The weight loss plan of the yellow-legged gull within the Medes Islands (Girona, Spain) has modified extraordinarily over the past many years, in line with a examine that analyzes the adjustments within the weight loss plan of this species over the past twenty years. Regarding these gulls, which eat strictly marine assets, landfills and meat industries ̶ that are plentiful within the space ̶ are these days the supply for meals of about 50% of their weight loss plan.
The progress of human inhabitants within the study space –aside from the abundance and availability of natural waste in landfills– would clarify the present feeding sample of the gulls, a species with a excessive skill to undertake to these habitats which have modified as a result of human exercise. Parallelly, the excessive availability of meals has triggered the populations of gulls, a state of affairs that entails some issues associated to direct and oblique interplay between seabirds and other people.
The examine, revealed within the journal Ecological Indicators, is led by members of the Group on Seabird Ecology of the Faculty of Biology and the Biodiversity Research Institute (IRBio) of the University of Barcelona. Among the individuals are the Institute of Marine Sciences (ICM-CSIC) and the Animal Health Research Centre (CReSA) of the Institute of Agrifood Research and Technology (IRTA).
Searching for meals assets
Human exercise has altered the options of the atmosphere since historical instances. A approach to introduce vital adjustments within the ecosystem and the wild fauna is the enter of meals subsidies to the pure atmosphere, that’s, meals leftovers people don’t eat, and that are eaten by different species. Over the final many years, the consumption mannequin of people has led to a rise within the manufacturing of meals subsidies, which have change into an important meals supply for a lot of wild fauna populations, such because the wild boar –frequent within the city and metropolis streets– or seabirds that eat fishing discards. Often, the rise within the availability of anthropogenic assets is strongly associated to the populational progress of species that know the best way to take and eat these. Such species, subsequently, can change into superabundant and may generate a number of issues akin to nuisances within the metropolis, transmission of ailments, accidents on the highway or airports, and so forth.
The yellow-legged gull: feeding from landfill waste
The Larus michahellis yellow-legged gull is a very tailored species to the usage of human-origin meals subsidies. This chook, which was initially marine, is these days plentiful in locations with many people, from the coast facet to inland.
“This species has a great feeding and behavioral plasticity, and this allows it to feed from sandwiches in school courtyards, to food remains from meat industries, through fishing discards and waste in landfills,” notes researcher Jazel Ouled-Cheikh, first writer of the article and member of the Department of Evolutionary Biology, Ecology and Environmental Sciences of the UB, IRBio and ICM-CSIC. “These food habits –adds the expert– turn it into a potential disease vector, apart from favoring demographic explosions, and therefore, it is necessary to study and understand the species to manage the populations and prevent potential conflicts.”
In the examine, the Group on Seabird Ecology particulars how the weight loss plan of the yellow-legged gull of the Medes Islands (Girona) has modified over the past twenty years. Through the evaluation of steady isotopes, the examine determines the elementary compounds of the feathers of the gulls to estimate and quantify their weight loss plan. The analyzed samples come from samples of chicks performed in situ within the Medes Islands throughout the breeding season of the species throughout the 2004-2018 interval. The non permanent perspective of the examine is prolonged due to the evaluation of samples of feathers of dissected fashions from the Darder Museum in Banyoles and the Natural History Museum of Barcelona; a first-year juvenile gull which died in 1916 and three extra juvenile that died within the nineties, taken close to the Medes Islands.
The findings of the examine reveal a number of vital adjustments within the weight loss plan of the yellow-legged gull throughout the examine interval: “Specifically, the seagull diet has gone from being based on a 70% marine contribution –mainly fish–in 1916, to values of about 30%”, says the professional Jazel Ouled-Cheikh. “However, the contribution of elements from landfills (meat products and other leftovers) was relatively low in 1916. The contribution of this resource to the diet of seagulls grew during the 1990s, until stabilizing around 50% in the present.”
The examine additionally evaluates the contribution of terrestrial invertebrates to the weight loss plan of this seabird, an consumption that additionally will increase progressively all through the examine interval, reaching present values of 30%.
“These variations in the diet of the yellow-legged gull population of the Medes Islands over time could be explained basically by two oscillating and closely related factors: the population size of the study colony and the availability of different food subsidies in the environment,” says the tenure-track 2 lecturer Raül Ramos (UB-IRBio).
The availability of various meals subsidies adjustments enormously in each time and space. The yellow-legged gull, like many different opportunistic species, can adapt to those variations by modifying its feeding technique. Thus, people from totally different locations might have very totally different diets relying on the native availability of those assets. “Therefore, the individuals can adapt their schedules and diet to the temporal patterns presented by the human activities that generate these subsidies. For example, they are able to change their diet on weekends when there is no fishing and, therefore, no fishing discards,” says Francisco Ramírez, member of IRBio and ICM-CSIC. “From an ecological point of view, this plasticity gives them a certain advantage over other more specialized, and often competing, species that can be affected.”
A brand new state of affairs for seabirds
This state of affairs of adjustments will likely be additional exacerbated by teh European Union-driven insurance policies that may cut back the accessibility of seagulls to meals subsidies. In this context, you will need to spotlight the neighborhood tips such because the Landfill Directive, which can result in a major discount within the obtainable waste at landfills. Likewise, the current and future utility of the European Landing Obligation coverage –the ban on dumping discards, the principle meals supply for a lot of seabirds right now–might finish the picture of seabirds following the route of the fishing boats to eat from them.
“If we consider the lack of food availability of the seagull (at least two of the three sources described in the study: landfill remains and fishing discards), in addition to the difficulty of covering the energy demand of these birds exclusively with the consumption of terrestrial invertebrates, everything points to a greater presence of seagulls in urban areas in the not-that-distant future, without forgetting the problems this situation involves,” warn the researchers.
“It is essential, therefore, to continue monitoring the Medes Islands gull colony, which is one of the most important in the Mediterranean. This monitoring must consider both the eating habits of this population of gulls and the movements of the specimens (using GPS devices, for example), as well as the study of their role as a reservoir of pathogenic microorganisms that they can transmit,” says Marta Cerdà, researcher at IRTA-CReSA. “Only in this way will we be able to have quality scientific data to find the reasons that push this species to interact more and more intensely and closely with human society, and all the associated risks that this brings.”
Jazel Ouled-Cheikh et al, Foraging within the Anthropocene: Feeding plasticity of an opportunistic predator revealed by long run monitoring, Ecological Indicators (2021). DOI: 10.1016/j.ecolind.2021.107943
University of Barcelona
Landfills and meat business: New meals sources for the Medes Islands yellow-legged gull (2021, September 10)
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