WhenToBird

Passerina caerulea · Cardinalidae

When Do Blue Grosbeaks Arrive in Colorado?

Adult male Blue Grosbeak
Photo: John Rosford, CC BY 4.0 via iNaturalist

Blue Grosbeaks reach Colorado in the second week of May, are common by mid May, peak in the second week of August (6.2% of checklists), and most are gone by the second week of September.

When to look

First arrivalsMay 8-14the second week of May
Common byMay 15-21mid May
PeakAug 8-14the second week of August
Most gone bySep 8-14the second week of September

Best: the second week of August. First arrivals the second week of May; most are gone by the second week of September. Peak: on about 6.2% of Colorado checklists.

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

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

0%2%4%6%8%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% of 36778 checklistsApr 22-30: 0.1% of 50885 checklistsMay 1-7: 0.3% of 44186 checklistsMay 8-14: 1.3% of 49011 checklistsMay 15-21: 3.7% of 40784 checklistsMay 22-31: 5.3% of 53073 checklistsJun 1-7: 4.8% of 32432 checklistsJun 8-14: 4.5% of 29978 checklistsJun 15-21: 4.1% of 29457 checklistsJun 22-30: 4.3% of 36072 checklistsJul 1-7: 4.4% of 28857 checklistsJul 8-14: 4.3% of 27224 checklistsJul 15-21: 5.0% of 27629 checklistsJul 22-31: 5.7% of 37318 checklistsAug 1-7: 6.3% of 25893 checklistsAug 8-14: 6.2% of 24870 checklistsAug 15-21: 5.9% of 24035 checklistsAug 22-31: 4.6% of 35691 checklistsSep 1-7: 3.4% of 27068 checklistsSep 8-14: 2.6% of 26709 checklistsSep 15-21: 1.8% of 26098 checklistsSep 22-30: 0.8% of 31550 checklistsOct 1-7: 0.2% of 24110 checklistsOct 8-14: 0.1% of 23352 checklistsOct 15-21: 0% of 21895 checklistsOct 22-31: 0% of 28319 checklistsNov 1-7: 0.1% of 21698 checklistsNov 8-14: 0% 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% 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. Baca CountyBest the second week of July · 34 checklists that week, 3,209 in all51%
  2. Otero CountyBest mid July · 77 checklists that week, 4,404 in all44%
  3. Kiowa CountyBest mid July · 42 checklists that week, 3,854 in all43%
  4. Huerfano CountyBest late May · 315 checklists that week, 3,008 in all36%
  5. Bent CountyBest mid July · 52 checklists that week, 5,275 in all35%
  6. Yuma CountyBest the second week of August · 57 checklists that week, 3,844 in all26%

Best spots

Share of checklists at the peak
  1. Lon Hagler ReservoirLarimer County, best mid August · 21 checklists that week, 1,172 in all89%
  2. Clear Spring Ranch ParkEl Paso County, best late July · 22 checklists that week, 2,355 in all81%
  3. Dry CreekBoulder County, best the second week of August · 62 checklists that week, 2,413 in all80%

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

Best time of day

In Colorado, the Blue Grosbeak 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 (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: 4.8% of 71991 checklists7 am: 3.1% of 159189 checklists8 am: 2.3% of 177206 checklists9 am: 1.8% 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: 0.8% of 82496 checklists4 pm: 0.9% of 71648 checklists5 pm: 1.4% of 52445 checklists6 pm: 1.9% 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%0.1%
May0.3%1.3%3.7%5.3%
June4.8%4.5%4.1%4.3%
July4.4%4.3%5.0%5.7%
August6.3%6.2%5.9%4.6%
September3.4%2.6%1.8%0.8%
October0.2%0.1%0%0%
November0.1%0%0%0%
December0%0%0%0%

Neighboring states

  • New Mexico: arrives early May, 1 week earlier than Colorado
  • Utah: arrives mid May, 1 week later than Colorado
  • Nebraska: arrives the second week of May, in the same week than Colorado
  • South Dakota: arrives mid May, 1 week later than Colorado

Common questions

When do Blue Grosbeaks arrive in Colorado?
Blue Grosbeaks reach Colorado in the second week of May, are common by mid May, peak in the second week of August (6.2% of checklists), and most are gone by the second week of September.
When do Blue Grosbeaks leave Colorado?
Most Blue Grosbeaks have left Colorado by the second week of September, when reports fall below half their usual rate. Stragglers are still reported until mid September.
When is the best time to see a Blue Grosbeak in Colorado?
The Blue Grosbeak is reported most often in the second week of August, on about 6.2% of Colorado checklists.
Where in Colorado are Blue Grosbeaks seen most often?
By county, Baca County, Otero County, and Kiowa County have the highest peak reporting rates for the Blue Grosbeak (counties with at least 200 checklists).