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First published online March 2, 2006
Journal of Experimental Biology 209, 1058-1063 (2006)
Published by The Company of Biologists 2006
doi: 10.1242/jeb.02122

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Sex differences in food intake and digestive constraints in a nectarivorous bird

Shai Markman^1,*, Hagar Tadmor-Melamed^1,2, Amichai Arieli² and Ido Izhaki¹

¹ Department of Biology, Faculty of Science and Science Education, University of Haifa at Oranim, Tivon, 36006, Israel
² Department of Animal Science, Faculty of Agricultural, Food and Environmental Quality Sciences, The Hebrew University of Jerusalem, Rehovot 76100, Israel

^* Author for correspondence at present address: School of Biosciences, Main Building, Park Place, Cardiff University, Cardiff CF10 3TL, UK (e-mail: markmans{at}cardiff.ac.uk)

Accepted 24 January 2006

Sex-specific foraging behaviour might be influenced by digestive constraints. However, evidence for sex differences in digestive performance is limited. Various physiological traits are known to be body size dependent. Therefore, we hypothesized that body size differences between male and female birds may lead to differences in their digestive characteristics. We predicted that if food intake and digestive functions are only governed by body mass, then males that are heavier than females would have higher food intake, food assimilation efficiency and gut transit time, but not after controlling for the effect of body mass.

We fed a diet of equicaloric solutions of sucrose and a 1:1 mixture of glucose and fructose (hexose mixture) solutions to Palestine sunbirds (Nectarinia osea). When fed sucrose solutions, males had longer transit times but similar absorption efficiencies as females. Transit times, corrected for differences in body mass and food intake, were still longer in males than in females when fed on sucrose solutions. The sex-specific differences in transit time disappeared when the birds were fed the hexose mixture.

Our results suggest that males take longer to digest than females when fed on sucrose-rich nectars as opposed to hexose-rich nectars, and therefore can allow themselves a relatively lower digestive capacity. This may suggest sex-specific co-evolution of sunbirds within mixed plant communities, which have both sucrose- and hexose-rich nectar-producing plants. Furthermore, future studies on digestion in birds may pay attention to sex-specific differences.

Key words: absorption efficiency, foraging, Palestine sunbird, Nectarinia osea, sexual dimorphism, transit time

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