WhenToBird

Larus smithsonianus · Laridae

When Do American Herring Gulls Arrive in Colorado?

Adult American Herring Gull
Photo: Priya Sandhu, CC BY 4.0 via iNaturalist

American Herring Gulls are winter birds in Colorado: the first arrive in early October, they are common by mid October, peak in mid November (4.5% of checklists), and most are gone by late March.

When to look

First arrivalsOct 1-7early October
Common byOct 15-21mid October
PeakNov 15-21mid November
Most gone byMar 22-31late March

Best: mid November. First arrivals early October; most are gone by late March. Peak: on about 4.5% of Colorado checklists.

  1. Janpeak season
  2. Febcommon
  3. Marcommon
  4. Apruncommon
  5. Maynot usually seen
  6. Junnot usually seen
  7. Julnot usually seen
  8. Augnot usually seen
  9. Sepuncommon
  10. Octcommon
  11. Novpeak season
  12. Decpeak season

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

0%2%4%6%Jan 1-7: 4.1% of 32254 checklistsJan 8-14: 3.8% of 23278 checklistsJan 15-21: 3.9% of 22933 checklistsJan 22-31: 3.4% of 30856 checklistsFeb 1-7: 2.9% of 21464 checklistsFeb 8-14: 2.4% of 22910 checklistsFeb 15-21: 2.5% of 28739 checklistsFeb 22-28: 3.1% of 21833 checklistsMar 1-7: 2.9% of 23066 checklistsMar 8-14: 2.7% of 23783 checklistsMar 15-21: 2.9% of 24797 checklistsMar 22-31: 2.6% of 38439 checklistsApr 1-7: 1.5% of 31676 checklistsApr 8-14: 0.9% of 35092 checklistsApr 15-21: 0.6% of 36778 checklistsApr 22-30: 0.2% of 50885 checklistsMay 1-7: 0.1% of 44186 checklistsMay 8-14: 0.1% of 49011 checklistsMay 15-21: 0.1% of 40784 checklistsMay 22-31: 0.1% of 53073 checklistsJun 1-7: 0.1% of 32432 checklistsJun 8-14: 0.1% of 29978 checklistsJun 15-21: 0.1% of 29457 checklistsJun 22-30: 0.1% of 36072 checklistsJul 1-7: 0% of 28857 checklistsJul 8-14: 0.1% of 27224 checklistsJul 15-21: 0.1% of 27629 checklistsJul 22-31: 0.1% of 37318 checklistsAug 1-7: 0.1% of 25893 checklistsAug 8-14: 0.1% of 24870 checklistsAug 15-21: 0.1% of 24035 checklistsAug 22-31: 0.1% of 35691 checklistsSep 1-7: 0.1% of 27068 checklistsSep 8-14: 0.2% of 26709 checklistsSep 15-21: 0.5% of 26098 checklistsSep 22-30: 0.6% of 31550 checklistsOct 1-7: 1.0% of 24110 checklistsOct 8-14: 1.6% of 23352 checklistsOct 15-21: 2.3% of 21895 checklistsOct 22-31: 3.2% of 28319 checklistsNov 1-7: 4.0% of 21698 checklistsNov 8-14: 4.7% of 21061 checklistsNov 15-21: 4.2% of 19855 checklistsNov 22-30: 4.5% of 25798 checklistsDec 1-7: 4.5% of 18626 checklistsDec 8-14: 3.8% of 19004 checklistsDec 15-21: 3.3% of 23103 checklistsDec 22-31: 3.9% of 30802 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 Colorado 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 Colorado

Best counties

Share of checklists at the peak
  1. Washington CountyBest the second week of November · 15 checklists that week, 2,511 in all45%
  2. Kiowa CountyBest mid November · 27 checklists that week, 3,854 in all43%
  3. Logan CountyBest late October · 33 checklists that week, 4,117 in all29%
  4. Pueblo CountyBest mid January · 883 checklists that week, 26,547 in all27%
  5. Crowley CountyBest the second week of December · 11 checklists that week, 1,883 in all25%
  6. Sedgwick CountyBest mid October · 24 checklists that week, 1,168 in all23%

Best spots

Share of checklists at the peak
  1. Horseshoe LakeLarimer County, best late November · 45 checklists that week, 747 in all96%
  2. Warren LakeLarimer County, best early March · 41 checklists that week, 712 in all90%
  3. Lake Pueblo State ParkPueblo County, best the second week of January · 105 checklists that week, 1,491 in all76%
  4. Larimer County LandfillLarimer County, best mid December · 26 checklists that week, 340 in all74%

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

Best time of day

In Colorado, the American Herring Gull is most often listed on checklists started between 1 and 3 pm (2.1% of those checklists).

0%1%2%3%12 am: too few checklists (512) to judge1 am: too few checklists (468) to judge2 am: too few checklists (513) to judge3 am: too few checklists (656) to judge4 am: too few checklists (1918) to judge5 am: too few checklists (16045) to judge6 am: 0.6% of 71991 checklists7 am: 1.1% of 159189 checklists8 am: 1.3% of 177206 checklists9 am: 1.5% of 165269 checklists10 am: 1.7% of 141029 checklists11 am: 1.9% of 115283 checklists12 pm: 2.1% of 96068 checklists1 pm: 2.1% of 89512 checklists2 pm: 2.1% of 86319 checklists3 pm: 2.0% of 82496 checklists4 pm: 1.5% of 71648 checklists5 pm: 0.8% of 52445 checklists6 pm: 0.4% of 40199 checklists7 pm: too few checklists (24246) to judge8 pm: too few checklists (7986) to judge9 pm: too few checklists (2004) to judge10 pm: too few checklists (888) to judge11 pm: too few checklists (450) 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
January4.1%3.8%3.9%3.4%
February2.9%2.4%2.5%3.1%
March2.9%2.7%2.9%2.6%
April1.5%0.9%0.6%0.2%
May0.1%0.1%0.1%0.1%
June0.1%0.1%0.1%0.1%
July0%0.1%0.1%0.1%
August0.1%0.1%0.1%0.1%
September0.1%0.2%0.5%0.6%
October1.0%1.6%2.3%3.2%
November4.0%4.7%4.2%4.5%
December4.5%3.8%3.3%3.9%

Neighboring states

  • Wyoming: arrives mid September, 2 weeks earlier than Colorado
  • Utah: arrives mid October, 2 weeks later than Colorado
  • Nebraska: arrives the second week of October, 1 week later than Colorado
  • South Dakota: arrives early October, in the same week than Colorado

Common questions

When do American Herring Gulls arrive in Colorado?
American Herring Gulls are winter birds in Colorado: the first arrive in early October, they are common by mid October, peak in mid November (4.5% of checklists), and most are gone by late March.
When do American Herring Gulls leave Colorado?
Most American Herring Gulls have left Colorado by late March, when reports fall below half their usual rate. Stragglers are still reported until early April.
When is the best time to see a American Herring Gull in Colorado?
The American Herring Gull is reported most often in mid November, on about 4.5% of Colorado checklists.
Where in Colorado are American Herring Gulls seen most often?
By county, Washington County, Kiowa County, and Logan County have the highest peak reporting rates for the American Herring Gull (counties with at least 200 checklists).