WhenToBird

Chroicocephalus philadelphia · Laridae

When Do Bonaparte's Gulls Arrive in Iowa?

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

Bonaparte's Gulls are winter birds in Iowa: they arrive in mid September, peak in early November (6.9% of checklists), and most are gone by the second week of December.

When to look

First arrivalsSep 15-21mid September
Common bySep 15-21mid September
PeakNov 1-7early November
Most gone byDec 8-14the second week of December

Best: early November. First arrivals mid September; most are gone by the second week of December. Peak: on about 6.9% of Iowa checklists.

  1. Jannot usually seen
  2. Febnot usually seen
  3. Marrare
  4. Aprcommon
  5. Mayuncommon
  6. Junnot usually seen
  7. Julnot usually seen
  8. Augnot usually seen
  9. Seprare
  10. Octpeak season
  11. Novpeak season
  12. Decuncommon

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

0%2%4%6%8%Jan 1-7: 0.1% of 5551 checklistsJan 8-14: 0% of 3498 checklistsJan 15-21: 0% of 3803 checklistsJan 22-31: 0% of 4807 checklistsFeb 1-7: 0% of 3613 checklistsFeb 8-14: 0% of 4173 checklistsFeb 15-21: 0% of 5796 checklistsFeb 22-28: 0% of 4394 checklistsMar 1-7: 0.1% of 5295 checklistsMar 8-14: 0.1% of 5679 checklistsMar 15-21: 0.1% of 5418 checklistsMar 22-31: 0.7% of 8613 checklistsApr 1-7: 1.8% of 6970 checklistsApr 8-14: 3.6% of 7511 checklistsApr 15-21: 4.6% of 8321 checklistsApr 22-30: 2.1% of 11976 checklistsMay 1-7: 1.0% of 11725 checklistsMay 8-14: 0.3% of 12626 checklistsMay 15-21: 0.1% of 9372 checklistsMay 22-31: 0.1% of 10330 checklistsJun 1-7: 0.1% of 5472 checklistsJun 8-14: 0% of 4568 checklistsJun 15-21: 0% of 3870 checklistsJun 22-30: 0% of 4780 checklistsJul 1-7: 0% of 4201 checklistsJul 8-14: 0% of 3605 checklistsJul 15-21: 0.1% of 3621 checklistsJul 22-31: 0% of 5093 checklistsAug 1-7: 0.1% of 3931 checklistsAug 8-14: 0.1% of 3488 checklistsAug 15-21: 0.1% of 3802 checklistsAug 22-31: 0.1% of 6293 checklistsSep 1-7: 0.1% of 5328 checklistsSep 8-14: 0.2% of 4622 checklistsSep 15-21: 0.2% of 4367 checklistsSep 22-30: 0.8% of 6086 checklistsOct 1-7: 1.3% of 4708 checklistsOct 8-14: 2.1% of 4791 checklistsOct 15-21: 4.1% of 4429 checklistsOct 22-31: 6.6% of 5633 checklistsNov 1-7: 7.4% of 4090 checklistsNov 8-14: 7.1% of 3416 checklistsNov 15-21: 5.3% of 3398 checklistsNov 22-30: 3.7% of 4679 checklistsDec 1-7: 1.2% of 3442 checklistsDec 8-14: 0.2% of 3322 checklistsDec 15-21: 0.1% of 4619 checklistsDec 22-31: 0.1% of 5113 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 Iowa 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 Iowa

Best counties

Share of checklists at the peak
  1. Marion CountyBest the second week of November · 59 checklists that week, 3,389 in all37%
  2. Polk CountyBest early November · 764 checklists that week, 37,521 in all19%
  3. Hancock CountyBest early November · 12 checklists that week, 449 in all17%
  4. Clay CountyBest mid April · 19 checklists that week, 844 in all16%
  5. Appanoose CountyBest late November · 12 checklists that week, 820 in all13%
  6. Buena Vista CountyBest late April · 127 checklists that week, 2,846 in all13%

Best spots

Share of checklists at the peak
  1. Saylorville Recreation Area (northwest)Polk County, best the second week of April · 36 checklists that week, 1,546 in all65%
  2. Big Creek State ParkPolk County, best early November · 26 checklists that week, 561 in all60%
  3. Saylorville Recreation Area (Camp Dodge)Polk County, best the second week of November · 23 checklists that week, 690 in all51%
  4. Lake MacBrideJohnson County, best early November · 34 checklists that week, 1,067 in all49%
  5. Big Creek Wildlife Management AreaPolk County, best early November · 31 checklists that week, 500 in all46%
  6. Saylorville Recreation Area (Rock Creek)Polk County, best late October · 120 checklists that week, 1,401 in all44%

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

Best time of day

In Iowa, the Bonaparte's Gull is most often listed on checklists started between 12 and 2 pm (1.4% of those checklists).

0%0.5%1%1.5%12 am: too few checklists (96) to judge1 am: too few checklists (99) to judge2 am: too few checklists (67) to judge3 am: too few checklists (82) to judge4 am: too few checklists (201) to judge5 am: too few checklists (1888) to judge6 am: 0.7% of 11313 checklists7 am: 1.0% of 25717 checklists8 am: 1.4% of 29755 checklists9 am: 1.2% of 28897 checklists10 am: 1.4% of 26343 checklists11 am: 1.3% of 21210 checklists12 pm: 1.4% of 17662 checklists1 pm: 1.4% of 16595 checklists2 pm: 1.1% of 16405 checklists3 pm: 1.0% of 17030 checklists4 pm: 1.0% of 17378 checklists5 pm: 1.1% of 14251 checklists6 pm: 0.7% of 10349 checklists7 pm: 0.4% of 6233 checklists8 pm: too few checklists (2002) to judge9 pm: too few checklists (392) to judge10 pm: too few checklists (186) to judge11 pm: too few checklists (87) 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%0%
February0%0%0%0%
March0.1%0.1%0.1%0.7%
April1.8%3.6%4.6%2.1%
May1.0%0.3%0.1%0.1%
June0.1%0%0%0%
July0%0%0.1%0%
August0.1%0.1%0.1%0.1%
September0.1%0.2%0.2%0.8%
October1.3%2.1%4.1%6.6%
November7.4%7.1%5.3%3.7%
December1.2%0.2%0.1%0.1%

Neighboring states

  • Missouri: arrives early October, 2 weeks later than Iowa
  • Wisconsin: arrives late March, 23 weeks earlier than Iowa
  • Minnesota: arrives early April, 22 weeks earlier than Iowa
  • Illinois: arrives early October, 2 weeks later than Iowa

Common questions

When do Bonaparte's Gulls arrive in Iowa?
Bonaparte's Gulls are winter birds in Iowa: they arrive in mid September, peak in early November (6.9% of checklists), and most are gone by the second week of December.
When do Bonaparte's Gulls leave Iowa?
Most Bonaparte's Gulls have left Iowa 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 Iowa?
The Bonaparte's Gull is reported most often in early November, on about 6.9% of Iowa checklists.
Where in Iowa are Bonaparte's Gulls seen most often?
By county, Marion County, Polk County, and Hancock County have the highest peak reporting rates for the Bonaparte's Gull (counties with at least 200 checklists).