WhenToBird

Spizella breweri · Passerellidae

When Do Brewer's Sparrows Arrive in Colorado?

Adult Brewer's Sparrow
Photo: Daughter Dad, CC BY 4.0 via iNaturalist

Brewer's Sparrows arrive in Colorado in late April, peak in early September (6.1% of checklists), and most are gone by early October.

When to look

First arrivalsApr 22-30late April
Common byApr 22-30late April
PeakSep 1-7early September
Most gone byOct 1-7early October

Best: early September. First arrivals late April; most are gone by early October. Peak: on about 6.1% of Colorado checklists.

  1. Jannot usually seen
  2. Febnot usually seen
  3. Marnot usually seen
  4. Apruncommon
  5. Maycommon
  6. Jununcommon
  7. Juluncommon
  8. Augpeak season
  9. Seppeak season
  10. Octuncommon
  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: 0.1% of 32254 checklistsJan 8-14: 0.1% of 23278 checklistsJan 15-21: 0.1% of 22933 checklistsJan 22-31: 0.1% of 30856 checklistsFeb 1-7: 0.1% of 21464 checklistsFeb 8-14: 0% of 22910 checklistsFeb 15-21: 0.1% of 28739 checklistsFeb 22-28: 0% of 21833 checklistsMar 1-7: 0% of 23066 checklistsMar 8-14: 0.1% of 23783 checklistsMar 15-21: 0% of 24797 checklistsMar 22-31: 0.1% of 38439 checklistsApr 1-7: 0.1% of 31676 checklistsApr 8-14: 0.1% of 35092 checklistsApr 15-21: 0.5% of 36778 checklistsApr 22-30: 1.8% of 50885 checklistsMay 1-7: 4.5% of 44186 checklistsMay 8-14: 5.2% of 49011 checklistsMay 15-21: 4.0% of 40784 checklistsMay 22-31: 2.0% of 53073 checklistsJun 1-7: 1.6% of 32432 checklistsJun 8-14: 1.3% of 29978 checklistsJun 15-21: 1.4% of 29457 checklistsJun 22-30: 1.7% of 36072 checklistsJul 1-7: 1.6% of 28857 checklistsJul 8-14: 1.4% of 27224 checklistsJul 15-21: 1.8% of 27629 checklistsJul 22-31: 1.8% of 37318 checklistsAug 1-7: 2.2% of 25893 checklistsAug 8-14: 3.8% of 24870 checklistsAug 15-21: 4.7% of 24035 checklistsAug 22-31: 6.0% of 35691 checklistsSep 1-7: 6.4% of 27068 checklistsSep 8-14: 6.1% of 26709 checklistsSep 15-21: 4.3% of 26098 checklistsSep 22-30: 2.5% of 31550 checklistsOct 1-7: 0.8% of 24110 checklistsOct 8-14: 0.3% 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: 0.1% of 19855 checklistsNov 22-30: 0.1% of 25798 checklistsDec 1-7: 0.1% of 18626 checklistsDec 8-14: 0.1% of 19004 checklistsDec 15-21: 0.1% 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. Costilla CountyBest late August · 37 checklists that week, 1,323 in all36%
  2. Saguache CountyBest late August · 89 checklists that week, 3,220 in all22%
  3. Jackson CountyBest mid August · 152 checklists that week, 7,472 in all21%
  4. Montezuma CountyBest the second week of September · 370 checklists that week, 15,992 in all21%
  5. Moffat CountyBest the second week of June · 252 checklists that week, 5,700 in all19%
  6. Alamosa CountyBest the second week of September · 100 checklists that week, 4,206 in all18%

Best spots

Share of checklists at the peak
  1. Dan Noble State Wildlife AreaSan Miguel County, best the second week of September · 20 checklists that week, 399 in all72%
  2. Case Reservoir Number 2Jackson County, best late August · 21 checklists that week, 474 in all65%
  3. Meadow Springs RanchLarimer County, best the second week of May · 25 checklists that week, 403 in all59%
  4. Heron Pond/Heller Open SpaceDenver County, best the second week of May · 69 checklists that week, 924 in all57%
  5. Floodwater B-6 Retention ReservoirLarimer County, best mid July · 21 checklists that week, 136 in all51%

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

Best time of day

In Colorado, the Brewer's Sparrow is most often listed on checklists started between 6 and 8 am (2.6% 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: 3.2% of 71991 checklists7 am: 2.3% of 159189 checklists8 am: 2.0% of 177206 checklists9 am: 1.7% of 165269 checklists10 am: 1.4% of 141029 checklists11 am: 1.2% of 115283 checklists12 pm: 1.1% of 96068 checklists1 pm: 1.1% of 89512 checklists2 pm: 1.0% of 86319 checklists3 pm: 1.0% of 82496 checklists4 pm: 1.2% of 71648 checklists5 pm: 1.5% of 52445 checklists6 pm: 1.4% 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
January0.1%0.1%0.1%0.1%
February0.1%0%0.1%0%
March0%0.1%0%0.1%
April0.1%0.1%0.5%1.8%
May4.5%5.2%4.0%2.0%
June1.6%1.3%1.4%1.7%
July1.6%1.4%1.8%1.8%
August2.2%3.8%4.7%6.0%
September6.4%6.1%4.3%2.5%
October0.8%0.3%0.1%0.1%
November0%0.1%0.1%0.1%
December0.1%0.1%0.1%0%

Neighboring states

  • Wyoming: arrives late April, in the same week than Colorado
  • New Mexico: arrives early August, 13 weeks later than Colorado
  • Utah: arrives mid April, 1 week earlier than Colorado
  • Arizona: arrives mid August, 15 weeks later than Colorado

Common questions

When do Brewer's Sparrows arrive in Colorado?
Brewer's Sparrows arrive in Colorado in late April, peak in early September (6.1% of checklists), and most are gone by early October.
When do Brewer's Sparrows leave Colorado?
Most Brewer's Sparrows have left Colorado by early October, when reports fall below half their usual rate.
When is the best time to see a Brewer's Sparrow in Colorado?
The Brewer's Sparrow is reported most often in early September, on about 6.1% of Colorado checklists.
Where in Colorado are Brewer's Sparrows seen most often?
By county, Costilla County, Saguache County, and Jackson County have the highest peak reporting rates for the Brewer's Sparrow (counties with at least 200 checklists).