WhenToBird

Chroicocephalus philadelphia · Laridae

When Do Bonaparte's Gulls Arrive in Delaware?

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

Bonaparte's Gulls are winter birds in Delaware: they arrive in early November, peak in the second week of January (6.0% of checklists), and most are gone by early May.

When to look

First arrivalsNov 1-7early November
Common byNov 1-7early November
PeakJan 8-14the second week of January
Most gone byMay 1-7early May

Best: the second week of January. First arrivals early November; most are gone by early May. Peak: on about 6.0% of Delaware checklists.

  1. Janpeak season
  2. Febcommon
  3. Marcommon
  4. Aprcommon
  5. Mayuncommon
  6. Junrare
  7. Julrare
  8. Augrare
  9. Seprare
  10. Octrare
  11. Novcommon
  12. Decpeak season

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

0%2%4%6%8%Jan 1-7: 5.3% of 5901 checklistsJan 8-14: 6.7% of 4091 checklistsJan 15-21: 6.5% of 3841 checklistsJan 22-31: 4.0% of 5084 checklistsFeb 1-7: 3.6% of 3705 checklistsFeb 8-14: 1.6% of 3991 checklistsFeb 15-21: 1.9% of 6056 checklistsFeb 22-28: 1.7% of 4036 checklistsMar 1-7: 1.4% of 3822 checklistsMar 8-14: 1.2% of 3873 checklistsMar 15-21: 1.1% of 3856 checklistsMar 22-31: 2.8% of 5702 checklistsApr 1-7: 3.7% of 4104 checklistsApr 8-14: 2.9% of 4456 checklistsApr 15-21: 2.4% of 4871 checklistsApr 22-30: 1.6% of 7249 checklistsMay 1-7: 1.8% of 6806 checklistsMay 8-14: 1.4% of 7229 checklistsMay 15-21: 0.9% of 6466 checklistsMay 22-31: 0.7% of 7437 checklistsJun 1-7: 0.7% of 3596 checklistsJun 8-14: 0.3% of 2847 checklistsJun 15-21: 1.0% of 2901 checklistsJun 22-30: 0.6% of 3644 checklistsJul 1-7: 0.4% of 3142 checklistsJul 8-14: 0.6% of 2767 checklistsJul 15-21: 0.9% of 2882 checklistsJul 22-31: 0.9% of 4175 checklistsAug 1-7: 0.8% of 3482 checklistsAug 8-14: 0.5% of 3477 checklistsAug 15-21: 0.3% of 3386 checklistsAug 22-31: 0.4% of 5028 checklistsSep 1-7: 0.5% of 3631 checklistsSep 8-14: 0.1% of 3507 checklistsSep 15-21: 0.1% of 3404 checklistsSep 22-30: 0.1% of 4252 checklistsOct 1-7: 0.1% of 3563 checklistsOct 8-14: 0.2% of 3440 checklistsOct 15-21: 0.3% of 3282 checklistsOct 22-31: 0.9% of 4025 checklistsNov 1-7: 1.3% of 3030 checklistsNov 8-14: 3.1% of 3141 checklistsNov 15-21: 3.4% of 2858 checklistsNov 22-30: 3.4% of 4104 checklistsDec 1-7: 2.9% of 2472 checklistsDec 8-14: 3.1% of 2415 checklistsDec 15-21: 2.5% of 3306 checklistsDec 22-31: 4.9% of 5527 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 Delaware 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.

Embed this map on your site

Where in Delaware

Best counties

Share of checklists at the peak
  1. Sussex CountyBest the second week of January · 2177 checklists that week, 91,027 in all11%
  2. Kent CountyBest early April · 621 checklists that week, 36,693 in all5.7%
  3. New Castle CountyBest the second week of April · 1835 checklists that week, 72,140 in all1.9%

Best spots

Share of checklists at the peak
  1. Cape Henlopen State Park (Wolfe Neck)Sussex County, best early February · 22 checklists that week, 192 in all75%
  2. Mare Marsh (Indian River Inlet)Sussex County, best early January · 20 checklists that week, 247 in all62%
  3. Mare MarshSussex County, best the second week of January · 237 checklists that week, 4,142 in all54%
  4. Rehoboth FlatsSussex County, best late November · 71 checklists that week, 2,369 in all33%
  5. Cape Henlopen State Park (southeast)Sussex County, best early January · 92 checklists that week, 1,265 in all32%
  6. Augustine BeachNew Castle County, best early April · 25 checklists that week, 427 in all27%

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

Best time of day

In Delaware, the Bonaparte's Gull is most often listed on checklists started between 12 and 2 pm (2.4% of those checklists).

0%1%2%3%12 am: too few checklists (129) to judge1 am: too few checklists (122) to judge2 am: too few checklists (102) to judge3 am: too few checklists (114) to judge4 am: too few checklists (210) to judge5 am: too few checklists (1334) to judge6 am: 1.4% of 8055 checklists7 am: 1.5% of 21367 checklists8 am: 1.8% of 25648 checklists9 am: 2.0% of 22669 checklists10 am: 1.9% of 20679 checklists11 am: 2.3% of 17516 checklists12 pm: 2.4% of 15361 checklists1 pm: 2.3% of 14319 checklists2 pm: 2.4% of 13726 checklists3 pm: 2.2% of 12793 checklists4 pm: 1.4% of 10392 checklists5 pm: 1.4% of 6859 checklists6 pm: 1.3% of 4542 checklists7 pm: too few checklists (2633) to judge8 pm: too few checklists (831) to judge9 pm: too few checklists (211) to judge10 pm: too few checklists (150) to judge11 pm: too few checklists (98) 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
January5.3%6.7%6.5%4.0%
February3.6%1.6%1.9%1.7%
March1.4%1.2%1.1%2.8%
April3.7%2.9%2.4%1.6%
May1.8%1.4%0.9%0.7%
June0.7%0.3%1.0%0.6%
July0.4%0.6%0.9%0.9%
August0.8%0.5%0.3%0.4%
September0.5%0.1%0.1%0.1%
October0.1%0.2%0.3%0.9%
November1.3%3.1%3.4%3.4%
December2.9%3.1%2.5%4.9%

Neighboring states

  • Maryland: arrives late October, 1 week earlier than Delaware
  • New Jersey: arrives late February, 15 weeks later than Delaware
  • District of Columbia: arrives mid March, 18 weeks later than Delaware
  • Pennsylvania: arrives the second week of March, 17 weeks later than Delaware

Common questions

When do Bonaparte's Gulls arrive in Delaware?
Bonaparte's Gulls are winter birds in Delaware: they arrive in early November, peak in the second week of January (6.0% of checklists), and most are gone by early May.
When do Bonaparte's Gulls leave Delaware?
Most Bonaparte's Gulls have left Delaware by early May, when reports fall below half their usual rate. Stragglers are still reported until mid May.
When is the best time to see a Bonaparte's Gull in Delaware?
The Bonaparte's Gull is reported most often in the second week of January, on about 6.0% of Delaware checklists.
Where in Delaware are Bonaparte's Gulls seen most often?
By county, Sussex County, Kent County, and New Castle County have the highest peak reporting rates for the Bonaparte's Gull (counties with at least 200 checklists).