TREMATODE PARASITISM AS A POSSIBLE FACTOR IN OVER-SUMMERING OF GREATER YELLOWLEGS (TRINGA MELANOLEUCA

The possible relationship between trematode infestation and over-summering was explored in Greater Yellowlegs (ninga melanoleuca). Birds were collected throughout the year in coastal Venezuela to examine seasonal and age-related variation in digenean trematode infestations. Yellowlegs were infested with eleven digenean genera. Only four genera were common to both adults and juveniles. Adults that had recently arrived on the wintering grounds were more infested with trematodes than juveniles. By spring, this relationship changed and juveniles ten- ded to contain more trematodes than adults, although the difference was not significant. The percentage of indivi- duals infested by digenean trematodes increased steadily from November to April-May. There was an inverse rela- tionship between fat loads and parasite loads of birds collected by the end of the vemal pre-migratory conditioning. Trematode infestations may cause enteritis, anemia and death of some individuals. Debilitated birds, particularly juveniles, may be unable to fatten prior to migration. Thus, trematode parasitism appears to be an important factor in over-summering behavior, at least for the Greater Yellowlegs. Accepted 12 N~ber 1994.