Perinatal behavior of northern elephant seal females and their young.

Abstract

Northern elephant seal females and pups were observed during four breeding seasons at Ano Nuevo Tstand, California. Six to seven days after a female arrived on the rookery she gave birth to a single pup which she nursed for four weeks. Estrus began 24 days after parturition and lasted an average of four days. Females spent a total of 34 days on the rookery before returning to sea. The only other time females came ashore was to moult, a period which lasted a few weeks. Most births occurred in the harem at night during the last two weeks of January. Cephalic presentations were more frequent than caudals (62% vs. 38%) and both were equally rapid. The placenta was delivered immediately after the pup or within an hour after birth. Stillbirths were infrequent and premature pups were never observed. The sex ratio was 49.4 males to 50.5 females. Eight females gave birth for the first time during their third year but most females are believed to give birth later. Three females gave birth on a different rookery than their own birthplace. The time of parturition from year to year was very consistent in individual females. Newborn pups weighed 65 lbs at birth and were 60 inches long. They are precocial and suckled for about four weeks before being weaned. Weaners moulted their natal pelage at four to six weeks of age, a time when they began entering the water. Most weaners left the rookery headed north during the month of April. Females accepted a pup by allowing it to nurse and rejected alien pups by biting them. Females emitted two vocalizations : a pup attraction call and a threat vocalization. Pups emitted a single vocalization which functioned in several situations. Scventy-two percent of the females observed nursed their own pups to weaning and rejected most of the suckling attempts of alien pups. A few females nursed an alien pup in addition to their own. Twenty-six percent of the females became separated from their pups or their pups died. One third of these females adopted an alien pup. Females that gave birth, but did not nurse for several days, did not copulate. The frequency and duration of suckling increased as pups developed. Pups attempted to suckle any available female but were rejected by most alien females. Sixty percent of marked pups suckled their mothers. The remaining forty percent were separated from their mothers and most of them died. Those that survived were adopted by an alien female or were suckled by several different females each day. Pup mortality at Ano Nuevo Island was very consistent over the four year period, ranging from 13.0% to 14.5%. Most mortalities were socially induced; pups separated from their mothers starved or were injured by adult males and females. The probability of separation was increased by high numbers of females and disturbances created by intrusions of breeding hulls into the harem.