The Population Density, Interspecific Territoriality, and Philopatry of Shrikes (Laniidae) and Bushshrikes (Malaconotidae) in a Mosaic of Natural and Human-Modified Acacia Savanna

In avian behavioural and spatial ecology, issues related to population density, territoriality, and philopatry are especially important. These are often interrelated. The aim of this study was to analyse these behaviours in shrikes inhabiting an acacia savanna in northern Namibia (400 ha). Population densities of one shrike and four bushshrike species were studied by means of the territory mapping method. About half of the study area had been modified by humans into cultivated fields, orchards, sport fields, and human settlements. This study was conducted in 2012/2013, 2017/2018, and 2019/2020. The most common species were the Black-backed Puffback (2.5 pairs/100 ha) and Crimson-breasted Shrike (1.9); the least common were the Southern White-crowned Shrike (0.8) and Brubru (1.0). Statistics for the Brown-crowned Tchagra indicated a density of 1.5 pairs/100 ha. While the density of the Brown-crowned Tchagra and Brubru remained stable over the years, the population densities of the Black-backed Shrike, Crimson-breasted Shrike, and Southern White-crowned Shrike showed a remarkable increase over the years 2012-2020. All bushshrike species showed a preference for patches of natural savanna vegetation. This was especially evident in the Crimson-breasted Shrike and the Brubru. However, the Southern White-crowned Shrike from the shrike family did not show this preference. The presented studies showed marked interspecific differences in territoriality and philopatry. Furthermore, even within the same species, marked temporal differences were shown in population density, probably also in philopatry. Within families, these behaviours may shape both resource competition and mate competition, while between families, these behaviours only shape resource competition.