WhenToBird

Aythya affinis · Anatidae

When Do Lesser Scaups Arrive in Colorado?

Adult male Lesser Scaup
Photo: Paul Lewis, CC BY 4.0 via iNaturalist

Lesser Scaups reach Colorado in the second week of October, are common by mid October, peak in early April (14% of checklists), and most are gone by early May.

When to look

First arrivalsOct 8-14the second week of October
Common byOct 15-21mid October
PeakApr 1-7early April
Most gone byMay 1-7early May

Best: early April. First arrivals the second week of October; most are gone by early May. Peak: on about 14% of Colorado checklists.

  1. Jancommon
  2. Febcommon
  3. Marpeak season
  4. Aprpeak season
  5. Maycommon
  6. Junrare
  7. Julnot usually seen
  8. Augnot usually seen
  9. Seprare
  10. Octuncommon
  11. Novcommon
  12. Deccommon

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

0%5%10%15%Jan 1-7: 6.1% of 32254 checklistsJan 8-14: 6.0% of 23278 checklistsJan 15-21: 5.1% of 22933 checklistsJan 22-31: 4.7% of 30856 checklistsFeb 1-7: 4.5% of 21464 checklistsFeb 8-14: 4.4% of 22910 checklistsFeb 15-21: 4.4% of 28739 checklistsFeb 22-28: 7.3% of 21833 checklistsMar 1-7: 8.7% of 23066 checklistsMar 8-14: 10% of 23783 checklistsMar 15-21: 12% of 24797 checklistsMar 22-31: 14% of 38439 checklistsApr 1-7: 15% of 31676 checklistsApr 8-14: 14% of 35092 checklistsApr 15-21: 13% of 36778 checklistsApr 22-30: 10% of 50885 checklistsMay 1-7: 5.0% of 44186 checklistsMay 8-14: 2.6% of 49011 checklistsMay 15-21: 1.6% of 40784 checklistsMay 22-31: 1.2% of 53073 checklistsJun 1-7: 1.1% of 32432 checklistsJun 8-14: 0.6% of 29978 checklistsJun 15-21: 0.7% of 29457 checklistsJun 22-30: 0.5% of 36072 checklistsJul 1-7: 0.5% of 28857 checklistsJul 8-14: 0.5% of 27224 checklistsJul 15-21: 0.4% of 27629 checklistsJul 22-31: 0.4% of 37318 checklistsAug 1-7: 0.3% of 25893 checklistsAug 8-14: 0.3% of 24870 checklistsAug 15-21: 0.3% of 24035 checklistsAug 22-31: 0.3% of 35691 checklistsSep 1-7: 0.3% of 27068 checklistsSep 8-14: 0.3% of 26709 checklistsSep 15-21: 0.6% of 26098 checklistsSep 22-30: 0.6% of 31550 checklistsOct 1-7: 0.7% of 24110 checklistsOct 8-14: 1.2% of 23352 checklistsOct 15-21: 2.8% of 21895 checklistsOct 22-31: 5.5% of 28319 checklistsNov 1-7: 8.0% of 21698 checklistsNov 8-14: 9.1% of 21061 checklistsNov 15-21: 7.4% of 19855 checklistsNov 22-30: 7.2% of 25798 checklistsDec 1-7: 6.6% of 18626 checklistsDec 8-14: 5.6% of 19004 checklistsDec 15-21: 4.9% of 23103 checklistsDec 22-31: 5.0% 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. Phillips CountyBest late March · 15 checklists that week, 1,052 in all47%
  2. Costilla CountyBest late March · 38 checklists that week, 1,323 in all46%
  3. Broomfield CountyBest early April · 433 checklists that week, 16,139 in all43%
  4. Kiowa CountyBest mid November · 27 checklists that week, 3,854 in all41%
  5. Adams CountyBest late March · 1457 checklists that week, 44,639 in all36%
  6. Sedgwick CountyBest early November · 24 checklists that week, 1,168 in all32%

Best spots

Share of checklists at the peak
  1. Big Stratton ReservoirEl Paso County, best late March · 20 checklists that week, 400 in all98%
  2. Brunner ReservoirBroomfield County, best the second week of April · 20 checklists that week, 494 in all93%
  3. Washington Park (south)Denver County, best the second week of April · 23 checklists that week, 823 in all92%
  4. Topminnow Bend Natural AreaLarimer County, best late March · 31 checklists that week, 748 in all91%
  5. Hodgson-Harris ReservoirBoulder County, best early April · 25 checklists that week, 1,007 in all91%
  6. Rocky Flats National Wildlife RefugeJefferson County, best late March · 37 checklists that week, 638 in all90%

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

Best time of day

In Colorado, the Lesser Scaup is most often listed on checklists started between 1 and 3 pm (6.0% of those checklists).

0%2%4%6%8%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: 2.5% of 71991 checklists7 am: 3.1% of 159189 checklists8 am: 4.1% of 177206 checklists9 am: 4.9% of 165269 checklists10 am: 5.1% of 141029 checklists11 am: 5.7% of 115283 checklists12 pm: 5.8% of 96068 checklists1 pm: 6.0% of 89512 checklists2 pm: 6.1% of 86319 checklists3 pm: 5.7% of 82496 checklists4 pm: 5.1% of 71648 checklists5 pm: 4.3% of 52445 checklists6 pm: 3.1% 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
January6.1%6.0%5.1%4.7%
February4.5%4.4%4.4%7.3%
March8.7%10%12%14%
April15%14%13%10%
May5.0%2.6%1.6%1.2%
June1.1%0.6%0.7%0.5%
July0.5%0.5%0.4%0.4%
August0.3%0.3%0.3%0.3%
September0.3%0.3%0.6%0.6%
October0.7%1.2%2.8%5.5%
November8.0%9.1%7.4%7.2%
December6.6%5.6%4.9%5.0%

Neighboring states

  • Wyoming: arrives late February, 18 weeks later than Colorado
  • New Mexico: arrives mid October, 1 week later than Colorado
  • Utah: arrives the second week of October, in the same week than Colorado
  • Nebraska: arrives mid October, 1 week later than Colorado

Common questions

When do Lesser Scaups arrive in Colorado?
Lesser Scaups reach Colorado in the second week of October, are common by mid October, peak in early April (14% of checklists), and most are gone by early May.
When do Lesser Scaups leave Colorado?
Most Lesser Scaups have left Colorado by early May, when reports fall below half their usual rate. Stragglers are still reported until early June.
When is the best time to see a Lesser Scaup in Colorado?
The Lesser Scaup is reported most often in early April, on about 14% of Colorado checklists.
Where in Colorado are Lesser Scaups seen most often?
By county, Phillips County, Costilla County, and Broomfield County have the highest peak reporting rates for the Lesser Scaup (counties with at least 200 checklists).