Adapting to urban ecosystems: unravelling the foraging ecology of an opportunistic predator living in cities

Abstract

The increasing urbanisation of the natural environment affects species differently. While most species cannot cope with these human impacts, others can persist or may even be favoured in these anthropogenic ecosystems. Among the different urban-adapted wildlife species, the populations of different species of opportunistic gulls have increased in urban areas and some have established breeding populations at a global scale. Although the ecology of these predators is relatively well-known in their natural environment, accurate knowledge about their urban ecology is very scarce. Here, we investigated the foraging ecology (habitat use, spatial movements and feeding) of an urban population of yellow-legged gulls (Larus michahellis) inhabiting the city of Barcelona (north-eastern Spain). We examined the diet of this urban population by analysing the stomach contents of chicks distributed throughout the urban area of Barcelona. The foraging movements of breeding gulls were investigated using GPS devices and habitat landscape information. The results show that this urban population of yellow-legged gull exploits different food resources, highlighting the consumption of urban birds and marine resources from fishery discards. In line with the diet results, GPS tracking data indicated that although yellow-legged gulls were able to use different types of habitats close to the city, they mainly foraged in urban and fishing port areas. In conclusion, yellow-legged gulls have adapted to exploit the food resources associated with urban environments. This study provides useful information to discuss management options measures to control the yellow-legged gull populations nesting in urban areas.

Behavioral rhythms of an opportunistic predator living in anthropogenic landscapes

“…The use of tracking devices has significantly improved the way we approach the movement of opportunistic species in response to both natural and human-induced environmental variability [19,26,27]. Tracking devices typically provide relevant information on the main foraging grounds of a particular organism, but can also inform on individuals' decision-making on a near realtime basis over larger periods of time [19,28].…”

Importance of predictable anthropogenic food subsidies for an opportunistic gull inhabiting urban ecosystems

“…For example, the presence of high and isolated buildings facilitates nesting in safe places without human disturbance. Additionally, the urban landscape of Barcelona surrounded by fishing ports, landfill installations, agricultural areas and freshwater habitats presents a diversity of trophic resources that can be exploited by gulls (Méndez et al 2020). An important amount of fishing activity is associated with the fishing port of Barcelona, with around 3200 tons of annual catches (Idescat 2019), providing a large volume of fishing discards, one of the main trophic resources exploited by the yellowlegged gull (Lopezosa et al 2019).…”

“…An important amount of fishing activity is associated with the fishing port of Barcelona, with around 3200 tons of annual catches (Idescat 2019), providing a large volume of fishing discards, one of the main trophic resources exploited by the yellowlegged gull (Lopezosa et al 2019). Similarly, the availability of organic waste in the city and in nearby garbage processing plants and landfills also offer important subsidiary food sources for this species (Méndez et al 2020). In addition to the exploitation of human-related resources randomly present in the city, PAFS provided by people are also available as a resource for yellow-legged gulls (~500 persons regularly feed birds, mainly pigeons and invasive parrots, in the city; Montalvo 2010).…”

“…Among the birds that have colonized urban environments, different species of opportunistic gulls have increased in urban areas and have even established breeding populations in cities around the world in the last few decades (Auman et al 2008(Auman et al , 2011Coulson and Coulson 2009;Washburn et al 2013;Spelt et al 2019;Méndez et al 2020;Coccon and Fano 2020). These opportunistic predators are favored by the presence of diverse trophic resources in urban environments (Rock 2005;Washburn et al 2013;Schwartz et al 2018;Méndez et al 2020;Coccon and Fano 2020). The yellow-legged gull (Larus michahellis) is one example of an opportunistic gull that has adapted to living in urban areas (Vidal et al 1998;Sorace and Gustin 2009).…”

“…For this reason, different management actions have been proposed to reduce the presence of gulls in urban habitats, such the use of particular structures to inhibit the installation of nests in the buildings or reducing access to food resources (Belant 1997). While there are many studies about the impact of PAFS on birds (Wilcoxen et al 2015), little information is available about the ecology of urban gulls (Spelt et al 2019;Méndez et al 2020), especially in relation to the importance of PAFS for urban populations.…”