Helminths and the northern bobwhite population decline: A review

Long-term data from the Breeding Bird Survey and Christmas Bird Count indicate that northern bobwhite (Colinus virginianus; hereafter, bobwhite) populations have declined since 1961 in all but 1 of the 31 states they occupy within the United States. This long-term population decline is largely due to habitat loss. However, several other factors, including parasitism, have been considered as possible contributors or even primary causes of the bobwhite population decline. We review recent research on the helminths that infect bobwhites, particularly in Texas, and compare the bobwhite–helminth system to other galliform–helminth systems. We hypothesize that helminths do not affect bobwhite populations under favorable habitat conditions and that any observed localized population impacts may be proximate causes of the bobwhite population decline rather than ultimate causes of the bobwhite population decline. Helminth survey data provide insufficient evidence of negative effects on individual bobwhites or on their populations. Although surveys provide important data and should continue, experimental studies are the best way to identify the impact that helminths may have on bobwhites at the population level.