Suckling observations of Galapagos sea lions

Milk is not cheap. Mammalian offspring are expected to wean during the early juvenile stages, whether through their own mechanisms or their mothers’ instigation. To not do so would result in a reproductive trade-off for the mother: continued investment in the health and growth of her current offspring, over a shorter birth interval, and the possibility of begetting a fitter pup. Here we show, for the first time, using 20 years of data, repeated suckling events between female Galápagos Sea Lions (GSL) Zalophus wollebaeki and their fully adult biological offspring well beyond the expected age of independence and when the offspring are themselves already reproductively active. This behavior, ‘supersuckling’, suggests that GSL mother-offspring relationships are more complex and longer-lasting than previously thought. To our knowledge, this behavior has not been previously documented in any marine mammal species.
, Data were collected between September 2003 and April 2023 on Isla Caamaño (0° 45’ S, 90° 16’ W) during 2 annual field seasons from October-December and February-April that cover the main reproductive period. Suckling observations were made through minimum twice daily rounds using non-invasive means. Morphometric measurements were collected during captures of individuals. All data collection was carried out with the knowledge and permission of the Galápagos National Park.
, , # Suckling observations and morphometric measurements of Galapagos Sea Lions

Dataset DOI: [10.5061/dryad.jq2bvq8jh](10.5061/dryad.jq2bvq8jh)

## Description of the data and file structure

GENERAL INFORMATION

This README.txt file was updated on 24 September 2025

A. Paper associated with this archive

Citation: Milking it: repeated post-weaning suckling events in Galápagos Sea Lions *Zalophus wollebaeki*

Data were collected between September 2003 and April 2023 on Isla Caamaño during 2 annual field seasons from October-December and February-April that cover the main reproductive period. The islet is located off the southern coast of Santa Cruz in the centre of the Galápagos archipelago and is home to a breeding colony of GSL that has been intensively studied since 2003. All individuals that are born on, or regularly use the islet, are marked and assigned a unique identification ('ID'). During the marking morphometric measurements are taken, some individuals have been captured multipl...,