Wamba, Democratic Republic of the Congo - December 10, 2025 Wamba, Democratic Republic of the Congo – Male bonobos have been shown to decipher the unreliable fertility signals of females, allowing them to focus their mating efforts where the chance of conception is highest, according to a study published December 9 in PLOS Biology. Unlike most mammals, female bonobos remain sexually receptive for a prolonged period and display a conspicuous pink swelling that is not a precise indicator of ovulation. Researchers observed wild bonobos in the Luo Scientific Reserve, recording sexual behaviors and estimating the status of females’ genital swelling. Urine samples were also collected to measure hormone levels and estimate ovulation timing. The study found that ovulation probability peaked between 8 and 27 days after maximum swelling, making it difficult for males to predict. Despite this, male bonobos timed their sexual advances carefully, targeting females who had reached maximum swelling earlier and whose infants were older, increasing the likelihood of conception. The findings show that males combine visual cues from swelling and information on reproductive history to maximize mating success. The study highlights that even imprecise signals can remain evolutionarily functional when animals use them flexibly. “In this study, we found that bonobo males, instead of trying to predict precise ovulation timing, use a flexible strategy—paying attention to the end-signal cue of the sexual swelling along with infant age—to fine-tune their mating efforts,” the authors said.