Behavioural Ecology
Universität Bielefeld > Faculty of Biology > Animal Behaviour > Behavioural Ecology

Sea Lion Project Galápagos

Behavioural and Molecular Ecology


The consequences of life-history decisions of individuals on reproductive success have only rarely been documented in sufficient detail to allow understanding phenomena at the level of population dynamics. This long-term study last for 15 years by now and analyses the consequences of life history decisions of male and female individuals under environmental uncertainty and models the demographic consequences of individual decisions in a large mammal, the Galápagos sea lion (Zalophus wollebaeki). Due to its island tameness, the population offers a unique opportunity to determine how male and female reproductive strategies, juvenile development, and juvenile and adult mortality rates together generate the population dynamics of a large marine predator. This is particularly interesting since Galápagos sea lions live in an environment characterised by high variance in food abundance due to frequent disturbances of the oceanic regime by El Niño, which creates a major decline in food resources. El Niños appear to depress juvenile growth, lower female fecundity and may lead to large increases of mortality in juveniles and adults. Effects appear to vary with sex and age class, correlated with reproductive strategy and diving ability. By modelling the effect of individual life history decisions on population dynamics, the study bridges the gap between life history and population dynamics. Moreover, it shows to what extent life history decisions allow adaptation to a highly variable environment or whether they must be understood more parsimoniously as passive tracking of environmental changes.

Individual projects

Cost of reproduction and female life histories

Stephanie Kalberer

Transition to independence

Dr. Paolo Piedrahita

Social relationships and their impact on male reproductive success

Dr. Kristine Meise

Ontogeny of the diving behaviour of juveniles

Dr. Jana Jeglinski

Mating strategies and reproductive success of males

Dr. Ulrich Pörschmann

Life history decisions and reproductive success of females

Dr. Birte Müller

Genetic and social structure of colonies

Dr. Jochen Wolf


Help us collecting data

If you want to contribute to our project and are in Galápagos, you can do so by keeping your eyes open for sea lions with coloured flipper tags. If you see one, please note the place and date where you saw it, the colour of the tag and the number printed on it. You can send the information either to, or just to any of our project team members. If you could provide a picture of the tag that would be most useful.

Every small bit of information is helpful and will enable us to understand the distribution and movements between different sea lion colonies.

Since the printed number on the tags may fade away, we punch holes in them corresponding to the number.


Publications of the project


Trillmich F, Meise K, Kalberer S, Mueller B, Piedrahita P, Pörschmann U, Wolf JBW and Krüger O (2016) On the challenge of interpreting census data: insights from a study of an endangered pinniped. PLoS One 11: e0154588.


Jeglinski JWE, Wolf JBW, Werner C, Costa DP and Trillmich F (2015) Differences in foraging ecology align with genetically divergent ecotypes of a highly mobile marine top predator. Oecologia 175: 1041-1052.


Piedrahita P, Meise K, Werner C, Krüger O and Trillmich F (2014) Lazy sons, self-sufficient daughters: are sons more demanding? Animal Behaviour 98: 69-78.

Meise K, Mueller B, Zein B and Trillmich F (2014) Applicability of single-camera photogrammetry to determine body dimensions of pinnipeds: Galapagos sea lions as an example. PLoS One 9: e101197.

Meise K, Piedrahita P, Krüger O and Trillmich F (2014) Being on time: size-dependent attendance patterns affect male reproductive success. Animal Behaviour 93: 77-86.

Krüger O, Wolf JBW, Jonker RM, Hoffman JI and Trillmich F (2014) Disentangling the contribution of sexual selection and ecology to the evolution of size dimorphism in pinnipeds. Evolution 68: 1485-1496.


Villegas-Amtmann S, Jeglinski JWE, Costa DP, Robinson PW and Trillmich F (2013) Individual foraging strategies reveal niche overlap between endangered Galapagos pinnipeds. PLoS One 8: e70748.

