WhenToBird

Setophaga pensylvanica · Parulidae

When Do Chestnut-sided Warblers Arrive in Massachusetts?

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

Chestnut-sided Warblers mostly pass through Massachusetts: the first show up in late April, they are common by early May, peak in mid May (11% of checklists), and most are gone by early July.

When to look

First arrivalsApr 22-30late April
Common byMay 1-7early May
PeakMay 15-21mid May
Most gone byJul 1-7early July

Best: mid May. First arrivals late April; most are gone by early July. Peak: on about 11% of Massachusetts checklists.

  1. Jannot usually seen
  2. Febnot usually seen
  3. Marnot usually seen
  4. Aprrare
  5. Maypeak season
  6. Juncommon
  7. Juluncommon
  8. Auguncommon
  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 43252 checklistsJan 8-14: 0% of 30096 checklistsJan 15-21: 0% of 28760 checklistsJan 22-31: 0% of 38135 checklistsFeb 1-7: 0% of 26442 checklistsFeb 8-14: 0% of 29034 checklistsFeb 15-21: 0% of 37383 checklistsFeb 22-28: 0% of 29977 checklistsMar 1-7: 0% of 29175 checklistsMar 8-14: 0% of 32399 checklistsMar 15-21: 0% of 34444 checklistsMar 22-31: 0% of 49126 checklistsApr 1-7: 0% of 36456 checklistsApr 8-14: 0% of 40908 checklistsApr 15-21: 0% of 42078 checklistsApr 22-30: 0.2% of 56465 checklistsMay 1-7: 3.4% of 56994 checklistsMay 8-14: 9.5% of 64079 checklistsMay 15-21: 14% of 52020 checklistsMay 22-31: 8.8% of 55402 checklistsJun 1-7: 5.8% of 30682 checklistsJun 8-14: 5.2% of 27557 checklistsJun 15-21: 4.9% of 26163 checklistsJun 22-30: 3.8% of 29576 checklistsJul 1-7: 3.5% of 23931 checklistsJul 8-14: 2.4% of 22389 checklistsJul 15-21: 1.5% of 22365 checklistsJul 22-31: 0.9% of 32631 checklistsAug 1-7: 0.8% of 25133 checklistsAug 8-14: 1.0% of 24610 checklistsAug 15-21: 1.3% of 25350 checklistsAug 22-31: 1.9% of 37198 checklistsSep 1-7: 2.0% of 27402 checklistsSep 8-14: 2.0% of 27700 checklistsSep 15-21: 1.6% of 28398 checklistsSep 22-30: 0.8% of 34646 checklistsOct 1-7: 0.2% of 28620 checklistsOct 8-14: 0.1% of 30144 checklistsOct 15-21: 0.1% of 28893 checklistsOct 22-31: 0.1% of 38869 checklistsNov 1-7: 0.1% of 29782 checklistsNov 8-14: 0% of 27582 checklistsNov 15-21: 0% of 26642 checklistsNov 22-30: 0% of 34390 checklistsDec 1-7: 0.1% of 25164 checklistsDec 8-14: 0% of 24892 checklistsDec 15-21: 0% of 29022 checklistsDec 22-31: 0% of 44323 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 Massachusetts 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 Massachusetts

Best counties

Share of checklists at the peak
  1. Berkshire CountyBest late May · 3139 checklists that week, 92,890 in all38%
  2. Franklin CountyBest mid June · 641 checklists that week, 41,382 in all28%
  3. Hampshire CountyBest mid May · 5225 checklists that week, 162,423 in all19%
  4. Worcester CountyBest mid May · 4484 checklists that week, 128,594 in all14%
  5. Hampden CountyBest mid May · 1220 checklists that week, 35,410 in all13%
  6. Essex CountyBest mid May · 6904 checklists that week, 213,973 in all13%

Best spots

Share of checklists at the peak
  1. Eugene D. Moran Wildlife Management AreaBerkshire County, best late May · 23 checklists that week, 483 in all95%
  2. West Branch Housatonic River ReservoirBerkshire County, best mid May · 40 checklists that week, 455 in all91%
  3. Muddy Brook Wildlife Management AreaWorcester County, best late May · 24 checklists that week, 289 in all86%
  4. October Mountain State ForestBerkshire County, best late May · 22 checklists that week, 473 in all85%
  5. Parsons Marsh ReserveBerkshire County, best early June · 24 checklists that week, 726 in all85%
  6. Quabbin Reservoir WatershedHampshire County, best mid May · 128 checklists that week, 1,878 in all85%

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

Best time of day

In Massachusetts, the Chestnut-sided Warbler is most often listed on checklists started between 6 and 8 am (3.6% of those checklists).

0%2%4%6%12 am: too few checklists (630) to judge1 am: too few checklists (657) to judge2 am: too few checklists (645) to judge3 am: too few checklists (850) to judge4 am: too few checklists (3787) to judge5 am: too few checklists (29743) to judge6 am: 4.5% of 108601 checklists7 am: 3.1% of 186104 checklists8 am: 2.4% of 185905 checklists9 am: 2.0% of 166049 checklists10 am: 1.6% of 150508 checklists11 am: 1.3% of 131024 checklists12 pm: 1.1% of 116804 checklists1 pm: 1.0% of 112055 checklists2 pm: 0.8% of 110246 checklists3 pm: 0.8% of 104376 checklists4 pm: 1.2% of 83736 checklists5 pm: 1.3% of 63723 checklists6 pm: 1.4% of 41435 checklists7 pm: too few checklists (21041) to judge8 pm: too few checklists (5240) to judge9 pm: too few checklists (1722) to judge10 pm: too few checklists (1094) to judge11 pm: too few checklists (704) 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%0.2%
May3.4%9.5%14%8.8%
June5.8%5.2%4.9%3.8%
July3.5%2.4%1.5%0.9%
August0.8%1.0%1.3%1.9%
September2.0%2.0%1.6%0.8%
October0.2%0.1%0.1%0.1%
November0.1%0%0%0%
December0.1%0%0%0%

Neighboring states

  • Rhode Island: arrives late April, in the same week than Massachusetts
  • New Hampshire: arrives late April, in the same week than Massachusetts
  • Connecticut: arrives late April, in the same week than Massachusetts
  • Vermont: arrives early May, 1 week later than Massachusetts

Common questions

When do Chestnut-sided Warblers arrive in Massachusetts?
Chestnut-sided Warblers mostly pass through Massachusetts: the first show up in late April, they are common by early May, peak in mid May (11% of checklists), and most are gone by early July.
When do Chestnut-sided Warblers leave Massachusetts?
Most Chestnut-sided Warblers have left Massachusetts by early July, when reports fall below half their usual rate. Stragglers are still reported until late July.
When is the best time to see a Chestnut-sided Warbler in Massachusetts?
The Chestnut-sided Warbler is reported most often in mid May, on about 11% of Massachusetts checklists.
Where in Massachusetts are Chestnut-sided Warblers seen most often?
By county, Berkshire County, Franklin County, and Hampshire County have the highest peak reporting rates for the Chestnut-sided Warbler (counties with at least 200 checklists).