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The effect of helper presence on egg size in cooperatively breeding birds

van Eekelen, Nadia (2019) The effect of helper presence on egg size in cooperatively breeding birds. Bachelor's Thesis, Life Science and Technology.


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Cooperative breeders receive help with offspring care from non-breeding individuals, named helpers. In the presence of helpers, parents can reduce their work-load without consequences for their offspring, a phenomenon called load-lightening. Load-lightening at the feeding stage is a common strategy among cooperative breeders. Russell et al. 2017 have shown that for the superb fairy-wren, load-lightening can already occur at the egg stage, in which females that are assisted by helpers lay smaller eggs. They predicted that load-lightening at the egg stage also is a widespread phenomenon among cooperatively breeding species. In this study, this prediction is tested by examining the effect of helper presence on egg size in ten cooperatively breeding bird species: the superb fairy-wren, carrion crow, sociable weaver, brown-headed nuthatch, acorn woodpecker, southern lapwing, Iberian magpie, laughing kookaburra, dunnock and the red-winged fairy-wren. For four of these species, it was demonstrated that females breeding in the presence of helpers laid smaller eggs than in the absence of helpers. In the other six species the effect was the other way around (helper presence increased egg size) or there was no effect at all. Therefore, load-lightening at the egg stage does not appear to be a widespread phenomenon in cooperatively breeding birds. However, there is a chance that the correlation between helper presence and egg size is non-causal, since both egg size and helper presence might be correlated to the quality of the territory and/or breeders. Future studies investigating the role of helper presence in cooperative breeders should take this into account.

Item Type: Thesis (Bachelor's Thesis)
Supervisor nameSupervisor E mail
Degree programme: Life Science and Technology
Thesis type: Bachelor's Thesis
Language: English
Date Deposited: 26 Jun 2019
Last Modified: 27 Jun 2019 07:45

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