WhenToBird

Chroicocephalus philadelphia · Laridae

When Do Bonaparte's Gulls Arrive in Utah?

Adult Bonaparte's Gull
Photo: Kevin Krebs, CC BY 4.0 via iNaturalist

Bonaparte's Gulls are winter birds in Utah: they arrive in early October, peak in early November (1.6% of checklists), and most are gone by the second week of December.

When to look

First arrivalsOct 1-7early October
Common byOct 1-7early October
PeakNov 1-7early November
Most gone byDec 8-14the second week of December

Best: early November. First arrivals early October; most are gone by the second week of December. Peak: on about 1.6% of Utah checklists.

  1. Janrare
  2. Febrare
  3. Marcommon
  4. Aprpeak season
  5. Maycommon
  6. Junrare
  7. Julnot usually seen
  8. Augrare
  9. Sepuncommon
  10. Octcommon
  11. Novpeak season
  12. Deccommon

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

0%0.5%1%1.5%2%Jan 1-7: 0.1% of 10857 checklistsJan 8-14: 0.1% of 8333 checklistsJan 15-21: 0.1% of 8360 checklistsJan 22-31: 0.1% of 10516 checklistsFeb 1-7: 0.1% of 7416 checklistsFeb 8-14: 0.1% of 8082 checklistsFeb 15-21: 0.2% of 9643 checklistsFeb 22-28: 0.1% of 7960 checklistsMar 1-7: 0.1% of 7998 checklistsMar 8-14: 0.2% of 8581 checklistsMar 15-21: 0.5% of 8637 checklistsMar 22-31: 0.7% of 13006 checklistsApr 1-7: 1.0% of 10562 checklistsApr 8-14: 1.5% of 11694 checklistsApr 15-21: 1.8% of 11382 checklistsApr 22-30: 1.4% of 16626 checklistsMay 1-7: 1.0% of 13523 checklistsMay 8-14: 0.6% of 14714 checklistsMay 15-21: 0.3% of 13711 checklistsMay 22-31: 0.2% of 16546 checklistsJun 1-7: 0.1% of 10284 checklistsJun 8-14: 0.1% of 9530 checklistsJun 15-21: 0.1% of 8854 checklistsJun 22-30: 0.1% of 10566 checklistsJul 1-7: 0.1% of 7987 checklistsJul 8-14: 0.1% of 7471 checklistsJul 15-21: 0.1% of 7240 checklistsJul 22-31: 0.1% of 9329 checklistsAug 1-7: 0.1% of 6521 checklistsAug 8-14: 0.2% of 6423 checklistsAug 15-21: 0.2% of 6208 checklistsAug 22-31: 0.1% of 9089 checklistsSep 1-7: 0.3% of 7081 checklistsSep 8-14: 0.3% of 7306 checklistsSep 15-21: 0.2% of 7208 checklistsSep 22-30: 0.2% of 8876 checklistsOct 1-7: 0.2% of 7265 checklistsOct 8-14: 0.6% of 7226 checklistsOct 15-21: 0.4% of 7007 checklistsOct 22-31: 1.4% of 8443 checklistsNov 1-7: 1.9% of 6711 checklistsNov 8-14: 1.7% of 6290 checklistsNov 15-21: 1.1% of 6169 checklistsNov 22-30: 1.5% of 8228 checklistsDec 1-7: 0.6% of 6011 checklistsDec 8-14: 0.5% of 6044 checklistsDec 15-21: 0.2% 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. Box Elder CountyBest mid November · 160 checklists that week, 9,867 in all23%
  2. Summit CountyBest early November · 214 checklists that week, 13,829 in all6.9%
  3. Piute CountyBest mid April · 24 checklists that week, 1,035 in all5.8%
  4. Duchesne CountyBest early April · 51 checklists that week, 2,692 in all5.3%
  5. Davis CountyBest the second week of November · 588 checklists that week, 39,952 in all5.3%
  6. Utah CountyBest mid April · 1881 checklists that week, 70,971 in all4.9%

Best spots

Share of checklists at the peak
  1. Willard Bay State Park (Dix Creek)Box Elder County, best late November · 43 checklists that week, 202 in all74%
  2. Willard Bay State ParkBox Elder County, best the second week of November · 25 checklists that week, 800 in all60%
  3. Jordan Willows ParkUtah County, best mid April · 140 checklists that week, 2,225 in all26%

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

Best time of day

In Utah, the Bonaparte's Gull is most often listed on checklists started between 12 and 2 pm (0.6% of those checklists).

0%0.5%1%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: 0.2% of 11714 checklists7 am: 0.5% of 33209 checklists8 am: 0.5% of 46944 checklists9 am: 0.4% of 46290 checklists10 am: 0.5% of 43144 checklists11 am: 0.6% of 36893 checklists12 pm: 0.6% of 32758 checklists1 pm: 0.6% of 30142 checklists2 pm: 0.6% of 29414 checklists3 pm: 0.6% of 29491 checklists4 pm: 0.5% of 29154 checklists5 pm: 0.4% of 22256 checklists6 pm: 0.4% of 17383 checklists7 pm: 0.4% 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
January0.1%0.1%0.1%0.1%
February0.1%0.1%0.2%0.1%
March0.1%0.2%0.5%0.7%
April1.0%1.5%1.8%1.4%
May1.0%0.6%0.3%0.2%
June0.1%0.1%0.1%0.1%
July0.1%0.1%0.1%0.1%
August0.1%0.2%0.2%0.1%
September0.3%0.3%0.2%0.2%
October0.2%0.6%0.4%1.4%
November1.9%1.7%1.1%1.5%
December0.6%0.5%0.2%0.2%

Neighboring states

  • Wyoming: arrives early September, 4 weeks earlier than Utah
  • Nevada: arrives early July, 12 weeks earlier than Utah
  • Colorado: arrives late September, 1 week earlier than Utah
  • Idaho: arrives early August, 8 weeks earlier than Utah

Common questions

When do Bonaparte's Gulls arrive in Utah?
Bonaparte's Gulls are winter birds in Utah: they arrive in early October, peak in early November (1.6% of checklists), and most are gone by the second week of December.
When do Bonaparte's Gulls leave Utah?
Most Bonaparte's Gulls have left Utah by the second week of December, when reports fall below half their usual rate.
When is the best time to see a Bonaparte's Gull in Utah?
The Bonaparte's Gull is reported most often in early November, on about 1.6% of Utah checklists.
Where in Utah are Bonaparte's Gulls seen most often?
By county, Box Elder County, Summit County, and Piute County have the highest peak reporting rates for the Bonaparte's Gull (counties with at least 200 checklists).