WhenToBird

Geothlypis tolmiei · Parulidae

When Do MacGillivray's Warblers Arrive in Colorado?

Adult female MacGillivray's Warbler
Photo: Julio Cesar Ruiz García, CC BY 4.0 via iNaturalist

MacGillivray's Warblers reach Colorado in early May, are common by the second week of May, peak in late May (4.4% of checklists), and most are gone by mid September.

When to look

First arrivalsMay 1-7early May
Common byMay 8-14the second week of May
PeakMay 22-31late May
Most gone bySep 15-21mid September

Best: late May. First arrivals early May; most are gone by mid September. Peak: on about 4.4% of Colorado checklists.

  1. Jannot usually seen
  2. Febnot usually seen
  3. Marnot usually seen
  4. Aprrare
  5. Maypeak season
  6. Junpeak season
  7. Julpeak season
  8. Augpeak season
  9. Seppeak season
  10. Octrare
  11. Novnot usually seen
  12. Decnot usually seen

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

0%2%4%6%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% of 21833 checklistsMar 1-7: 0% of 23066 checklistsMar 8-14: 0% of 23783 checklistsMar 15-21: 0% of 24797 checklistsMar 22-31: 0% of 38439 checklistsApr 1-7: 0% of 31676 checklistsApr 8-14: 0% of 35092 checklistsApr 15-21: 0.1% of 36778 checklistsApr 22-30: 0.1% of 50885 checklistsMay 1-7: 0.8% of 44186 checklistsMay 8-14: 3.1% of 49011 checklistsMay 15-21: 4.4% of 40784 checklistsMay 22-31: 4.5% of 53073 checklistsJun 1-7: 4.2% of 32432 checklistsJun 8-14: 4.4% of 29978 checklistsJun 15-21: 4.5% of 29457 checklistsJun 22-30: 4.2% of 36072 checklistsJul 1-7: 4.4% of 28857 checklistsJul 8-14: 3.7% of 27224 checklistsJul 15-21: 2.8% of 27629 checklistsJul 22-31: 1.8% of 37318 checklistsAug 1-7: 1.6% of 25893 checklistsAug 8-14: 2.3% of 24870 checklistsAug 15-21: 2.7% of 24035 checklistsAug 22-31: 3.7% of 35691 checklistsSep 1-7: 3.9% of 27068 checklistsSep 8-14: 3.2% of 26709 checklistsSep 15-21: 2.0% of 26098 checklistsSep 22-30: 0.9% of 31550 checklistsOct 1-7: 0.3% 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% of 21698 checklistsNov 8-14: 0.1% of 21061 checklistsNov 15-21: 0% of 19855 checklistsNov 22-30: 0% of 25798 checklistsDec 1-7: 0% of 18626 checklistsDec 8-14: 0% of 19004 checklistsDec 15-21: 0% of 23103 checklistsDec 22-31: 0.1% 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. Costilla CountyBest late August · 37 checklists that week, 1,323 in all23%
  2. La Plata CountyBest early September · 523 checklists that week, 21,744 in all21%
  3. San Juan CountyBest the second week of July · 134 checklists that week, 2,012 in all20%
  4. Cheyenne CountyBest mid May · 129 checklists that week, 1,388 in all19%
  5. Eagle CountyBest late June · 583 checklists that week, 15,893 in all17%
  6. Pueblo CountyBest mid May · 1089 checklists that week, 26,547 in all17%

Best spots

Share of checklists at the peak
  1. Reynolds ParkJefferson County, best the second week of July · 39 checklists that week, 610 in all62%
  2. Gregory CanyonBoulder County, best early June · 34 checklists that week, 500 in all62%
  3. Pike National ForestEl Paso County, best mid June · 20 checklists that week, 434 in all56%
  4. Fish Creek FallsRoutt County, best late June · 22 checklists that week, 277 in all55%
  5. Walker Ranch ParkBoulder County, best late June · 31 checklists that week, 365 in all55%

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

Best time of day

In Colorado, the MacGillivray's Warbler is most often listed on checklists started between 6 and 8 am (2.8% of those checklists).

0%1%2%3%4%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: 3.3% of 71991 checklists7 am: 2.6% of 159189 checklists8 am: 2.1% of 177206 checklists9 am: 1.7% of 165269 checklists10 am: 1.3% of 141029 checklists11 am: 1.0% of 115283 checklists12 pm: 0.8% of 96068 checklists1 pm: 0.8% of 89512 checklists2 pm: 0.7% of 86319 checklists3 pm: 0.6% of 82496 checklists4 pm: 0.7% of 71648 checklists5 pm: 0.8% of 52445 checklists6 pm: 0.9% 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%
March0%0%0%0%
April0%0%0.1%0.1%
May0.8%3.1%4.4%4.5%
June4.2%4.4%4.5%4.2%
July4.4%3.7%2.8%1.8%
August1.6%2.3%2.7%3.7%
September3.9%3.2%2.0%0.9%
October0.3%0.1%0.1%0.1%
November0%0.1%0%0%
December0%0%0%0.1%

Neighboring states

  • Wyoming: arrives the second week of May, 1 week later than Colorado
  • New Mexico: arrives late April, 1 week earlier than Colorado
  • Utah: arrives early May, in the same week than Colorado
  • South Dakota: arrives late May, 3 weeks later than Colorado

Common questions

When do MacGillivray's Warblers arrive in Colorado?
MacGillivray's Warblers reach Colorado in early May, are common by the second week of May, peak in late May (4.4% of checklists), and most are gone by mid September.
When do MacGillivray's Warblers leave Colorado?
Most MacGillivray's Warblers have left Colorado by mid September, when reports fall below half their usual rate. Stragglers are still reported until late September.
When is the best time to see a MacGillivray's Warbler in Colorado?
The MacGillivray's Warbler is reported most often in late May, on about 4.4% of Colorado checklists.
Where in Colorado are MacGillivray's Warblers seen most often?
By county, Costilla County, La Plata County, and San Juan County have the highest peak reporting rates for the MacGillivray's Warbler (counties with at least 200 checklists).