Density dependence of daily activity in three ungulate species

Juan Ignacio Ramirez*, Joeri A. Zwerts, Marijke van Kuijk, Palma Iacobelli, Xuqing Li, Natalie Herdoiza, Patrick A. Jansen

*Corresponding author for this work

Research output: Contribution to journalArticleAcademicpeer-review


Daily activity in herbivores reflects a balance between finding food and safety. The safety-in-numbers theory predicts that living in higher population densities increases safety, which should affect this balance. High-density populations are thus expected to show a more even distribution of activity—that is, spread—and higher activity levels across the day. We tested these predictions for three ungulate species; red deer (Cervus elaphus), roe deer (Capreolus capreolus), and wild boar (Sus scrofa). We used camera traps to measure the level and spread of activity across ten forest sites at the Veluwe, the Netherlands, that widely range in ungulate density. Food availability and hunting levels were included as covariates. Daily activity was more evenly distributed when population density was higher for all three species. Both deer species showed relatively more feeding activity in broad daylight and wild boar during dusk. Activity level increased with population density only for wild boar. Food availability and hunting showed no correlation with activity patterns. These findings indicate that ungulate activity is to some degree density dependent. However, while these patterns might result from larger populations feeling safer as the safety-in-numbers theory states, we cannot rule out that they are the outcome of greater intraspecific competition for food, forcing animals to forage during suboptimal times of the day. Overall, this study demonstrates that wild ungulates adjust their activity spread and level based on their population size.

Original languageEnglish
Pages (from-to)7390-7398
Number of pages9
JournalEcology and Evolution
Issue number12
Publication statusPublished - Jun 2021


  • behavior
  • camera traps
  • food availability
  • hunting
  • landscape of fear
  • safety-in-numbers
  • temperate forest


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