Lenz TL, Mueller B, Trillmich F and Wolf JBW (2013) Divergent allele advantage at MHC-DRB through direct and maternal genotypic effects and its consequences for allele pool composition and mating. Proceedings of the Royal Society of London B 280: 20130714.

Meise K, Krüger O, Piedrahita P and Trillmich F (2013) Site fidelity of male Galapagos sea lions: a lifetime perspective. Behavioral Ecology and Sociobiology 67: 1001-1011.

Jeglinski JWE, Goetz KT, Werner C, Costa DP and Trillmich F (2013) Same size same niche? Foraging niche separation between sympatric juvenile Galapagos sea lions and adult Galapagos fur seals. Journal of Animal Ecology 82: 694-706.

Kraus C, Mueller B, Meise K, Piedrahita P, Pörschmann U and Trillmich F (2013) Mama's boy: sex differences in juvenile survival in a highly dimorphic large mammal, the Galapagos sea lion. Oecologia 171: 893-903.

Meise K, Krüger O, Piedrahita P, Mueller A and Trillmich F (2013) Proximity loggers on amphibious mammals: a new method to study social relations in their terrestrial habitat. Aquatic Biology 18: 81-89.


Jeglinski JWE, Werner C, Robinson PW, Costa DP and Trillmich F (2012) Age, body mass and environmental variation shape the foraging ontogeny of Galapagos sea lions. Marine Ecology Progress Series 453: 279-296.


Mueller B, Pörschmann U, Wolf JBW and Trillmich F (2011) Growth under uncertainty: the influence of marine variability on early development of Galapagos sea lions. Marine Mammal Science 27: 350-365.


Jeglinski JWE, Mueller B, Pörschmann U and Trillmich F (2010) Field-Based Age Estimation of Juvenile Galapagos Sea Lions (Zalophus wollebaeki) Using Morphometric Measurements. Aquatic Mammals 36: 262-269.

Pörschmann U, Trillmich F, Mueller B and Wolf JBW (2010) Male reproductive success and its behavioural correlates in a polygynous mammal, the Galápagos sea lion (Zalophus wollebaeki). Molecular Ecology 19: 2574-2586.


Kunc H, Wolf JBW (2008) Seasonal changes of vocal rates and their relation to territorial status in male Galápagos sea lions (Zalophus wollebaeki). Ethology 114: 381-388.

Trillmich F, Rea L, Castellini M, Wolf JBW (2008) Age-related changes in hematocrit in the Galápagos sea lion (Zalophus wollebaeki) and the Weddell seal (Leptonychotes weddellii). Marine Mammal Science 24: 303-314.

Trillmich F & Wolf JBW (2008) Parent-offspring and sibling conflict in Galápagos fur seals and sea lions. Behavioral Ecology and Sociobiology 62: 363-375.

Wolf JBW, Harrod C, Brunner S, Salazar S, Trillmich F, Tautz D (2008) Tracing early stages of species differentiation: ecological, morphological and genetic divergence of Galápagos sea lion populations. BMC Evolutionary Biology 8:150.

Wolf JBW, Trillmich F (2008) Kin in space. Social viscosity in a spatially and genetically sub-structured network. Proceedings of the Royal Society of London B 275: 2063-2069.


Wolf JBW, Mawdsley D, Trillmich F, James R (2007) Social structure in a colonial mammal: Unravelling hidden structural layers and their foundations by network analysis. Animal Behaviour 74: 1293-1302.

Wolf JBW, Tautz D, Trillmich F (2007) Galápagos and Californian sea lions are separate species: genetic analysis of the genus Zalophus and its implications for conservation management. Frontiers in Zoology 4: 1-13.

Wolf JBW, Trillmich F (2007) Beyond habitat requirements: individual fine-scale site fidelity in a colony of the Galapagos sea lion (Zalophus wollebaeki) creates conditions for social structuring. Oecologia 152, 553-567.


Wolf JBW, Kauermann G, Trillmich F (2005) Males in the shade: habitat use and sexual segregation in the Galápagos sea lion (Zalophus californianus wollebaeki). Behavioral Ecology and Sociobiology 59: 293-302.