WhenToBird

Birding spot · Boulder County, Colorado

Birding at Base Line Reservoir: What You'll See Each Week

In November, the birds most often reported at Base Line Reservoir are Ring-billed Gull (95%), Common Goldeneye (90%), and Common Merganser (80%). It is busiest in spring, when 51 species turn up on at least 1 in 20 checklists, and species counts peak in late April (57 species). 129 species have been reported here across 1,607 complete checklists from 379 birders.

Species by week

0204060Jan 1-7: 33 species on 5%+ of 89 checklistsJan 8-14: 25 species on 5%+ of 11 checklistsJan 15-21: 27 species on 5%+ of 12 checklistsJan 22-31: 25 species on 5%+ of 16 checklistsFeb 1-7: 30 species on 5%+ of 17 checklistsFeb 8-14: low data (9 checklists)Feb 15-21: 36 species on 5%+ of 18 checklistsFeb 22-28: 26 species on 5%+ of 21 checklistsMar 1-7: 35 species on 5%+ of 47 checklistsMar 8-14: 36 species on 5%+ of 18 checklistsMar 15-21: 50 species on 5%+ of 18 checklistsMar 22-31: 37 species on 5%+ of 43 checklistsApr 1-7: 44 species on 5%+ of 82 checklistsApr 8-14: 44 species on 5%+ of 26 checklistsApr 15-21: 51 species on 5%+ of 41 checklistsApr 22-30: 57 species on 5%+ of 52 checklistsMay 1-7: 55 species on 5%+ of 33 checklistsMay 8-14: 57 species on 5%+ of 13 checklistsMay 15-21: low data (3 checklists)May 22-31: low data (5 checklists)Jun 1-7: 29 species on 5%+ of 12 checklistsJun 8-14: low data (0 checklists)Jun 15-21: low data (4 checklists)Jun 22-30: low data (2 checklists)Jul 1-7: low data (0 checklists)Jul 8-14: low data (2 checklists)Jul 15-21: low data (2 checklists)Jul 22-31: low data (1 checklists)Aug 1-7: low data (2 checklists)Aug 8-14: low data (1 checklists)Aug 15-21: low data (5 checklists)Aug 22-31: low data (2 checklists)Sep 1-7: low data (7 checklists)Sep 8-14: low data (9 checklists)Sep 15-21: 24 species on 5%+ of 24 checklistsSep 22-30: 35 species on 5%+ of 75 checklistsOct 1-7: 30 species on 5%+ of 27 checklistsOct 8-14: 38 species on 5%+ of 26 checklistsOct 15-21: 41 species on 5%+ of 19 checklistsOct 22-31: 45 species on 5%+ of 134 checklistsNov 1-7: 44 species on 5%+ of 97 checklistsNov 8-14: 46 species on 5%+ of 181 checklistsNov 15-21: 48 species on 5%+ of 85 checklistsNov 22-30: 41 species on 5%+ of 47 checklistsDec 1-7: 37 species on 5%+ of 80 checklistsDec 8-14: 33 species on 5%+ of 65 checklistsDec 15-21: 34 species on 5%+ of 55 checklistsDec 22-31: 32 species on 5%+ of 69 checklistsJanFebMarAprMayJunJulAugSepOctNovDec
Number of species reported on at least 5% of complete checklists, by week (4 per month). Grey bars: fewer than 10 checklists, not counted.

In November: what to expect

  1. 1Ring-billed Gull95%
  2. 2Common Goldeneye90%
  3. 3Common Merganser80%
  4. 4Bufflehead60%
  5. 5Canada Goose58%
  6. 6Western Grebe55%
  7. 7Ruddy Duck55%
  8. 8American Crow54%
  9. 9Hooded Merganser43%
  10. 10Mallard40%
  11. 11Common Loon39%
  12. 12Black-billed Magpie37%
  13. 13Cackling Goose34%
  14. 14Pied-billed Grebe30%
  15. 15Red-breasted Merganser28%

Share of complete checklists at this spot that reported the bird in November. The sparkline is the whole year, with this month highlighted.

Season by season

Winter 34 species

  1. Common Goldeneye92%
  2. Ring-billed Gull90%
  3. Bufflehead52%
  4. Canada Goose52%
  5. Mallard50%

Spring 51 species

  1. Gadwall70%
  2. Mallard67%
  3. Common Goldeneye57%
  4. Bufflehead51%
  5. Canada Goose49%

Summer 37 species

  1. Double-crested Cormorant73%
  2. American White Pelican55%
  3. Barn Swallow42%
  4. Red-winged Blackbird39%
  5. Common Merganser36%

Fall 46 species

  1. Ring-billed Gull94%
  2. Common Merganser73%
  3. Common Goldeneye55%
  4. Western Grebe53%
  5. Canada Goose49%

Specialties

Birds reported far more often here than across Colorado.

Nearby spots

Frequency is the share of complete checklists at this location that listed the bird, 2016–2025. Busy places report more of everything, and the weekly chart counts species on at least 5% of checklists so a few stray reports do not inflate it. How to read it.