Wildlife Inventories

First Spring Sightings
The following tables list the reports of first sightings for given species within Boulder County. Clicking on a link opens a new tab.

Boulder County Bird and Wildlife Inventories

General Description of Methods and Uses of Wildlife Data Collection
Since 1979, Boulder County Audubon Society volunteers have submitted monthly observations of birds and mammals from 50 mapped areas within Boulder County. Some observers submit a complete list of all birds or mammals seen or heard. Others submit only uncommon or noteworthy sightings. We receive reports from approximately 20-40 observers each month. In recent years many of these reports have come from postings on the Colorado Field Ornithologists’ “CObirds” web site. We also include observations from the Boulder Christmas Bird Count, Indian Peaks Four-Season Bird Counts, and other counts and birdathons. For a few common birds we have no numerical data, as they have simply been listed as “present” from month to month.

Since there are no controls for observer effort or hours, Boulder County Wildlife Inventory data indicate relative, rather than absolute, numbers of wildlife in Boulder County. We have found the data particularly useful for tracking population trends within groups of birds. For example, the data clearly show a recent decline in numbers of wintering Ferruginous and Rough-legged Hawks as a proportion of all raptors reported. A similar decline in relative numbers of Red-headed and Lewis’s Woodpeckers also is apparent.

The data also can be used to track seasonal occurrence and distribution of birds and mammals. For example, December and January numbers of loons, grebes, and cormorants increased dramatically during the last two decades as Boulder experienced a series of milder than average winters. The location entries for Yellow Warbler and Black-headed Grosbeak suggest gradual range expansions into higher-elevation woodlands.

The data are particularly useful in tracking rare and adventive species. Recent increases in observed numbers of Trumpeter Swans, Pacific Loons, and Broad-winged Hawks show up clearly, as does the recent explosion in numbers of Eurasian Collared Doves and Great-tailed Grackles.

Recommended citation: Boulder County Audubon Society. 1979-2008. Monthly Wildlife Inventories. www.boulderaudubon.org

Acknowledgments: We thank the several hundred volunteers who have contributed sightings to the wildlife inventory. Alex and Gillian Brown have coordinated the inventory and compiled inventory data since 1987. Previous compilers were Joe Krieg, Tom Van Zandt, and Ridi Van Zandt (1979-84), and Bill Kaempfer (1984-87). Data entry onto spreadsheets was carried out by Jean-Pierre Georges, Steve Jones, Tom Erickson, Laura Stevenson, and Richard Stromp.

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