Research and Management of the Brown-headed Cowbird in Western Landscapes, eds. M. L. Morrison et al [Review]

The Brown-headed Cowbird, once appropriately known as the Buffalo-bird, initially occupied a range similar to that of the American Bison.As agriculture advanced, for example as clearings appeared in forests, cowbirds expanded their range to cause adverse effects on many species including the Kirtland's Warbler in Michigan.A conference held in Sacramento, California, 23-25 October 1997, involved almost all experts in the field, and included papers on cowbird ecology, cowbird management, and cowbird control.An overview essay precedes each of the three sections.Scott Robinson, University of Illinois, summarizes the 12 papers reporting factors affecting the abundance and distribution of cowbirds.James N. M. Smith, University of British Columbia, reviews the 15 papers dealing with host selection, impact on hosts, and criteria for taking management action.Linnea S. Hall and Stephen I. Rothstein give an overview of the five papers dealing with the efficacy of control and proposed alternatives to standard control practices.The reader quickly becomes aware of the prodigious amount of effort represented by these papers; several individual studies involved over 100 observers and innumerable hours of field studies and desk analysis.In monetary terms, a million dollars a year is spent annually trapping cowbirds in California.Habitat remains extremely important.Some wilderness areas in Idaho have no cowbirds at all; farther south, in the Sierra Nevada, cowbirds are progressively less common at higher elevations.In Coastal Sage Scrub in California, only 3 of 217 nests were parasitized.Common Yellowthroats had lower parasitism and predation rates and higher nesting success when they nested in extensive cattail marshes.Western species, especially Sage Sparrows, Horned Larks, and Western Meadowlarks, largely avoid parasitism because cowbirds arrive after initiation of their nests.Scarcity of observation perches in shrub-steppe areas also tends to decrease parasitism.Cowbird abundance is strongly influenced by distance to cattle; most cowbird flights are less than 3 km; cowbirds are usually absent 7 km from feeding areas.Rotation of livestock away from host breeding habitat thus becomes a promising management tool.Smith's overview suggests that cowbird management programs are indicated when over 60% of nests are parasitized, and rarely indicated when nest para-C.

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