Comparison of digestive efficiency in the parasitic great spotted cuckoo and its magpie host nestlings MANUEL SOLER 1,2 *, LIESBETH DE NEVE 1,3 , TOMÁS PÉREZ-CONTRERAS 1 and LUIS A. RUBIO 4 1 Departamento de Zoología, Facultad de Ciencias, Universidad de Granada, E-18071 Granada, Spain 2 Grupo Coevolución, Unidad Asociada al CSIC, Universidad de Granada, Granada, Spain 3 Department of Biology, Terrestrial Ecology Unit, Ghent University, B-9000 Gent, Belgium 4 Estación Experimental del Zaidín (INAN, CSIC), Profesor Albareda 1, 18008 Granada, Spain Received 13 August 2013; revised 10 October 2013; accepted for publication 10 October 2013 Altricial nestlings are under strong selection pressures to optimize digestive efficiency because this is one of the main factors affecting nestling growth and survival. Bird species vary in their ability to assimilate different nutrients and current theory predicts that nestlings should also be able to adjust their nutritional physiology to feeding frequency. Variation in parental provisioning to nestlings would select for flexibility in nestling digestive physiology, which would allow maximization of nutrient assimilation. In the present study, by making use of a brood parasite–host study system in which great spotted cuckoo nestlings (Clamator glandarius) are reared by magpie (Pica pica) host foster parents when sharing the nest with host nestlings, we tested several predictions of the adaptive digestive efficiency paradigm. A hand-feeding experiment was employed in which we fed both great spotted cuckoo and magpie nestlings with exactly the same diet simulating one food abundance period and one food deprivation period. The results obtained show that cuckoo nestlings ingested more food, gained significantly more weight during the abundance period, and assimilated a higher proportion of the ingested food than magpie nestlings. These results demonstrate for the first time that cuckoo nestlings enjoy digestive adaptations that favour a rapid processing of the ingested food, thereby maximizing their intake rate but without decreasing digestive efficiency. © 2013 The Linnean Society of London, Biological Journal of the Linnean Society, 2014, 111, 280–289. ADDITIONAL KEYWORDS: body mass gain – body mass loss – brood parasitism – Clamator glandarius – food intake – Pica pica. INTRODUCTION Growth and survival of altricial nestlings depend on complex interactions among several factors, such as food availability, parental provisioning, nutritional need, nestling begging, nestling digestive efficiency, and predation risk. Digestive efficiency is the less studied of those factors, and has usually been ignored in the abundant literature on nutritional need and begging behaviour (Wright et al., 2010). However, digestive efficiency is one of the most important factors affecting growth and survival because rapid growth is selected for by the risk of nest predation (Ricklefs, 1984) and growth is mainly limited by digestive capacity. This is because the success of a high food intake rate will be limited by the speed and efficiency in assimilating resources (Konarzewski et al., 1996; Caviedes-Vidal & Karasov, 2001). Indeed, in altricial species, the digestive system comprises a much higher proportion of body mass early after hatching than in adulthood. Furthermore, during the first days of the nestling period, digestive anatomical structures (Lilja, 1983; Caviedes-Vidal & Karasov, 2001), as well as morphological traits related to begging efficiency (such as oral commissures and tarsus length (Soler & Soler, 1990) or gape size (Gil et al., 2008), show an accelerated growth as compared to the rest of the body. Thus, the extraordinarily rapid early development of the digestive system can be *Corresponding author. E-mail: msoler@ugr.es Biological Journal of the Linnean Society, 2014, 111, 280–289. With 5 figures © 2013 The Linnean Society of London, Biological Journal of the Linnean Society, 2014, 111, 280–289 280 Downloaded from https://academic.oup.com/biolinnean/article-abstract/111/2/280/2415943 by guest on 30 May 2020