The abundance of a widespread brood parasite, the Brown-headed Cowbird (Molothrus ater), has decreased by ∼30% in North America over the past 5 decades. Within a community, brood parasite abundance may be expected to positively correlate with host brood parasitism frequency and intensity, but evidence for this correlation is mixed. Few studies have examined if long-term changes in brood parasite abundance have resulted in changes to host parasitism frequency. We measured cowbird abundance, brood parasitism frequency and intensity of 4 riparian songbird species, and host abundance and richness in 2001–2004 and 2012–2014 in riparian vegetation of the south Okanagan Valley of British Columbia, Canada. We compared our data to historical data for the same parameters previously collected between ∼1960 and the early 1990s in the same area. We found that cowbird abundance decreased by ∼80% over 2 decades in the Okanagan Valley, mirroring or exceeding regional-scale trends. Host abundance and richness increased as cowbird abundance decreased. However, songbird brood parasitism frequency and intensity either increased or remained relatively high over more than 4 decades. We discuss possible explanations for this apparent disconnect between brood parasite abundance and host parasitism frequency and intensity, which offer opportunity for further study. Temporal changes in brood parasite abundance, such as the decline of Brown-headed Cowbirds in North America and the Common Cuckoo (Cuculus canorus) in Europe, should not be assumed to lead to correlated changes to host parasitism frequency and intensity.