The Role of Predators in Shaping Urban Bird Populations. 4. The Urban Predation Paradox and Its Probable Causes

• Published in: Biology bulletin of the Russian Academy of Sciences 2022-12, Vol.49 (9), p.1406-1432
• Main Author: Morozov, N. S.
• Format: Article
• Language: English
• Subjects: Biochemistry; Biomedical and Life Sciences; Birds; Birds of prey; Carnivores; Cell Biology; Corvus cornix; Ecology; Food; Interspecific relationships; Life Sciences; Nests; Parasitism; Predation; Predators; Prey; Species richness; Urban environments; Urban populations; Urbanization; Zoology
• ISSN: 1062-3590; 1608-3059
• DOI: 10.1134/S1062359022090242

As concluded in the previous paper, the order of synurbization of predators ( Corvus cornix first of all) and prey species, as well as relatively low or moderate proportions of predated nests in some avian prey species in selected Russian cities, are consistent with the so-called urban predation paradox. The paradox observed for terrestrial vertebrates (mostly birds and mammals) in a number of North American and Western European cities, refers to the predation relaxation of prey species in spite of a simultaneous predator proliferation in urban environments. The most plausible explanation of the paradox is based on the suggestion that the abundance of food for predators is often higher in urban landscapes than in more natural ones. As a result, despite the high densities and considerable species richness of predators, especially generalist mesopredators, the per capita predation pressure (per active nest or individual prey) is hypothesized to be lower in cities than in nonurbanized areas. The food subsidies to predators in urban landscapes are provided (1) in the form of anthropogenic food that can be consumed by predators (especially by generalist predators like corvids, gulls, some carnivores) and/or by their prey species and (2) through those resources and human activities (e.g., application of organic fertilizers) that increase habitat (primary) productivity in urban green spaces. Initially, dense urban populations of fully synanthropic species such as Columba livia f. domestica , Passer domesticus , and Rattus norvegicus that highly dependent on anthropogenic food resources, and also of some partially synanthropic species, e.g., Apus apus and Passer montanus , could have been of prime importance as prey for specialist predators like some birds of prey and owls colonizing cities. By significantly part taking the predation pressure by specialist predators, such prey species might have facilitated the urbanization process for some other prey species. The proportions of some synurbic prey species in the diets of urban predators tend to increase with time as the densities of the former increase. In urban habitats, some predators can also expand the range of the species they prey upon or switch to different prey directly or indirectly due to altered abiotic conditions, such as increased temperatures in winter and early spring (enabling an earlier start of breeding in prey and predatory species), artificial light at night (enabling twilight and nocturnal for