Plains zebra time budgets, social behavior, and communication during the 2021-2022 Laikipia-Samburu ecosystem drought

Anthropogenically induced climate change has significantly increased the frequency of acute weather events, such as drought. As human activities amplify environmental stresses, animals may be forced to prioritize survival over behaviors less crucial to immediate fitness, such as socializing. Yet, social bonds may also buffer organisms from the deleterious effects of environmental conditions. We investigated how the highly social plains zebra (Equus quagga) modify their activity budgets, social networks, and multimodal communication during a drought. This dataset contains a) activity budget, b) steps per minute as a proxy for foraging effort, c) nearest neighbor association data, d) interaction rate, e) juvenile social interaction partner data, and f) multimodal communication data.

Methods
Ethical statement

This study was conducted on a population of wild plains zebras living in Ol Pejeta Nature Conservancy (0°00 N, 36°56 E), in Laikipia, Kenya. 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 (1835F).

Study animals

Our sample comprised 21 focal harems with an average harem size of 5 members (2-13 individuals) (Table S1). This population has been monitored continuously since 2008, and we have pedigrees of all focal individuals. We were able to individually identify zebras based on their unique stripes. Individuals were classified into one of four age/sex classes: stallion, non-lactating female, lactating female, and juvenile (Table S2). Juveniles were defined as pre-dispersal individuals, including pre-dispersed, sexually mature males as old as 4 years (N = 4 in 2021, N = 2 in 2022), who are nonreproductive and still operate in the juvenile social niche (Klingel, 1965; personal observation).

Data collection

Data collection occurred daily between July 13th and September 30th, 2021 (hereafter “early drought”), and June 13th and August 12th, 2022 (hereafter “late drought”). Two focal follows were conducted each day by vehicle, the first occurring between 08:00-12:00 and the second between 12:30-16:30. A single harem was the subject of each observation period, and two harems were followed per day. At the beginning of each observation period, we recorded the presence or absence of members, including newly born foals, and scored the body condition of each individual using the plains zebra body condition scale, a qualitative measure of overall body condition (Ginsberg, 1988). 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. The focal individual’s behavior was continuously captured using a Canon Vixia HR R700, and a Sennheiser ME66 directional microphone in a Rode Blimp windshield and a Tascam Dr-100MKII Linear PCM recorder sampling at 48kHz. As it is challenging to extract meaningful behavior from video recordings taken while the vehicle is in motion, if individuals engaged in continuous travel for an extended duration (>15 continuous minutes), we terminated the video recording and manually recorded the start and end time of travel for later integration into time budget calculations. Between each 30-minute block, we conducted a scan sample of the entire harem and recorded the behavior and nearest neighbor of each member of the harem, operationalized as being within one body length.

All video was coded for behaviors of interest using ELAN video annotation software (version 4.8.1). To investigate changes in activity budget across years, we coded 1 to 3 equally spaced five-minute sub-samples from each video (i.e. 5-10 minutes, 15-20 minutes, 25-30 minutes), depending on the video length. We scored nearest neighbor of the focal animal every five minutes. Within the sub-samples, we counted steps-per-minute. We also scored all activities performed by the focal animal during the sub-samples to construct time budgets (Table 2). Social behaviors were grouped into two broad categories, “passive socializing”, which were defined as proximity-based social behaviors produced concurrently with a self-maintenance behavior (i.e. resting in physical contact, grazing side-by-side), and “active socializing”, which included dedicated social behaviors with no additional self-maintenance function (e.g. aggression, affiliation, etc.).

To analyze multimodal communication, we coded all interactions captured by our focal follow videos. Our coding scheme is published in detail elsewhere (Hex & Rubenstein, 2024). In brief, we coded all concurrent visual, acoustic, tactile, and/or chemical signals produced. An interaction was defined as beginning when two individuals entered one body length of one another and the sender was 1) oriented towards the receiver, 2) the signal was produced in the direction of the receiver, 3) the sender approached the receiver, and/or 4) the sender made physical contact with the receiver. An interaction was defined as terminated when either 1) one individual moved beyond one body length of the other without being followed, or 2) the parties ceased interacting for at least 10 seconds (e.g., began to graze or sleep in proximity).

We only coded interactions in which the video was zoomed in enough for reliable coding of all areas of interest, and in which the focal individual was in focus and entirely in frame, unobscured by foliage or non-focal animals. We eliminated 263 interactions from early drought and 118 interactions from late drought which did not meet this criterion. To improve the interpretability of our results, we cleaned our data prior to analysis by removing multimodal postures containing a component observed in fewer than two interactions. After cleaning, we were left with 336 high quality interactions comprising 1,461 multimodal postures for early drought, and 115 interactions comprising 439 multimodal postures for late drought.

References

Ginsberg, J.R. (1988). Social organization and mating strategies of an arid-adapted ungulate: the Grevy’s zebra. [Doctoral dissertation, Princeton University].

Hex, S. B., Rubenstein, D. I. (2024). Using networks to visualize, analyse and interpret multimodal communication. Anim. Behav. 207, 295-317.