GENERAL AND COMPARATIVE ENDOCRINOLOGY 51, 183-190 (1983) Annual Variation in the Concentrations of Circulating Hormones in Capercaillie (Tetmo urogal~us) R. HISSA, S. SAARELA, J. BALTHAZART," ANDR.J. ETCHES-~ Department of Zoology, Zoophysiological Laboratory, Wniversity of O&U, 90100 Oulu, Finland, *Laboratoire de Biochimie G&&ale et Compare’e, UniversitC de Lidge, Facuite de Msdecine, 4(100-L&e, Belgium, and fDepartment of Animal and Poultry Science, University of Guelph, Guelph, Ontario, Canada Accepted September 8, 1982 Seasonal variation in the levels of irnmunoreactive lutropin (LH), follitropin (FSH), pro- lactin (PRL), corticosterone (B), thyroxine (T4), and triiodothyronine (T,) was measured in the plasma of male and female capercaillies (Terra0 urogallus, Galliformes) in captivity (latitude N 67”). In male caper&&es there was an increase in the concentrations of LH and FSH beginning in March and reaching Eheir maxima in May, which correlated with the nesting period. The concentration of plasma PRL increased from the end of April and reached its highest level simultaneously with the rapid fall of plasma LH and FSH concen- trations. It remained elevated until August. Plasma ‘I, level was depressed after levels of plasma FSH and LH had reached their maxima and was correlated to simultaneous ele- vation of plasma PRL level. No dramatic seasonal changes in plasma Tj level ‘were noted. In the female capercaillie no marked changes in plasma FSH and LH concentrations were observed. Although four of six females laid eggs only one of them managed to terminate its nesting successfully; five eggs hatched. Changes in prolactin concentration in females parallel those in males. No marked variations were observed in plasma corticosterone concentrations. On the basis of these results it seems probable that captive female caper- caillie show depressed gonadotrophin secretion, resulting in unsuccessful nesting. On the other hand it has to be emphasized that gonadotrophin assays may not be sensitive enough, especially in the female, to measure LH and FSH in the volumes of plasma put in the assays. INTRODUCTION There is a large and comprehensive lit- erature on photoperiodic time measure- ment and gonadotrophin secretion in birds (see, e.g., Follett, 1981). Some component of the photoperiod plays an external role which initiates reproductive activity at the appropriate time of the year in temperate- zone birds. The increasing length of pho- toperiod induces an elevation of gonadotro- phin secretion followed by an increase of the gonad weight (e.g., Nicholls et al., 1973; Nicholls, 1974; Follett et al., 197.5; Follett, 1976). Most avian species in the middle and high latitudes stop breeding during the summer because they become photorefractory. The reproductive organs regress in synchrony wit.h the decrease of plasma gonadotrophin levels (Nicholls, 1974; Scanes et al., 1974; Wilson and Follett; 1974, Haase et al., 1975; Sharp et al., 1975). Several hypotheses have been put forward to explain photorefracto- riness (see, e.g., Cusick and Wilson, 1972; Meier and Dusseau, 1973; Farner, 1975; Sharp and Moss, 1977; Stokkan and Sharp, 1980). The objective of this study was to con- tribute to the general body of knowledge about seasonal changes in hormones, espe- cially in gallinaceous birds. The seasonal changes of hormone levels of the plasma of captive adult male and female capercailhe (Tetruo urogallus, Galliiormes) in ;Northern Finland were measured. The hormones measured were lutropin (LH), follitropin (FSH), prolactin (PRL), corticosterone (B), thyroxine (T4), and triiodothyronine (T,). Since it was anticipated that the environ- 183 0016-6480/83 $1.50 Copyright 0 1983 by Academic Press. Inc. Ail rights of reproduction in atiy form reserved.