Studies analyzing changes in the diet of this species over the past two decades have shown that the diet of Caspian gulls in the Medes Islands (Girona, Spain) has changed considerably over the past decades. For seagulls, which severely eat marine resources, the region’s abundant landfills and the meat industry now account for around 50% of their diet.

Study of population growth In addition to the abundance and availability of organic waste in landfills, the region describes the current feeding patterns of seagulls able to adapt to habitats altered by human activity. At the same time, the high availability of food has caused populations of gulls. This is a situation with some problems related to direct and indirect interactions between seabirds and humans.

Studies published in the journal Ecological indicatorIs led by members of the Marine Bird Ecology Group of the Faculty of Biology and the Institute of Biodiversity (IRBio) of the University of Barcelona. Participants include the Institute of Marine Sciences (ICM-CSIC) and the Animal Health Research Center (CReSA) of the Institute for Agro-Food Research and Technology (IRTA).

Find food resources

Human activity has changed the characteristics of the environment since ancient times. With the ecosystem Wild animals Is the introduction of food subsidies in the natural environment. In other words, it’s the food scraps that humans don’t eat and that other species eat. In recent decades, patterns of human consumption have led to an increase in the production of food subsidies. It has become an essential food source for many populations of wild animals, including the wild boar, which is often found in cities and streets. Throw out seabirds that eat peach. In many cases, the increased availability of human-made resources is strongly associated with the increase in populations of species that know how to ingest and eat them. As a result, these species can become excessive and cause certain problems such as urban obstruction, disease transmission, road and airport accidents.

Caspian Gull: Bait from landfill waste

Larusmichahellis Caspian Gull Seagull Is a species perfectly adapted to the use of food subsidies of human origin. Originally a seabird, the bird now lives in populated areas, from the coast to the interior.

“This species has excellent food and behavioral plasticity, which allows it to feed on schoolyard sandwiches, food debris from the meat industry, fishing waste and landfill waste. You can ”, explains researcher Jazel Ouled-Cheikh. Articles and members of the Department of Evolutionary Biology, Ecology and Environmental Sciences of UB, IRBio and ICM-CSIC. “These eating habits enrich the expert, but in addition to facilitating a demographic explosion, they make them a potential vector of disease. Therefore, they manage the population and potentially. Species must be studied and understood to avoid conflict. “

In this study, a group on seabird ecology details how the diet of Caspian gulls in the Medes Islands (Girona) has changed over the past two decades. Through stable isotope analysis, studies determine the basic compounds of seagull feathers to estimate and quantify their diet. The sample analyzed comes from a sample of chicks made the In the Medes Islands during the breeding season of the species during the period 2004-2018. The temporary perspective of the study was extended through the analysis of model feather samples dissected from the Banyoles Dadder Museum and the Barcelona Natural History Museum. A first-year gull that died in 1916 and three other seagulls that died in the 1990s were captured near the Medes Islands.

The results reveal significant changes in the diet of Caspian gulls during the study period. “Concretely, the food of the seagulls is about 30% of the marine contribution of 70% (mainly fish) in 1916″, explains the expert Jazel Ouled-Cheikh. “However, the contribution of elements (meat products and other leftovers) from landfills was relatively small in 1916. The contribution of this resource to seagull food increased in the 1990s and is now stable at around 50%. low.”

The study also assesses the contribution of terrestrial invertebrates to this diet of seabirds. This intake also increases gradually throughout the study period to reach its current value of 30%.

“The evolution over time of the land population of the Medes Islands can be explained by two oscillating and closely related factors. The population of research colonies and the availability of various food subsidies in the environment. “Tenure Track 2 instructor Raül Ramos (UB-IRBio) explains.

The availability of various food subsidies varies considerably both over time and space. Caspian gulls, like many other opportunistic species, can adapt to these fluctuations by altering their foraging strategies. Therefore, individuals in different places can have very different diets depending on the local availability of these resources. “Therefore, individuals can adapt their schedules and diets to the temporal patterns presented by the human activities that generate these subsidies. For example, they can change their schedules. dieter Francisco Ramírez, member of IRBio and ICM-CSIC, said: “On weekends, when there is no fishing and therefore no wasted fishing, this plasticity is another species. competitor more specialized and often affected. . “

New scenario for seabirds

The situation of this change will be exacerbated by policies led by the European Union that reduce access to food subsidies for seagulls. In this regard, it is important to highlight Community guidelines such as the Landfill Directive. This will significantly reduce the waste available at the landfill. Likewise, the current and future application of the European compulsory disembarkation policy aimed at banning the dumping of litter, which is today the main source of food for many seabirds, could put an end to the image of seabirds. following the route that fishing vessels eat seabirds. There are.

the availability of seagulls (at least two of the three sources described in the study: landfills and fishing waste), the difficulty of meeting the energy needs of these birds solely by the consumption of terrestrial invertebrates Moreover, everything shows that the presence of seagulls in urban areas in the not too distant future does not forget the problems associated with this situation ”, warn the researchers.

“Therefore, it is imperative to continue monitoring the gull colonies of the most important Medes Islands in the Mediterranean. This monitoring must take into account both the eating habits of this population of gulls and the movement of the specimens (GPS device). Use), for example) and study their role as reservoir of pathogenic microorganisms that they can transmit ”, explains Marta Selda, researcher at IRTA-CReSA. “Only then will we be able to obtain quality scientific data as to why this species encourages it to interact more and more closely with human society and all the associated risks it poses.”