Characteristics of sun bear chest marks and their patterns of individual variation

Animal coloration is widely involved in a variety of social interactions, and mammals can convey information to conspecifics by visual signals, such as colored or contrasting body marks. The sun bear (Helarctos malayanus) has a vibrant and unusual chest mark. Here, we describe the characteristics of sun bear chest marks and their patterns of individual variation by (1) sex, (2) time, and (3) some biochemistry values related to fur pigmentation. Sun bear pictures were taken from 2009 to 2018 at the Bornean Sun Bear Conservation Centre and Free the Bears sanctuary. We hypothesize that chest marks may serve in conspecific communication and, thus, we mainly expect that (a) these marks allow for sexual recognition and, thus, they should show remarkable differences by sex; (b) marks do not change over time because their consistency allows for easier intraspecific recognition; and (c) patterns of variation may be dependent on the age and/or physical condition of an individual. The most common shapes of sun bear chest marks (n = 63 M and 108 F) were U (M = 60.3%, F = 57.4%) and V (M = 31.8%, F = 32.4%) shapes. We did not detect differences in shape patterns by sex and, over the years, chest mark shape never changed for the same bear (n = 49 individuals, 16 M and 33 F). The number of dark dots in chest marks showed large amounts of individual variation (mean +/- SD = 37.7 +/- 26.8 dots; range = 1-143), and the quantity of dark dots increased with bear age. The complexity of sun bear chest marks might be related to the existence of complex interactions among individuals of the same species, which may allow for recognition and evaluation of their individual characteristics, such as age and health. Experimental approaches are needed to understand the potential functions of sun bear chest marks.