Symbiosis between the Javan rhinoceros and slender-billed crow: A novel inferred cleaning mutualism

Abstract

Over the past century, the Javan rhinoceroses' (Rhinoceros sondaicus) secluded nature and low population size have led to a gap in knowledge of their ecology. With fewer than 80 individuals surviving in a single population in West Java, Indonesia, the Javan rhinoceros is one of the most critically endangered mammals in the world. As part of a pilot bioacoustics study of the Javan rhinoceros in 2019, we systematically reviewed camera trap footage from the core Javan rhinoceros range in Ujung Kulon National Park (UKNP). In doing so, we discovered a previously unknown interaction between the Javan rhinoceros and the slender-billed crow (Corvus enca), in which the crow finds and eats ectoparasites from the rhinoceros (Figure 1). We describe this interaction and suggest that it may represent a cleaning mutualism with benefits for both the crow and the rhinoceros.

Keywords: behavioral convergent evolution; cleaning mutualism; novel symbiosis; rhinoceros conservation.

FIGURE 1

(a) On September 23, 2018 in Ujung Kulon National Park, a slender‐billed crow (Corvus enca) examines the ear of a female Javan rhinoceros (Rhinoceros sondaicus) in search of ectoparasites (presumably ticks and leeches) in a case of apparent symbiotic mutualism. (b) A female Javan rhinoceros (Rhinoceros sondaicus) pivots her ear to solicit parasite removal by a slender‐billed crow (Corvus enca).

FIGURE 2

The inguinal region of a black rhinoceros (Diceros bicornis) displaying a variety of ticks. Similar folds of the Javan rhinoceros (Rhinoceros sondaicus) almost certainly harbor similar ectoparasite burdens since ticks are abundant on sympatric Sumatran rhinoceroses (Dicerorhinus sumatrensis) that are managed in sanctuaries in Indonesia.