WhenToBird

Molothrus ater · Icteridae

When Do Brown-headed Cowbirds Arrive in Utah?

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

Brown-headed Cowbirds reach Utah in mid April, are common by late April, peak in late May (19% of checklists), and most are gone by mid July.

When to look

First arrivalsApr 15-21mid April
Common byApr 22-30late April
PeakMay 22-31late May
Most gone byJul 15-21mid July

Best: late May. First arrivals mid April; most are gone by mid July. Peak: on about 19% of Utah checklists.

  1. Jannot usually seen
  2. Febnot usually seen
  3. Marnot usually seen
  4. Apruncommon
  5. Maypeak season
  6. Junpeak season
  7. Julcommon
  8. Auguncommon
  9. Seprare
  10. Octnot usually seen
  11. Novnot usually seen
  12. Decnot usually seen

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

0%10%20%30%Jan 1-7: 0.2% of 10857 checklistsJan 8-14: 0.3% of 8333 checklistsJan 15-21: 0.3% of 8360 checklistsJan 22-31: 0.2% of 10516 checklistsFeb 1-7: 0.2% of 7416 checklistsFeb 8-14: 0.2% of 8082 checklistsFeb 15-21: 0.1% of 9643 checklistsFeb 22-28: 0.1% of 7960 checklistsMar 1-7: 0.2% of 7998 checklistsMar 8-14: 0.3% of 8581 checklistsMar 15-21: 0.3% of 8637 checklistsMar 22-31: 0.3% of 13006 checklistsApr 1-7: 0.3% of 10562 checklistsApr 8-14: 0.9% of 11694 checklistsApr 15-21: 1.9% of 11382 checklistsApr 22-30: 5.4% of 16626 checklistsMay 1-7: 13% of 13523 checklistsMay 8-14: 17% of 14714 checklistsMay 15-21: 21% of 13711 checklistsMay 22-31: 19% of 16546 checklistsJun 1-7: 17% of 10284 checklistsJun 8-14: 15% of 9530 checklistsJun 15-21: 15% of 8854 checklistsJun 22-30: 13% of 10566 checklistsJul 1-7: 12% of 7987 checklistsJul 8-14: 10% of 7471 checklistsJul 15-21: 7.2% of 7240 checklistsJul 22-31: 4.4% of 9329 checklistsAug 1-7: 2.9% of 6521 checklistsAug 8-14: 2.6% of 6423 checklistsAug 15-21: 1.8% of 6208 checklistsAug 22-31: 1.7% of 9089 checklistsSep 1-7: 1.0% of 7081 checklistsSep 8-14: 0.7% of 7306 checklistsSep 15-21: 0.4% of 7208 checklistsSep 22-30: 0.2% of 8876 checklistsOct 1-7: 0.2% of 7265 checklistsOct 8-14: 0.2% of 7226 checklistsOct 15-21: 0.2% of 7007 checklistsOct 22-31: 0.1% of 8443 checklistsNov 1-7: 0.3% of 6711 checklistsNov 8-14: 0.2% of 6290 checklistsNov 15-21: 0.1% of 6169 checklistsNov 22-30: 0.3% of 8228 checklistsDec 1-7: 0.6% of 6011 checklistsDec 8-14: 0.3% of 6044 checklistsDec 15-21: 0.1% of 6721 checklistsDec 22-31: 0.2% of 9982 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 Utah 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 Utah

Best counties

Share of checklists at the peak
  1. Morgan CountyBest the second week of May · 118 checklists that week, 3,178 in all33%
  2. Box Elder CountyBest late May · 361 checklists that week, 9,867 in all33%
  3. Cache CountyBest late May · 853 checklists that week, 21,769 in all30%
  4. Utah CountyBest mid May · 2219 checklists that week, 70,971 in all29%
  5. Wasatch CountyBest late May · 409 checklists that week, 7,780 in all27%
  6. Juab CountyBest mid May · 120 checklists that week, 2,572 in all27%

Best spots

Share of checklists at the peak
  1. Willard Bay State ParkBox Elder County, best late May · 35 checklists that week, 800 in all87%
  2. 10th West ParkCache County, best late May · 43 checklists that week, 771 in all79%
  3. CloverwoodSalt Lake County, best the second week of June · 20 checklists that week, 834 in all75%
  4. Trapper ParkCache County, best mid May · 22 checklists that week, 491 in all75%
  5. Dry CreekUtah County, best mid June · 61 checklists that week, 2,498 in all73%

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

Best time of day

In Utah, the Brown-headed Cowbird is most often listed on checklists started between 6 and 8 am (12% of those checklists).

0%5%10%15%20%12 am: too few checklists (242) to judge1 am: too few checklists (178) to judge2 am: too few checklists (169) to judge3 am: too few checklists (162) to judge4 am: too few checklists (284) to judge5 am: too few checklists (1984) to judge6 am: 16% of 11714 checklists7 am: 9.9% of 33209 checklists8 am: 6.7% of 46944 checklists9 am: 5.3% of 46290 checklists10 am: 4.3% of 43144 checklists11 am: 3.8% of 36893 checklists12 pm: 3.2% of 32758 checklists1 pm: 2.9% of 30142 checklists2 pm: 2.5% of 29414 checklists3 pm: 2.4% of 29491 checklists4 pm: 2.5% of 29154 checklists5 pm: 3.8% of 22256 checklists6 pm: 4.9% of 17383 checklists7 pm: 5.4% of 13099 checklists8 pm: too few checklists (6647) to judge9 pm: too few checklists (1753) to judge10 pm: too few checklists (599) to judge11 pm: too few checklists (307) 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
January0.2%0.3%0.3%0.2%
February0.2%0.2%0.1%0.1%
March0.2%0.3%0.3%0.3%
April0.3%0.9%1.9%5.4%
May13%17%21%19%
June17%15%15%13%
July12%10%7.2%4.4%
August2.9%2.6%1.8%1.7%
September1.0%0.7%0.4%0.2%
October0.2%0.2%0.2%0.1%
November0.3%0.2%0.1%0.3%
December0.6%0.3%0.1%0.2%

Neighboring states

  • Wyoming: arrives mid April, in the same week than Utah
  • Nevada: arrives late March, 3 weeks earlier than Utah
  • Colorado: arrives the second week of April, 1 week earlier than Utah
  • Idaho: arrives mid April, in the same week than Utah

Common questions

When do Brown-headed Cowbirds arrive in Utah?
Brown-headed Cowbirds reach Utah in mid April, are common by late April, peak in late May (19% of checklists), and most are gone by mid July.
When do Brown-headed Cowbirds leave Utah?
Most Brown-headed Cowbirds have left Utah by mid July, when reports fall below half their usual rate. Stragglers are still reported until late August.
When is the best time to see a Brown-headed Cowbird in Utah?
The Brown-headed Cowbird is reported most often in late May, on about 19% of Utah checklists.
Where in Utah are Brown-headed Cowbirds seen most often?
By county, Morgan County, Box Elder County, and Cache County have the highest peak reporting rates for the Brown-headed Cowbird (counties with at least 200 checklists).