Sleeping giants: temporal, seasonal, and spatial variations in the 24-h activity budget of Hippopotamus amphibius

TL;DR

This study reveals new insights into hippo behavior, showing they are active both day and night, challenging previous assumptions about their habits.

Contribution

The first 24-h observational activity budget of hippos and the first behavioral data from Botswana.

Findings

Hippos show a clear circadian rhythm with activity peaks at sunrise, sunset, midday, and midnight.

Hippos fed during only a quarter of the night and were active for a similar proportion of the day.

Aquatic vegetation plays a more significant role in their diet than previously assumed.

Abstract

Understanding animal activity budgets is essential for assessing habitat use and ecological roles, with important implications for conservation. Despite their ecological significance, the behavior of Common Hippopotamus (Hippopotamus amphibius) remains poorly studied, particularly at night. This study aimed to (i) quantify the 24-h activity budget of hippos; (ii) evaluate how behavior changed over the day and varied seasonally; (iii) examine how behavior varied between different areas; and (iv) between age classes. This study presents the first 24-h observational activity budget of hippos and the first behavioral data from Botswana. Hippo behavior varied significantly by time of day, season, study area, and age class. Hippos exhibited a well-defined circadian rhythm, with activity peaking and dipping at sunrise, sunset, around midday, and midnight. Contrary to the persistent assumption that hippos rest in water by day and graze on land all night, hippos in this study fed during only a quarter of the night and were active for a similar proportion of the day. Hippos often spent hours of the day on land feeding or basking in the sun, challenging the idea that they rely heavily on water to prevent their skin from cracking. Resting and feeding behaviors varied with fluctuating water levels, with aquatic vegetation playing a more significant role in their diet than previously assumed. These findings provide valuable insights into hippo ecology and can help predict how they may respond to environmental changes, particularly in regions experiencing increasing human pressures.

This study provides the first observational 24-h activity budget of hippos and the first behavioral data from Botswana. Behavior varied by time of day, season, study area, and age class, following a clear circadian rhythm with peaks at sunrise, sunset, midday, and midnight. Contrary to the common view that hippos rest in water by day and graze all night, they fed during only a quarter of the night and were equally active during the day.

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