WhenToBird

Setophaga virens · Parulidae

When Do Black-throated Green Warblers Arrive in Delaware?

Adult Black-throated Green Warbler
Photo: Ken Clark, CC BY 4.0 via iNaturalist

Black-throated Green Warblers mostly pass through Delaware: they arrive in late August, peak in mid September (8.1% of checklists), and most are gone by the second week of October.

When to look

First arrivalsAug 22-31late August
Common byAug 22-31late August
PeakSep 15-21mid September
Most gone byOct 8-14the second week of October

Best: mid September. First arrivals late August; most are gone by the second week of October. Peak: on about 8.1% of Delaware checklists.

  1. Jannot usually seen
  2. Febnot usually seen
  3. Marnot usually seen
  4. Apruncommon
  5. Maycommon
  6. Junrare
  7. Julnot usually seen
  8. Auguncommon
  9. Seppeak season
  10. Octpeak season
  11. Novnot usually seen
  12. Decnot usually seen

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

0%5%10%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: 1.1% of 7249 checklistsMay 1-7: 4.9% of 6806 checklistsMay 8-14: 6.7% of 7229 checklistsMay 15-21: 2.9% of 6466 checklistsMay 22-31: 0.9% of 7437 checklistsJun 1-7: 0.1% of 3596 checklistsJun 8-14: 0% of 2847 checklistsJun 15-21: 0% of 2901 checklistsJun 22-30: 0% of 3644 checklistsJul 1-7: 0% of 3142 checklistsJul 8-14: 0% of 2767 checklistsJul 15-21: 0% of 2882 checklistsJul 22-31: 0% of 4175 checklistsAug 1-7: 0% of 3482 checklistsAug 8-14: 0.1% of 3477 checklistsAug 15-21: 0.1% of 3386 checklistsAug 22-31: 1.3% of 5028 checklistsSep 1-7: 4.5% of 3631 checklistsSep 8-14: 6.8% of 3507 checklistsSep 15-21: 7.3% of 3404 checklistsSep 22-30: 9.8% of 4252 checklistsOct 1-7: 6.6% of 3563 checklistsOct 8-14: 3.8% of 3440 checklistsOct 15-21: 1.0% of 3282 checklistsOct 22-31: 0.2% of 4025 checklistsNov 1-7: 0% of 3030 checklistsNov 8-14: 0.1% 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. New Castle CountyBest mid September · 1441 checklists that week, 72,140 in all18%
  2. Kent CountyBest the second week of May · 1320 checklists that week, 36,693 in all2.6%
  3. Sussex CountyBest the second week of May · 2987 checklists that week, 91,027 in all2.6%

Best spots

Share of checklists at the peak
  1. WoodlawnNew Castle County, best late September · 42 checklists that week, 1,011 in all52%
  2. Middle Run Valley ParkNew Castle County, best mid September · 139 checklists that week, 2,212 in all45%
  3. White Clay Creek State ParkNew Castle County, best the second week of May · 83 checklists that week, 547 in all38%
  4. White Clay Creek State Park (Lost Stream)New Castle County, best the second week of May · 97 checklists that week, 534 in all37%
  5. Brandywine Creek State ParkNew Castle County, best late September · 40 checklists that week, 1,222 in all36%
  6. Ashland Nature CenterNew Castle County, best late September · 303 checklists that week, 4,658 in all30%

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

Best time of day

In Delaware, the Black-throated Green Warbler is most often listed on checklists started between 6 and 8 am (3.6% 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: 3.0% of 8055 checklists7 am: 3.8% of 21367 checklists8 am: 2.4% of 25648 checklists9 am: 1.2% of 22669 checklists10 am: 0.8% of 20679 checklists11 am: 0.7% of 17516 checklists12 pm: 0.6% of 15361 checklists1 pm: 0.5% of 14319 checklists2 pm: 0.5% of 13726 checklists3 pm: 0.6% of 12793 checklists4 pm: 0.6% of 10392 checklists5 pm: 0.6% of 6859 checklists6 pm: 0.5% 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%1.1%
May4.9%6.7%2.9%0.9%
June0.1%0%0%0%
July0%0%0%0%
August0%0.1%0.1%1.3%
September4.5%6.8%7.3%9.8%
October6.6%3.8%1.0%0.2%
November0%0.1%0%0%
December0%0%0%0%

Neighboring states

  • Maryland: arrives mid August, 1 week earlier than Delaware
  • New Jersey: arrives mid April, 17 weeks earlier than Delaware
  • District of Columbia: arrives mid August, 1 week earlier than Delaware
  • Pennsylvania: arrives mid April, 17 weeks earlier than Delaware

Common questions

When do Black-throated Green Warblers arrive in Delaware?
Black-throated Green Warblers mostly pass through Delaware: they arrive in late August, peak in mid September (8.1% of checklists), and most are gone by the second week of October.
When do Black-throated Green Warblers leave Delaware?
Most Black-throated Green Warblers have left Delaware by the second week of October, when reports fall below half their usual rate. Stragglers are still reported until mid October.
When is the best time to see a Black-throated Green Warbler in Delaware?
The Black-throated Green Warbler is reported most often in mid September, on about 8.1% of Delaware checklists.
Where in Delaware are Black-throated Green Warblers seen most often?
By county, New Castle County, Kent County, and Sussex County have the highest peak reporting rates for the Black-throated Green Warbler (counties with at least 200 checklists).