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Incoming links: Jan Komdeur
Jan Komdeur 2026-11-05
Jan Komdeur is a researcher in animal behaviour and evolution, particularly cooperative breeding. His 1994 study of the Seychelles warbler asked whether older offspring staying with their parents actually improve the parents' reproductive success. Observing larger families alone cannot answer this: good territories might support both more helpers and more surviving young.[ref]
Experimental evidence for helping and hindering by previous offspring in the cooperative-breeding Seychelles warbler Acrocephalus sechellensis by Jan Komdeur. Abstract: study question and territory-quality controls; Behavioral Ecology and Sociobiology 34, 175–186, 1994
Jan Komdeur therefore removed helpers from breeding groups and compared outcomes while controlling for territory quality, group size and breeder age. One helper improved parental reproductive success; two or more helpers on medium-quality territories could reduce it relative to one helper. The experiment makes cooperative breeding a quantitative, context-dependent question. A helper may contribute care and gain inclusive fitness, while additional group members may also compete for resources or breeding opportunities.[ref]
Experimental evidence for helping and hindering by previous offspring in the cooperative-breeding Seychelles warbler Acrocephalus sechellensis by Jan Komdeur. Abstract and removal experiments: one-helper benefit and multiple-helper cost on medium-quality territories
Seychelles warbler 2026-11-05
The Seychelles warbler, Acrocephalus sechellensis, is a small songbird of the Seychelles islands. Its natural geographic restriction is an example of endemism. Long-term field monitoring has made it a useful subject for studying cooperative breeding, in which additional individuals help care for young.[ref]
Seychelles Warbler Project overview. Project overview: endemic passerine and long-term study
In this species, older offspring can remain with their parents and help defend the breeding area or feed younger offspring. That observation raises a causal question: do helpers increase reproductive success, or do productive breeding areas simply produce and retain more helpers? Jan Komdeur's 1994 removal experiment addressed this by reducing groups and controlling comparisons for area quality, initial group size and breeder age.[ref]
One additional caregiver improved parental reproductive success under the tested conditions. Two or more in medium-quality areas could instead reduce success relative to one. Competition over reproduction or resources were proposed explanations, rather than established universal causes. The experiment therefore shows why counting helpers alone cannot establish a steadily increasing benefit: the effect depends on ecological and social context.[ref]
Experimental evidence for helping and hindering by previous offspring in the cooperative-breeding Seychelles warbler Acrocephalus sechellensis by Jan Komdeur. Removal results; alternative explanations for reduced success in larger groups