WhenToBird

Sternula antillarum · Laridae

When Do Least Terns Arrive in Delaware?

Adult Least Tern
Photo: datadan, CC BY 4.0 via iNaturalist

Least Terns reach Delaware in early May, are common by late May, peak in late July (10% of checklists), and most are gone by mid August.

When to look

First arrivalsMay 1-7early May
Common byMay 22-31late May
PeakJul 22-31late July
Most gone byAug 15-21mid August

Best: late July. First arrivals early May; most are gone by mid August. Peak: on about 10% of Delaware checklists.

  1. Jannot usually seen
  2. Febnot usually seen
  3. Marnot usually seen
  4. Aprrare
  5. Maycommon
  6. Junpeak season
  7. Julpeak season
  8. Augpeak season
  9. Sepuncommon
  10. Octnot usually seen
  11. Novnot usually seen
  12. Decnot usually seen

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

0%5%10%15%Jan 1-7: 0% of 5901 checklistsJan 8-14: 0% of 4091 checklistsJan 15-21: 0% of 3841 checklistsJan 22-31: 0% of 5084 checklistsFeb 1-7: 0% of 3705 checklistsFeb 8-14: 0% of 3991 checklistsFeb 15-21: 0% of 6056 checklistsFeb 22-28: 0% of 4036 checklistsMar 1-7: 0% of 3822 checklistsMar 8-14: 0% of 3873 checklistsMar 15-21: 0% of 3856 checklistsMar 22-31: 0% of 5702 checklistsApr 1-7: 0% of 4104 checklistsApr 8-14: 0.1% of 4456 checklistsApr 15-21: 0.1% of 4871 checklistsApr 22-30: 0.5% of 7249 checklistsMay 1-7: 1.3% of 6806 checklistsMay 8-14: 2.5% of 7229 checklistsMay 15-21: 3.6% of 6466 checklistsMay 22-31: 5.1% of 7437 checklistsJun 1-7: 4.9% of 3596 checklistsJun 8-14: 5.0% of 2847 checklistsJun 15-21: 7.3% of 2901 checklistsJun 22-30: 7.6% of 3644 checklistsJul 1-7: 8.7% of 3142 checklistsJul 8-14: 9.9% of 2767 checklistsJul 15-21: 9.9% of 2882 checklistsJul 22-31: 11% of 4175 checklistsAug 1-7: 10% of 3482 checklistsAug 8-14: 9.1% of 3477 checklistsAug 15-21: 4.9% of 3386 checklistsAug 22-31: 2.4% of 5028 checklistsSep 1-7: 1.7% of 3631 checklistsSep 8-14: 0.7% of 3507 checklistsSep 15-21: 0.1% of 3404 checklistsSep 22-30: 0% of 4252 checklistsOct 1-7: 0% of 3563 checklistsOct 8-14: 0.1% of 3440 checklistsOct 15-21: 0% of 3282 checklistsOct 22-31: 0% of 4025 checklistsNov 1-7: 0% of 3030 checklistsNov 8-14: 0% of 3141 checklistsNov 15-21: 0% of 2858 checklistsNov 22-30: 0% of 4104 checklistsDec 1-7: 0% of 2472 checklistsDec 8-14: 0% of 2415 checklistsDec 15-21: 0% of 3306 checklistsDec 22-31: 0% 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.

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Where in Delaware

Best counties

Share of checklists at the peak
  1. Sussex CountyBest mid July · 1282 checklists that week, 91,027 in all19%
  2. Kent CountyBest mid July · 735 checklists that week, 36,693 in all6.1%
  3. New Castle CountyBest the second week of July · 897 checklists that week, 72,140 in all0.6%

Best spots

Share of checklists at the peak
  1. Shell Beach Pond (northeast)Sussex County, best late July · 38 checklists that week, 1,671 in all78%
  2. Cape Henlopen State ParkSussex County, best mid July · 71 checklists that week, 3,103 in all77%
  3. Caleb PondSussex County, best mid July · 38 checklists that week, 1,655 in all69%
  4. Cape Henlopen State Park (south 2)Sussex County, best mid July · 31 checklists that week, 1,368 in all63%
  5. Cape Henlopen State Park (southeast)Sussex County, best the second week of July · 20 checklists that week, 1,265 in all50%
  6. Prime Hook National Wildlife RefugeSussex County, best late July · 39 checklists that week, 1,281 in all44%

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

Best time of day

In Delaware, the Least Tern is most often listed on checklists started between 5 and 7 pm (2.4% of those checklists).

0%1%2%3%4%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: 3.1% of 8055 checklists7 am: 2.2% of 21367 checklists8 am: 2.0% of 25648 checklists9 am: 2.0% of 22669 checklists10 am: 2.0% of 20679 checklists11 am: 1.8% of 17516 checklists12 pm: 1.8% of 15361 checklists1 pm: 1.9% of 14319 checklists2 pm: 1.8% of 13726 checklists3 pm: 1.8% of 12793 checklists4 pm: 1.8% of 10392 checklists5 pm: 2.3% of 6859 checklists6 pm: 2.7% 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
January0%0%0%0%
February0%0%0%0%
March0%0%0%0%
April0%0.1%0.1%0.5%
May1.3%2.5%3.6%5.1%
June4.9%5.0%7.3%7.6%
July8.7%9.9%9.9%11%
August10%9.1%4.9%2.4%
September1.7%0.7%0.1%0%
October0%0.1%0%0%
November0%0%0%0%
December0%0%0%0%

Neighboring states

  • Maryland: arrives late April, 1 week earlier than Delaware
  • New Jersey: arrives late April, 1 week earlier than Delaware
  • Virginia: arrives late April, 1 week earlier than Delaware
  • New York: arrives mid May, 2 weeks later than Delaware

Common questions

When do Least Terns arrive in Delaware?
Least Terns reach Delaware in early May, are common by late May, peak in late July (10% of checklists), and most are gone by mid August.
When do Least Terns leave Delaware?
Most Least Terns have left Delaware by mid August, when reports fall below half their usual rate. Stragglers are still reported until early September.
When is the best time to see a Least Tern in Delaware?
The Least Tern is reported most often in late July, on about 10% of Delaware checklists.
Where in Delaware are Least Terns seen most often?
By county, Sussex County, Kent County, and New Castle County have the highest peak reporting rates for the Least Tern (counties with at least 200 checklists).