Contrasting effects of cooperative group size and number of helpers on maternal investment in eggs and nestlings
Section snippets
Study System
We conducted our study in the indigenous cloud forest archipelago of the Taita Hills, southeast Kenya (3°25′S, 38°20′E), where the medium-sized, insectivorous placid greenbul inhabits dense cloud forest understory. This habitat occurs in a highly scattered and fragmented pattern in the study area, where the landscape is dominated by exotic plantations and small-scale subsistence agriculture (Burgess et al., 2007; Lovett & Wasser, 1993; Pellikka et al., 2009). Cloud forest remnants vary in both
Prehatching Maternal Investment
When examining variation in egg size using the reduced data set for which the number of helpers could be determined (Table 1), the model with group size was better supported than the model including number of helpers (ΔAICc = 2.42). However, since the null model was as well supported as the model with group size (AIC weight: 0.43 and 0.44, respectively), evidence for group size as a predictor of egg size variation was inconclusive for this data set. Yet, when including all nests that reached the
Discussion
We have shown that females of a tropical cooperative breeder modulate both their pre- and posthatching reproductive investment in relation to social conditions. Contrary to our predictions, females with more potential helpers in the group did not systematically reduce their investment during the breeding event. Rather, they employed an additive strategy during the prehatching stage by producing larger eggs in larger groups, while they practised load lightening in the posthatching stage by
Author Contributions
D.V.L. and L.C. analysed the data and drafted the manuscript. D.V.L. and B.A. collected the data. M.G. facilitated data collection. L.L. and E.M. designed the study and helped draft the manuscript. All authors critically revised the manuscript and gave final approval for publication.
Data Availability
Code and data to reproduce all analyses and figures will be made available on request.
Declaration of Interest
The authors declare no competing interests.
Acknowledgments
We thank the Kenyan government, the Kenya Wildlife service and the Kenya Forest Service for permitting research in the Taita Hills and L. Chovu, P. Kafusi, J. Kiiru, A. Mwakulombe, O. Mwakesi, M. Makomba and V. Otieno Onyango for fieldwork. Kenya Forest Service kindly facilitated access to the forest fragments. We also thank Peter Njoroge and the National Museums of Kenya for support. This work was funded by the Fonds Wetenschappelijk Onderzoek (FWO) grant G.0308.13N, the Alexander von Humboldt
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