WhenToBird

Tachycineta bicolor · Hirundinidae

When Do Tree Swallows Arrive in Colorado?

Adult Tree Swallow
Photo: Carter Dorscht, CC0 1.0 via iNaturalist

Tree Swallows reach Colorado in late March, are common by the second week of April, peak in the second week of May (19% of checklists), and most are gone by late July.

When to look

First arrivalsMar 22-31late March
Common byApr 8-14the second week of April
PeakMay 8-14the second week of May
Most gone byJul 22-31late July

Best: the second week of May. First arrivals late March; most are gone by late July. Peak: on about 19% of Colorado checklists.

  1. Jannot usually seen
  2. Febnot usually seen
  3. Marrare
  4. Aprpeak season
  5. Maypeak season
  6. Junpeak season
  7. Julpeak season
  8. Auguncommon
  9. Seprare
  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%20%Jan 1-7: 0% of 32254 checklistsJan 8-14: 0% of 23278 checklistsJan 15-21: 0% of 22933 checklistsJan 22-31: 0% of 30856 checklistsFeb 1-7: 0% of 21464 checklistsFeb 8-14: 0% of 22910 checklistsFeb 15-21: 0% of 28739 checklistsFeb 22-28: 0.1% of 21833 checklistsMar 1-7: 0.1% of 23066 checklistsMar 8-14: 0.2% of 23783 checklistsMar 15-21: 0.6% of 24797 checklistsMar 22-31: 1.9% of 38439 checklistsApr 1-7: 4.7% of 31676 checklistsApr 8-14: 9.2% of 35092 checklistsApr 15-21: 14% of 36778 checklistsApr 22-30: 17% of 50885 checklistsMay 1-7: 19% of 44186 checklistsMay 8-14: 19% of 49011 checklistsMay 15-21: 19% of 40784 checklistsMay 22-31: 18% of 53073 checklistsJun 1-7: 17% of 32432 checklistsJun 8-14: 15% of 29978 checklistsJun 15-21: 16% of 29457 checklistsJun 22-30: 15% of 36072 checklistsJul 1-7: 15% of 28857 checklistsJul 8-14: 14% of 27224 checklistsJul 15-21: 12% of 27629 checklistsJul 22-31: 9.3% of 37318 checklistsAug 1-7: 6.5% of 25893 checklistsAug 8-14: 5.2% of 24870 checklistsAug 15-21: 3.3% of 24035 checklistsAug 22-31: 2.3% of 35691 checklistsSep 1-7: 1.4% of 27068 checklistsSep 8-14: 1.1% of 26709 checklistsSep 15-21: 0.3% of 26098 checklistsSep 22-30: 0.1% of 31550 checklistsOct 1-7: 0.1% of 24110 checklistsOct 8-14: 0.1% of 23352 checklistsOct 15-21: 0.1% of 21895 checklistsOct 22-31: 0.1% of 28319 checklistsNov 1-7: 0.1% of 21698 checklistsNov 8-14: 0.1% of 21061 checklistsNov 15-21: 0.1% of 19855 checklistsNov 22-30: 0.1% of 25798 checklistsDec 1-7: 0.1% of 18626 checklistsDec 8-14: 0% of 19004 checklistsDec 15-21: 0% of 23103 checklistsDec 22-31: 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. Routt CountyBest the second week of June · 341 checklists that week, 10,504 in all45%
  2. Rio Grande CountyBest late April · 133 checklists that week, 4,655 in all40%
  3. Jackson CountyBest mid May · 114 checklists that week, 7,472 in all37%
  4. Chaffee CountyBest the second week of May · 705 checklists that week, 14,510 in all36%
  5. La Plata CountyBest late April · 813 checklists that week, 21,744 in all36%
  6. Douglas CountyBest late May · 2132 checklists that week, 60,057 in all33%

Best spots

Share of checklists at the peak
  1. South Platte Pk\ Carson Nature AreaArapahoe County, best late May · 38 checklists that week, 2,247 in all91%
  2. Ramah Reservoir State Wildlife AreaEl Paso County, best early May · 34 checklists that week, 930 in all90%
  3. South Platte Pk\ Carson Nature Area (Cooley Lake)Arapahoe County, best late June · 20 checklists that week, 1,101 in all87%
  4. Harriman LakeJefferson County, best late June · 57 checklists that week, 3,241 in all86%
  5. City and County of Broomfield Joint City/County Land - GeneralBroomfield County, best mid May · 36 checklists that week, 390 in all85%
  6. Mount Ouray State Wildlife AreaChaffee County, best late May · 28 checklists that week, 793 in all83%

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

Best time of day

In Colorado, the Tree Swallow is most often listed on checklists started between 6 and 8 am (9.2% of those checklists).

0%5%10%15%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: 11% of 71991 checklists7 am: 8.6% of 159189 checklists8 am: 7.8% of 177206 checklists9 am: 6.8% of 165269 checklists10 am: 6.1% of 141029 checklists11 am: 5.6% of 115283 checklists12 pm: 5.1% of 96068 checklists1 pm: 4.9% of 89512 checklists2 pm: 4.7% of 86319 checklists3 pm: 5.0% of 82496 checklists4 pm: 5.7% of 71648 checklists5 pm: 7.4% of 52445 checklists6 pm: 9.0% 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%0%0%0%
February0%0%0%0.1%
March0.1%0.2%0.6%1.9%
April4.7%9.2%14%17%
May19%19%19%18%
June17%15%16%15%
July15%14%12%9.3%
August6.5%5.2%3.3%2.3%
September1.4%1.1%0.3%0.1%
October0.1%0.1%0.1%0.1%
November0.1%0.1%0.1%0.1%
December0.1%0%0%0%

Neighboring states

  • Wyoming: arrives early April, 1 week later than Colorado
  • New Mexico: arrives late February, 4 weeks earlier than Colorado
  • Utah: arrives the second week of March, 2 weeks earlier than Colorado
  • Nebraska: arrives mid March, 1 week earlier than Colorado

Common questions

When do Tree Swallows arrive in Colorado?
Tree Swallows reach Colorado in late March, are common by the second week of April, peak in the second week of May (19% of checklists), and most are gone by late July.
When do Tree Swallows leave Colorado?
Most Tree Swallows have left Colorado by late July, when reports fall below half their usual rate. Stragglers are still reported until early September.
When is the best time to see a Tree Swallow in Colorado?
The Tree Swallow is reported most often in the second week of May, on about 19% of Colorado checklists.
Where in Colorado are Tree Swallows seen most often?
By county, Routt County, Rio Grande County, and Jackson County have the highest peak reporting rates for the Tree Swallow (counties with at least 200 checklists).