% of 6702 checklistsOct 8-14: 0.6% of 6863 checklistsOct 15-21: 0.6% of 6284 checklistsOct 22-31: 0.7% of 8287 checklistsNov 1-7: 0.4% of 7584 checklistsNov 8-14: 0.2% of 6056 checklistsNov 15-21: 0.1% of 5597 checklistsNov 22-30: 0.3% of 7140 checklistsDec 1-7: 0.3% of 4623 checklistsDec 8-14: 0.1% of 4920 checklistsDec 15-21: 0.2% of 6416 checklistsDec 22-31: 0.2% of 7659 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 New Hampshire 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 New Hampshire

Best counties

Share of checklists at the peak
  1. Strafford CountyBest early May · 1458 checklists that week, 41,888 in all28%
  2. Rockingham CountyBest early May · 2815 checklists that week, 84,864 in all25%
  3. Merrimack CountyBest early May · 1495 checklists that week, 36,980 in all19%
  4. Hillsborough CountyBest late April · 1838 checklists that week, 50,125 in all18%
  5. Cheshire CountyBest early May · 1289 checklists that week, 39,834 in all16%
  6. Belknap CountyBest late April · 440 checklists that week, 13,295 in all14%

Best spots

Share of checklists at the peak
  1. Father Lawless Fields Town ParkStrafford County, best late April · 70 checklists that week, 1,274 in all79%
  2. Cammett FieldsRockingham County, best late April · 25 checklists that week, 296 in all75%
  3. Pickering Ponds Recreation AreaStrafford County, best late June · 124 checklists that week, 5,064 in all74%
  4. Cocheco River ReservoirStrafford County, best mid June · 21 checklists that week, 2,281 in all56%
  5. Odiornes PointRockingham County, best early May · 226 checklists that week, 5,375 in all53%

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

Best time of day

In New Hampshire, the Brown-headed Cowbird is most often listed on checklists started between 6 and 8 am (11% of those checklists).

0%5%10%15%12 am: too few checklists (219) to judge1 am: too few checklists (192) to judge2 am: too few checklists (176) to judge3 am: too few checklists (234) to judge4 am: too few checklists (1042) to judge5 am: too few checklists (6352) to judge6 am: 14% of 23140 checklists7 am: 8.6% of 43401 checklists8 am: 6.8% of 48039 checklists9 am: 4.7% of 43328 checklists10 am: 3.8% of 37073 checklists11 am: 3.5% of 32028 checklists12 pm: 3.0% of 27396 checklists1 pm: 2.9% of 25182 checklists2 pm: 3.0% of 24318 checklists3 pm: 2.9% of 21974 checklists4 pm: 3.4% of 17958 checklists5 pm: 4.1% of 14528 checklists6 pm: 4.7% of 9144 checklists7 pm: too few checklists (5341) to judge8 pm: too few checklists (1845) to judge9 pm: too few checklists (578) to judge10 pm: too few checklists (346) to judge11 pm: too few checklists (256) 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%0.2%0.2%0.1%
February0.1%0.1%0.2%0.8%
March0.7%2.3%4.0%7.1%
April9.9%13%15%17%
May18%17%15%11%
June9.7%8.3%8.9%7.3%
July7.1%5.6%3.4%2.1%
August1.8%1.4%1.1%0.8%
September0.5%0.4%0.5%0.6%
October0.6%0.6%0.6%0.7%
November0.4%0.2%0.1%0.3%
December0.3%0.1%0.2%0.2%

Neighboring states

  • Massachusetts: arrives early March, in the same week than New Hampshire
  • Vermont: arrives early March, in the same week than New Hampshire
  • Rhode Island: arrives late February, 1 week earlier than New Hampshire
  • Maine: arrives the second week of March, 1 week later than New Hampshire

Common questions

When do Brown-headed Cowbirds arrive in New Hampshire?
Brown-headed Cowbirds reach New Hampshire in early March, are common by late March, peak in early May (17% of checklists), and most are gone by the second week of July.
When do Brown-headed Cowbirds leave New Hampshire?
Most Brown-headed Cowbirds have left New Hampshire by the second week of July, when reports fall below half their usual rate. Stragglers are still reported until mid August.
When is the best time to see a Brown-headed Cowbird in New Hampshire?
The Brown-headed Cowbird is reported most often in early May, on about 17% of New Hampshire checklists.
Where in New Hampshire are Brown-headed Cowbirds seen most often?
By county, Strafford County, Rockingham County, and Merrimack County have the highest peak reporting rates for the Brown-headed Cowbird (counties with at least 200 checklists).