Multimodal communication of adult, subadult, and infant plains zebras (Equus quagga)

Juveniles occupy a different social niche than adults, engaging in a smaller diversity of social contexts and perceiving greater social risks. Either or both of these factors may influence the form communication takes in immaturity and its developmental trajectory. We investigated the relative influence of these social forces on the development of multimodal communication in plains zebras (Equus quagga). Juveniles possessed smaller repertoires than adults, with lower combinatorial flexibility and greater stereotypy, particularly for signals used in submission. When interacting with adults, juveniles used a larger fraction of their repertoire, but with reduced combinatorial flexibility. The usage of a contextually flexible signal, “snapping”, also shifted across development, beginning as a stereotyped, submissive signal before diversifying into the full range of adult usage.

Methods
Study species and subjects

We conducted our study on a population of ~2,000 wild plains zebras living in Ol Pejeta Nature Conservancy of Laikipia, Kenya (0°00 N, 36°56 E). This population experiences natural predation and is not provisioned. Our sample comprised 22 focal harems with an average harem size of 5 members (2-13 individuals). To supplement our sample size for the immature age class, we included additional data collected ad libitum from a subset of 5 of the 22 followed harems followed between July 9th and August 9th, 2019. All other methods were the same across all sample periods. This inclusion allowed us to double our sample of immature individuals (2019 sample = 10). We are able to individually identify zebras based on their unique stripes. All research was conducted with the permission of Ol Pejeta Nature Conservancy and the Kenyan Ministry of Wildlife (NACOSTI/P/21/11647), and was in compliance with the guidelines of the Princeton University Institutional Animal Care and Use Committee (IACUC 1835F).

Observations and collection of data

Data collection occurred daily between July 13th and September 30th, 2021 and June 13th and August 12th, 2022 on the Eastern Sector of Ol Pejeta Conservancy. During this period, we conducted multiple focal follows of each harem, with a median inter-follow interval/harem 14.2 ± 6.6 days (range 2-35 days), allowing us to capture a range of behaviors from each individual. Focal follows occurred between 08:00-16:30, during which time we followed two harems a day, one in the morning block, and another in the afternoon block. Each focal harem was continuously followed for 2-4 hours. Within each observation period, a single individual from the harem was selected as the focal animal, to be followed for two consecutive 30 minute blocks before a new focal individual was selected. All behaviours, including interactions, were captured with video using a Canon Vixia HR R700. Audio was recorded using a Sennheiser ME66 directional microphone in a Rode Blimp windshield and a Tascam Dr-100MKII Linear PCM recorder sampling at 48kHz.