WhenToBird

Setophaga pensylvanica · Parulidae

When Do Chestnut-sided Warblers Arrive in Delaware?

Adult male Chestnut-sided Warbler
Photo: Matt Felperin, CC BY 4.0 via iNaturalist

Chestnut-sided Warblers mostly pass through Delaware: they arrive in mid August, peak in early September (9.2% of checklists), and most are gone by early October.

When to look

First arrivalsAug 15-21mid August
Common byAug 15-21mid August
PeakSep 1-7early September
Most gone byOct 1-7early October

Best: early September. First arrivals mid August; most are gone by early October. Peak: on about 9.2% of Delaware checklists.

  1. Jannot usually seen
  2. Febnot usually seen
  3. Marnot usually seen
  4. Aprrare
  5. Mayuncommon
  6. Junrare
  7. Julnot usually seen
  8. Augpeak season
  9. Seppeak season
  10. Octuncommon
  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% of 4456 checklistsApr 15-21: 0% of 4871 checklistsApr 22-30: 0.1% of 7249 checklistsMay 1-7: 2.2% of 6806 checklistsMay 8-14: 5.5% of 7229 checklistsMay 15-21: 2.5% of 6466 checklistsMay 22-31: 0.9% of 7437 checklistsJun 1-7: 0% 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: 0.4% of 3477 checklistsAug 15-21: 2.3% of 3386 checklistsAug 22-31: 8.1% of 5028 checklistsSep 1-7: 9.8% of 3631 checklistsSep 8-14: 10% of 3507 checklistsSep 15-21: 7.5% of 3404 checklistsSep 22-30: 5.0% of 4252 checklistsOct 1-7: 2.2% of 3563 checklistsOct 8-14: 0.4% 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. New Castle CountyBest early September · 1538 checklists that week, 72,140 in all21%
  2. Kent CountyBest mid September · 498 checklists that week, 36,693 in all2.1%
  3. Sussex CountyBest mid September · 1465 checklists that week, 91,027 in all1.0%

Best spots

Share of checklists at the peak
  1. Middle Run Valley ParkNew Castle County, best early September · 152 checklists that week, 2,212 in all54%
  2. WoodlawnNew Castle County, best early September · 34 checklists that week, 1,011 in all53%
  3. White Clay Creek State Park (Lost Stream)New Castle County, best mid May · 46 checklists that week, 534 in all45%
  4. Brandywine Creek State ParkNew Castle County, best early September · 40 checklists that week, 1,222 in all44%
  5. Ashland Nature CenterNew Castle County, best early September · 240 checklists that week, 4,658 in all41%
  6. White Clay Creek State ParkNew Castle County, best mid May · 37 checklists that week, 547 in all33%

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

Best time of day

In Delaware, the Chestnut-sided Warbler is most often listed on checklists started between 6 and 8 am (3.5% 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: 2.5% of 8055 checklists7 am: 3.9% of 21367 checklists8 am: 2.2% of 25648 checklists9 am: 1.1% of 22669 checklists10 am: 0.7% of 20679 checklists11 am: 0.6% of 17516 checklists12 pm: 0.5% of 15361 checklists1 pm: 0.5% of 14319 checklists2 pm: 0.5% of 13726 checklists3 pm: 0.4% of 12793 checklists4 pm: 0.8% of 10392 checklists5 pm: 0.7% 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%0%0.1%
May2.2%5.5%2.5%0.9%
June0%0%0%0%
July0%0%0%0%
August0%0.4%2.3%8.1%
September9.8%10%7.5%5.0%
October2.2%0.4%0%0%
November0%0%0%0%
December0%0%0%0%

Neighboring states

  • Maryland: arrives the second week of August, 1 week earlier than Delaware
  • New Jersey: arrives late April, 15 weeks earlier than Delaware
  • District of Columbia: arrives the second week of August, 1 week earlier than Delaware
  • Pennsylvania: arrives late April, 15 weeks earlier than Delaware

Common questions

When do Chestnut-sided Warblers arrive in Delaware?
Chestnut-sided Warblers mostly pass through Delaware: they arrive in mid August, peak in early September (9.2% of checklists), and most are gone by early October.
When do Chestnut-sided Warblers leave Delaware?
Most Chestnut-sided Warblers have left Delaware by early October, when reports fall below half their usual rate.
When is the best time to see a Chestnut-sided Warbler in Delaware?
The Chestnut-sided Warbler is reported most often in early September, on about 9.2% of Delaware checklists.
Where in Delaware are Chestnut-sided Warblers seen most often?
By county, New Castle County, Kent County, and Sussex County have the highest peak reporting rates for the Chestnut-sided Warbler (counties with at least 200 checklists).