Birding spot · Boulder County, Colorado
Birding at Sombrero Marsh: What You'll See Each Week In November, the birds most often reported at Sombrero Marsh are Mallard (78%), Northern Shoveler (72%), and Red-winged Blackbird (58%). It is busiest in spring, when 61 species turn up on at least 1 in 20 checklists, and species counts peak in mid May (70 species). 135 species have been reported here across 1,269 complete checklists from 294 birders.
Species by week 0 20 40 60 80 Jan 1-7: low data (9 checklists) Jan 8-14: low data (5 checklists) Jan 15-21: low data (3 checklists) Jan 22-31: 22 species on 5%+ of 10 checklists Feb 1-7: 25 species on 5%+ of 12 checklists Feb 8-14: low data (6 checklists) Feb 15-21: 45 species on 5%+ of 19 checklists Feb 22-28: 27 species on 5%+ of 23 checklists Mar 1-7: 37 species on 5%+ of 36 checklists Mar 8-14: 40 species on 5%+ of 43 checklists Mar 15-21: 35 species on 5%+ of 36 checklists Mar 22-31: 42 species on 5%+ of 84 checklists Apr 1-7: 39 species on 5%+ of 47 checklists Apr 8-14: 45 species on 5%+ of 87 checklists Apr 15-21: 49 species on 5%+ of 79 checklists Apr 22-30: 47 species on 5%+ of 43 checklists May 1-7: 61 species on 5%+ of 58 checklists May 8-14: 63 species on 5%+ of 74 checklists May 15-21: 70 species on 5%+ of 37 checklists May 22-31: 66 species on 5%+ of 60 checklists Jun 1-7: 56 species on 5%+ of 35 checklists Jun 8-14: 58 species on 5%+ of 17 checklists Jun 15-21: 53 species on 5%+ of 14 checklists Jun 22-30: 56 species on 5%+ of 17 checklists Jul 1-7: low data (9 checklists) Jul 8-14: low data (5 checklists) Jul 15-21: low data (7 checklists) Jul 22-31: 43 species on 5%+ of 27 checklists Aug 1-7: 54 species on 5%+ of 17 checklists Aug 8-14: 50 species on 5%+ of 10 checklists Aug 15-21: low data (9 checklists) Aug 22-31: 46 species on 5%+ of 21 checklists Sep 1-7: 60 species on 5%+ of 36 checklists Sep 8-14: 45 species on 5%+ of 26 checklists Sep 15-21: low data (8 checklists) Sep 22-30: 41 species on 5%+ of 21 checklists Oct 1-7: 46 species on 5%+ of 28 checklists Oct 8-14: 42 species on 5%+ of 26 checklists Oct 15-21: 42 species on 5%+ of 24 checklists Oct 22-31: 46 species on 5%+ of 33 checklists Nov 1-7: 37 species on 5%+ of 29 checklists Nov 8-14: 40 species on 5%+ of 14 checklists Nov 15-21: 45 species on 5%+ of 19 checklists Nov 22-30: 39 species on 5%+ of 12 checklists Dec 1-7: low data (8 checklists) Dec 8-14: 38 species on 5%+ of 11 checklists Dec 15-21: 39 species on 5%+ of 10 checklists Dec 22-31: low data (5 checklists) Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec 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 Mallard 78% 2 Northern Shoveler 72% 3 Red-winged Blackbird 58% 4 Green-winged Teal 46% 5 Northern Pintail 46% 6 Ring-necked Duck 46% 7 Black-billed Magpie 41% 8 Bufflehead 38% 9 Canada Goose 36% 10 House Finch 35% 11 Blue Jay 34% 12 American Wigeon 32% 13 Black-capped Chickadee 32% 14 Canvasback 32% 15 American Coot 30% 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 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 .
Mallard78%
Northern Shoveler72%
Red-winged Blackbird58%
Green-winged Teal46%
Northern Pintail46%
Ring-necked Duck46%
Black-billed Magpie41%
Bufflehead38%
Canada Goose36%
House Finch35%
Blue Jay34%
American Wigeon32%
Black-capped Chickadee32%
Canvasback32%
American Coot30%