Cover illustration of Primates vol. 65 (2024)

Cover illustration (Fig. 1): left: proboscis monkey (Nasalis larvatus), upper right: black and gold howler monkey (Alouatta caraya), bottom right: mountain gorillas (Gorilla beringei beringei). The photographs were taken by Ikki Matsuda, Isadora Alves de Lima, and Martha Robbins, respectively; all rights reserved.

Fig. 1

Cover illustration of Primates, 2024

In order to select the cover illustration of the 2024 issues of Primates, the immediate past Editor-in-Chief Masayuki Nakamichi asked Associate Editors, winners of the Primates 2022 Most-Cited Paper Award and Social Impact Award, and members of the Primate Society of Japan (PSJ) (Primates is a semi-official journal of PSJ) to submit candidate photographs. I sincerely thank everyone who offered photos of various primate species. Among the many fine photos offered in 2021, 2022, and 2023, I finally selected three photos of different species, in consultation with the two Vice Editors-in-Chief, Jim Anderson and Satoshi Hirata, and the immediate past Editor-in-Chief, Masayuki Nakamichi. The following are explanatory notes provided by researchers who took the photographs and/or who have conducted observations on the primates for years (Shoji Kawamura, Editor-in-Chief).

Proboscis monkey (Fig. 2): this photo shows a female proboscis monkey (Nasalis larvatus) with an infant resting in a mangrove tree (Sonneratia caseolaris), taken in the Lower Kinabatangan, Sabah, Malaysia. The infant, just after birth, is covered with black fur all over its body. Over a period of about 2 years, the fur gradually changes to a colour similar to that of the adult, and finally the black colour of the face skin changes to the same colour as the adult, as the monkey becomes a juvenile. With the help of local governments and universities, Matsuda has been conducting long-term ecological studies of proboscis monkeys in the riverside forest (Sukau) and mangrove forests (Abai) in the Lower Kinabatangan since 2005. The proboscis monkey is a member of the Afro-Eurasian monkey subfamily Colobinae, and is unique to Borneo. It is a foregut fermenter and has a natural diet generally dominated by leaves, fruits (mostly unripe), and seeds. They are large, sexually dimorphic and arboreal colobines living in social groups that typically consist of a single adult male and multiple females, although mixed-sex groups occasionally contain several adult males; there are also all-male groups and sometimes solitary males. They are categorized as ‘Endangered’ under the IUCN Red List and listed under Appendix I of the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) (Ikki Matsuda).

Fig. 2

Proboscis monkey (Nasalis larvatus). ^©Ikki Matsuda

Black and gold howler monkeys (Fig. 3) are South American atelids found in forests of the Cerrado, Pampa, Pantanal, Chaco, and Caatinga in Brazil, Argentina, Paraguay, and Bolivia. They are characterized by marked sexual dimorphism. All infants are born with a blonde pelage that starts to darken in young males and reaches full black at adulthood. Females continue blonde throughout their lives or turn light brown as they age. Black and gold howlers live in social groups of 2 to around 20 individuals, often led by a single dominant adult male. The bulk of their diet is composed of leaves and fruit, complemented with flowers, stems, seeds, and bark. Howler monkeys play an important role in the structuring and regeneration of their forested habitat via seed dispersal. A highly flexible diet helps them to adapt to disturbed and anthropogenic habitat patches. Urbanization causes habitat loss and fragmentation and increases the risk of interaction with humans. The presence of howler monkey groups in city squares is uncommon anywhere in the species range. Under these circumstances, howlers may supplement their diet with food from people, exposing them to the risk of contagion from infectious agents of human diseases. They can also be hit by cars, electrocuted in power lines, and chased by people and domestic dogs. This photo was taken in September 2022 in an urban square in Manoel Viana, state of Rio Grande do Sul, Brazil. The group consists of an adult male (not shown in the picture), an adult female, two subadult males, a juvenile male, a juvenile female (also not shown), and an infant male (Isadora Alves de Lima).

Fig. 3

Black and gold howler monkey (Alouatta caraya). ^©Isadora Alves de Lima

Mountain gorillas (Fig. 4) live in cohesive social groups, typically consisting of one or more adult males (silverbacks), adult females, and immatures of all ages. A typical day for mountain gorillas consists of alternating periods of feeding and resting. During rest sessions, such as pictured here, members of the group are often in close spatial proximity. Adults may groom each other or simply rest near one another, while infants and juveniles play. The photo was taken when I was visiting a PhD student working in the Virunga volcanoes in 2009. The photo is of Cantsbee’s group, monitored by the Dian Fossey Gorilla Fund. Cantsbee, the silverback, was born in 1978, into one of the original groups habituated by Dian Fossey. Cantsbee was a young, subordinate silverback in a multimale group when I conducted my PhD research in the early 1990s. Eventually, he came to be the alpha male of a very large group and he sired many offspring (Martha M. Robbins).

Fig. 4

Mountain gorillas (Gorilla beringei beringei). ^©Martha Robbins