WhenToBird

Molothrus ater · Icteridae

When Do Brown-headed Cowbirds Arrive in Connecticut?

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

Brown-headed Cowbirds reach Connecticut in mid January, are common by mid March, peak in late April (30% of checklists), and most are gone by the second week of July.

When to look

First arrivalsJan 15-21mid January
Common byMar 15-21mid March
PeakApr 22-30late April
Most gone byJul 8-14the second week of July

Best: late April. First arrivals mid January; most are gone by the second week of July. Peak: on about 30% of Connecticut checklists.

  1. Janrare
  2. Febrare
  3. Marcommon
  4. Aprpeak season
  5. Maypeak season
  6. Juncommon
  7. Julcommon
  8. Auguncommon
  9. Seprare
  10. Octuncommon
  11. Novrare
  12. Decrare

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

0%10%20%30%40%Jan 1-7: 1.9% of 18950 checklistsJan 8-14: 2.0% of 13676 checklistsJan 15-21: 2.3% of 13377 checklistsJan 22-31: 2.2% of 17004 checklistsFeb 1-7: 2.2% of 10218 checklistsFeb 8-14: 2.8% of 11568 checklistsFeb 15-21: 3.3% of 15916 checklistsFeb 22-28: 4.3% of 11413 checklistsMar 1-7: 5.9% of 10754 checklistsMar 8-14: 7.4% of 12051 checklistsMar 15-21: 11% of 12616 checklistsMar 22-31: 14% of 17801 checklistsApr 1-7: 20% of 13186 checklistsApr 8-14: 25% of 14428 checklistsApr 15-21: 28% of 14738 checklistsApr 22-30: 31% of 21753 checklistsMay 1-7: 30% of 22494 checklistsMay 8-14: 28% of 23363 checklistsMay 15-21: 24% of 20219 checklistsMay 22-31: 23% of 20778 checklistsJun 1-7: 22% of 12234 checklistsJun 8-14: 22% of 12491 checklistsJun 15-21: 20% of 10856 checklistsJun 22-30: 19% of 11964 checklistsJul 1-7: 18% of 9437 checklistsJul 8-14: 14% of 8599 checklistsJul 15-21: 8.6% of 8252 checklistsJul 22-31: 6.2% of 11329 checklistsAug 1-7: 5.4% of 8116 checklistsAug 8-14: 5.0% of 8051 checklistsAug 15-21: 5.0% of 8502 checklistsAug 22-31: 4.5% of 13673 checklistsSep 1-7: 4.0% of 9873 checklistsSep 8-14: 2.7% of 9735 checklistsSep 15-21: 2.7% of 10120 checklistsSep 22-30: 3.2% of 12543 checklistsOct 1-7: 3.9% of 10735 checklistsOct 8-14: 4.4% of 10869 checklistsOct 15-21: 4.7% of 10436 checklistsOct 22-31: 4.5% of 13808 checklistsNov 1-7: 4.5% of 10507 checklistsNov 8-14: 3.7% of 9827 checklistsNov 15-21: 3.4% of 9904 checklistsNov 22-30: 2.6% of 13396 checklistsDec 1-7: 2.8% of 8974 checklistsDec 8-14: 2.7% of 9468 checklistsDec 15-21: 2.5% of 11614 checklistsDec 22-31: 1.6% of 16616 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 Connecticut 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 Connecticut

Best counties

Share of checklists at the peak
  1. New London CountyBest late April · 1871 checklists that week, 65,205 in all39%
  2. Windham CountyBest late April · 721 checklists that week, 19,034 in all39%
  3. Tolland CountyBest early May · 1600 checklists that week, 39,004 in all34%
  4. Litchfield CountyBest early May · 2259 checklists that week, 69,766 in all31%
  5. Middlesex CountyBest late April · 1582 checklists that week, 39,919 in all30%
  6. New Haven CountyBest late April · 5410 checklists that week, 139,721 in all29%

Best spots

Share of checklists at the peak
  1. Quinebaug Fish HatcheryWindham County, best early May · 33 checklists that week, 1,048 in all77%
  2. Game Farm PondNew Haven County, best early May · 41 checklists that week, 1,312 in all74%
  3. Greenwich Point ParkFairfield County, best early May · 63 checklists that week, 2,871 in all72%
  4. Hop Brook LakeNew Haven County, best early May · 20 checklists that week, 556 in all70%

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

Best time of day

In Connecticut, the Brown-headed Cowbird is most often listed on checklists started between 6 and 8 am (19% of those checklists).

0%10%20%30%12 am: too few checklists (325) to judge1 am: too few checklists (367) to judge2 am: too few checklists (488) to judge3 am: too few checklists (792) to judge4 am: too few checklists (2722) to judge5 am: too few checklists (9489) to judge6 am: 21% of 33657 checklists7 am: 18% of 62964 checklists8 am: 16% of 70645 checklists9 am: 12% of 64870 checklists10 am: 9.9% of 58827 checklists11 am: 8.5% of 51689 checklists12 pm: 7.6% of 45288 checklists1 pm: 7.0% of 44765 checklists2 pm: 7.3% of 44173 checklists3 pm: 7.3% of 41979 checklists4 pm: 8.7% of 33219 checklists5 pm: 11% of 24828 checklists6 pm: 10% of 15856 checklists7 pm: too few checklists (8126) to judge8 pm: too few checklists (1994) to judge9 pm: too few checklists (533) to judge10 pm: too few checklists (349) to judge11 pm: too few checklists (286) 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
January1.9%2.0%2.3%2.2%
February2.2%2.8%3.3%4.3%
March5.9%7.4%11%14%
April20%25%28%31%
May30%28%24%23%
June22%22%20%19%
July18%14%8.6%6.2%
August5.4%5.0%5.0%4.5%
September4.0%2.7%2.7%3.2%
October3.9%4.4%4.7%4.5%
November4.5%3.7%3.4%2.6%
December2.8%2.7%2.5%1.6%

Neighboring states

  • Rhode Island: arrives late February, 5 weeks later than Connecticut
  • Massachusetts: arrives early March, 6 weeks later than Connecticut
  • New Jersey: arrives late March, 9 weeks later than Connecticut
  • New York: arrives mid February, 4 weeks later than Connecticut

Common questions

When do Brown-headed Cowbirds arrive in Connecticut?
Brown-headed Cowbirds reach Connecticut in mid January, are common by mid March, peak in late April (30% of checklists), and most are gone by the second week of July.
When do Brown-headed Cowbirds leave Connecticut?
Most Brown-headed Cowbirds have left Connecticut by the second week of July, when reports fall below half their usual rate. Stragglers are still reported until mid December.
When is the best time to see a Brown-headed Cowbird in Connecticut?
The Brown-headed Cowbird is reported most often in late April, on about 30% of Connecticut checklists.
Where in Connecticut are Brown-headed Cowbirds seen most often?
By county, New London County, Windham County, and Tolland County have the highest peak reporting rates for the Brown-headed Cowbird (counties with at least 200 checklists).