WhenToBird

Agelaius phoeniceus · Icteridae

When Do Red-winged Blackbirds Arrive in Colorado?

Adult male Red-winged Blackbird
Photo: infiniteuniverse, CC0 1.0 via iNaturalist

Red-winged Blackbirds are in Colorado all year, but most are here in spring: numbers build from early March, peak in early May (53% of checklists), and fall back by late June. In the quietest week (early September) they are still on about 16% of checklists.

When to look

Numbers buildMar 1-7early March
PeakMay 1-7early May
Fall back byJun 22-30late June
FewestSep 1-7early September

Best: early May. Here all year; numbers build from early March and fall back by late June. Peak: on about 53% of Colorado checklists.

  1. Januncommon
  2. Febcommon
  3. Marpeak season
  4. Aprpeak season
  5. Maypeak season
  6. Junpeak season
  7. Julcommon
  8. Augcommon
  9. Sepuncommon
  10. Octcommon
  11. Novcommon
  12. Decuncommon

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

0%20%40%60%Jan 1-7: 17% of 32254 checklistsJan 8-14: 18% of 23278 checklistsJan 15-21: 18% of 22933 checklistsJan 22-31: 19% of 30856 checklistsFeb 1-7: 23% of 21464 checklistsFeb 8-14: 23% of 22910 checklistsFeb 15-21: 24% of 28739 checklistsFeb 22-28: 31% of 21833 checklistsMar 1-7: 35% of 23066 checklistsMar 8-14: 38% of 23783 checklistsMar 15-21: 41% of 24797 checklistsMar 22-31: 44% of 38439 checklistsApr 1-7: 45% of 31676 checklistsApr 8-14: 46% of 35092 checklistsApr 15-21: 49% of 36778 checklistsApr 22-30: 53% of 50885 checklistsMay 1-7: 54% of 44186 checklistsMay 8-14: 52% of 49011 checklistsMay 15-21: 50% of 40784 checklistsMay 22-31: 46% of 53073 checklistsJun 1-7: 42% of 32432 checklistsJun 8-14: 38% of 29978 checklistsJun 15-21: 36% of 29457 checklistsJun 22-30: 35% of 36072 checklistsJul 1-7: 33% of 28857 checklistsJul 8-14: 29% of 27224 checklistsJul 15-21: 27% of 27629 checklistsJul 22-31: 25% of 37318 checklistsAug 1-7: 22% of 25893 checklistsAug 8-14: 20% of 24870 checklistsAug 15-21: 18% of 24035 checklistsAug 22-31: 16% of 35691 checklistsSep 1-7: 15% of 27068 checklistsSep 8-14: 16% of 26709 checklistsSep 15-21: 17% of 26098 checklistsSep 22-30: 21% of 31550 checklistsOct 1-7: 24% of 24110 checklistsOct 8-14: 27% of 23352 checklistsOct 15-21: 28% of 21895 checklistsOct 22-31: 27% of 28319 checklistsNov 1-7: 25% of 21698 checklistsNov 8-14: 23% of 21061 checklistsNov 15-21: 23% of 19855 checklistsNov 22-30: 21% of 25798 checklistsDec 1-7: 21% of 18626 checklistsDec 8-14: 19% of 19004 checklistsDec 15-21: 20% of 23103 checklistsDec 22-31: 19% 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. Broomfield CountyBest the second week of May · 601 checklists that week, 16,139 in all84%
  2. Adams CountyBest the second week of May · 1284 checklists that week, 44,639 in all74%
  3. Washington CountyBest early June · 47 checklists that week, 2,511 in all72%
  4. Morgan CountyBest late May · 143 checklists that week, 5,181 in all67%
  5. Logan CountyBest early May · 102 checklists that week, 4,117 in all67%
  6. Yuma CountyBest mid May · 133 checklists that week, 3,844 in all65%

Best spots

Share of checklists at the peak
  1. Two Ponds National Wildlife RefugeJefferson County, best late May · 24 checklists that week, 349 in all100%
  2. Kelly Open SpaceDenver County, best late April · 29 checklists that week, 426 in all100%
  3. West Lake (Tabor Lake)Jefferson County, best the second week of April · 20 checklists that week, 444 in all100%
  4. Horseshoe Natural AreaArapahoe County, best late June · 20 checklists that week, 523 in all100%
  5. Wingate South ParkJefferson County, best the second week of July · 23 checklists that week, 164 in all100%
  6. Plaster ReservoirBroomfield County, best the second week of June · 31 checklists that week, 2,987 in all100%

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

Best time of day

In Colorado, the Red-winged Blackbird is most often listed on checklists started between 6 and 8 am (38% of those checklists).

0%10%20%30%40%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: 39% of 71991 checklists7 am: 38% of 159189 checklists8 am: 37% of 177206 checklists9 am: 33% of 165269 checklists10 am: 28% of 141029 checklists11 am: 25% of 115283 checklists12 pm: 24% of 96068 checklists1 pm: 25% of 89512 checklists2 pm: 27% of 86319 checklists3 pm: 30% of 82496 checklists4 pm: 33% of 71648 checklists5 pm: 35% of 52445 checklists6 pm: 36% 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
January17%18%18%19%
February23%23%24%31%
March35%38%41%44%
April45%46%49%53%
May54%52%50%46%
June42%38%36%35%
July33%29%27%25%
August22%20%18%16%
September15%16%17%21%
October24%27%28%27%
November25%23%23%21%
December21%19%20%19%

Neighboring states

  • Wyoming: arrives mid February, 2 weeks earlier than Colorado
  • New Mexico: arrives mid February, 2 weeks earlier than Colorado
  • Utah: arrives late February, 1 week earlier than Colorado
  • Nebraska: arrives early March, in the same week than Colorado

Common questions

When do Red-winged Blackbirds arrive in Colorado?
Red-winged Blackbirds are in Colorado all year, but most are here in spring: numbers build from early March, peak in early May (53% of checklists), and fall back by late June. In the quietest week (early September) they are still on about 16% of checklists.
When do Red-winged Blackbirds leave Colorado?
Red-winged Blackbirds never fully leave Colorado: numbers fall back below half their usual rate by late June, but some are still reported in every week, about 16% of checklists at the low.
When is the best time to see a Red-winged Blackbird in Colorado?
The Red-winged Blackbird is reported most often in early May, on about 53% of Colorado checklists.
Where in Colorado are Red-winged Blackbirds seen most often?
By county, Broomfield County, Adams County, and Washington County have the highest peak reporting rates for the Red-winged Blackbird (counties with at least 200 checklists).