Species-specific patterns in fecal glucocorticoid and androgen levels in zoo-living orangutans (Pongo spp.)

► Fecal glucocorticoid (GC) assay (3α,11β-dihydroxy-CM) and fecal androgen assay (epiandrosterone) were biologically validated and used to measure 830 fecal samples from 112 orangutans housed in European zoos. ► Species differences in fecal GC levels were strongest in larger zoo groups, with Bornean orangutans showing higher stress hormone levels than Sumatran orangutans under these conditions. ► Fecal androgen levels were higher in captive Bornean than in Sumatran orangutan males. ► Species differences in glucocorticoid and androgen output are likely linked to ecological and behavioral differences between the two islands.