DOI: 10.7291/d18084
title: Elephant seal female breeding histories at Año Nuevo

description: The elephant seal (Mirounga angustirostris) breeding colony at Año Nuevo,
 California, was founded in 1961, and since monitored closely until the
 present. Since 1968 a research group at the University of California,
 Santa Cruz, has studied it in detail. Individually identified females were
 monitored during the breeding season, and pupping records of many
 throughout their lifetimes were assembled. We address here the maximum
 reproductive success of females using the lifetime breeding histories.
 Females lived to a maximum of 23 years and were observed breeding in as
 many as 17 seasons. One female was observed with a pup nearby in 16
 consecutive seasons, from age 4 through age 19. We compared females that
 gave birth to 10 or more pups (Supermoms) with females that bred at least
 once but produced fewer than 10 pups (Generic moms). Less than 17% of
 female weanlings bred at least once. Only 0.87% of females in the sample
 became Supermoms. We conclude that exceptional reproductive success in
 elephant seals is associated with giving birth annually, living long and
 weaning pups successfully. Once female elephant seals begin reproducing
 they are pregnant or nursing throughout life until they die.
description: Plastic cattle tags were affixed in the hind flippers of pups
 soon after weaning every since since, and one some occasions in juveniles
 or adults whose age was not known. Tags lasted throughout the lifetime of
 many animals, though some were lost. Observations of the colony were
 carried out every year from 1968-2018, including every month but most
 thoroughly during the winter breeding season. Numbers were read off the
 plastic tags whenever possible to identify individual females, and many
 were then marked with hair dye to facilitate subsequent observations of
 mother-pup behavior. Our sample in this study was the 7735 female pups
 tagged over 1963-2005, 1294 of which were observed breeding at least once,
 and 103 of which became Supermoms and were seen in at least 10 breeding
 seasons. An interactive graphical display of female
 histories is provided at
 http://conditdatacenter.org:3838/condit/ESealHistory. (But it is a
 personal web site and not guaranteed as a permanent archive.)
description: The dataset includes a single table with a single row for every
 breeding event of tagged females at the Año Nuevo colony. All breeding
 observations of a single female appear consecutively in the table in the
 default sorting. Full descriptions of the data can be found in the
 accompanying paper, cited below. Users interested in
 publishing results with these data should consult the principal
 investigators to best understand details of the methods.  Those PIs might
 request co-authorship on publications based largely on the data.
 Column headings and definitions
 animalID: an arbitrary number identifying
 individuals year: the breeding season, including
 December of the previous year plus December-March of the designated
 year age: the female's age in years, blank for
 animals tagged as adults and thus of unknown age
 firstday: the first date observed lastday:
 the last date observed sightings: the number of days
 on which the female was observed sightpostpart: the
 number of days sighted beyond 6 days after the first sighting (assumed
 parturtion date) pup: the number of days on which the
 female was observed with one pup (with a pup but not two or more
 pups) puppostpart: the number of days observed with
 exactly one pup beyond 6 days after first sighting
 area: the main breeding beach, defined as one at which the
 female was seen most, or with a pup (local names at Año Nuevo)
 allarea: each area observed, with the number of observations at
 each birthregion: tagging colony for weanlings only
 (AN=Año Nuevo; all other designations are for colonies at least 100 km
 distant) birthyr: year of birth
 pupwt: weight in kilograms of the pup's weight at
 weaning success: fate of the pup (weaned_pup or lost
 pup; other designations indicate insufficient sightings)
 pupsex: observed pup sex