WhenToBird

Molothrus ater · Icteridae

When Do Brown-headed Cowbirds Arrive in Vermont?

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

Brown-headed Cowbirds reach Vermont in early March, are common by late March, peak in early May (14% of checklists), and most are gone by early July.

When to look

First arrivalsMar 1-7early March
Common byMar 22-31late March
PeakMay 1-7early May
Most gone byJul 1-7early July

Best: early May. First arrivals early March; most are gone by early July. Peak: on about 14% of Vermont checklists.

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

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

0%5%10%15%Jan 1-7: 0.4% of 12234 checklistsJan 8-14: 0.3% of 8293 checklistsJan 15-21: 0.4% of 7885 checklistsJan 22-31: 0.3% of 10534 checklistsFeb 1-7: 0.4% of 7212 checklistsFeb 8-14: 0.4% of 8144 checklistsFeb 15-21: 0.6% of 10480 checklistsFeb 22-28: 1.1% of 7932 checklistsMar 1-7: 1.1% of 8192 checklistsMar 8-14: 2.2% of 9383 checklistsMar 15-21: 2.9% of 10620 checklistsMar 22-31: 4.7% of 16257 checklistsApr 1-7: 6.8% of 12568 checklistsApr 8-14: 9.4% of 14677 checklistsApr 15-21: 12% of 14106 checklistsApr 22-30: 13% of 19617 checklistsMay 1-7: 15% of 18143 checklistsMay 8-14: 13% of 19626 checklistsMay 15-21: 11% of 17779 checklistsMay 22-31: 8.9% of 20310 checklistsJun 1-7: 8.1% of 11493 checklistsJun 8-14: 6.6% of 10215 checklistsJun 15-21: 6.2% of 9951 checklistsJun 22-30: 5.6% of 11050 checklistsJul 1-7: 4.4% of 8690 checklistsJul 8-14: 3.2% of 7679 checklistsJul 15-21: 2.0% of 7687 checklistsJul 22-31: 1.3% of 10712 checklistsAug 1-7: 0.9% of 7703 checklistsAug 8-14: 0.8% of 7743 checklistsAug 15-21: 0.7% of 8314 checklistsAug 22-31: 0.5% of 12428 checklistsSep 1-7: 0.4% of 9526 checklistsSep 8-14: 0.5% of 8493 checklistsSep 15-21: 0.3% of 8283 checklistsSep 22-30: 0.3% of 10352 checklistsOct 1-7: 0.4% of 8802 checklistsOct 8-14: 0.7% of 9088 checklistsOct 15-21: 0.5% of 7739 checklistsOct 22-31: 0.5% of 10907 checklistsNov 1-7: 0.3% of 7868 checklistsNov 8-14: 0.2% of 7223 checklistsNov 15-21: 0.5% of 7224 checklistsNov 22-30: 0.4% of 8375 checklistsDec 1-7: 0.4% of 6580 checklistsDec 8-14: 0.4% of 6800 checklistsDec 15-21: 0.4% of 8334 checklistsDec 22-31: 0.4% of 10579 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 Vermont 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 Vermont

Best counties

Share of checklists at the peak
  1. Addison CountyBest early May · 2132 checklists that week, 77,064 in all19%
  2. Grand Isle CountyBest the second week of May · 246 checklists that week, 8,507 in all19%
  3. Franklin CountyBest the second week of May · 1096 checklists that week, 25,284 in all18%
  4. Windham CountyBest early May · 1903 checklists that week, 39,105 in all18%
  5. Rutland CountyBest late April · 1598 checklists that week, 46,909 in all16%
  6. Chittenden CountyBest early May · 4246 checklists that week, 109,477 in all14%

Best spots

Share of checklists at the peak
  1. Whitney/Hospital Creek Wildlife Management AreaAddison County, best the second week of May · 24 checklists that week, 667 in all62%
  2. Lower Otter Creek Wildlife Management AreaAddison County, best the second week of May · 41 checklists that week, 1,322 in all56%
  3. Otter Creek SwampsAddison County, best late April · 35 checklists that week, 254 in all46%
  4. Missisquoi National Wildlife Refuge (southeast)Franklin County, best mid May · 46 checklists that week, 306 in all45%

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

Best time of day

In Vermont, the Brown-headed Cowbird is most often listed on checklists started between 5 and 7 am (11% of those checklists).

0%5%10%15%12 am: too few checklists (384) to judge1 am: too few checklists (418) to judge2 am: too few checklists (568) to judge3 am: too few checklists (1183) to judge4 am: too few checklists (3460) to judge5 am: 12% of 10340 checklists6 am: 11% of 30951 checklists7 am: 6.6% of 64150 checklists8 am: 4.8% of 70252 checklists9 am: 4.2% of 55280 checklists10 am: 3.3% of 47111 checklists11 am: 2.8% of 37615 checklists12 pm: 2.5% of 32195 checklists1 pm: 2.7% of 30185 checklists2 pm: 2.5% of 29679 checklists3 pm: 2.4% of 26483 checklists4 pm: 3.0% of 20110 checklists5 pm: 3.8% of 15993 checklists6 pm: 3.7% of 12110 checklists7 pm: too few checklists (8203) to judge8 pm: too few checklists (4425) to judge9 pm: too few checklists (1829) to judge10 pm: too few checklists (597) to judge11 pm: too few checklists (309) 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
January0.4%0.3%0.4%0.3%
February0.4%0.4%0.6%1.1%
March1.1%2.2%2.9%4.7%
April6.8%9.4%12%13%
May15%13%11%8.9%
June8.1%6.6%6.2%5.6%
July4.4%3.2%2.0%1.3%
August0.9%0.8%0.7%0.5%
September0.4%0.5%0.3%0.3%
October0.4%0.7%0.5%0.5%
November0.3%0.2%0.5%0.4%
December0.4%0.4%0.4%0.4%

Neighboring states

  • New Hampshire: arrives early March, in the same week than Vermont
  • Massachusetts: arrives early March, in the same week than Vermont
  • Connecticut: arrives mid January, 6 weeks earlier than Vermont
  • Rhode Island: arrives late February, 1 week earlier than Vermont

Common questions

When do Brown-headed Cowbirds arrive in Vermont?
Brown-headed Cowbirds reach Vermont in early March, are common by late March, peak in early May (14% of checklists), and most are gone by early July.
When do Brown-headed Cowbirds leave Vermont?
Most Brown-headed Cowbirds have left Vermont by early July, when reports fall below half their usual rate. Stragglers are still reported until early August.
When is the best time to see a Brown-headed Cowbird in Vermont?
The Brown-headed Cowbird is reported most often in early May, on about 14% of Vermont checklists.
Where in Vermont are Brown-headed Cowbirds seen most often?
By county, Addison County, Grand Isle County, and Franklin County have the highest peak reporting rates for the Brown-headed Cowbird (counties with at least 200 checklists).