Abstract
We have conducted a breeding bird monitoring program in GTNP since the early 1990s, utilizing fixed-area census sites of around 5 ha in size. The sites are located throughout the park in all habitat types and elevations, and number 30 in all. Some have been censused each year in June, at the height of the breeding season, others have been censused repeatedly but more sporadically, and others less frequently. the power of these census data to interpret variation in bird species, composition and breeding densities, species to species, site to site and especially year to year, clearly increases with the longevity of the data set. With the data from some sites now covering 18 successive years (1991-2008), it is possible to attempt some interpretation of the bird species variables. One such is reported here. The influence of snow meltout date on breeding density of a common species of the sagebrush flats, Brewer's Sparrow Spizella breweri.