193 31 Relationship between nutritional status and prolactin levels in the Common Eider, a capital incubator FRANÇOIS CRISCUOLO 1 , OLIVIER CHASTEL², GEIR. WING GABRIELSEN 3 , ANDRÉ LACROIX 2 AND YVON LE MAHO 1 1 Centre d'Ecologie et Physiologie Energétiques, CNRS, 23 rue Becquerel, F-67087 Strasbourg Cedex 2, France; 2 Centre d'Etudes Biologiques de Chizé, CNRS, F-79360 Villiers-En-Bois, France ; 3 Norwegian Polar Institute, The Polar Environmental Center, Hjalmar Johansensgate l4, N-9296 Tromsø Norway e-mail: f.criscuolo@c-strasbourg.fr ABSTRACT In Common Eider, only females incubate while fasting for 25 days. When their body condition is deteriorated at hatching, females often abandon their ducklings. To therefore investigate how body condition may mediate parental care in eiders, we studied the effect of a change in the duration of incubation on their plasma prolactin, i.e. the main parental hormone in birds. Birds with shortened incubation have higher body masses and showed higher levels of plasma prolactin levels at hatching than the control group, suggesting that circulant prolactin at hatching is linked to body condition. The females that underwent an extended incubation started to feed again and displayed a "normal" body mass but unexpectedly a very high plasma prolactin concentration. Key Words: Somateria mollissima, prolactin, Svalbard, incubation, feeding patterns INTRODUCTION Prolactin is involved in the initiation and maintenance of incubation behaviour in birds (Hall 1991, Buntin 1996, Sharp et al. 1998), in addition to its large variety of actions (i.e. in lipid metabolism, Hall et al. 1986). Eggs act as tactile and visual stimuli in most birds, since their removal results in a decrease in plasma prolactin and the termination of parental behaviour (Buntin 1986, Hall & Goldsmith 1983, Ramsey et al. 1985). However, prolactin secretion can be modulated by several factors such as food restriction (Hall et al. 1986) or be endogenously timed as it has been showed in pelagic birds, prolactin levels being maintained regardless of direct stimulations from the nest or eggs (Hector & Goldsmith 1985, Lormée et al. 1999, Garcia et al. 1996, Jouventin & Mauget 1996, Vleck et al. 2000). Incubation behaviour competes with foraging, thus inducing restricted access to food. Anorexia has evolved as a means to ensure greater nest attendance (Mrosovsky & Sherry 1980), to enhance the chances of hatching success. However, the amount of adult body reserves available to incubate is a key factor in determining incubation constancy (Aldrich & Raveling 1983, Chastel et al. 1995, Chaurand & Weimerskirch 1994, Cherel et al. 1994). This suggests a potential control of prolactin secretion (thus of parental behaviour) by adult body condition in capital incubators, i.e. birds which does not feed during incubation. The female Common Eider Somateria mollissima can indeed be defined as a true capital incubator (Drent & Daan 1980) since it relies entirely on its body nutrient reserves during 24-26 days of incubation (Korschgen 1977). Moreover, the female behaves as a brood-tender or not, depending on its remaining body reserves at hatching (Bustnes & Erikstad 1991). Knowing that plasma prolactin concentration is high in female eiders taking care of the brood (Criscuolo et al, in press) as observed in other species (Ball 1991), we checked whether prolactin is endogenously controlled (i.e. by adult body reserves). To modify the female body condition at hatching, the incubation length was experimentally shortened or prolonged by swapping eggs between nest with different laying dates. Prolonged incubating females were found to start feed again, since we observed successive dive cycles during recesses at sea (Criscuolo et al. in press). Thus, for these females, to test whether the nutritional status of the bird can influence its prolactin concentration, we determined the plasma concentrations of triacylglycerols as a sign of feeding and of β-hydroxybutyrate as a sign of fasting (Le Maho et al. 1981). METHODS The study was conducted in Kongsfjorden, on the western coast of the Svalbard Archipelago (78°55' N), on female eiders nesting on Prins Heinrich Island (1998 and 2000) from early June to mid-July. Antarctic Biology in a Global Context, pp 193-197. Edited by A.H.L. Huiskes, W.W.C. Gieskes, J. Rozema, R.M.L. Schorno, S.M. van der Vies & W.J. Wolff. ©2003 Backhuys Publishers, Leiden, The Netherlands.