Effects of ingested petroleum on the plasma prolactin levels during incubation and on the breeding success of paired mallard ducks.

Abstract

Mated mallard ducks consuming food contaminated with South Louisiana crude oil take significantly longer to complete their reproductive cycles than birds given uncontaminated food. This prolongation is due primarily to an abnormally long period of gonadal maturation. The hatchability among eggs incubated by contaminated birds was significantly lower than that of control birds (53%vs. 71%). The group of oil-fed birds produced significantly fewer ducklings per breeding pair than the groups consuming uncontaminated food. Prolactin concentrations increased significantly during the period of oviposition in control females that successfully completed the cycle and hatched live ducklings. This increase continued during the first half of incubation and prolactin concentrations remained high throughout the duration of the incubation phase, dropping sharply at the time of hatching. Contaminated birds showed qualitatively similar patterns of change throughout the cycle; mean concentrations during oviposition and incubation were significantly lower than the corresponding concentrations in control birds. Although the 17 oil-fed females all laid eggs, only 7 showed signs of incubation and 6 of these produced young. The low reproductive success among contaminated birds may be related to the low plasma prolactin concentrations during these phases of the reproductive cycle.