Nonhuman primates can create art that reflects their own individual personalities and moods, according to an analysis of hundreds of drawings made by five female orangutans at Tama Zoological Park in Japan. Describing the apes’ creations in the journal Animals, the researchers note that the drawing style of some orangutans changes with the seasons, possibly reflecting fluctuations in their state of mind.

The five artists were provided with drawing materials to enrich their daily lives, and collectively created almost 1,500 drawings between 2006 and 2016. The vast majority of these artworks were produced by one particularly prolific orangutan named Molly, whose creations were notable for their complexity in comparison to the drawings of her fellow apes.

In their new study, the authors analyze 790 of the orangutans’ drawings, also conducting a separate assessment of 656 of Molly’s works. Their findings revealed that “the drawing behavior of these five orangutans is not random and that differences among individuals might reflect differences of styles, states of mind, and motivation to draw.”

Individual artistic preferences were seen in the colors used by each orangutan, as well as the shapes they chose to draw and the amount of canvas space they covered. For instance, Molly’s drawings contained less contrast than those of the other animals, as she pressed her crayons more lightly against the canvas.

Comparing the five artists, the researchers reveal that “the drawings by Molly were the most complex (more amply filled than pictures by other individuals, with the use of more shapes and colors) followed by those drawn by Yuki. Kiki also showed differences to the other individuals with her simple but strongly marked drawings (i.e., one color used, pressing hard on the crayon).”

Intriguingly, the authors also noted changes in Molly’s artistic output as the seasons changed. In spring, for instance, she tended to use purple as her dominant color, while green became more prominent in summer and winter. Red, meanwhile, was reserved for pictures made when another orangutan gave birth.

In comparison to her winter drawings, Molly’s summer creations tended to include more “loops”, which the researchers say “could be a cue indicating a good mood due to the weather and the presence of more visitors.”

In general, the orangutans filled their canvases with three basic motifs, described by the study authors as loops, circles, and “fan patterns”. Similar drawing styles have been observed in other non-human primates, including chimpanzees, while human children also tend to use these structures in their art.

“Drawings by chimpanzees, human children, and orangutans therefore have a lot in common,” say the researchers, who conclude that their work may “give some clues about the emergence of drawings in human beings.”