WhenToBird

Molothrus ater · Icteridae

When Do Brown-headed Cowbirds Arrive in North Dakota?

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

Brown-headed Cowbirds reach North Dakota in mid April, are common by early May, peak in late May (45% of checklists), and most are gone by the second week of July.

When to look

First arrivalsApr 15-21mid April
Common byMay 1-7early May
PeakMay 22-31late May
Most gone byJul 8-14the second week of July

Best: late May. First arrivals mid April; most are gone by the second week of July. Peak: on about 45% of North Dakota checklists.

  1. Jannot usually seen
  2. Febnot usually seen
  3. Marnot usually seen
  4. Apruncommon
  5. Maypeak season
  6. Junpeak season
  7. Julpeak season
  8. Auguncommon
  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%20%40%60%Jan 1-7: 0.1% of 1694 checklistsJan 8-14: 0% of 1210 checklistsJan 15-21: 0.1% of 1263 checklistsJan 22-31: 0% of 1984 checklistsFeb 1-7: 0% of 1209 checklistsFeb 8-14: 0.3% of 1307 checklistsFeb 15-21: 0.1% of 1655 checklistsFeb 22-28: 0.2% of 1619 checklistsMar 1-7: 0.2% of 1653 checklistsMar 8-14: 0.3% of 1818 checklistsMar 15-21: 0.1% of 2103 checklistsMar 22-31: 0.2% of 3714 checklistsApr 1-7: 0.2% of 2955 checklistsApr 8-14: 1.3% of 3550 checklistsApr 15-21: 2.9% of 4104 checklistsApr 22-30: 11% of 5712 checklistsMay 1-7: 30% of 5328 checklistsMay 8-14: 42% of 5885 checklistsMay 15-21: 44% of 5344 checklistsMay 22-31: 46% of 7512 checklistsJun 1-7: 44% of 4329 checklistsJun 8-14: 40% of 4287 checklistsJun 15-21: 41% of 3798 checklistsJun 22-30: 40% of 4361 checklistsJul 1-7: 35% of 2939 checklistsJul 8-14: 27% of 2407 checklistsJul 15-21: 19% of 2254 checklistsJul 22-31: 9.9% of 2852 checklistsAug 1-7: 7.4% of 2119 checklistsAug 8-14: 4.3% of 2044 checklistsAug 15-21: 4.4% of 2124 checklistsAug 22-31: 2.3% of 3168 checklistsSep 1-7: 0.8% of 2449 checklistsSep 8-14: 0.4% of 2310 checklistsSep 15-21: 0.1% of 2092 checklistsSep 22-30: 0% of 2565 checklistsOct 1-7: 0.1% of 2071 checklistsOct 8-14: 0% of 1918 checklistsOct 15-21: 0.1% of 1907 checklistsOct 22-31: 0.1% of 2589 checklistsNov 1-7: 0% of 1858 checklistsNov 8-14: 0% of 1753 checklistsNov 15-21: 0% of 1483 checklistsNov 22-30: 0% of 1928 checklistsDec 1-7: 0% of 1337 checklistsDec 8-14: 0% of 1309 checklistsDec 15-21: 0% of 1642 checklistsDec 22-31: 0% of 1830 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 North Dakota 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 North Dakota

Best counties

Share of checklists at the peak
  1. Sioux CountyBest mid May · 22 checklists that week, 340 in all84%
  2. Sheridan CountyBest the second week of July · 11 checklists that week, 620 in all76%
  3. Renville CountyBest late June · 27 checklists that week, 415 in all75%
  4. McHenry CountyBest mid May · 58 checklists that week, 1,118 in all73%
  5. Emmons CountyBest early June · 22 checklists that week, 687 in all73%
  6. Grant CountyBest late May · 22 checklists that week, 605 in all70%

Best spots

Share of checklists at the peak
  1. Des Lacs National Wildlife RefugeWard County, best late May · 32 checklists that week, 116 in all95%
  2. Oak ParkWard County, best early June · 34 checklists that week, 777 in all81%
  3. BOR LandsStark County, best late May · 25 checklists that week, 357 in all81%
  4. Denbigh Experimental ForestMcHenry County, best late May · 25 checklists that week, 329 in all80%

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

Best time of day

In North Dakota, the Brown-headed Cowbird is most often listed on checklists started between 6 and 8 am (30% of those checklists).

0%10%20%30%40%12 am: too few checklists (74) to judge1 am: too few checklists (45) to judge2 am: too few checklists (42) to judge3 am: too few checklists (68) to judge4 am: too few checklists (274) to judge5 am: too few checklists (1538) to judge6 am: 39% of 4242 checklists7 am: 27% of 9520 checklists8 am: 19% of 13065 checklists9 am: 17% of 13356 checklists10 am: 16% of 12128 checklists11 am: 14% of 10772 checklists12 pm: 13% of 10316 checklists1 pm: 10% of 9169 checklists2 pm: 11% of 8880 checklists3 pm: 9.9% of 8688 checklists4 pm: 9.1% of 8201 checklists5 pm: 11% of 6687 checklists6 pm: 12% of 5455 checklists7 pm: 15% of 3926 checklists8 pm: too few checklists (2024) to judge9 pm: too few checklists (602) to judge10 pm: too few checklists (181) to judge11 pm: too few checklists (89) 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%0.1%0%
February0%0.3%0.1%0.2%
March0.2%0.3%0.1%0.2%
April0.2%1.3%2.9%11%
May30%42%44%46%
June44%40%41%40%
July35%27%19%9.9%
August7.4%4.3%4.4%2.3%
September0.8%0.4%0.1%0%
October0.1%0%0.1%0.1%
November0%0%0%0%
December0%0%0%0%

Neighboring states

  • South Dakota: arrives early April, 2 weeks earlier than North Dakota
  • Minnesota: arrives early April, 2 weeks earlier than North Dakota
  • Nebraska: arrives mid March, 4 weeks earlier than North Dakota
  • Iowa: arrives the second week of March, 5 weeks earlier than North Dakota

Common questions

When do Brown-headed Cowbirds arrive in North Dakota?
Brown-headed Cowbirds reach North Dakota in mid April, are common by early May, peak in late May (45% of checklists), and most are gone by the second week of July.
When do Brown-headed Cowbirds leave North Dakota?
Most Brown-headed Cowbirds have left North Dakota by the second week of July, when reports fall below half their usual rate. Stragglers are still reported until the second week of August.
When is the best time to see a Brown-headed Cowbird in North Dakota?
The Brown-headed Cowbird is reported most often in late May, on about 45% of North Dakota checklists.
Where in North Dakota are Brown-headed Cowbirds seen most often?
By county, Sioux County, Sheridan County, and Renville County have the highest peak reporting rates for the Brown-headed Cowbird (counties with at least 200 checklists).