Longitudinal Fecal Steroid Excretion in Maned Wolves ( Chrysocyon brachyurus) Agnes L. Velloso,* ,1 Samuel K. Wasser² Steve L. Monfort,‡ and James M. Dietz* * University of Maryland, College Park, Maryland; † Center for W ildlife Conservation and University of Washington School of Medicine, Seattle, Washington; and ‡ Conservation and Research Center, National Zoological Park, Smithsonian Institution, Front Royal, Virginia Accepted July 7, 1998 This study used a fecal steroid monitoring technique to evaluate reproductive cycles in male (4) and female (15) maned wolves, endangered South American canids. A radiolabeled testosterone infusion on a male revealed a fast and predominantly fecal route of excretion for this steroid. Testosterone was also excreted as eight unidenti- fied metabolites, which was not the primary form of this steroid quantified in our assays. Fecal steroid concentra- tions (estradiol, E 2 ; progestins, P; testosterone, T) in males and acyclic, nonpregnant (pseudo-pregnant), and pregnant females were monitored over four breeding seasons (October–January). Significant differences were detected between longitudinal P profiles of cyclic and acyclic females during estrus, luteal phase, and after birth/end of pseudo-pregnancy. Concentrations of P were also significantly higher in pregnant, compared to non- pregnant females, from proestrus to the end of the pregnant luteal phase. Although levels of T were higher in males than in females throughout the breeding season, no cyclicity in male fecal T concentrations was detected. Values of fecal P, T, and the ratio P/T were useful for differentiating gender and detecting pregnancy in fe- males. Similarities to available data on other canids and the management and conservation implications of these findings were discussed.  1998 Academic Press Key Words: fecal steroids; progestins; estradiol; testoster- one; hormones; maned wolves. The maned wolf (Chrysocyon brachyurus), largest of the South American canids, is a grassland species threatened with extinction, mostly due to habitat loss. Its behavior, social structure, and reproduction in the wild are poorly known (Dietz, 1984), and captive studies have focused mainly on behavior and diseases. Wasser et al. (1995) described the fecal steroid profiles of captive female maned wolves, based upon data collected over one breeding season. Results from that first account suggested that fecal concentrations of estradiol and progestins may be useful to distinguish female reproductive status, which would be of great assistance in improving the historically poor captive breeding of this species (Krug, 1985). However, no information is available describing male reproductive– endocrine rhythms in maned wolves, and the potential for utilizing reproductive steroid hormone excretion to sex wolves has been untested. An improved under- standing of maned wolf reproductive physiology will provide important basic information that should facili- tate the captive breeding and management of this species. A reliable noninvasive assessment of reproduc- tive status should also provide an important tool for field studies. The specific objectives of the present study were to (1) determine the time course and dynamics of [ 14 C]tes- tosterone metabolism and the relative proportion of radiolabel excreted into urine and feces; (2) character- ize longitudinal testicular-endocrine profiles in males; (3) extend the reproductive database for females by 1 To whom reprint requests should be addressed at Rua Raimundo Magalha ˜es, 86, Rio de Janeiro, RJ 22451-150, Brazil. Fax: 55-21-239-1688. General and Comparative Endocrinology 112, 96–107 (1998) Article No. GC987147 96 0016-6480/98 $25.00 Copyright  1998 by Academic Press All rights of reproduction in any form reserved.