The objectives of this study are to describe Streaked Horned Lark breeding phenology and clutch size; assess reproductive success; identify habitat features important to breeding; and assess the effects of herbicide and prescribed fire on breeding habitat. Field work was conducted on Puget lowland breeding sites during the 2002, 2003 and 2004 seasons, and on coastal Washington and Columbia River island breeding sites during the 2004 field season. On six study sites, combined nest success was 32% in 2004. Nesting success was 33% on the coast and Columbia River sites and was 28% on the three Puget lowland sites. Nest success was 28% in 2002 and 21% in 2003 on the Puget lowland sites. Predation and nest abandonment were primary reasons for nest failure. Territorial Streaked Horned Larks selected habitats that were sparsely vegetated by relatively short annual grasses and with a relatively high percent of bare ground (particularly associated with gravel, cobbles, or sand on the coast), and avoided areas dominated by shrubs and perennial grasses. Lark abundance increased and vegetation changed dramatically in response to September experimental burns on the 13th Division Prairie, Ft. Lewis.