Population dynamics of the helminth community from migrating blue-winged teal: loss of helminths without replacement on the wintering grounds

The main and interactive effects of host and seasonal factors on abundance of 22 common helminth species from fall and spring migratory blue-winged teal collected in the Texas Panhandle were examined. Although abundances of many common helminth species were greater in immature than adult birds just off the breeding grounds, fall-collected adults had higher abundances of most helminth species than did both juvenile and adult birds from the wintering grounds in Mexico. While total abundance of helminths declined on the wintering grounds to only 54% of that from fall-collected birds, overall species composition and abundances of some helminth species were equivalent in the host population throughout the year, regardless of changing geographic locality and migratory stress. The helminth fauna acquired in the northern latitude breeding grounds was not replaced by an ecologically equivalent fauna in the southern latitude wintering grounds. Only one species, Corynosoma constrictum, was lost without replacement during the wintering period. Schistorphus cucullatus, a parasite of the Raillidae, occurred in birds on the wintering grounds but was lost without replacement on the breeding grounds. Thus, most of these helminth species were capable of ubiquitous transmission across the range of this host and (or) infections of the respective species persisted through the migratory stress period. This study suggests that diversity in the helminth community of a migratory host species over its entire geographic range may largely result from differences between separate populations that have become isolated over time as a result of establishing specific migratory corridors, rather than from the short-term effects of environmental differences between regions representing the extremes of the overall migratory range (breeding and wintering grounds).