WhenToBird

Cistothorus palustris · Troglodytidae

When Do Marsh Wrens Arrive in Colorado?

Adult Marsh Wren
Photo: Kathy Richardson, CC BY 4.0 via iNaturalist

Marsh Wrens reach Colorado in late February, are common by early March, peak in mid April (1.8% of checklists), and most are gone by early January.

When to look

First arrivalsFeb 22-28late February
Common byMar 1-7early March
PeakApr 15-21mid April
Most gone byJan 1-7early January

Best: mid April. First arrivals late February; most are gone by early January. Peak: on about 1.8% of Colorado checklists.

  1. Jancommon
  2. Febcommon
  3. Marpeak season
  4. Aprpeak season
  5. Maypeak season
  6. Juncommon
  7. Julcommon
  8. Augcommon
  9. Sepcommon
  10. Octpeak season
  11. Novpeak season
  12. Deccommon

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

0%1%2%3%Jan 1-7: 0.9% of 32254 checklistsJan 8-14: 0.8% of 23278 checklistsJan 15-21: 0.9% of 22933 checklistsJan 22-31: 0.8% of 30856 checklistsFeb 1-7: 0.8% of 21464 checklistsFeb 8-14: 0.7% of 22910 checklistsFeb 15-21: 0.6% of 28739 checklistsFeb 22-28: 0.8% of 21833 checklistsMar 1-7: 1.0% of 23066 checklistsMar 8-14: 1.5% of 23783 checklistsMar 15-21: 1.7% of 24797 checklistsMar 22-31: 1.6% of 38439 checklistsApr 1-7: 1.9% of 31676 checklistsApr 8-14: 1.6% of 35092 checklistsApr 15-21: 1.7% of 36778 checklistsApr 22-30: 2.0% of 50885 checklistsMay 1-7: 1.6% of 44186 checklistsMay 8-14: 1.5% of 49011 checklistsMay 15-21: 1.3% of 40784 checklistsMay 22-31: 1.3% of 53073 checklistsJun 1-7: 1.4% of 32432 checklistsJun 8-14: 1.0% of 29978 checklistsJun 15-21: 1.0% of 29457 checklistsJun 22-30: 0.9% of 36072 checklistsJul 1-7: 1.2% of 28857 checklistsJul 8-14: 1.1% of 27224 checklistsJul 15-21: 1.2% of 27629 checklistsJul 22-31: 1.0% of 37318 checklistsAug 1-7: 0.9% of 25893 checklistsAug 8-14: 1.1% of 24870 checklistsAug 15-21: 0.8% of 24035 checklistsAug 22-31: 0.9% of 35691 checklistsSep 1-7: 0.9% of 27068 checklistsSep 8-14: 0.9% of 26709 checklistsSep 15-21: 0.9% of 26098 checklistsSep 22-30: 1.0% of 31550 checklistsOct 1-7: 1.2% of 24110 checklistsOct 8-14: 1.4% of 23352 checklistsOct 15-21: 1.6% of 21895 checklistsOct 22-31: 1.7% of 28319 checklistsNov 1-7: 1.7% of 21698 checklistsNov 8-14: 1.5% of 21061 checklistsNov 15-21: 1.5% of 19855 checklistsNov 22-30: 1.3% of 25798 checklistsDec 1-7: 1.1% of 18626 checklistsDec 8-14: 1.1% of 19004 checklistsDec 15-21: 1.5% of 23103 checklistsDec 22-31: 1.0% of 30802 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 Colorado 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 Colorado

Best counties

Share of checklists at the peak
  1. Saguache CountyBest late April · 100 checklists that week, 3,220 in all32%
  2. Rio Grande CountyBest mid July · 171 checklists that week, 4,655 in all30%
  3. Delta CountyBest mid April · 284 checklists that week, 6,509 in all29%
  4. Bent CountyBest mid November · 23 checklists that week, 5,275 in all17%
  5. Alamosa CountyBest mid July · 141 checklists that week, 4,206 in all16%
  6. Baca CountyBest the second week of November · 26 checklists that week, 3,209 in all15%

Best spots

Share of checklists at the peak
  1. Sweitzer Lake State ParkDelta County, best early May · 25 checklists that week, 852 in all83%
  2. Monte Vista National Wildlife RefugeRio Grande County, best mid July · 64 checklists that week, 1,219 in all83%
  3. Mount Ouray State Wildlife AreaChaffee County, best late January · 21 checklists that week, 793 in all79%
  4. Jim Hamm Nature PreserveBoulder County, best late May · 39 checklists that week, 1,349 in all77%
  5. Russell LakesSaguache County, best the second week of May · 30 checklists that week, 853 in all77%

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

Best time of day

In Colorado, the Marsh Wren is most often listed on checklists started between 6 and 8 am (1.5% of those checklists).

0%0.5%1%1.5%2%12 am: too few checklists (512) to judge1 am: too few checklists (468) to judge2 am: too few checklists (513) to judge3 am: too few checklists (656) to judge4 am: too few checklists (1918) to judge5 am: too few checklists (16045) to judge6 am: 1.7% of 71991 checklists7 am: 1.4% of 159189 checklists8 am: 1.5% of 177206 checklists9 am: 1.4% of 165269 checklists10 am: 1.3% of 141029 checklists11 am: 1.1% of 115283 checklists12 pm: 1.0% of 96068 checklists1 pm: 1.0% of 89512 checklists2 pm: 1.0% of 86319 checklists3 pm: 0.9% of 82496 checklists4 pm: 1.0% of 71648 checklists5 pm: 1.0% of 52445 checklists6 pm: 1.1% of 40199 checklists7 pm: too few checklists (24246) to judge8 pm: too few checklists (7986) to judge9 pm: too few checklists (2004) to judge10 pm: too few checklists (888) to judge11 pm: too few checklists (450) 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
January0.9%0.8%0.9%0.8%
February0.8%0.7%0.6%0.8%
March1.0%1.5%1.7%1.6%
April1.9%1.6%1.7%2.0%
May1.6%1.5%1.3%1.3%
June1.4%1.0%1.0%0.9%
July1.2%1.1%1.2%1.0%
August0.9%1.1%0.8%0.9%
September0.9%0.9%0.9%1.0%
October1.2%1.4%1.6%1.7%
November1.7%1.5%1.5%1.3%
December1.1%1.1%1.5%1.0%

Neighboring states

  • Wyoming: arrives late March, 4 weeks later than Colorado
  • New Mexico: arrives mid September, 21 weeks earlier than Colorado
  • Utah: arrives mid August, 23 weeks later than Colorado
  • Nebraska: arrives mid April, 7 weeks later than Colorado

Common questions

When do Marsh Wrens arrive in Colorado?
Marsh Wrens reach Colorado in late February, are common by early March, peak in mid April (1.8% of checklists), and most are gone by early January.
When do Marsh Wrens leave Colorado?
Most Marsh Wrens have left Colorado by early January, when reports fall below half their usual rate. Stragglers are still reported until early February.
When is the best time to see a Marsh Wren in Colorado?
The Marsh Wren is reported most often in mid April, on about 1.8% of Colorado checklists.
Where in Colorado are Marsh Wrens seen most often?
By county, Saguache County, Rio Grande County, and Delta County have the highest peak reporting rates for the Marsh Wren (counties with at least 200 checklists).